. CASE FOR MOON FIRST - 09 Moon as our gateway

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MOON AS OUR GATEWAY

So, the Moon in this vision is a gateway to the solar system, where we can develop techniques we need, and also at the same time explore a celestial body that is proving much more interesting than expected. By the time I get to the end of that, then it comes over as an interesting and positive alternative. But there are many steps to it before readers can see the vision.

It's a matter of familiarity. We've had decades to get used to the Mars colonization ideas. These ideas I'm describing now may seem unfamiliar, even unlikely and implausible, but give them some time, to think them over, and perhaps you too will find this an exciting and interesting future?

Along the way, settlement is sure to happen. Eventually colonization may happen also. But I'd like to suggest, it doesn't need to be the main driving force behind our space exploration, no more than it is the driving force behind Antarctic study, or exploration of the sea bed and so forth. And that this future with humans working together with robots for remote exploration, our mobile eyes on the solar system and galaxy, is an equally exciting one. And one that is likely to be much more interesting, in many ways than a future where our main motivation for going into space is to turn planets and everything else into the closest possible copies of Earth, or at least, habitats for humans, as quickly as possible. Perhaps this can help towards a future where we can find out and explore first, and learn from this amazing universe we live in.

And also I'd suggest it is more practical, and less likely to lead to disappointment. When you look at Mars and your main thought is "how can I turn this into something like Earth?" you may miss many other possible futures that may be far easier to achieve and may perhaps be of great benefit for humanity in ways you can't anticipate.

If you plan everything out and set a goal to achieve before you know what is there, then your plans may not match the reality, and you may miss out on things that you couldn't plan for because there was no way for anyone to know about them in advance.

So, rather than a grand overarching plan, I think human space exploration has to be flexible, and continually adjusted based on new discoveries. You can do your long term plans, and at each stage we plan carefully for the near future, but you also do many tests and experiments and explore different avenues, because the most likely thing is that we don't know everything yet that needs to be known, so can't plan for the future in detail in space. Our plans are almost sure to need to be changed.

THE ROMANCE OF SPACE ELEMENT

Whatever the commercial or science value of humans in space, it's also a great adventure for humans. We don't need to be ashamed of this. It's one of the things that help humans to venture into the unknown and to try out new things which may be risky, yet turn out to be of great value in the future.

As to how much money to spend to finance such things, I don't know, that's for politicians, but even the ISS cost little when spread over the populations that supported it. $8 per person per year in the US. Think how much we spend on movies, and computer games by comparison. ("Is the ISS the most expensive single item ever built?"). The ISS would be designed differently if it was purely a zero g research lab in orbit (no need to have humans there 24/7), and differently also if it was a human factors research lab. I think the romance of space is a lot of the reason for the ISS design, with humans there 24/7.

Acknowledging this as a motive for ourselves, and also for other space organizations, could make it easier to have more realistic plans. Because then it means we don't have to do grand plans where details are spelt out for decades, to explain why the humans are going there. The early Antarctic explorers didn't have a detailed plan to show how their exploration would benefit humanity in the future. It did, in surprising ways, but they had no way of anticipating that.

Let's acknowledge that we don't know for a certainty if human exploration is the best way to find out about the Moon, or whatever the objective is right now, and that we don't know for sure what the future of humans will be in space, but that it's a great adventure. Also, as with almost any adventure into the unknown, it may be the best way ahead into a future we can't see yet. And if we don't do this, we'll never find out what the role is for humans in space exploration and how they can work with the robots in space.

I say this because it will permit much more open and flexible exploration if we are not required to explain what the humans are doing there and why they are there as part of some plan with every step mapped out for a decade or two into the future. I think the end result of a more flexible adventurous approach like this would be that we find new ways for humans to explore space and may avoid blind alleys that could lead to space exploration stagnating, just because of the lack of some new idea that may make all the difference.

INTERNATIONAL CO-OPERATION AND ROLE FOR CHINA - USA POLICY

It's impossible for the USA to co-operate with China in space in missions lead by NASA, because of a 2011 bill that prohibits the US from co-operating with China in space, and prohibits NASA facilities from hosting official Chinese visitors. This is due to fears of espionage and China getting an advantage from learning about US technology.

"None of the funds made available by this Act may be used for the National Aeronautics and Space Administration (NASA) or the Office of Science and Technology Policy (OSTP) to develop, design, plan, promulgate, implement, or execute a bilateral policy, program, order, or contract of any kind to participate, collaborate, or coordinate bilaterally in any way with China"

That's why no Chinese taikonauts have ever been to the International Space Station, because NASA is prohibited from inviting them. As a result, China is building its own space station.

There are calls for the US to change its policy towards China, but this may be a long process. John Logsdon of the George Washington University's Space Policy Institute told Space.com:

"It will take presidential leadership to get started on enhanced U.S.-Chinese space cooperation . The first step is the White House working with congressional leadership to get current, unwise restrictions on such cooperation revoked, Then, the United States can invite China to work together with the United States and other spacefaring countries on a wide variety of space activities and, most dramatically, human spaceflight."

A recent report "China Dream, Space Dream China’s Progress in Space Technologies and Implications for the United States" mentions many of the concerns that were behind the US non co-operation with China in space law, but also says that as China increases in space capabilities and uses space more, it also increases in vulnerability too, the more it relies on space assets:

"Although China is probably truthful when it says that it is not in a space race, such statements mask the true intent of its space program: to become militarily, diplomatically, commercially, and economically as competitive as the United States is in space.... As China’s space program increases in capability, it can be expected to wield this power in ways that, according to Bonnie Glaser, not only “persuade its neighbors that there is more to gain from accommodating Chinese interests” but also “deter countries from pursuing policies that inflict damage on Chinese interests.”

"Nevertheless, although China’s space program may pose challenges for the United States and its space power neighbors, it may also present opportunities for scientific collaboration on the Earth’s environment and outer space. In addition, it may make human spaceflight safer by providing additional capabilities to rescue stranded or imperiled astronauts through the use of common docking apparatus. Moreover, what is unwritten in Chinese analyses is that as China becomes more invested in space capabilities it takes on the same vulnerabilities as the United States. Although China would not have the same asymmetries as the United States in a conflict in the Western Pacific, the goal of having a global, 24- hour, all-weather remote sensing capability and spending nearly $1 billion per year until 2020 to establish a global satellite navigation system and associated technologies indicates that China is devoting significant effort and resources to establish a system that is similar in architecture to that of the U.S. military’s space program. With this trajectory, China will have as much to lose as it has to gain from the management or mismanagement of the outer space global commons. It is in this vein that some sort of strategic accommodation that ameliorates the worst effects of competition could be achieved. "

China does have plans to send humans to the Moon eventually. As with the US and Russia in the 1960s and 1970s, its main reasons for doing this seem to be similar to other nations, reasons of national prestige, to show their technical prowess, as advertising for their space technology capabilities and to achieve results of scientific value.

Emily Lakdawalla has a useful summary of past and future robotic Chinese missions to the Moon. Plans include a robotic sample return in 2017 and a mission to the far side (probably) in 2020 (according to Weiren Wu, their chief lunar exploration engineer). That last would be a particularly impressive and prestigious feat for them, as nobody has achieved it before.

Paul Spudis says in his new book (chapter 8, If Not Now, When, If Not Us, Who?) that he considers that the developing Chinese deep space capabilities, to send robotic spacecraft and eventually humans to the Moon and further afield, are a defense issue for the US.

I like much of what he says in the book. But I can't follow his reasoning here. Anything that China can do, the US and Russia could do forty to fifty years ago. If it was a military advantage for China to be able to send it'sChang'e 2 to the L2 position for instance, as he says in this chapter, why doesn't the US have spacecraft there already, to swoop down on geostationary satellites from an unexpected direction in a war situation? So I don't find it very plausible myself that the Chinese deep space lunar and asteroid encounter robotic missions have a military purpose behind them.

We have several civilian spacecraft at the EML1 position at present, including Advanced Composition Explorer, Deep Space Climate Observatory, and the Gaia spacecraft. EML2 isn't used so much, since after all, though as close to the Moon as EML1, there is no direct communication with Earth. I don't think we have any spacecraft there at present (do correct me if you know of any)?

But Chang'e actually went to the Sun Earth L2. That's a natural spot for any spacecraft to go on its way to an interplanetary target, as it is a waypoint on the "interplanetary super highway" - from which it is easy to go to a further away deep space target, such as an asteroid, which is what it did next. I think this just shows that China has an interest in deep space exploration. Similarly India has just sent a spacecraft to Mars, more of a technological challenge than a mission to L2 and an asteroid, but nobody sees this as a military issue.

Some of what they do in space is of course of military significance. Their ASAT test in LEO in 2007 was; definitely. However, the US did an ASAT test in 1985, destroying a defunct weather satellite using a portable missile launched from an F-15 fighter. The US was way ahead of the present day China in these capabilities back in 1985.

I think their motives for deep space missions must surely be the same as everyone else. Nobody else seems to think that their own deep space missions, currently, are of any military significance. Neither the US, nor Russia nor the ESA, nor any of the other space agencies think deep space is of any military value at all. We don't get secret defense payloads launched to deep space (and we'd know about it if there were any, as it is easy to track spacecraft after launch from Earth, by following their trajectory, and even into deep space from monitoring their radio communications with Earth). So why should China?

We do many things that have no immediate economic or practical or defence value. One nice parallel with our space activities I think are the Olympics. These also bring together nations from many different countries in friendly co-operation and competition. Just as China takes part in the Olympics, despite many differences of opinion and concerns about human rights, and so on, let's encourage it to take part in international space ventures too.

The Chinese are interested in collaborating from their side.

Yang Liwei, China's first astronaut said:

“China will not rule out cooperating with any country, and that includes the United States,” said Yang Liwei, China’s first astronaut. “The future of space exploration lies in international cooperation. It’s true for us, and for the United States, too.”

Similarly, Zhou Jianping, chief engineer of China's manned space program, said:

"It is well understood that the United States is a global leader in space technology. But China is no less ambitious in contributing to human development ... Cooperation between major space players will be conducive to the development of all mankind,"

from: China open to Sino-US space cooperation

Also China has signed an agreement with the UN to open up the Chinese space station to spacecraft, science experiments and astronauts from around the world.

ESA, RUSSIA AND CHINA

Though the US can't collaborate with China, without a major political change of direction, Europe and Russia are able to co-operate. and indeed are keen to do so. They already co-operate in many ways.

Johann-Dietrich Woerner, Director General of ESA outlining his vision for the ESA village and Space 4.0 in his visit to China in April 2016 said:

“Let’s open space. Space is beyond all borders so let’s also have the cooperation beyond borders, When you ask astronauts, and I’m sure also the Chinese astronauts will tell you the same: they cannot see any border from space. So this is a very nice vision. We should use this and cooperate worldwide on different schemes, and I think Moon Village has its value for that.”

The ESA village idea is based on many different habitats from different countries in one village on the Moon. Unlike the ISS which is a single facility, it would be possible for China to have its own separate habitat in the village.

For these reasons I think that actually it would be good for the ESA to lead the Moon initiative, at least for as long as the US has this stance on China. The ESA has this capability and also willingness to collaborate with all of the US, Russia, and China. With the ESA leading, then US could, I think, be part of a moon village with China also taking part. That could be an interesting future.

Chinese taikonauts, crew of Shenzhou-10 after 15 days in space. (Credit: CNSA)

Meanwhile, the ESA has put an experiment on the Shijan 10 Chinese satellite, has sent personnel to visit Chinese facilities, plans to send an astronaut to the Chinese space station in 2022, and several ESA astronauts are learning Chinese. It can't invite the Chinese back to the ISS of course because of the US law. But it's a starting point towards greater collaboration in space in the future. Also Sweden (a member state of the EU) will put an experiment on the Chang'e 4 mission to the lunar far side, to measure the solar wind and look at what its role could be in the formation of water at the lunar poles.

The Chinese have also recently signed an international agreement with the UN to open their space station to spacecraft, science experiments and astronauts from other nations around the world.

For these reasons, unless the US change their policy, I think the ESA is the natural leader for future human Moon space initiatives. That's just because if they lead, then both US and China can take part, but if the US lead, China will be excluded. I think that it will help future international relations between countries in space if China can be part of the initiative. Which in turn may make it easier to achieve a peaceful future in space longer term.

COULD SOME CO-OPERATION BE POSSIBLE BETWEEN THE US AND AN ESA VILLAGE THAT INCORPORATES CHINA?

So first, some multilateral coordination is possible. From the NASA FAQ:

"Q4: "May I travel to China to attend conferences?"

"A4: Public Law 112-55 states that NASA may not engage in any bilateral activities with China or Chinese-owned companies. However, NASA employees, contractors and grant recipients are permitted to attend some multilateral, widely-attended conferences such the 2012 IAU General Assembly held in Beijing."

Space.com interviewed Marcia Smith, space policy analyst and editor of SpacePolicyOnline.com for an article on Chinese US co-operation. She said:

"The U.S. and China have a complex relationship. It is not like the U.S.-Soviet Cold War rivalry that was driven by military and ideological competition. Today, the U.S.-Chinese situation has those elements, but our mutually dependent trade relationship makes it a whole different kettle of fish."

She told them that the US at times had low-level agreements with the Soviets from the early 1960s on sharing biomedical data.

"But the bold cooperation on human spaceflight — the equivalent of inviting China to join the ISS partnership — waited for regime change," Smith told Space.com "It is U.S.-Russian cooperation, not U.S.-Soviet. Perhaps when there is regime change in China, we will see the same kinds of possibilities emerge."

Until then, "one would hope that low-level cooperation, akin to U.S.-Soviet space cooperation in the 1960s or 1980s, might be possible," Smith added. The law does allow multilateral, not bilateral, cooperation, she said. "The door is not completely shut."

So - if ESA, Russia and China with other partners were involved in a lunar village, then there might be some low level co-operation, and also some multilateral co-operation.

It's a rather different situation from the ISS in LEO because of the geographical nature of the Moon, because there are some geographically comparatively small areas of the Moon of exceptional interest, and because the OST which ensures that no State can lay claim to any area of the Moon as their own.

So, for instance, there's no reason for the Chinese to put their space station in an orbit to give easy access to the ISS and vice versa. But one can easily envision a situation where the US, if they had renewed interest in the Moon, set up a base within a few kilometers of the ESA village near one of the lunar poles. Suppose, for sake of illustration, that the US set up a base just a few hundred meters from the ESA village. That might well happen in the natural course of events, because there are only a few areas, that are especially favoured for solar power, high points that catch the sunlight nearly all year round. Geographically limited a bit like the summit of a mountain. If both examine the Moon to find the optimal place to site a base, then they might end up in the same region even without advance planning. It might be a bit like the US and China both setting up a science station on the summit of Mount Everest.

So for instance, suppose they are both on the rim of Shackleton crater, say, within a few hundred meters of each other. Would the astronauts be able to go over and chat with the ESA village astronauts?Including the Chinese astronauts? Could they land on the same landing pad, an area glassed over to remove dust? What about using the ESA 3D printer, if it was made by a European firm, but also used by the Chinese to apply regolith shielding to their habitat as well?

Also, would US astronauts be permitted to visit the village if they landed on the Moon close to it? You can have lots of different associations from sharing the same power supply and vehicles, 3D printers etc to just being located within a few hundred meters or kilometers for mutual support in the event of an emergency.

I'd have thought that at a minimum they could set up a base within a few kilometers walking or driving range of the ESA village, and offer mutual support in an emergency. And if perhaps not officially, once you have many astronauts there, that they could unofficially visit each other on occasion as individuals. Or is that a step too far?

Also, probably commercial US space could take paying Chinese passengers to the ESA village. So there might well be lots of multilateral co-operation. And perhaps eventually that could lead to the US revisiting their policy on China?

HOW AN INTERNATIONAL LUNAR VILLAGE SAVES MONEY, AND IS SAFER THAN SEPARATE BASES SPREAD OVER THE MOON -THROUGH USE OF COMMUNAL RESOURCES

I think an international effort would save money for all concerned and is also much safer and more equitable. It's much like a village on Earth, with a shop, post office, maybe a hardware shop etc.

• Landing pad and beacon already in place. Will simplify landing to have a flat surface of lunar glass, no dust, and beacon to land there. Also good to create a lunar glass surface around the village to reduce the levels of dust brought in after EVAs. Each country can do this for itself of course, on its own little patch of the Moon for its habitats, but it avoids duplicated effort if it is done once only.

• Can use the best site available . Especially at the lunar poles there may not be that many sites, just a few square kilometers total. In an international effort then all the habitats can be built at the most optimum site. Similarly there may be some caves that are optimal. If there's one lunar village, it can be built at the very best site for humans on the Moon. Otherwise, latecomers to the scene will have less good sites.

• Minimizes contamination. If some areas need to be preserved for scientific study, then putting all the habitats in one place reduces contamination

• Services already in place. Especially for new arrivals, it may be a great benefit to be able to hook into the villages electricity and oxygen generation and fuel generation capabilities, and power storage until you develop your own.

• Able to develop a large space such as a cave. This especially applies to the lunar caves. If the caves are large, as they may be, it might be possible to develop the entire interior of a cave like a Stanford Torus / O'Neil cylinder. If so, again it makes much more sense for everyone to be in the same cave rather than have a half dozen here trying to develop one cave, a dozen in another place and three astronauts in another place all trying to create their own habitats.

• 3D printing of the regolith shielding. If someone has already brought a 3D printer to the Moon able to make shielding for habitats by sintering the regolith or making it into some form of concrete using resin or whatever, then everyone else from then on can use the same machinery and don't need to bring their own printers with them. This is likely to be a large machine.

• Similarly for cranes, or for vehicles to travel over the surface or any other complex heavy machinery that can be used communally by the entire village

• Ability for neighbours in the village to give each other practical help. Especially in case of an accident, but also simple things like you have short term trouble with your oxygen supply, or CO₂ scrubbing, or even just, that temporarily you run out of salt or whatever it is. Or your plants die and your neighbours can give you new seedlings.

• Shared medical help

• Also to help with advice and tips. Maybe the Americans have an expert in environmental control and spacesuits, and the Russians have a good doctor expert at heart conditions or an osteopathic surgeon, and the Europeans have an expert in the technology of the rovers, and the Japanese, an expert in telerobotics, or whatever, they can just call by, look at the situation, and give their advice in person.

• Refuges in an emergency. Any of the habitats can be an emergency shelter for all the others.

• As it develops further you'll have specialized shops and facilities. Hotel for tourists, workshop area for mending the vehicles and equipment, lab area for researchers, tele-operations and communications hub, electronics fabrication and 3D printers, the folk involved in mining the lunar resources, etc. etc. In a lunar village this can develop early on. If every nation has a different habitat scattered around over the surface of the Moon, then it may be a long time before each tiny research station / settlement reaches this level of specialization.

In this way, the different habitats in the village can be maintained by different space agencies but with shared utilities etc. That's partly why I think the ESA village is one of the most promising of all the human moon mission plans to actually come to something. Why duplicate everything? And the bases need to be close together because of the difficulty of moving around on the Moon and the swiftness with which issues could arise. If the other bases are hundreds of kilometers away they wouldn't be able to share much or do much to help each other in a real emergency, not in the hostile vacuum conditions of the Moon.

SPACE ASSETS AND STRATEGIC, ECONOMIC AND MILITARY SIGNIFICANCE OF SPACE

If we can co-operate in the early stages, much as we do in Antarctica, not necessarily doing everything together, but in a spirit of collaboration and friendly competition, I think this is the best way to set us on course towards a peaceful future in space. Also, though the peaks of (almost) eternal light are geographically quite small, still, there is plenty of space for an ESA type village and many habitats at each one.

If there are indeed hundreds of millions of tons of ice at the poles (which we don’t yet know for sure), there is plenty there for everyone for the foreseeable future, at least until we get large scale mining of ice from asteroids or comets.

Luckily the Outer Space Treaty is also flexible enough to incorporate many future developments of space law. It rules out any possibility of "stake holding" where countries claim ownership of territories in space, or individuals do so supported by their country. But that's a plus as it means we don't need to be concerned that China, or anyone else, will try to lay stake to some region of the Moon. There are many ideas for adding some form of "space ownership" of assets in space, which are compatible with it, based for instance on the ownership of your habitats, already included in the treaty, maybe accompanied by extra provisions for functional ownership, or based on a controlled safety zone etc.

The details need to be worked out by space lawyers.

IDEA THAT WE SHOULD ALL SHARE IN THE SPACE MINING BOOM - AND OF A SOVEREIGN WEALTH FUND

The Outer Space Treaty says that “the exploration and use of outer space shall be carried out for the benefit and in the interests of all countries and shall be the province of all mankind”

In the US the idea of relying on free market enterprise in space to benefit humanity is popular. But in Europe there’s more support for something extra on top of that.

We tend to think that all of humanity should benefit directly financially, or in other ways, from the space mining boom (If we have one). This idea is called the "common heritage of mankind" in the Moon treaty. That’s rather a broad statement to make, there are many on both sides of the pond of course with both views.

Anyway I’m from Europe and perhaps this influences my thinking, but I’m very keen on the common heritage of mankind approach. Perhaps it may be interesting to hear why?

One idea discussed on "the conversation" is the idea that space industry could be a basis for a sovereign wealth fund, which could then be used to guarantee a minimum wage world wide, similar to the Alaska sovereign wealth fund, but applied globally rather than to a single country.

That could eliminate the worst of poverty, hunger, access to clean water and sanitation, education etc. world wide. Just a few dollars a week sovereign wealth fund would eliminate a lot of third world poverty and allow small farmers to invest in tools, a bicycle, other things that would transform their future.

Also, if we had a trillion dollar space industry it might be much less of an imbalance if those new trillionaires were balanced by everyone having a guaranteed minimum wage.

This sovereign wealth fund also could be used to support space projects. A trillionaire who has earned their wealth from space might choose to spend it all on a platinum plated house and yacht on Earth. There’s no reason why they would plough it back into space except for their own particular mining operations, likely to be largely robotic. They might be like Bill Gates or Warren Buffet and engage in big philanthropic projects, in medicine and so on. But again they might not. It would all just depend on who they are. That seems too much like pot luck to me, once you start talking about trillionaires rather than billionaires.

While a sovereign wealth fund might be used to fund many projects in space of benefit to all humanity.

Another possibility is some way of ensuring that the space industry provides ways for the poorer countries to get into space and set up their own mining operations - that rather than being squeezed out from ever mining in space by the wealthy countries who get there first, they get assisted to take part in it too.

But personally I prefer the sovereign wealth fund approach. It does work. Norway used it to great success with its offshore oil industry, even though the industry naysayers said it would never work and drive the big players away. But when Norway went ahead anyway and put in place a big tax funding its sovereign wealth fund - there was no shortage of oil companies ready to extract the oil under the new conditions.

TAPERED TAX RECOGNIZING RISKS

Of course, any kind of sovereign wealth tax would need to recognize risks in the early stages. A company that is attempting something that is just on the border of possible should be given all the encouragement it needs, and the last thing you would want to do at that point is a hefty tax or to request them to divert funds elsewhere to support other mining companies. Perhaps it should be tax free initially, even tax breaks from whatever is their national tax.

But once they are up and running and have a healthy balance sheet, then why not tax them, like everyone else, and if so, why not have an element of that tax used for a global sovereign wealth fund?

Or similar, maybe a fund used to combat world poverty, to provide clean water for all, to support worthwhile projects in space, or one way or another, to recognize that the assets in space are the heritage of all mankind. That would certainly have my vote.

But if it is just another industry at a similar level to the others, billion dollars type companies, similar in size to Microsoft or SpaceX, I don't see it as a huge issue either way.

There are many other issues here. For instance what about communally used space assets? Whoever sets up Hoyt’s cislunar tether system would be in a position where they could charge pretty much what they like to use it, way above the actual costs of maintenance. How would that work?

I'm sure there will be much here to occupy space lawyers, economists, and politicians for decades to come. This is an article I wrote about: Will Anyone Ever Own Their Own Land In Space - And May We Get Wars In Space In The Future?

It is a very technical subject and I'm no expert, so perhaps that article is most useful for the links to expert opinion and the questions it raises.

ROBOTS AND HUMANS TOGETHER

Paul Spudis and Dennis Wingo have presented detailed plans leading up to a human outpost on the Moon and then to a base with a more or less continual presence of humans there. Though they have differences of detail in their visions, they both have the same basic idea, to send robots first to scout out the Moon, and then to set up a human base at one or other of the lunar poles, with much of the early work of constructing the base done telerobotically from Earth.

Both of their visions are based around the idea that it will be easy to extract volatiles from ice deposits in the perpetually dark craters at the poles. And both think that this water will not only be useful for humans in situ, but also help to fuel spacecraft shuttling back and forth between the Moon and Earth, and start a lunar economy based on exports of water and fuel to LEO and to other spacecraft. The main idea here is that it would be much easier to supply water to space from the Moon than from Earth.

Dennis Wingo outlines their similarities and differences here in this review of Paul Spudis's book, "The Value of the Moon". BTW do check out Paul Spudis' beautiful graphic, showing the outline of his vision. Dennis Wingo reproduces it part way down the page in that review.

ROBOTIC SCOUTING PHASE - NEED TO GO BACK AND FIND OUT WHAT'S THERE FIRST

I'm presenting a more fluid approach here. It starts the same way, scout out the polar ice. But it's not the only thing we can do right now. As well as searching for ice at the poles, which of course we should do, we can also scout out:

• The lunar caves, the largest possibly several kilometers wide and over 100 kilometers long - think how that could change the picture!

• Are there volatiles actively reaching the surface right now from deep down? Scout the geologically new features like the Ina depression, do more exploration from orbit looking for ice deposits with ground penetrating radar, looking for the transient lunar phenomena and gases from the interior and close up photography

• Permanent shadows as far as 68 degrees from the poles. Do any of these have ice deposits at some depth below the surface?

• Check out to see if Arwin Crotts' deposits of ice exist a few meters below the surface. It may be a long shot, but the implications would be revolutionary if they exist.

• Test Dennis Wingo's hypothesis of platinum group metals on the Moon, and test to see if Wieczorek et al are right, that the magnetic anomalies beyond the rim of the Aitken crater are deposits of high purity valuable metals.

• Generally get a better understanding of the Moon as a whole. Expect the unexpected.

We can certainly build a lunar base at the poles, a scientific base for humans. The ice is not really needed for that, if it is the best place to send humans for scientific reasons. The total fuel needed to get to the Moon, including descent to the surface, is similar to the amount needed to get to Mars. And as for the return journey, then the amount needed is small. The propellant needed for the Apollo lunar ascent module was 5,200 pounds, or around 2,360 kg out of the launch mass of the lunar module of 15,200 kg. and ascent stage mass of 4,700 kg. It's very different from Mars, there's not much need really for a "Moon One", analogous to "Mars One", as we can get our astronauts back pretty easily from there.

Their plans may well describe exactly what we do. They are worked out in detail, and if the assumptions they make are correct, and we make no new surprising discoveries on the Moon, then one or the other of these plans may well be the best way we can possibly explore the Moon. It's great to have them worked out in such detail already.

However, we have had so many surprising discoveries about the Moon in the last few years, just from orbit. Given how little explored it is on the ground, I think that it's just a little too soon to commit to detailed plans like that about how exactly humans will return to the Moon. I think that we should do open ended research with robots on the surface for a few years first before we commit to detailed plans for the later stages.

They both have plans for prospecting robots that explore the lunar poles to look for the best deposits of volatiles. Of course we need to do that. But I'm talking here about a more open ended and extensive exploration, not focused only on the places that seem the best places for humans right now. Because we should "expect the unexpected", I think, at this stage.

This might not be a long period of exploration, and the more robots we have, the quicker it would be. But we have done so little direct exploring of the Moon on the surface to date, that surely open ended exploration may still turn up many surprises. The Moon has roughly the same surface area as the US, China and Russia put together, with a varied terrain and many geological features to explore on the ground that we can't study easily from orbit. The volatiles were a relatively recent discovery after all, which changed everyone's ideas about how best to explore the Moon. Perhaps future discoveries may change those ideas again, in detail or dramatically.

This could be done with humans, as with Apollo, but nowadays robots are a much more cost effective way of doing it. They'd be doing open ended scientific research, and along the way also checking out resources for humans, and getting a fuller picture of the Moon. It would also give us an opportunity to study the Moon with the less intrusive robots, before humans arrive with their large rockets, the fuel from those rockets, and the extra organics that will accompany them to all the landing sites they visit. This can give us a baseline, and we can take this golden opportunity of a few years, to study things that we won't be able to study later once the lunar "atmosphere" is augmented by human activities on the Moon - such as water transport in the thin lunar atmosphere.

LUNOX - HOW WE WOULD HAVE DONE IT IN THE 1990s

As an example to show how our ideas change with new discoveries from the Moon, if we'd gone to the Moon in the 1990s, without a preliminary reconnaissance of the Moon first, we'd have used equipment like this to mine lunar oxygen from the regolith.

Unmanned lander goes first with a lunar oxygen production plant/storage facility and a nuclear power reactor

"Two "Loader" bulldozers collect and sort ~500kg/hour of ilmenite-rich lunar soil, which is fed into the LUNOX plant and processed into liquid oxygen propellant. The process is based on H2 reduction of lunar regolith in a fluidized-bed reactor, solid-state high-temperature electrolysis and Stirling-cycle O2 liquefaction and refrigeration"

Exploring in a pressurized rover

Refueling their landing craft.

You can read the details here: Lunar Base Studies in the 1990s 1993: LUNOX. Imagine if we had done that, gone to all the work of building and launching these machines, and then later on, found abundant ice at the lunar poles?

We might have other surprises like this, which we don't know about yet.

ROBOTIC MISSIONS TO THE MOON, ALREADY PLANNED, OR NEAR FUTURE, FROM 2017 ONWARDS

This first exploratory robotic phase looks likely to be an international effort, with missions from different countries and from private enterprises adding together to give us a complete picture. And the exiting thing is, that it seems it's really going to happen this time. Starting in 2017, we really are going to get lots of new robotic missions to the Moon. Not just China, though China plan to send missions to the lunar north and south poles in 2017 and to get a sample return from the far side in 2018.

We'll also get several attempts at the Lunar X prize landing on different points on the Moon in 2017, with several confirmed launch reservations, and others expected to follow soon.

Then, astrobiotic, one of the X-prize contenders, offered to carry payloads from other Lunar x contenders on their first mission , offering a price of 1.2 million dollars per kilogram to the lunar surface on their Griffin spacecraft. They have partnered with DHL for the logistics on Earth. They plan to send their first mission to the Moon’s Lacus Mortis region which seems to be the location for a skylight entrance to a lunar cave. Their plan was to run a Formula 1-like race on the Moon between their own Andy rover and the other rovers they carry with them to the Moon (Team Hakuto and Team AngelicvM from Chile) to see who can travel 500 meters fastest to win the lunar X prize (they will share the prize money, whoever wins). However Astrobiotic dropped out of the Lunar X-Prize saying the 2017 timetable was unachievable and now plan to go to the Moon in 2018

With astrobiotic out of the race, Team Hakuto from Japan have negotiated a new ride to the Moon with TeamIndus. I'm not sure what their current plans are but originally their plan was to explore a possible lunar cave skylight with their Moonraker lander (named after legend of English smugglers in Wiltshire, not the James Bond film). This mission is of especial scientific interest and of interest to human exploration of the Moon for the future, whether they do it or not, so let's look at it in a bit of detail:

(click to show on Youtube)

Moonraker, pulling the two wheeled Tetris. After competing for the 500 meters travel time on the Moon for the Lunar X prize with the other rovers brought there by astrobiotics (assuming it's not won already by another lunar X mission), its mission goal is to go on to lower Tetris into the skylight of a lunar cave. The rover has four independently driven wheels (it can also use them to "turn on the spot"). It has four instead of six wheels to give space for larger wheels as this helps reduce slip on steep slope. (Six wheels have advantages for travel over rugged terrain, but for their particular challenge of approaching a lunar cave over possibly steep terrain, preventing slip was more important to them). When it gets to the cave entrance it will use itself as an anchor as it lowers Tetris down into the cave, to explore it.

They plan to target the partially collapsed skylight in the Lacus Mortis region (originally their target was the Marius pit). For details of those features, see the section of this booklet: Example lunar cave skylights - Lacus Mortis, Marius pit and the King-y natural bridge. For details about why the caves are interesting, see Lunar caves and Lunar caves as a site for a lunar base. The team is led by Professor Kazuya Yoshida, designer of theMinerva II asteroid hopping robots for the Hayabusa 2 mission to an asteroid (currently on its way to an encounter in 2018).

The Andy rover (for Team astrobiotics itself) may also include the VESA gravimeter which could explore variation in gravity around the pit and use that to map out any underground voids, which should show clear gravitational signatures if a large lava tube cave exists underground.

They may also include their innovative tetramorph cube rover - a fast and lightweight semi-autonomous folding rover small enough to pack inside the 30 by 30 by 30 cms of a cubesat - and can then unfold and do pioneer exploration to scout out difficult territory that you can't risk exploring for the first time with the main rover. Early prototype of tetramorph unfolding:

(click to watch on Youtube)

Visualization of tetramorph in folded and unfolded position. See also Tetramorph Avionics: My Experience of Building a Lunar Rover

The same techniques of tether bots, gravimeters, and high speed high risk exploration pioneer rovers could be used to explore the similar Mars cave "skylights" robotically, after testing first on the Moon.

The lunar flashlight cubesat will launch piggyback on the first SLS "Exploration Mission 1" in late 2018. It will use laser light to look at the permanently dark shadows at the lunar poles to search for volatiles.

Lunar flashlight - artist's impression

Other confirmed cubesats for the SLS launch include the Lunar Polar Hydrogen Mapper shown above - cubesat from Arizona university to map water resources on the moon - see also the section Cubesat explorers and rep rap printing

NASA is also partnering with the commercial lunar companies like astrobiotic in its lunar CATALYST program. India also plan a second lunar probe, Chandrayaan 2 at the end of 2017 or early 2018 , following on from its successful lunar orbiter Chandrayaan 1. This time it will be a combined orbiter and lander-rover. The rover will be 29 - 95 kg and operate for at least 14 days under solar power. Japan has a plan, not yet approved, to send a lunar rover landing by 2018. Then there's the ESA and Russia's Luna 27 to the south pole Aitken basin, some time in the early 2020s.

HOW OUR IDEAS MIGHT CHANGE AS A RESULT OF A LONGER PERIOD OF ROBOTIC EXPLORATION

So, there's a fair bit of this robotic scouting going to happen anyway. The main idea is to increase the emphasis on this initial scouting phase, and slightly de-emphasize the later plans, for the time being, until we find out a little more.

There is ice at the poles, for instance, the LCROSS impact shows that. But how easy is it to extract it? We might get many surprises. Perhaps with a thorough understanding as a result of these studies, we position a human base a few tens, or hundreds of kilometers away from what seems the most obvious place right no, based on our knowledge to date. Perhaps the best place for a base is indeed on one of the peaks of (almost) eternal light, as Dennis Wingo and Paul Spudis both suggest, and the ESA do also. However, there are quite a few of those peaks at both poles, and the best one in terms of light might not be the best for humans in other ways.

For an example, we don't know yet, but there might be deposits with 100% pure ice or other volatiles, who knows, if we explore enough. Perhaps these are on the surface in some unexpected place, or perhaps below the surface. These might be much better for in situ resource utilization than the obvious first choices based on a few prospecting trips and optimizing for the amount of light available to the base. Perhaps we would need a better scientific understanding of the Moon before we can find them. This is just one possibility.

We may also find sites of exceptional scientific interest that need to be protected. Dennis Wingo spoke about developing the North pole for industrial work, so separated by a lunar diameter from the South pole which is for scientific research. That makes sense on present day understanding, but what if there is some uniquely interesting scientific site at the North pole? Perhaps it might even be the other way around, after we've done the preliminary studies?

So we need to know not just where to locate the base, but where not to put it also. And generally explore anything that's unusual and interesting, as you don't know what it will turn up.

Or we may get surprising discoveries about the lunar caves which make them go to the top of the list. The caves have an even temperature just as for the poles. It's true that the lunar poles are dramatically better sites for solar panels, when you work out the average power generated, as Dennis Wingo shows in his recent paper. But should the amount of solar power available be the main factor for choosing a landing site? It is a factor of course, but solar panels are quite lightweight. When you have a stable surface to spread them out on, as for the Moon, and no weather to disturb them, they can even be thin film, spread over a large area. They can also perhaps be made on the Moon itself.

You can compensate for less power by having more panels - and adding facilities to store the power for the 14 day lunar night. That is definitely possible, using hydrogen fuel cells, or good batteries, or in many other ways. Suppose for instance that some of the lava tube based lunar caves are large enough to fit an entire city inside, with smooth, close to airtight walls, easy to turn into large habitats with natural cosmic radiation protection? That by itself might outweigh the solar power advantages of the peaks of (almost) eternal light. Or there may be resources in the caves that we don't know about yet, or in some of them only, available nowhere else. Also, if there is ice near to a cave, a cave close to the poles say, that would combine the best of both worlds. Or they may have other advantages including ones that nobody has thought of yet.

Also, if we have biologically closed systems, nearly all the water can be recovered and used again just as water. So it might not be so important to have the main human base close to the ice. It might of course be that the best place for the humans is close to the ice, especially if the ice is the basis for an industrial operation that they have to oversee. But again, maybe that's not the best place for them. Maybe the ice has to be kept free of organics for scientific reasons, or even industrial reasons, and that it's best if the humans are some way away from it. Just as a "for instance". Or perhaps, the main base is somewhere else and there is an outpost, only visited occasionally, near the ice deposits.

Or it might be that Dennis Wingo and Paul Spudis are right and that the peak of (almost) "eternal light" with the most solar power is the best place to send humans, and that this also is a place so rich in ice that it will be a source of fuel not just for the Moon but for cislunar space as well.

If so, we might find this out early on. We might find a place that is so good as a base, that we feel there is no need to look any further. But if we base our entire strategy on this, before we know for sure, and then it turns out to be wrong, that could be a huge setback. Also, if it is more or less right but less than optimal, we might miss some opportunity that could have reduced the cost of the human mission considerably.

You could probably go on almost for ever looking for better and better sites for a base. I'm not suggesting that. But I think perhaps a few extra years searching in a more open ended way early on could bring dividends later.

As an example, Russia hope to send humans to the surface of the Moon some time around 2029. If that was the timescale, we'd have about 13 years for robotic exploration of the Moon and more research in LEO before we go there, plenty of time for quite a decent preliminary study of the lunar surface at the rate of several robotic missions a year, which seems quite likely based on the ones already planned for 2017 to 2018. But a dramatic discovery such as thick layers of pure ice at the poles might speed that all up.

MEANWHILE TIME TO REDISCOVER THE ADVENTURE IN HUMAN SPACEFLIGHT IN LEO

However, I'm not saying to stop human spaceflight as we explore the Moon with robotics. Rather, I think we need to be more adventurous with human space flight as well, at the same time. But before we start adventurous human exploration further afield, I think that just as with the early Gemini missions, we need to start being adventurous closer to Earth first.

I think that we need to start working on human factors research. The ISS is not really a human factors research facility. First - why is there so much emphasis on growing food for astronauts in zero g? It's interesting pure research to discover that some plants manage fine in zero g. But as for practical applications, we don't really know whether or not astronauts will typically need to grow food in zero g in the future.

Also the ISS has given us lots of information about the harmful effects of zero gravity on health. Also lots of research into using exercise in zero g to help counteract some of the worst effects. But there's been no research at all into possibilities of using artificial gravity to counteract those effects. Before we do deep space missions, we need to look into this. See my Can Astronauts Spend Years In Space - And How Quickly Can They Recover On Return To Earth? for more details about the motivation for doing this.

We can start research into both of these in LEO.

BIOLOGICAL CLOSED SYSTEMS RESEARCH IN LEO

We can also do biological closed systems research in LEO. See if we can duplicate the BIOS-3 results in space. The experiments in growing plants on the ISS seem to lack an overall direction and focus. I think it is more a case of "we have a facility in zero g, and astronauts in it, so let's see if we can grow food there for the astronauts?"

It's interesting research but it's not so clear that it will help with future deep space missions. Even a very slow spin can give you a hundredth of a g for the plants, which is enough to change the gene expression of every cell in the plant, turning many genes on or off. Within 2 minutes of starting a centrifuge in the ISS, the cells in the plants change gene expression of numerous genes. So when checking effects of various levels of gravity - theyhave to preserve the cells within minutes of stopping the centrifuge - or actually in the centrifuge. Plants are also sensitive to tiny amounts of gravity. For instance in an experiment with lentil seedlings, they responded to two thousandths of a g, and interpolation suggests they are sensitive to levels of less than a ten thousandth of a g.

In future interplanetary missions, we may spin the habitats and greenhouses with a counter balance using tethers to achieve whatever g we want for the plants. Or we might just spin the growing plants themselves in centrifuges.

A proposal from 2010 explored the idea of a "Farm module" which combined artificial gravity with fish and plants in space.

From 2010, this module idea has a rotating cylinder in the center if I understand right. The fish tanks and tomatoes are suspended from it, and then further out you have lettuces shown below and dwarf wheat above.

For the Moon we are particularly interested in how well plants grow at lunar levels of gravity. And also of course, how humans manage at lunar g. Again, there is very little data, just the few days of astronaut EVAs on the Moon, with 1960s and 1970s monitoring equipment. Also, there has been no attempt to achieve almost biologically closed systems in space, where nearly all the food and oxygen for humans comes from plants, even though it has been achieved on the Earth already by the Russians with BIOS-3.

For a lunar base, I think we need experiments in growing plants at lunar g. The obvious place to do that is on the Moon of course, but we can speed things up by testing this right away in LEO, testing long term adaptation of plants and humans in lunar gravity. We will need some kind of base in LEO anyway at some point, if we have frequent missions to the Moon.

JOE CARROLL'S TETHER EXPERIMENTS IN ARTIFICIAL GRAVITY - WHICH WE COULD DO RIGHT NOW

We could test humans in LEO in artificial lunar gravity right now, for days. We could set that up probably within a year (it didn't take long to get the Gemini tether experiment together back in the 1960s and we know much more now than they did then). Then we could do more experiments like that for weeks, then longer periods, using existing technology.

We seem to have lost our sense of exploration and adventure in space compared to the spirit of adventure we had in the 1960s. We are no longer doing bold new tests of things that nobody has done before, as they did with the Gemini program - the first EVA, the first tether, the first docking in space etc. It's mainly repeats now, of things done before. Yet there is so much we have hardly even looked at yet. Let's start exploring new possibilities for human spaceflight, which we can do right away, in LEO.

Even with future advances, it's probably safer to do preliminary experimental work of this sort in LEO rather than on the Moon. It's easier also, with a faster turn around time for the experiments, and it's less expensive to do these experiments in LEO rather than to have to go to the Moon. Especially right now when we are still at an early stage of research, and may have many false starts. Doing these experiments in LEO will also mean we can try many other gravity levels, and also learn how to achieve artificial gravity for interplanetary missions. This can go on at the same time as the early robotic exploration of the Moon.

So, I'd follow Joe Carroll's idea of an artificial gravity research gravity in LEO myself. It can start off as simple as just one space module with a counterweight. And indeed the first experiments are even simpler than that. He has been advocating it for years. He's an expert on space tethers and several of his tethers have flown in space. Tim Cole has also shared some ideas on the matter which I will mention here.

And the idea actually dates back to the 1960s. We now know that Sergey Korolev had a plan to tether a Voskhod with its spent final stage which he put forward in 1965-6. It was going to be a 20 day flight to upstage the Americans. It would have included a pilot, and a physician and the artificial gravity experiments would have lasted for 3=4 days during the flight. He died unexpectedly in January 1966 and the mission was postponed to February 1966 then cancelled outright. So we came very close to doing this experiment way back in 1966. (See page 17 of this thesis).

Joe Caroll's idea similarly is to start with a tether spin experiment with a module tethered to its final stage, which goes into orbit anyway. The way he does it, all the delta v put into spinning up the assembly get released at the end of the experiment. This boosts the spacecraft when the tether is released as well as achieving a controlled re-entry of the final stage into the Pacific (at present its reentry is uncontrolled). It uses no extra fuel unless the tether is severed by space debris, which from his experience in improving tether design is now a very low probability event. He would only use the excess fuel carried by the Soyuz in event that more is needed than expected during the launch, and use it only if not needed (usual situation|). This means that the Soyuz would still get to the ISS even in that worst case scenario.

It can be designed to be safe and could be done right away, as quickly as the Gemini tether mission was put together, for a near future crew mission to the ISS. They'd use the longer phasing approach of several days, so you could test several days of artificial gravity. The Soyuz TMA or any other crewed spacecraft can do Joe Carroll's tether spin on the way to the ISS, deliberately use the longer two day phasing approach to get to the ISS and do your first experiments on the way. The cost wouldn't be much as human spaceflight experiments go, just to add a tether to a Soyuz TMA mission that is going to the ISS anyway. They still have the older two day approach as a fallback option so that should be no problem either. They would be able to cut the tether at any time and continue in zero g if there were any issues arising during the experiments.

Though this would be a short experiment, there are many things you can test in a short mission. It would of course test things such as tether dynamics and tether spin up. Also radio communications during tether spins, and orientation of the panels to achieve adequate solar power throughout the orbit.

Also, in particular, it would give us the first real data on spin tolerances of humans in artificial gravity. We don't have anything on that - evidence that astronauts have much higher spin tolerances in zero g than on the ground. Skylab researchers speculated that this might be because the otoliths which sense gravity (as a linear acceleration) along the spin axis on Earth are not stimulated in space. Tim Peake recently demonstrated this anecdotally by tumbling at 60 rpm inside the ISS for a couple of minutes with no nausea and only very momentary dizziness when he stopped. But it's not been tested experimentally in space, neither for long periods of time, nor as an experiment, and we don't even have anecdotal evidence on long duration tolerance of the slower spin rates of a tether spin experiment. (See below Small centrifuge based artificial gravity experiments in LEO )

Also there are immediate changes in physiology, e.g. blood pressure, blood platelet counts etc. and those could be measured and tested under AG. I think it would also be interesting (my own suggestion) to find out if gradual transitions through partial gravity first might help with the space sickness which many astronauts experience for a couple of days when they are first exposed to zero g.

Based on that you could do longer missions later on. But ground experiments can't even simulate AG for a few minutes. To simulate it for hours or a couple of days in space would be a huge step forward for the field.

This video shows a 600 meter tether at 1 rpm joining a Soyuz TMA to its final stage to achieve lunar gravity. Even the most highly susceptible people have no problems with 1 rpm in rotating room experiments on the Earth long term. So probably this would be fine for everyone in space also - that is if the Earth experiments are a reasonable guideline, which nobody knows of course (that's why we need to do the experiment). There are some indications that in space, with spins around a horizontal axis (above your head) and no gravity pulling sideways along the rotation axis, that we can tolerate spins better than on Earth. Though the data is very limited so far.

(click to watch on Youtube)

All these videos are done in Orbiter, a remarkable space mission simulator by Dr. Martin Schweiger with lots of add ons contributed by enthusiasts.

Thanks to Gattispilot, for making the tethers, and for techy advice about how to attach everything together.

Note that the video shows an "eyeballs out" configuration. The tests would only go from low g up to full g, but still, this is not the most comfortable orientation for the crew. Joe Carroll's plan is for an "eyeballs in" configuration. It's just that for techy reasons I found it much easier to position the Soyuz in the simulator in this "eyeballs out" orientation . The tether would be brighter than this, and you may notice a cube at the center of gravity of the tether - this is just to indicate where the center of gravity is and would not be there in reality.

NB, there's a detail to be sorted out here - do you deploy the solar panels before or after the tether experiment? If deploy before the experiment, their supports need to be strong enough to withstand the artificial gravity - this is probably easier if the solar arrays are orientated radially to the axis of rotation during the tether spin. This is best if possible as then you have no power limitations for the experiment.

If you leave deployment of the arrays until later - it is a case of how long you can manage without external power for the experiment. You'd be dependent on the storage batteries for power. Early Soyuz spacecraft before the solar power systems had 2 days of battery power. Not sure about the TMA.

Based on these very early tether spin experiments, we can answer basic questions such as, can humans tolerate spinning for two days, and if so what tether length and spin rate is tolerated? (The experiment is designed so it is easy to abort from it at any time - you just cut the tether, and then continue to the ISS). And what are the immediate effects on the human body of artificial gravity? What is the gravity prescription for health (what g level, how many hours a day or do we need it full time) and how easy is it to apply the desired levels using AG?

Another experiment you could do in the near future is a tether experiment launched from the ISS. The crew would take the crew module to the ISS with the final stage still attached. Then to do an experiment, they leave the ISS, fly far enough away from the ISS so that a severed tether won't endanger the station, spin up, do the experiment for several days, then spin down and return to the ISS. This idea was suggested by Tim Cole in 2012.

Based on those preliminary results from the Soyuz TMA, or any other crewed capsule that goes to orbit with a third stage which you can use as a counterweight, you'd work towards designing a larger AG research lab in the future for longer duration studies. It might be based around using the newer modules from the ISS when it is decommissioned, for a hub for spacecraft to dock to and for zero g research, and then tethered habitats for the crew going round it. If it gets more elaborate, perhaps it would also use spent final stages, fitted out in advance as "wet workshops" like the early ideas for Skylab.

This then would create a small facility in orbit. It doesn't need to be a big hundred billion dollar facility like the ISS, just a small space station to start with, which can also be a basis for a staging post in LEO later on. It could also be a facility for research into closed systems, growing plants and so on. It would have a science component of course, like the ISS, but the main objective would be human factors. It would be forward looking, helping us to find out what role humans can play in space in the future. Which of course would have science benefits in turn. Once we know more about what humans can do and how best to support them, we can then send them on science expeditions further and further afield into our solar system.

It could have a zero gravity module attached to the hub. So, there's no reason why you can't combine zero gravity with artificial gravity in the same station.

It would start small, based on this idea that we are still experimenting, and are not yet very experienced in space travel. At this stage, I think we need to try out ideas, and lots of them, to see what works. This could lead to advances that we would never get if we proceed in a linear planned out way with some grand plan for the future, based only on the knowledge we have so far.

So, it is open ended, and low cost (as human spaceflight programs go). It doesn't have to have a continual human presence, unlike the ISS, which is one of the things that makes the ISS so expensive. There's a strong emphasis on closed systems, doing our best to get biological closed systems working in space, which are, after all, a central part of nearly all human space exploration plans further afield, So let's get started on those right away in LEO. If astronauts stay healthy in some level of artificial gravity, and if we can perfect biologically closed systems so that they produce all their own food and oxygen, then you could send them supplies only once a year, perhaps, or less, and then you could start to occupy it continuously. So then the costs would go right down, and typically at least some of the astronauts would stay up there for several years at a time. If you can achieve this much, then you would get a lot of confidence and experience for long duration missions further afield, not just to Mars or Venus, perhaps eventually also to Jupiter's Callisto, and beyond.

See also my Science 2.0 blog posts on this:

• Crew Tether Spin - With Final Stage - On Routine Mission To ISS - First Human Test Of Artificial Gravity?

• Ingenious Idea: Soyuz Crew in Tether Spin On Way to ISS - For Artificial Gravity - Almost No Extra Fuel -

• Could Spinning Hammocks Keep Astronauts Healthy in Zero g?

• Can Spinning Habitats Solve Zero g Problem? And Answer Low g Questions?

• Crew Tether Spin For Artificial Gravity On Way To ISS- Stunning New Videos- Space Show Webinar- Sunday

• Can Astronauts Spend Years In Space- And How Quickly Can They Recover On Return To Earth?

SMALL CENTRIFUGE BASED ARTIFICIAL GRAVITY EXPERIMENTS IN LEO

This is open research, so we don't know where it is headed. So we should certainly also try small scale centrifuges as well, such as MIT researchers recommended in this paper.

"In order to truly address the operational aspects of short-radius AG, a centrifuge must be made available on orbit. It's time to start truly answering the questions of "how long", "how strong", "how often", and "under what limitations" artificial gravity can be provided by a short radius device."

For plants of course, but also for humans. Artificial gravity was a priority for the ISS up until the loss of Columbia in 2003, first in NASA Ames, then later on the project was passed on to the Japanese space agency, then called NASDA, now called JAXA, who built a Centrifuge Accommodations Module which however never flew because the Space Shuttle was needed to get it into orbit. See page 55 of this paper. Then in 2010 there were proposals to send a centrifuge to the ISS, but it never happened.

We don't know what any of this will be useful for. Perhaps short arm centrifuges turn out to be a vital capability for human health for deep space missions, or perhaps it's the key to health for lunar habitats, or maybe it makes exercise in space much more effective, or maybe it just makes it more comfortable for astronauts in zero g to eat their meals or use a toilet with brief periods of artificial gravity. As basic research, we don't know where it is going until we try it.

It seems that we can tolerate faster spins in zero g than on Earth. Here is Tim Peake spinning at about 60 rpm in the ISS. for a couple of minutes, no nausea, only momentary dizziness when he stops.

(Click to watch on Youtube)

He says he is pretty sure he couldn't tolerate that on Earth. So anecdotally it suggests that we can tolerate very high spin rates in zero g. Taking the radius as 0.25 meters at a guess, his head and feet will be both under full g, his torso around zero g as he spins. Could he spin like this indefinitely? If so, it's very promising I think for the use of a short arm centrifuge to counteract health issues of humans in zero g.

He says his "vestibular system switches off" - but that's just an informal theory of an astronaut. We do have a more detailed hypothesis as well - the experimenters for the Skylab litter chair experiment hypothesized that the reason their subjects could tolerate back and forth spins and continuous spins without getting nauseous in space was because the otoliths aren't stimulated in the same way, because there is no gravity acting in the direction of the spin axis.

So first, background information. Our vestibular system is a system of canals in our ear that help us to tell whether we are spinning or stationary. For some reason spinning motions make many humans nauseous. Rats don't get nauseous when they spin so it is to do with human physiology. On page 95 of Packing for Mars, by Mary Roach she mentions that NASA Ames researcher Bill Toscano has a defective vestibular system. He only realised this when they put him on the spinning chair and he experienced no nauseous effects at all from the spinning. So, he at least, could spend 24/7 at 30 rpm for full gravity with no ill effects. The same is also true for some deaf people.

But of course we don't want our space stations to be only usable by some deaf people and others with a defective vestibular system. The vestibular system is not the whole story though. If it was, then conditions while spinning in space would be identical to those on the Earth. But to complicate things we also have the otoliths.

The otoliths are small particles of calcium carbonate in the viscous fluid of the inner ear. They sense linear accelerations, as distinct from the vestibular system which senses spinning motions. So technically, no, your vestibular system doesn't "switch off" in orbit. You can still sense whether you are spinning, but for some reason you don't get sick. That seems to be because of the otoliths.

This is something we can say pretty much for certain as a result of Skylab tests. So now I'll summarize some of the results from Chapter 11, Experiment M131. Human Vestibular Function in Biomedical results from Skylab.

All of this was done to study space sickness, and not to study artificial gravity. Still, it's the only real experimental data we have on artificial gravity too. In the rotating litter chair they tested the astronauts with both back and forth movements and with spinning motions but only briefly for a few minutes at a time, long enough for the astronauts to do 30 - 60 head movements. Many of the astronauts experienced normal zero g space sickness for the first few days of the mission - so these experiments were done after those symptoms dissipated.

The rotating litter chair used for tests of effects of spinning and back and forth movements on the astronauts in Skylab. It's purpose was to try to understand space sickness, but it also gave our only data so far on effects of spinning motions in space on humans fast enough to generate artificial gravity. There haven't been any follow up experiments on the ISS or MIR or the Chinese space station. So, so far, this is the only data we have on effects of artificial gravity on humans in space..

First the astronauts observations, some quotes from the report, all from (Sec.2,Ch.11)- the M II A end point here is defined as "moderate malaise":

"Preflight, on three widely separated occasions, the M II A endpoint was consistently elicited after 30 to 60 head movements while those astronauts were being rotated at 12.5 r/min (Scientist Pilot) or 15 r/min (Pilot). When rotation tests were carried out in the workshop, both of these astronauts were virtually symptom free; their minimal responses, which were transient, did not even qualify for a score of one point. This was true even when the angular velocities were increased (in two steps) to 30 r/min." (Skylab 2)

It is also noteworthy that both the Commander and Scientist Pilot reported that while engaged in spinning rapidly about their long axes or "running" around the inside of the workshop, they experienced immediate reflex vestibular side effects, mainly "false sensations" of rotation. Based on past experience, both astronauts expected that motion sickness would follow the reflex effects and were surprised by their immunity." (Skylab 2)

- Skylab 2

"Under experimental conditions in the workshop the virtual failure to elicit symptoms of motion sickness in any of the five astronauts who were exposed to a stressful type of accelerative stimuli in a rotating chair (on or after mission day 8) implies that, under the stimulus conditions, susceptibility was lower aloft than on the ground, where symptoms were elicited preflight and postflight. The amount of this decrease in susceptibility could not be measured because the "ceiling" on the test (30 r/min) was so quickly reached." (conclusion)

- conclusions

So - they tested them up to 30 rpm with no symptoms and couldn't test them at any higher spin rate. They were symptom free in space.

Interestingly the lack of susceptibility to nausea actually persisted for a day or two after the flight. The commander of skylab 3 did experience a "vague malaise" in one experiment at 30 rpm, on mission day 52 which persisted for around 30 minutes, but it was not typical of acute motion sickness and so might have had other causes.

"The Commander was tested in the rotating litter chair on two widely separated occasions preflight and demonstrated similar susceptibility levels each time. On mission days 26 and 41 he was symptom free when rotated clockwise, respectively, at 20 and 30 r/min. On mission day 52 he was rotated counterclockwise at 30 r/min and experienced what he described as a slight vague "malaise" that persisted for approximately 30 minutes following the test. The question arises whether secondary etiological factors accounted for both the appearance and nature of this symptom, which is not typical of acute motion sickness, or whether the astronaut was not quite adapted to counterclockwise rotation. Postflight, the Commander was symptom free on the day after recovery when he executed head movements with the rotating litter chair stationary and on the second day postflight when it was rotating clock-wise at 15 r/min. On the fifth day postflight an endpoint was reached that approximated his pre-flight susceptibility level."

(etiological here just means"causal")

The data in their tables is very striking. Here are the results for Skylab 4 for instance.

There, MIIA is a level of mild malaise. During tests at 30 rpm then the astronauts experienced no symptoms at all in zero g, in experiments that evoked symptoms of mild malaise both before and after. They don't say how long the experiments were in minutes, as the results are expressed in terms of the numbers of head movements made.

So why did this happen? Our otoliths are separate from the vestibular system. Instead of sensing turning motions, they sense linear acceleration. In any spin on Earth you have these two things at once - the spin sensed by the vestibular system, and the linear acceleration due to gravity along the axis sensed by the otolith system. They concluded that the reason the astronauts did not get nauseous while spinning was because the otolith system was abnormally stimulated in space and had almost no influence on the vestibular canals. You might think that would make the astronauts more sick, but actually it turns out that the otolith system is part of what makes us feel nauseous and with it almost completely disabled in zero g, we no longer experience nausea in conditions that would make us nauseous in space. They conclude this by a process of elimination, since the vestibular system is stimulated in the same way but the otolith system is not, so it's the only thing that has changed in zero g.

So, let's look at this in a bit more detail. For those interested in the techy details I'll include quotes from the report, but I'll explain them in less technical language, so you can also just skip the quotes and go to the non techy summary after each one. So first, on, the otoliths

"The rotating litter chair was used in the stationary as well as the rotating mode. In the stationary mode when head movements were executed aloft, the canals were stimulated in the same way as on the ground, but the otolith organs were stimulated in an abnormal manner because the impulse linear accelerations generated were not combined with a gravity vector as they would have been on the ground. These impulse linear accelerations were transient but well above threshold for stimulation of the otolith receptors. When the rotating litter chair was rotating, the intensity of the stimuli generated by head movement was a function of the rotational velocity, and although the angular and crosscoupled angular accelerations stimulating the semicircular canals aloft were the same as on the ground, the impulse and Coriolis accelerative forces generated aloft were not combined with a gravitational vector. These forces, nevertheless, were substantial at all levels of angular velocity used, and at 30 r/min the centripetal force was, respectively, 0.3 g and 0.6 g at radii of 1 and 2 feet."

So, the canals were stimulated exactly as on the ground but the otoliths were stimulated in an abnormal manner in zero g. The main difference in space is that there was no gravity acting along the spin axis towards what on Earth would be the ground - this is what they mean by the "gravitational vector"

..."Loss of the g-load would affect the "modulating influence" of the otolithic system. If the otolithic influence was inhibitory the responses elicited by stimulation of the canals are said to be "exaggerated" (ref. 30). The observations bearing on this point in parabolic flight, however, indicated reduced responses to canalicular stimulation (refs. 31, 32, 33) during the weight-less phase." (page 58)

So - the "moderating influence" of the otolithic system is different in zero g because of the abnormal way it is stimulated. If in normal use the otolithic system had a "modulating influence" then you'd expect this to make things worse. But instead it seems that the effect of disengaging the otolith in this way actually lead to much less motion sickness while spinning, not more of it.

..."The difference in susceptibility between workshop and terrestrial conditions is readily traced to gravireceptors (mainly in the otolith organs; touch, pressure, and kinesthetic receptor systems possibly contributing) for the reason that stimulation of the canals was the same aloft as on the ground, and visual inputs were always excluded. If it is assumed that the otolith system is responsible, then the absence of stimulation to the otolithic receptors due to gravity must have a greater influence (tending to reduce the vestibular disturbance) than the disturbing influences of the transient centrifugal linear and Coriolis accelerations generated when head and trunk movements were executed in the rotating litter chair. Al-though these transient accelerative forces, as pointed out in the section on Procedure, are substantial their effectiveness as stimuli are virtually unknown. The otolithic zonal membrane has considerable mass, and transient accelerations lasting fractions of a second might have little or no effect. The absence of gravity, causing what has been termed "physiological deafferentation" of the otolith receptor system, would be expected to reduce not only the indirect modulating influence of the otolithic system on the canalicular system but also its opportunity to interact directly with this system"

Because the stimulation of the canals is the same in space and on the ground, then by a process of elimination, it must be the difference in stimulation of the otoliths that made the astronauts less susceptible to motion sickness. The membrane around the otolith has a lot of mass which reduces the effect of sudden short accelerations. Because of the absence of gravity,which disables most of the influence of the otolith system, what they call "physiological deafferentation", then the otoliths not only have less effect on the vestibular canals, they also are less able to interact with them.

I suggest it should be a top priority to research this further, and find out what is going on, test it for longer periods of time, test it for higher spin rates. It shouldn't just be something that astronauts do out of curiosity and fun. Someone should be measuring and testing them, and finding out why they have such high spin tolerance in space and what its limits are (if any)!

And then based on those results, the next step would be to see if it can be used to generate artificial gravity and perhaps prevent deterioration of health in space. We need to find out what effects these spin motions have on health. I think this seems very promising for the possibility of short arm centrifuges dealing with issues of human health in zero g.

From the data so far, it seems almost certain that astronauts could withstand a few minutes of Artificial Gravity (AG) in a non zero g centrifugal toilet for instance. Zero gravity toilets are tricky to use. Also what about while eating, another thing that becomes much harder in zero g - but if they don't get nauseous then why not eat while spinning too? And what about sleeping? Could they tolerate eight hours of AG while asleep? And during exercise? And if they had AG during all those activities, then what effect would that have on their bodies, would they avoid most of the effects of zero g? Might it actually be healthier even to change between zero and AG back and forth every day? What level of AG is needed etc?

There are bound to be some effects. The cells of plants change gene expression of numerous genes within two minutes of the centrifuge starting. To check effects of artificial gravity on plants they have to preserve the cells within minutes of stopping the centrifuge - or actually in the centrifuge. They are also extraordinarily sensitive to minute levels of gravity. In an experiment with lentil seedlings, they responded to two thousandths of a g, and interpolation suggests they are sensitive to levels of less than a ten thousandth of a g.

Humans have many physiological changes right away when they enter zero g. As with the plant cells, these effects are almost instantaneous. You get them even in hyperbolic zero g test flights. Their average blood pressure in the arteries (mean arterial pressure) decreases right away to below what it is even when lying down (though later it increases in a long duration zero g flight, then adjusts in the opposite direction with higher heart rate than normal on return to Earth for up to 15 days).

So, there are bound to be easily measurable changes in the astronauts' physiology immediately when they start spinning in zero g. Tim Peake's body must have responded in numerous ways to those spinning motions. But we don't seem to have any experimental data on this yet.

These "short arm centrifuges" don't need to be big heavy machines as they are on Earth. Here they have to be strong enough to hold up the weight of a human along the spin axis ("downwards" on Earth) as well as exerting a similar force towards the spin axis for the artificial gravity. But in space, they can be as simple as a hammock in structure, because they only need to hold the weight of a human in one direction only - away from the spin axis. They don't need to be rigid structures either. Like a small version of the fairground swing rides - except that with no gravity along the rotation axis, the swings would just hang out horizontally.

Swing carousel, photo by Wittkowsky, mediawiki commons

My rough diagram of a small version of this inside a space station is like this:

Sketch to show two possible orientations for a spinning hammock inside a large space station module. To prevent this from spinning up the station, then there'd be a counter rotating weight automatically spun in the opposite direction to the astronaut, perhaps attached to the "floor". The motors would not need to be powerful in zero g. It's like spinning a cycle wheel - easy to spin up, and you could stop it just by putting out your hand.

For a very small one meter diameter centrifuge like this, you can achieve full g at 30 rpm and with the astronauts moving at only a little over 3 meters per second so it is very safe. That's around seven miles per hour - faster than a jog, but easy running speed so it's not that fast (a little faster than the average speed for the London marathon). For more about it see my Could Spinning Hammocks Keep Astronauts Healthy in Zero g?

Idea for early short arm centrifuge experiments in LEO.

And here is a 2011 idea for a 1.4 meter radius centrifuge to be located in the permanent multipurpose module:

Sketch of the AGREE centrifuge for the ISS. From page 15 of Design and Validation of a Compact Radius Centrifuge Artificial Gravity Test Platform. It would have replaced the four racks at the end of the Permanent Multipurpose Module. Astronauts would cycle in a seated position. This is one exercise excellent for health which you can do with an extremely compact radius centrifuge like this. Chris Trigg concludes: "Given the compact design, subject positioning, available sensors, tested accuracies, and validated operations, the MIT Compact Radius Centrifuge represents one of the most unique yet realistic centrifuges currently in available for artificial gravity research. It is hoped that through these future studies the MIT CRC will provide a better understanding of the effects and capabilities of an inflight-centrifuge, and perhaps contribute in some small way to progressing towards the inevitable trip to Mars. "

a sketch for a human powered artificial gravity in the ISS .

NASA also took out a patent on the idea, here is a drawing - it's for two cyclists, powered by either one or by a third cyclist outside the centrifuge

And this shows it in experimental use on the ground. It's never flown in space.

The ISS is so full of equipment, that it would be hard to find a space for even a small centrifuge now, although the modules themselves are easily large enough for it.

Inside the Tranquility module when first installed - with a diameter of 4.48 meters, there is enough space for a small centrifuge, but you couldn't do it now with it lined and full of equipment.

Perhaps a very small scale experiment of this type could be done in the new largely empty BEAM inflatable module in the ISS or some future inflatable module?

Beam module expansion Progress The inflatable beam module. Internal diameter is a little over three meters. Though it's smaller than the ISS modules, it is also nearly empty.

Cutaway diagram of the BEAM module now attached to the ISS (credit Bigelow aerospace).

It's a bit small inside, but apart from those four obstructions near the center there would be enough room for a small hammock style centrifuge, with the astronaut reclined to one side of the axis, as in a hammock, for first experiments in effects of artificial gravity on humans in space. It's also large enough for the MIT compact centrifuge / cycling exercise machine described by Chris Trigg.

If we can't do it within the current ISS, it's certainly well within the possibility for future space stations or modules, for instance any of the larger Bigelow modules if placed in LEO would have plenty of space for an artificial gravity centrifuge.

Cutaway image of the much larger B330 credit Bigelow aerospace. There's plenty of space for a large centrifuge here.

Indeed, though I hope the main aerospace agencies will do these experiments in the near future as they move towards deep space missions and the return to the Moon, if they don't, I wouldn't be surprised if private entrepreneurs explore it instead. For instance artificial gravity for toilet facilities or for eating and drinking could make space hotels much more convenient for tourists, so surely they will explore that if we have space hotels in the future. And if artificial gravity helps to keep the tourists healthy on return to Earth, able to stand immediately on return to Earth for instance, again that's a strong incentive for artificial gravity sleeping or exercise artificial gravity in space for medium duration tourist visits. Also artificial gravity could help prevent space sickness in hotels for tourists too.

NASA has recently been tasked by Congress with spending at least $55 million by 2018 on a "habitation augmentation module" that could be used in cislunar space and eventually for journeys to Mars. So I wonder if there is any possibility of a centrifuge for that?

The idea of using a small arm centrifuge in space instead of a large tether has some advantages in LEO, if it works

• More habitable volume available for the astronauts as the space station continues to function under zero gravity, and they don't need a surface to walk on either, so they can continue to use any of the surfaces such as ceilings and floors for any purpose (compare page 103 of this report, though there it's given as a reason for zero gravity missions)

• Astronauts can have individually tailored levels of artificial gravity. That could be due to variation in spin tolerance, or for some other reason, they could set their gravity levels in the small centrifuges to whatever they want.

• Gravity can be intermittent - if you only need gravity for an hour or so a day or only while asleep or exercising etc.

• Zero gravity when you want it

• Easy to dock (with a tether system you need central hub modules to use for docking).

Then, depending on what the reasons are for extra spin tolerance for astronauts in zero g - the same thing might well work in lunar gravity too. For instance if it is due to conflicting sensations between the otoliths and the vestibular system, the astronauts would sense much reduced linear acceleration along the axis, not quite zero, but small compared to the level of artificial gravity perceived from the spinning motion. Could that mean that you can tolerate rapid spins in a lunar habitat too just as you can in the ISS, or perhaps intermediate between zero gravity and Earth gravity in tolerance? There's no way to know except by experimenting and researching. And whether it works for humans, it would also be an extra tool in our toolkit for other things, for instance some plants may do better with extra g even in lunar gravity.

However the least cost way to get started on this is in LEO first. We could do that in the very near future if there was the interest in doing it, and develop the understanding and ideas we need to then design the follow up experiments for the Moon. Then finally, we can design habitats for humans and greenhouses for plants on the Moon using the results of all this research. Again this could go through very quickly, a few years at most to get the early LEO experiments underway, if there was sufficient funding and interest in it.

Again this is a situation where a process of open discovery and development could lead to much better designs for lunar habitats than a "design it all first" approach. Perhaps the first habitat on the Moon should be an experimental module to test various ideas for closed systems and artificial gravity and human and plant tolerance of lunar gravity before we progress to build an entire village there.

For ideas for augmenting lunar gravity using centrifuges see my earlier section above: Artificial gravity on the moon to augment lunar gravity

See also my

• Can Astronauts Spend Years In Space - And How Quickly Can They Recover On Return To Earth?

• Could Spinning Hammocks Keep Astronauts Healthy in Zero g

AFTER LUNAR MAPPING IS OVER

Once the lunar mapping and research phase with robots is done, which might happen very quickly, only a few years with small capable rovers and satellites Google X prize style - then you start thinking about where humans would go on the Moon and what their role would be.

You could wind down the Artificial Gravity and biological closed systems labs in LEO at this stage, if we know the answers to the main questions already. We use the results of their research to design the habitats on the Moon and at L1 and L2 etc. Or the LEO lab could be retained as a staging post for missions to higher orbits. and the Moon when needed, or for continued AG research.

I'd see all this as costing less than the ISS to keep going, once the ISS ends, so it shouldn't impact at all on robotic exploration of the solar system. That's because the facilities are capable of running themselves without humans on board, controlled from Earth. Humans go there for weeks or months at a time first, then they are only occupied 24/7 by humans once you have closed systems working there, so much reduced resupply from Earth.

So, meanwhile we continue robotic missions to Mars, but also to many other places. The robotic exploration perhaps can step up even, since now it would be seen as part of the human exploration, on the Moon, and further afield. It might start to pay for itself as well on the Moon.

And if the humans on the Moon only need supplies once a year or less frequently, again it would probably cost less than the ISS to keep a lunar facility going, once it has been constructed, as it's the supply missions that are the biggest ongoing cost. We could run both the lunar base and the AG lab in LEO at the same time, for less cost, perhaps, than the ISS alone. So this period of time in LEO refining biologically closed systems and working on Artificial Gravity would lead to dividends later on as we design habitats for the Moon and then further afield.

Then building the lunar base would involve ISRU so again it might be easier to build than the ISS was. Meanwhile you have the private space industry, tourism etc. developing which could lead to many facilities in space that are designed for tourists, but can also be used by astronauts or are jointly run by tourist companies and space exploration companies / government entities funded as basic research.

And maybe by this time we have commercial resource utilization already too. If along the way you find that there are those resources on the Moon of commercial value, then it might be that humans on the spot are useful, and could be sent there as a natural part of commercial development. But if it costs less to extract the ice with a purely robotic facility, that might undercut a facility manned by humans. I think we might end up with some optimal mix of humans and robots at this stage.

So then, after a few years of exploration from Earth, when humans go to the Moon, they would have a whole network of robots on the surface that they can control via close telepresence and lunar communications satellites as well. This would also give us valuable experience for exploration of the solar system further afield. As well as that, the work on sending many robots to the Moon would mean that we have learnt a lot about the best and most mobile designs for them, and dealt with bugs such as the Chinese rover that couldn't furl its panels at night. By then, these lunar robots will be robust, mobile, semi autonomous and easily controlled. So it will then be much easier to build the human base from Earth via telepresence, and the robots will be much more capable tools for the humans on the Moon to control.

There are many dangers in any space walk on the Moon, including hazards of falling over and damaging your spacesuit (which could kill you), also the solar storms and cosmic radiation. So, I expect that most future exploration will involve controlling rovers on the surface via telepresence, or exploring the surface in enclosed rovers. There wouldn't be so much by way of EVAs by humans on the surface of the Moon as in Apollo, though of course there would still be some of that.

In this vision, one advantage of the caves idea (if those large lunar caves exist) is that you'd end up with a much more spacious habitat for humans to live in, easier to "build" than a city dome, which could be a plus if it turns out that they don't spend that much time on the surface. They could enjoy the lunar gravity inside the caves. Indeed, eventually, with kilometer scale caves filled with breathable air, they could explore the dream of human powered flight and lunar gravity athletics as well :). And as with the Stanford Torus ideas, they could have habitats with plants and so on inside the caves.

So, this is just a draft idea of how it might continue. In the spirit of this approach, we'd need to be ready to adapt it quickly and change plans depending on what we discover along the way.

We might find out something early on that makes either the poles or one of the caves an obvious first site for humans on the Moon, and go there earlier. We might also do early human missions to the Moon to test systems to use later on. Also commercial space may do it for adventure and tourism. Space Adventures have already advertised to tourists for the idea of a mission to fly around the Moon and back to Earth. It doesn't seem that it is going to go ahead quite yet, but we may see private missions like this in the future.

There's no reason why we can't have missions like this, and countries that have never sent astronauts to the Moon, including Russia, China, ESA, etc. might be keen to do this at an early stage to show that they can do it. The closed systems recycling is not needed at all for short duration missions to the Moon of up to a couple of months or so. (More on this in the section below, and see the conclusions, break even for recycling after a couple of months or so). So, this is not like a prescription to say we shouldn't do that :). It's just a case of taking the long view and showing what that turns up.

For more about the ideas for artificial gravity research in this section see my

• Can Spinning Habitats Solve Zero g Problem? And Answer Low g Questions?

• Could Spinning Hammocks Keep Astronauts Healthy in Zero g?

• Ingenious Idea: Soyuz Crew in Tether Spin On Way to ISS - For Artificial Gravity - Almost No Extra Fuel

• Crew Tether Spin - With Final Stage - On Routine Mission To ISS - First Human Test Of Artificial Gravity?

• Crew Tether Spin For Artificial Gravity On Way To ISS - Stunning New Videos - Space Show Webinar - Sunday

• Can Astronauts Spend Years In Space - And How Quickly Can They Recover On Return To Earth?

For more about the BIOS-3 results and other ideas for ways we can achieve biological closed systems in space, see

• Could Astronauts Get All Their Oxygen From Algae Or Plants? And Their Food Also?

• Beautiful Edible Orange Zinnia - First Zinnia But Not First Flower In Space - And Astronaut Choices

MINI MOONS AND ASTEROID REDIRECT MISSIONS

Although most of the focus here is on the Moon as our most likely first destination, I think I should just digress for a short while to talk about mini moons and quasi-satellites of Earth, a rather surprising recent discovery in Earth Moon space. Also I'll look at the asteroid redirect mission which has been subject of so much study recently.

Earth's first 'quasi-satellite' identified

That seems bizarre at first, but think it through. It’s in a one year orbit around the sun like Earth and it's orbit has the same semimajor axis as Earth (by Kepler's third law that the period depends only on the semi-major axisand since it orbits the sun exactly once a year). So, if at some point it is between Earth and the sun, then half a year later, it’s going to be further away from the sun than Earth. That makes it still in the same direction in space from the Earth.

So - it’s a bit strange to call it a moon since it’s always in the same direction from Earth. But on the other hand, each year it crosses the Earth to Sun line twice, so in that sense, it sort of is in an orbit around Earth, but only in a rotating co-ordinate system.

This shows its orbit though not so easy to follow what is going on as its orbit is so unusual, this is in a rotating frame so with Earth stationary and from this point of view it seems to “orbit” Earth. It’s inclination is not as huge as it seems in this video, it’s inclination is only a bit over 7 degrees so it is pretty much in the same plane as Earth’s orbit:

(click to watch on Youtube)

The NASA announcement is here: Small Asteroid Is Earth's Constant Companion. The Wikipedia article with more details is here: (469219) 2016 HO3 and see also Surprise! Newfound Asteroid Is 'Quasi-Moon' of Earth

It’s about 5 km / sec delta v to get to it from Earth in an energy efficient orbit, and about 1 km / second to get back to Earth, relying on aerobraking in the Earth’s atmosphere. NHATS Object/Trajectory Details. It's

Could we do anything useful with it? Assuming two metric tons per cubic meter for a very rough idea, and diameter 40 to 100 meters as they suggest, that would be . between 2.26 million tons and 8.38 million tons so it's a lot of material. By comparison a Stanford Torus requires 10 million tons. So you could do a fair bit with it, depending what it is made up of.

If it has useful resources then you could also supply them to LEO or to the Earth’s surface using that 1 km / sec return trajectory with aerobraking. If it is an iron meteorite, you could mine it for the metals and return them. But we don't know what it is yet, could be a source of volatiles also. Might be useful in some way. If nothing else it could be useful for shielding for a spinning space habitat if there was a reason to build one there.

Or perhaps it is useful where it is at some point? Or just of scientific interest.

Also, I wonder if it could be the first of many smaller objects in similar orbits. At any time the Earth probably has at least one asteroid of diameter a meter orbiting it and probably many smaller ones

Path of a simulated mini moon. It approaches Earth along the yellow path, orbits it in this complex fashion for a number of "orbits" then escapes into interplanetary space again along the red line. At any time Earth probably has at least one asteroid of diameter a meter or more in an orbit like this, along with many other smaller "mini moons". The inset shows 1999 JM8 which is much larger than any of the expected mini moons, just included because the smaller mini moons are expected to look much like their larger cousins, only smaller. From: Simulations Show Mini-Moons Orbiting Earth

We actually know of one mini moon that's done this sort of thing, 2006 RH120 which is 2-3 meters in diameter and orbited Earth for three quarters of a year from September 2006 to June 2007. At it's closest, on 14th June 2006, it was 275,000 km from Earth, or about 71.5% of the distance to the Moon. At first it was thought to be a piece of lunar hardware but the observations weren't consistent with that. Bill Gray suggests it might instead be a piece of lunar rock ejected by an impact because it would be hard for a normal asteroid to lose so much energy relative to the Earth and Moon to get into such an orbit, while it would be easy for a rock ejected from the Moon to get into it. Assuming a density of 2 tons per cubic meter, then it could be up to 28 tons of material. A one meter diameter mini moon would be approximately one ton of material if of the same density. So a rather small amount of material.

I wonder if Earth has a cloud of these more distant moons as well?

Anyway this leads on to the asteroid redirect mission. This is a mission proposal by NASA which, if I understand right, they came up with basically because the Obama administration tasked them with sending humans to Mars but without going back to the Moon. Since a mission to Mars would be a long and dangerous mission, they needed something safer to do closer to home first to test the systems. So they came up with this idea of sending humans to a nearby asteroid. The problem is that even near Earth asteroids are not easy to get to as they only do occasional flybys of Earth, perhaps every decade or so. So you have a small window of opportunity to get there and back unless you are prepared to wait on the asteroid for a decade before it comes back to Earth's vicinity again and even those missions are long duration for our first flight beyond LEO for decades.

So then they came up with the idea of instead getting one of these asteroids and returning it into an orbit around Earth (or around the Moon) a bit like one of these mini moons.

One way of looking at it is, that since they were not permitted to send the astronauts to the Moon itself, they would create their own mini moon instead for them to visit first before going to Mars. It is also a mission you can do without first creating a dedicated lunar lander on the other hand landing a human occupied vessel on an asteroid has its challenges too.

Well that's how the project seems to me, I know this is a somewhat biased way of looking at it as I've never been keen on the idea :). Not the idea of doing this as a human mission which you do as your only precursor mission before going to Mars. But it does make sense as one mission of many you could do in the context of large scale exploration of cislunar space and further afield.

So, if you redirect a very small seven meter diameter asteroid, as they proposed, or a seven meter diameter boulder removed from an asteroid, you can choose what orbit to put it into. After studying many ideas they came up with the Distant Retrograde orbit.

What makes this proposal tricky is that first, even for a five hundred ton asteroid, only seven meters in diameter, though of minimal risk to Earth, they didn't want to return it to LEO for safety reasons. The safest is to return it to lunar orbit, but most orbits of the Moon are very unstable, that's for orbits around the Moon in the same direction that the Moon itself slowly rotates. Satellites close to the Moon get tugged this way and that by the gravitational anomalies and the satellite soon hits the Moon. For that reason also, we don't expect to find any natural satellites, even small ones, orbiting the Moon in a prograde direction. There are a few "frozen orbits" but they are very hard to get into, we can do them with our satellites but not likely a natural satellite would find them. Also the frozen orbits are very inclined orbits, and they are only stable over time periods of years and decades, not for millions of years.

However the retrograde orbits are more stable. These are only retrograde (i.e. orbiting in the "wrong direction") from the point of view of the Moon. They orbit Earth in the same direction as the Moon itself. Indeed from Earth they seem like a reasonably regular orbit, with a period of exactly one lunar month, except that they are in a more elliptical orbit. They come closer to the Earth than the Moon and as they do so they orbit Earth more quickly (by Kepler's equal areas rule). That then takes them ahead of the Moon and then as they move further away from Earth than the Moon, they slow down and then eventually fall behind the Moon, and complete the cycle. In this way they continually orbit the Moon but in the retrograde direction.

There are orbits like this at any distance from the Moon, even "orbiting" it so far away that when closest to Earth they dip down nearly all the way to LEO. Some of these orbits are very stable, with orbits of up to a century or more.

So, this could be a good orbit to nudge an asteroid into, or a boulder recovered from an asteroid, as it would be very accessible from both Earth and the Moon.

This diagram shows a typical DRO:

From Asteroid Final destination (Understanding NASA's Asteroid Redirect Mission).

Another possibility is to return it directly to the EML2 or EML1. These are not stable positions but it is easy to do station keeping around them and may be the location of a future human occupied base. For an idea of how the calculations go, Hop David shows how to put one of the asteroids into an orbit around Earth and eventually send it to EML1, asteroid 2008 HU4 in his case, with only 25 meters per second delta v - his calculation is for 2015. He first redirects it so that it does a close flyby of the Earth Moon system. He arranges for a flyby of the Moon in just the right direction to capture it into the Earth Moon system. Then he does another burn to get it to do a second swing by of the Moon, and a final nudge parks it in the EML2 position just a short way beyond the far side of the Moon. From there it is also easy to move it to EML1 if preferred, the similar point of balance between the Moon and Earth on the near side of the Moon.

An asteroid like 2008 HU4, about 7 meters in diameter, would weigh be around 500 tonnes and that's a lot of material if we had to send it all to EML1 from Earth, or even from the Moon. It may be well worth doing, even if it is just used as solar storm shielding. Depending on the asteroid, it could also be useful as a source of water which could be split into hydrogen and oxygen. It could also be a source of nitrogen, and also, iron, nickel and platinum group metals. So it could be used for propellants, and life support and structural components as well as the radiation shielding.

I wonder if one of these mini moons could be of interest for a human mission also? They are far more of a challenge to reach in one sense, because of their erratic orbits, but on the other hand you don't have to descend to the surface of the Moon, and they do spend a fair bit of time close to Earth if we happen to catch a large one that is in it's vicinity for a few months. So they could be an interesting target for a human mission if we can catch them at he right moment. Could one of them even perhaps be redirected into a DRO orbit during some suitable point in its erratic trajectory around the Earth Moon system?

2016 HO3 could also be of interest for a human mission - but a long one - it's either 154 days with only 8 days there for 6.114 km/s total delta v or 154 days including 8 days there for a 11.955 km / s delta v - but with frequent opportunities once a year at least and almost any time if you permit it to use more delta v. It seems more likely to be a robot destination.

I think these close flyby asteroids or mini moons could well be useful as part of our exploration of the Earth Moon system, either "as is" or redirected to a more convenient orbit. I don't think they are any kind of a substitute for going back to the Moon. But going to them as well as the Moon could be interesting, and a different challenge from a mission to the lunar surface as well as potentially useful for getting shielding and other resources for habitats in the Earth Moon system, for instance at the Earth Moon L1 and L2 positions balanced above the far side of the Moon or the near side. The mass of a small asteroid. 500 tons isn't that much, but it would be sufficient radiation shielding at one ton per square meter for a spherical habitat 12.6 meters in diameter - not so shabby! It could well be a useful support base between Earth and the Moon where a permanent crew can stay safely for years on end as they explore the Moon via telepresence and support the surface explorations there. It could also be a useful refuge for astronauts who encounter a solar storm during the 3 day journey from the Moon to Earth. And having done this asteroid return once, you can return more asteroids and do it many times.

• Detailed study from 2012 of the possibility of returning an up to 7 meters or so diameter, 500 tonne asteroid to cislunar space, alternatively a 7 meter rock from a larger asteroid. It's all done robotically, and total cost was estimated at $2.6 billion. Returning an Entire Near-Earth Asteroid in Support of Human Exploration Beyond Low-Earth Orbit

TERRAFORMING THE MOON

Longer term, some have suggested we could terraform the Moon. Surprisingly, we can - well - sort of. With its weak gravity it can’t keep an atmosphere for long, but it can keep it for longer than you might expect. Thousands of years. It is a bit like building a huge domed city on the Moon - to turn a lifeless lump of rock into a habitat. The main difference is that it uses a lot more mass per unit area of atmosphere than a city dome because it is open above, and you have to keep replenishing it. The atmosphere does though have the advantage of shielding from even quite large meteorites. It seems like a project for a megatechnology future.

I work out here using work by Landis, that a comet 600 km in diameter, and 0.5% nitrogen from the Kuiper belt (say) (where there is more nitrogen) could spin it up to a 24 hour day, give it an ocean 1.3 km deep and it would have an atmosphere that lasts for thousands of years. Ordinary photosynthesis would take 100,000 years to make the water into a breathable atmosphere, so you’d do better if you have vast amounts of fusion power or similar to split it using electricity.

There are many major challenges however, including reactions of the atmosphere with the lunar crust and the need to keep replenishing the atmosphere without harming its inhabitants.

Other approaches such as city domes, lunar cave colonies and perhaps eventually paraterraforming (covering with a transparent”roof” to make a kind of a “world house” to keep in the atmosphere) are all easier than terraforming. And terraforming is a long timescale mega project. So not suggesting we try it :), but theoretically it is interesting to look at it.

So first, on atmospheric loss, it loses its atmosphere quickly. Geoffery Landis looked into this.

• The Moon loses its hydrogen and helium very quickly, on a timescale of fifteen minutes on the sunlit side, just because the gravity isn't strong enough to hold them in place.

• It loses heavier gases like nitrogen and oxygen over time periods of thousands of years, longer than most civilizations last.

• When the atmosphere is very thin, it loses nitrogen and oxygen much more quickly, as a result of the atoms getting ionized and then swept away by electric fields associated with the solar wind. They get lost in about 100 days. But if we can thicken the atmosphere up enough, this mechanism is no longer significant (the number of atoms ionized is the same or even increased a bit, but it's a tiny fraction of the atmosphere), and then the atmosphere will last for thousands of years.

See his Air Pollution on the Moon for details. His main focus there is the adverse effect of the atmosphere created as a byproduct of industry on the Moon, leading to degradation of the valuable high vacuum there. But he does briefly touch on terraforming at the end.

Then Gregory Benford, the hard science fiction writer, thinks we can terraform it, in this rather intriguing article: A Terraformed Moon Would Be an Awful Lot Like Florida.

He envisions hitting the Moon with a hundred comets the size of Halley's comet - at the same time spinning it up so it has a day of 60 hours.(I'm not sure of his calculation, it seems that the number of comets needed is more like 10,000, see below).

Presumably you would keep adding new comets to it - but if he is right that 100 comets are enough - then just adding one new comet a century would keep it going - and you could do that without harm to the citizens of the Moon by breaking the comet up into tiny pieces before it impacts onto the lunar atmosphere. So what would it look like if we could terraform it? Well here is an artist's impression of a terraformed Moon.

Terraformed Moon by Exospace on deviantART

I prefer this to ideas for terraforming Mars, because there is no life on the Moon to be impacted by it. Also the Moon is close to Earth, and it is clear that it has to maintain a high technology to keep it terraformed, so if both Earth and Moon have high technology, they can work together. The Moon is at a fixed distance, and we can set up some easy way of getting back and forth with space elevators or space tether systems. And use the same factories - and exchange materials from one to the other easily etc. It is similar to the idea of a very huge Stanford Torus, to terraform the Moon. It turns a lifeless though very large region into a habitable area.

With Mars, then if it can be terraformed, it's on the thousands of years timescale, with lots to go wrong. It may seem like a new earth but if you can terraform it as quickly as that, it needs mega technology to stay terraformed, and it might unterraform as quickly as it terraformed.

• PLANTS HAVE TO WORK SIX TIMES HARDER - TO MAINTAIN THE OXYGEN IN AN ATMOSPHERE SIX TIMES THE MASS PER SQUARE METER

On Mars the plants have to work roughly three times harder than on Earth so it needs about three times as much oxygen to achieve the same partial pressure on the surface. For the Moon the plants have to work six times harder, but they get about double the levels of sunlight they get on Mars for photosynthesis.

If you work it out in detail, there is very little between them in this respect

Detailed calculation: to achieve an Earth normal 10 tons per square meter of atmosphere pressure in lunar gravity - you need 60 tons per square meter of gas in mass. The plants need to maintain 12.7 tons of oxygen per square meter (2.095*9.807/1.622) instead of the 2..095 tons per square meter of oxygen for Earth. On Mars they need to maintain 5.54 tons per square meter (2.095*9.807/3.711). So they need to create 2.29 times as much oxygen on the Moon. Earth (and so the Moon) gets 2.25 times as much sunlight as Mars. So there isn't much in it.

• CHECKING THE CALCULATION - 100 COMETS - OR 10,000 COMETS??

Let's check his Halley's comet calculation, calculation indented and I'll include all the steps in detail to make it easy to check.

With a radius of the Moon of 1737.4 km I make the surface area of the Moon 4×π×1737.4² = 37,932,328 square kms. For an Earth pressure atmosphere we need (9.807/1.622)×10 tons per square meter, or around 60 tons per square meter, and multiply also by 10⁶ for the number of square meters per square kilometer, that's 37,932,328 × 10⁶×60 = 2.28×10¹⁵ tons or 2.28 quadrillion tons. Halley's comet is242.5 billion tons.

So you would need around 2.28 quadrillion/242.5 billion or 9,402 of Halley's comet.

Geoffrey Landis assumes a one psi atmosphere, of pure oxygen, at the Armstrong limit so about 6.9% and works out the total mass needed as two hundred trillion tons or about 825 Halley comets..But he works that out as 50 to 100 Halley comets so must be assuming a larger mass for Halley's comet of two to four trillion tons - it's an early paper from 1990 so I think he is just using older data for Halley's comet.

So, I think Gregory Benford's 100 Halley comets probably comes from Geoffrey Landis's paper. - it means 100 comets the size of Halley but with an older figure for the mass of Halley. And both are assuming the thinnest atmosphere a human can breathe without the moisture lining their lungs boiling.

Approaching it another way, our 2.28 quadrillion tons of atmosphere for an Earth normal atmosphere corresponds to around 2.28 million cubic kilometers of ice assuming average density of 1 (there are a billion tons to a cubic kilometer of water). Or assuming a density of 0.532 tons / cubic meter (same as comet 67p) that's 4.3 million cubic kilometers

So solving for radius, then you get

π×r³×4/3 =4.3 ×10⁶

So r = cube root(4.3×10⁶×3/(4×π))

= 100 km approx.

So in short, it seems that you need more like 10,000 copies of Halley's comet, or you could hit the Moon with a comet of about 200 km in diameter - or larger if the density is less than 0.532, less if it is more than 0.532. If you did that, you'd have enough material for an instant atmosphere. That is if it is all potential atmosphere, but of course a lot would be water, perhaps 80% which you'd need to convert to atmosphere somehow, perhaps split the hydrogen and oxygen to create an oxygen atmosphere. In Geoffrey Landis' paper he suggests UV from the sun could split the water to generate oxygen:

"Alternatively, if we could find an icecube fifty kilometers on an edge and crash it into the moon, the moon would acquire an atmosphere of water vapor. That, as it happens, is just fine--in a relatively short time (well, "short" might mean as much as hundreds of years) ultraviolet from the sun will split off the hydrogen, which leaks away, leaving atomic oxygen, which will quickly combine to form ordinary O2--just what we need to breath."

If you aim is to make a CO₂ atmosphere, then assuming it is 80% water, then you'd need

r = cube root(5×3.83×10⁶×3/(4×π))

= 166 km approx. Or 332 km in diameter.

If the aim is nitrogen, with 0.5% of the comet made of nitrogen, and needing 78% of the atmosphere as nitrogen, you are talking about cube root((100/0.5)×0.78×3.83×10⁶×3/(4×π)) or 522 kim in radius, so about 1044 km in diameter. There would then be plenty of water, and carbon dioxide.

Once we can move large comets easily from the outer to the inner soar system, this could be possible selecting a large comet of a suitable composition. You'd have a lot of water as well which would be useful.

SPINNING IT UP TO A 24 HOUR DAY

How much mass would you need to use to spin it up to a

hour day?

Well it’s radius is 1,737 km

A comet could impact at 53 km / sec and possibly up to 70 km / sec if you could deflect a very long period comet to hit the Moon

Impact Cratering Mechanics

The angular momentum of the Moon in its current 28 day spin is 2.32×10^{29} kgm^2/s

see Robert Walker

's answer to What is the angular momentum of the moon in its rotation around its axis?

Using L = rmv then the angular momentum imparted by an impact by a 2.28 quadrillion tons, 200 km in diameter comet (the minimum needed if it is entirely Earth atmosphere, implausibly) would be

mass: 2.28 × 10^{18} kg

Radius = 1,737 km or 1,737,000 m

Velocity 70 km / sec or 70,000 m/s

Angular momentum 2.28 ×10^{18} ×70,000 × 1,737,000 = 2.772252 × 10^{29}

So that would seem to be enough to more than halve its rotational period

655.728 hour rotational sidereal period Moon Fact Sheet

But suppose we have a larger impact like that comet that’s only 0.5% nitrogen? Let’s see how much mass we need to achieve a 24 hour day.

We need

2.32×10^{29}× (655.728/24 -1) = M ×70,000 × 1,737,000

M = 2.32×10^{29}× (655.728/24 -1) / (70,000 × 1,737,000) kg

= 5× 10^{19}

It’s diameter would be around 200×( 5× 10^19/ (2.28 ×10^18 ))^(1/3) or about 600 km in diameter. Or probably a bit smaller than that since it would be denser.

A large comet would both add enough nitrogen, and water for some lakes and seas as well as spin it up to 24 hours.

Suppose most of it is ice. Then

Surface area of Moon: 37.9 million square kilometers The Moon Compared to Earth - Universe Today

So that’s 5×10^{19}/ (37.9 ×10^{12} ×1000) tons/ m2

= 1319 meters or about 1.3 km in depth of water.

So if you impact it with a large 600 km diameter comet (may be a bit smaller given that it’s going to be denser than the average comet) at 70 km/sec it would spin the moon up to a 24 hour day and add an ocean 1.3 km deep. And it would add more than enough nitrogen for a full nitrogen atmosphere.

• BUFFER GAS - SUCH AS NITROGEN, NEEDED FOR A BREATHABLE ATMOSPHERE

Then - for a breathable atmosphere - then you need to have a buffer gas, which on Earth is nitrogen (CO₂ is poisonous to humans in large concentrations). You can have a thinner pure oxygen atmosphere with no buffer gas, but this is a fire risk (as we found out in practice with the Apollo 1 disaster), so not likely to be used for terraforming or large scale habitats, though it is used for spacesuits as it reduces the pressure inside the suit so makes them more flexible and easier to use and the fire risk can be managed in a spacesuit by using fireproof materials. It's not really feasible though to make a terraformed Moon in its entirety fire resistant.

So most of that weight needs to be nitrogen - unless you have some alternative buffer gas. Halley's comet has hardly any ammonia (NH₃). As for Kuiper belt objects, their interior composition is highly varied from rocky all the way to solid ice,

The compositions of Kuiper belt objects - but I can't find much about the ammonia and nitrogen abundances inside the objects (rather than on the surface). There are some meteorites also that are rich in nitrates. But finding enough nitrogen might be a problem if that's our buffer gas, seems to me. Titan has a dense nitrogen atmosphere, and is larger than our Moon and has an Earth pressure atmosphere so it has enough nitrogen, it's just in the wrong place and inaccessible from Earth. It doesn't seem practical to transport its atmosphere to the Moon. Also, it's unique and interesting in its own right, as the only moon of its type in our solar system.

So, it seems that we depend on comets. If a comet is only 0.4% ammonia, or nitrogen etc., you need nearly 200 times as many comets for the nitrogen, so two million copies of Halley's comet. Or a comet 6.3 times larger turning our 200 km comet into a 1,260 km diameter dwarf planet.

Maybe you have to hunt around - there are lots of Kuiper belt objects, we only have discovered a tiny fraction of them and maybe one of them has lots of nitrogen? For all we know, maybe when we expand the search, maybe we find tens of thousands of nitrogen rich Kuiper belt objects the size of Halley's Comet - far too small to spot from Earth with existing telescopes? We can't really do a decent calculation here unless someone has a good idea of a source with a well known nitrogen rich composition.

If we find one, then we have to move it into the inner solar system and hit the Moon (gently) before the nitrogen rich ammonia (or more difficult, nitrogen ice) gets a chance to evaporate. If it is a large body and we move it into the inner solar system quickly, this seems feasible, without going into details of the calculation. It would be a bit like storing ice through the summer which they used to do in high latitudes before freezers and refrigerators. Or for that matter, with the level of technology we are imagining here, we could just cover the comet with a reflective layer to keep it cool for the journey.

• REACTION OF OXYGEN WITH THE LUNAR CRUST

Another problem - if you want an oxygen rich atmosphere - well the Earth had reduced iron and it took millions of years to oxidize it before we managed to get an oxygen rich atmosphere. Basically, all the reduced iron has to rust. A process that has already happened on Earth, and on Mars (it's the reason the surface is red) - but not yet on the Moon.

So - same is likely to happen on the Moon. Maybe we can speed it up but for a long time all the oxygen we create will get absorbed by the lunar crust through chemical reactions, as happened on Earth in the early stages of the Great Oxygenation Event

"The upper few kilometers of the lunar surface contain several times 10¹⁸ kg of iron(II) which in the presence of water would readily react with oxygen to form iron(III). Such an amount of iron(II) could easily absorb all of the oxygen in the Earth atmosphere.

"A large fraction of the Moons crust consists of oxides of calcium, magnesium, and iron(II), which in the presence of water would react to form hydroxides that would (partly) dissolve in the forming seas to create a poisonously alkaline fluid, with pH 10--11. If enough oxygen were available to oxidize the dissolved iron(II) hydroxides, insoluble iron(III) hydroxides would precipitate on the sea floors and shores, creating vast quantities of slightly poisonous, orange mud. Such reactions would be violent and fast in the upper part of the crust, but their rate would decrease with increasing depth. The oxidizing, hydration, and other processes would continue for ages. In the meantime oxygen and other pressures would not be stable. Most of important all: the absorption of such enormous amounts of oxygen, water, by the upper part of the crust of the Moon would make the rocks expand by perhaps as much as ten percent or more. One can wonder if such expansion would be a tranquil process. It could create strong quakes for possibly many thousands of years. "

from: An Atmosphere for the Moon

So, the upshot of all this is, the terraforming the Moon may well be possible with future technology which may not be that far away, especially with nuclear fusion or such like. But I think it may be a little harder than Greg Benford suggests in his article.

Terraformed lunar far side by Ittiz.

If I've got the figures right here, you need 10,000 Halley comets, or a giant comet 200 km in diameter. If you need to supply nitrogen as a buffer gas from comets with the same composition as Halley, you need two million copies of Halley's comet, or a larger dwarf planet perhaps up to 1,260 km diameter depending on how much nitrogen it has in its composition. After that, you would have many issues with reaction of the water with the dry lunar surface. And then the plants would have to work six times harder than on Earth to produce the same partial pressure of oxygen.

Do be sure to correct me if I have made any mistakes here!

Of course many of these issues would also turn up for Mars, and if you compare it with Mars it doesn't seem so bad.

Mars would need similarly huge amounts of nitrogen for instance, less per surface area but more in absolute terms.

Comparison of mass of nitrogen needed for Mars and the Moon: the Mars surface area is 144.8 km² and for the Moon, 37.9 km². To get the same atmospheric pressure, the Moon has to have 2.29 times as much mass per square meter than Mars. So the amount of mass needed for Mars is 144.8/(37.9* 2.29) so Mars needs 1.67 times the mass for the Moon. Or about 3.34 million Halley comets to supply it with nitrogen, unless it is available indigenously.

The plants have to work six times harder just as for the Moon. The atmosphere lasts longer on Mars, but it's not a permanent feature without megaengineering - it will disappear over millions of years timescales. On Mars you need to have global mirrors or greenhouse gases and still supply some volatiles with comets, for the Moon you don't need to compensate for reduced sunlight but need a constant input of volatiles.

New carbon cycles have to be set in place in both cases to return carbon to the atmosphere and these have to be based on novel principles as Earth's cycles won't work in the same way, especially the long term conversion of limestone back to CO₂ as a result of subduction due to continental drift won't work on the Moon or Mars. As for the Moon, Mars also has deserts which are extremely dry and will take up much of the water if water is added to the planet (though it doesn't have the problem of oxygen reacting with the surface materials). And so on.

So - the Moon might not be so bad if you compare it to Mars, maybe you could terraform it a bit faster as a smaller object needing less total mass, and it doesn't need any supplemented sunlight or greenhouse gases. But it seems an impractically mega project even so with present day technology.

To last longer than a few thousand years, it would need constant maintenance in the form of extra volatiles from comets, which you could do safely by breaking up the comets into small chunks and sending those to hit the lunar atmosphere.But the same is true for ideas of terraforming Mars they need constant maintenance in the form of orbiting mirrors or greenhouse gases and need some resupply of volatiles as well to keep it terraformed (if it worked).

In the case of Mars constant maintenance is needed because the planet is too cold to remain habitable without orbiting mirrors or greenhouse gases, while in the cases of the Moon it is because its gravity can't hold onto its atmosphere. Mars loses its atmosphere also, but on much longer timescales.

However, it's not really that much different.

The timescales are similar too for creating the atmospheres. To create an oxygen rich atmosphere on Mars means sequestering out all the carbon assuming there is enough CO₂ to make an Earth density atmosphere which most think there isn't (at most enough for 10%) and that process would take around 100,000 years using photosynthesis, as a result of which Mars would of course cool down even further without CO₂ to warm it up so need more greenhouse gases or orbital mirrors.

I'm not suggesting we terraform either. I don't think we are anywhere near the stage where it makes much sense to attempt terraforming, a trillion dollars a year project that you have to commit to for thousands of years, whether it is for the Moon or for Mars or anywhere else. We find it hard to commit to a space project for a few decades and a few billion dollars a year. That's apart from planetary protection issues. And as well, we just don't know anything like enough about how ecosystems work, getting unpleasant surprises with "toy ecosystems" the size of Biosphere II, and not able to make even tiny changes to the atmosphere of Earth. If we could make a 0.01% change in the amount of CO₂ in the atmosphere the global warming crisis would be over right away.

However, just as a matter of the physics. the Moon can in principle be terraformed though with many issues you'd have to sort out. But the same is true for Mars. I don't see them as that much different actually. Not with present day ideas of terraforming. We would need to understand this all in a lot more detail than we do now to see which is best, if either can be terraformed in practice. For more on this see: It is not at all clear that we can terraform Mars

Terraforming the Moon is another of those topics that doesn't seem to have a lot of attention in the academic literature. But apart from Greg Benford's article, here are forum discussions which are a good source of ideas, though of course not peer reviewed:

• Issues concerning the very difficult terraformation of Luna [Archive]

• Terraforming the Moon - Your opinion, please (Page 1) / Terraformation / New Mars Forums

And then the An Atmosphere for the Moon and there's the Universe Today's HOW DO WE TERRAFORM THE MOON?

However there's another solution,

PARATERRAFORMING THE MOON

Paraterraforming means covering the surface with habitats, eventually domed cities and eventually the entire surface covered in habitats. Eventually they could merge together to make a kind of a sky to hold the atmosphere in - with lots of partitions for safety.

That needs far less atmosphere - because instead of 60 tons of mass per square meter to supply atmospheric pressure - you just have as much air as is needed to fill your greenhouses, which may have heights measured in meters. Even if the greenhouses are a hundred meters high, that's 122.5 kilograms per square meter instead of 60 tons per square meter of air, a huge saving (using density of air of 1.225 kg / m² )

Can a complex closed ecosystem work with a shallower atmosphere like that? They thought it might with Biosphere II but it proved harder than expected, still there doesn't seem to be any major reasons why not. You still have the problem also of oxygen and chemical reactions. But maybe at the same time that you enclose them from above, you can insulate them from the subsurface as well so they don't lose their oxygen through chemical reactions with the lunar soil. One way to do that would be to turn the surface into glass, though you might instead want to use bulldozers to remove a few meters depth of regolith, turn the layer below into glass then replace the regolith to use as soil. This is quite reminiscent of Biosphere II where one of the main reasons it failed was because of chemical reactions involving the concrete the habitat was made of.

This has many advantages

• You need much less by way of air, because it only needs to cover the surface to a depth of meters rather than kilometers.

• You ned much less water, because you can use lined ponds, and generally, insulate surface habitats from the ground, rather than just pour the water onto the surface which is covered to considerable depth with dry regolith over dry rock. Drier even than the Sahara sands.

• Insulating habitats from the ground would also prevent those issues of moon quakes.

• You can reduce losses of water and air. As I said above, a 1 kg loss per person per day would be a thousand tons lost per day. That could be reduced to almost zero by using ionic fluids based liquid airlocks, or other techniques to make sure that almost no water or air is lost when you go in and out, and much improved recycling. Same also if the entire surface is covered in

• If you have really good technology here, to keep air and water inside your habitats, you may even be able to retain parts of the Moon as hard vacuum for factories and processes that need vacuum, or the pristine original surfaces for scientific study.

• You can start by living in the caves, which if they are as large as theory suggests, may be huge O'Neil colony sized habitats already set up for you. Then move up to domed cities in craters. There's a natural progression there on the Moon which could gradually lead to paraterraforming in the future.

I can't find an illustration of a paraterraformed Moon but the same idea can be used for large asteroids and small moons too, if you can tolerate the low gravity. Here is an artist's impression of a paraterraformed Phobos by Ittiz

WE ARE LIKE THE EARLY ANTARCTIC EXPLORERS

I've touched on this comparison a few times already but let's follow it through a bit further this time. We are like the first explorers to get to Antarctica.

To colonize space right now - Mars, the Moon or anywhere - is like Shackleton saying “Oh, we managed to survive a winter here, huddled under a boat and hunting seals, amazing, let’s colonize Antarctica”.

Those remaining on Elephant Island in Antarctica waving farewell to Shackleton and his five crew as he set off in the James Caird boat to find rescue in South Georgia. They managed to survive a winter in Antarctica, but they didn’t say “Oh great, let’s colonize Antarctica :) “ Ernest Shackleton and the Endurance expedition, The voyage of the James Caird, Elephant Island

(they weren’t first to overwinter, that honour goes to the Southern Cross Expedition)

Norway's most significant historic site in Antarctica Southern Cross expedition - first to over winter in Antarctica Southern Cross Expedition

Mars may look more habitable than Antarctica but that’s mainly because it is so dry. If it did have enough water, the whole planet would be covered in a thick sheet of ice. It is very very cold there, especially at night when the air gets so cold that some of it starts to freeze out as dry ice, even in equatorial regions, for many nights of the year forming the ice / CO₂ frosts photographed by Viking.

Actually Antarctica is far more habitable than either Mars or the Moon. It has a breathable atmosphere to start with, it's hard to beat that, no radiation problems, and you don’t have to hold in the air in against an outwards pressure of several tons per square meter. That is why space habitats like the ISS are such massive feats of engineering, with living quarters made up of tubes with rounded ends, or spheres, or in future perhaps, donut shaped space settlements. Everything has to be contained in rounded surfaces of strong materials.

Also they usually have few or tiny windows, because it is a challenge to make a transparent pane to withstand several tons per square meter of outwards pressure. If the interior is pressurized to Earth sea level equivalent, as for the ISS, then it has nearly a ton pressing outwards on a tiny window 30 cms by 30 cms (ten tons per square meter). It's much the same on Mars also, as there's only 1% difference in the amount of outwards pressure on the walls of a habitat on the Moon and on Mars, when pressurized to Earth sea level equivalent.

Even the summit of Mount Everest is far far more habitable than Mars.

Compared to the surface of Mars, the summit of Mt .Everest is a paradise and would be a wonderful place to grow your tomatoes compared to Mars. You can almost breathe the air, with only supplemental oxygen, you don’t have to wear a spacesuit, your lungs won’t be damaged irreversibly with the water lining them boiling, you just need to warm it up and supply a bit of extra oxygen, easy peasy :). Well not really but compared to Mars it is.

If Shackleton's party had had that as their main objective, to "live off the land" they might well have succeeded for a while, killing seals and penguins for food and using their fat for fuel to keep warm, a bit like high tech Inuit. After all Shackleton's party did survive an Antarctic winter while he and five companions set off to find rescue for them in a small open boat. However with early twentieth century technology, however enthusiastic the first settlers were; soon, surely their children would decide they'd had enough, and want to come home, and not continue with the harsh difficult way of life their parents had chosen.

Instead of attempting this, the early Antarctic explorers did their exploring, and scientific study, and then came back to their warm comfortable homes at the end of each expedition. For year after year they continued to explore, built temporary bases, then more comfortable ones, and now we have many bases in Antarctica that are occupied all the year round (though with fewer people there in the Antarctic winter).

So, I think it's the same with space. First, we don't need to colonize space for the human interest. As with Antarctica, there will be plenty of interest with scientific exploration, adventure and tourism. Then, if we go into space to try to colonize right now, we will never succeed. Instead people will just get discouraged.

It is just too hard. Would you colonize a mountain plateau 30 kilometers into the atmosphere, more than three times the height of Mount Everest? At that height you'd have the same atmospheric pressure as Mars, but it would be much more hospitable in other ways. Perhaps it could be done, but why live in a place where everything is so difficult to do? Unless you have some very strong reason for living there, people just wouldn't set up home in a place like that, Not once the novelty wore off. But you'd go there for adventures, you'd have scientists studying, and so on.

There is no sign at all that we have come to an end of the science we can do in Antarctica, or that people will lose interest in going there as tourists, or going on adventures there. Yet, we are nowhere near to starting up a true colony there, and nobody has that as an objective at present.

Maybe eventually we will find a way to live in such harsh conditions as the Moon easily. Maybe we can do this with 3D printers, and biologically closed systems, living in the lunar caves, and eventually on a paraterraformed Moon. Maybe this will lead us to find a way towards a more sustainable future here on Earth as well. Still, if we achieve the ability to do this easily, the technology would still work much better on Earth than in space. You can use much the same design for your colony - except that you can drop all the cosmic radiation shielding, forget about airlocks and spacesuits, and just have windows and doors, instead, which you can walk out of, into a breathable atmosphere.

Put that habitat almost anywhere on Earth, in a desert, or floating on the sea - and that would be a far easier place to live than any space habitat. So if those self sustained habitats became possible in the future, even as a spinoff from space habitat research, I think most of them would be built on Earth rather than in space, at least to start with. Let's meet this miraculous future when it happens, if it does. Meanwhile it's not realistic to send colonists into space in the hope that 3D printers will save the day. They are likely to die waiting for the technology to be invented.

So, in this vision of the future, we have humans in space, but they aren't there to colonize. They are there rather to explore and study, and for adventure and so on, for many of the same reasons we have people in Antarctica. In the near future anyway. I think this is just being realistic; choosing a future that is within our reach rather than a rather beguiling far future science fiction fantasy that is probably centuries or even thousands of years out of reach, such as a terraformed Mars.

In this way, without that imperative that we have to colonize as quickly as possible, and turn everything into the nearest to a pale imitation of Earth as we can manage - then we can have a more open ended future. It gives us space to consider other possibilities; or at least, to look at them. For instance, in one possible future we could introduce Earth life to Mars, accidentally and irreversibly, perhaps from a crashed human occupied spaceship, creating a new geological era on Mars. But we don't have to do that. There is no need quite yet to make such an irrevocable decision for ourselves and all future civilizations on Earth.

Let's study Mars carefully from orbit first. There is no hurry, and this would be a fascinating exploration using telepresence, once we can get humans there. Maybe we will know enough in the future to make such far reaching decisions, but meanwhile, let's keep our options open for the future.

This next video is not telepresence as such; rather, it's a new way to explore the Mars landscape to help with controlling the rovers from Earth. However, I think it gives as good idea of what telepresence might be like for those operating rovers on Mars in real time from orbit, some time in the future with this vision.

(click to watch on Youtube)

See Scientists Can Virtually Wander Around Mars for Miles with HoloLens

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