Introduction

By Michel Lamontagne with Richard Osbourne and Adam Crowl

Building a starship, as any other large scale project, is a question of scope, cost, time and motivation.

If humanity was willing to take its time, ten thousand years for example, building a starship might be a minor endeavor of a solar system spanning society. But we’re in a hurry, we would like to see a starship built in the next century.

What resources exactly does that entail? Is it a gigantic endeavor that will divest a substantial part of the resources of humanity? Or is it merely expensive, on par with other large projects such as aircraft carriers or power plants? Might it be the project of a single romantic trillionnaire a century from now_(ah)?

A fusion starship, as we envision it today, cannot be built and launched from the Earth. However, most of its components can be built on Earth, and the final ship assembled and launched from space. Therefore some form of space based construction infrastructure will be required. Going beyond the immediate vicinity of the Earth, many of the fusion designs require He3 from the gas giants, and these designs will require extensive space infrastructures and some form of a space economy.

The infrastructure required to build a starship can be divided into three types of facilities:

1. Ground based facilities and launch systems.

2. Orbital assembly and manufacturing capabilities, such as required for Firefly and starship using D2 fusion exclusively.

3. An extensive interplanetary infrastructure, with resources drawn from the gas giants, as required for Daedalus and other He3 fusion designs.

Ground and launch infrastructure

Any starship construction program will need some form of ground and launch infrastructure. The extent of the infrastructure required to build a starship will depend on the level of corresponding space infrastructure. For a simple space assembly, using Earth materials only, a fuel production facility and a spaceport should be enough. An existing space agency, or a private contractor such as SpaceX, could provide the required production and control facilities. As the main communication antennas will be in space, existing ground communication systems will be more than adequate for communication with the space probe.

If you exclude the fuel, most of the starships designs are quite light, in the same order as small seagoing ships, or of a dozen large aircraft. So these could be built in similar construction facilities as for aircraft or space vehicles. The larger costs by far will be deuterium and He3 production, as well as research facilities to develop the required technologies and transportation from the Earth’s surface up to orbit.

Launch systems

After decades of development and thousands of proposals, from fission rockets() to Longstrom loops() and space elevators(), it seems, in the end, that all that is required for the construction of a workable space infrastructure is classic rockets and spaceplanes using conventional fuels. The fundamental new developments are high flight rates and complete re-usability with quick turn around. Many companies are looking into vehicles with those capabilities, with SpaceX, Blue Origin and Reaction Engines the clear forerunners.

It is also interesting to note that all of the systems under development are pilotless. Automated ships remove the risk of fatal accident that plagued the Space Shuttle program, and automated supply ships are already used for the International Space Station.

In a decade or two SpaceX is planning on launching 12m diameter vehicles. These could deliver 300+ tonne payloads to Mars to support building a colony using a heavy launchers called Starships. The SpaceX ITS infrastructure must be completely recoverable to meet the goals of the Mars colonization projects. The first stage of the Starship launcher would return to Earth and land at the launch site, using up 8% of its fuel capacity for the return boost. The turnaround time of this stage would be measured in hours, work limited to minor cleanups between flights and refuelling. The second stage would be a true spaceship, capable of a variety of missions, with the capability of being refueled on Mars with suitable installations. It could return to Earth from very high orbits at high velocity using aerobraking to save fuel and be quickly refurbished for new missions(). The cargo bay of a ITS second stage, configured for LEO cargo transport, might hold up to 350 tonnes of deuterium or heavy sub assemblies for the Starship.

The Reaction Engines Skylon would be a very cost effective Single Stage To Orbit (SSTO) launcher at high flight rates, for smaller elements and bulk cargo. Serving an extensive orbital construction facility, it might be all the transportation required for the construction of a starship.

Alternatively, Reaction Engine’s proposed Skylon spaceplane could handle smaller cargos, but with lower fuel use since it uses atmospheric oxygen for part of its flight path, for an overall similar economic performance. All Skylon images by Adrian Mann.

Using conventional chemical rockets exclusively, ITS will require 8000 tonnes of propellant to move 350 tonnes to LEO(). In turn, these 350 tonnes can be used to move about 100 tonnes to a Lunar construction orbit. Skylon would do the same work with half the propellant. Thus one or two million tonnes of propellant might be required to transport all the material and fuel required for a 20 000 tonne space probe.

This might be thought of as excessive, in this age where sending one kg of material to high orbit costs over 10 000$. However, consider this - We don’t often think about how much our power supplies weight, but a 1 gigawatt coal-fired power plant, operating at 35% efficiency, turning the heat of burning coal into electricity, consumes 0.1 tons of coal per second. Over a year it burns 3,000,000 tonnes of coal, produces ten million tonnes of carbon dioxide and probably about 150,000 tonnes of ash. So building a starship would require less fuel than a single year of operation for a single coal powered electrical power plant. And the cost to orbit for a vehicle such as the SpaceX Starship could be as low as 50, or even 10$ per kg.

Launch costs

Skylon or SpaceX, if operating on large volumes, can provide transportation costs two to three orders of magnitude lower than those of today()(). The requirements for a large space solar infrastructure or for a Martian settlement would provide a market sufficiently important to bring down space access to less than 50$ per kg at LEO and 140$ per kg at high orbit(). It is not unthinkable that the 20 000 tonnes of fuel required for the Firefly could be put into orbit for less than 3 billion dollars (2016). This would be done using an infrastructure that provided other tangible advantages to humanity.

Fuel production

Fusion fuel production, not the starship itself, is the largest cost of interstellar flight using fusion drives. It may be possible, for ships burning deuterium exclusively, to produce all the required fuel on Earth. This is explored extensively in section 4.

As far as propellant for launch vehicles is concerned, oxygen, hydrogen, kerosene and methane productions are all commercially available processes and are considered commodity goods for our purpose. The costs that were considered are in the following table:

Launch cost economics

Launch cost economics is a complex subject, source of endless debates. We present a simplified analysis here, for transportation to LEO, using the following equation:

P_c = Payload cost ($/kg)

Pc = (De+Co*Vg+In+Vg*Vf*(Ma+Fu))/Pm*Vg*Vf

De = Development costs ; Research, management and testing. Safety requirements for crewed vehicles. Flight proofing.

Co = Construction of the vehicle ; Materials and manufacturing, person hours, testing.

Vg = Vehicles per generation ; Number of vehicles built per design generation.

In = Infrastructure ; Manufacturing plants, tooling and launch sites for a series of vehicles

Vf = Vehicle flights; Number of flights a vehicle can do.

Ma = Maintenance cost per flight; Clean up, repair, upgrades, fueling, set up on pad.

Fu = Fuel cost per flight

Pm= Payload mass (kg)

Environmental impact is not included as a cost but needs to be taken into account in the overall analysis. This parameter doomed fission pulsed propulsion and exotic fuels using fluorine, and might become an issue at high flight rates.

The table below gives the results for the above equation. It is based on the requirements of a 20 000 tonne starship such as Firefly.

Orbital assembly

The simplest starship building infrastructure possible would reside entirely on Earth. However, there are presently no realistic designs to launch a fusion starship as a single unit. So a starship will need to be launched as a series of sub elements and assembled in space. The International Space Station is presently the only existing example of this type of construction. It quite ably demonstrates the possibilities of this approach.

Assembly element size for space construction is limited by the payload fairing dimensions of available launchers. The standard large fairing today is 5.2m() diameter for Ariane 5 or Atlas. Saturn 5 could have provided a 10 to 12 m fairing, such as the one proposed for the Mini Orion(). The largest rocket being seriously considered today, the SpaceX ITS, proposes a 12m fairing. This is a good assumption for the largest dimension a sub assembly could have. The Skylon SSTO space plane could transport payloads in the 5m fairing size class in its cargo hold. Inflatable components, such as the Bigelow modules(), can extend a little beyond the limitation of the fairing and provide interesting living areas. Tethers Unlimited Spidefabs() offer an alternative to traditional construction methods and can allow the construction of large space infrastructures with a very high density of packaging in the transportation vehicle().

Space debris in low orbit is presently an issue that must be taken into account. The International Space Station is regularly moved to avoid debris, and has been hit a number of times. The very large dimensions of some of the starship designs make collisions unavoidable, and some of mitigation measures would be required. Reaction engines has proposed the use of enclosed assembly areas, that would have transparent Whipple shields to protect the construction space.

Orbital assembly can be done in both low Earth Orbit (LEO) and higher orbits, such as the Earth Moon Lagrange points EML4 and EML5. It is conceivable that at the time the first starships are built the space debris issue will have been solved and LEO will be a possible construction site. However, there are other reasons that may make construction of the space probe in high orbit desirable.

Whipple shield

A whipple shield is a protective system composed of a series of thin layers of material spaced slightly apart. When a high velocity object impacts the shield’s first layer, it is destroyed and turned into a gas. This gas spreads out, and impacts the second layer over a much wider area, therefore with less effect. Eventually, the gas becomes too spread out and cannot penetrate the next layer. This method of protection is used extensively in the Internal Space Station and other orbital craft. It was invented by Fred Whipple.

Orbital transfer

If the debris question can be solved, why not just build the ship in low orbit and then use its own fusion engine to send it on its way? A first reason is the neutron radiation from the drive. Although the atmosphere is thick enough to shield somebody on the ground from the neutron radiation created by the starship drive, it doesn’t offer any protection to other vehicles in orbit, or to people in high flying aircraft, so that is a first level of risk that would be difficult to mitigate. The second, more important reason is the high level or energetic x-rays and ultraviolets put out by a fusion drive; these are powerful enough to drive through the atmosphere. They would blind anyone looking directly at a nearby operating fusion drive in a fraction of a second. So the drive has to be put into action far from the Earth. The distance of the moon is about right, perhaps erring a little on the safe side.

To move the starship to a higher orbit requires either another vehicle with a safer drive, rather like a sea liner being moved by tugs, or the transportation of sub elements by Orbital Transfer Vehicles(OTV). As the ship already needs to be separated into components to leave the Earth”s atmosphere in a launch vehicle, it probably makes sense to only assemble these at the higher orbit. This becomes a problem in transportation optimization, rather like trucking vs sea transportation and containers vs bulk cargo.

There are five main ways that have been proposed to power orbital transfer vehicles. Chemical, nuclear thermal, nuclear electric, solar electric and beamed electric. Single use chemical propulsion and solar electric are the norm today. Just as for launch vehicle, re usability would change the economics of orbital transfer tremendously.

Electric thrusters have been optimised up till now fow high specific impulse, to create the lowest propellant use possible for missions that do not allow maintenance. The possibility of maintenance and repair is inherent in the circular nature of the OTV mission cycle. OTVs can periodically return to a maintenance area. This might allow for the use of more powerful but less reliable thrusters, such as MPD drives. Development of electric thrusters has been slow. A test facility in orbit would allow for the rapid and continuous testing of multiple configurations, and the significant economical advantage from the use of electrical thrusters would favor their adoption.

Very large solar panels arrangements have been demonstrated by the Japanese Jaxa space agency. Their latest solar sail, at 2500m2(), is already close to the 4000m2 set of solar panels that would be required for a 1 MW solar tug. Using similar construction but more efficient solar cells, 10 solar tugs, making 2-3 month round trips, could move above 5000 tonnes per year.

The same analysis that was used to show the gains of reusability can be used for orbital transfer. Following the radical reduction in cost possible with high volume reusable launchers, the cost of moving to a higher orbit goes down significantly. The solar electric or nuclear electric thrusters are clearly the most economical solution for the volumes needed for the construction of most starships. In the starship section of the report, different technologies have been used by the designers, depending on what they believe is the most likely system to be used.

As for the launch vehicles, the orbital transfer vehicles are unmanned. This reduces cost and complexity tremendously, since there is no need to transport a crew and their living environment. Docking, fuel and cargo transfer operations may be supervised and teleoperated, and the OVTs are provided with robot arms moving on rails, or similar active elements, that can be used for inspection and repair.

Low thrust vehicles follow very different trajectories than high thrust vehicles. They cannot profit from the Oberth effect, and therefore require much higher deltaV for the same mission. Despite this, their reduced fuel use makes them more economical than high thrust vehicles. At least for most situations that concern the construction of starships.

Orbital assembly might be partially automated, but since we don’t expect to build large series of starships, it will require some human involvement, just to create the tasks required. This might mean actual construction personnel in space, and orbital stations. However, if we expect the starships to be able to maintain themselves without human intervention as they get further from the Solar System, the same robots and intelligent agents should be able to carry out the largest part of the ship assembly. Or to at least assist and participate in order to learn the required techniques so they can be applied later during the trip.

Orbital manufacturing

Rather than bringing completed assemblies up from the Earth, it might be possible to send up raw materials, or to get these materials from asteroids or the moon, to supply manufacturing in space. The advent of 3D printers, computer models and fabrication software has made the idea of a software bank containing the entire ship in a virtual form, with all the necessary assembly and fabrication instructions, a near future possibility.

The need for manufacturing capability depends on the economics of building the mining sites to provide the resources, the raw material treatment required to produce usable feedstock for the manufacturing plants and the cost of transportation.

Transportation cost dominate the cost of everything in space. Lowering the transportation costs can leave margins that might be sufficient to finance the construction of the base infrastructure. But not necessarily. For example, the table for Orbital Transfer Vehicles shows that moving 20 000 tonnes of equipment from the Earth would cost 5 billion 2016 dollars with the most efficient system proposed. If this material came from the Moon, this cost could be reduced by half, leaving 2.5 billion dollars to develop Moon infrastructure. This may just be enough to finance moon mining and refinement of ores. But it’s probably a tight margin. So the economical case is not that clear.

Orbital manufacturing implies some kind of space construction station, and human presence in space. Construction facilities such as the Reaction Engines Orbital Assembly Structure, than is paired with the Skylon Space Plane, or a station built from Bigelow modules would be required. These are capital intensive infrastructures, and again, the economic case for these needs to be done. The huge leverage gained by reducing launch costs reduces the gain possible from these activities. At least for the case of Starships, it may well be that, excepting the fuel, manufacturing on Earth and space assembly is all the technology required.

Modularity

The use of standardized elements such as containers may become widespread with the development of space infrastructure. If the main item transported is fuel, a modularized fuel tank, with efficient insulation and an on board refrigeration system, would provide long term storage without evaporation and fuel loss, in particular for deuterium or helium. A similar form factor could serve for many functions in space vehicles, in particular if lower costs of transportation to orbit reduce the need for extreme optimization of vehicle masses.

Beyond Earth

Many of the fusion designs require He3 to operate. All of the starships required deuterium. It was shown in the original Project Daedalus Report that the most likely source for He3 would be the atmosphere of the gas giants. Deuterium might also be extracted there. And since the fuel is by far the major part of a fusion starship’s mass, it might make sense to assemble the ship near the fuel source, in orbit around one of the gas giants, rather than move the fuel back to the Earth-Moon system. This would require an infrastructure extending into the further reaches of the solar system, where the sun becomes a small dot in the vastness of space: an interplanetary infrastructure.

Interplanetary infrastructure

In 100 years, the construction of a fusion powered Starship should be achievable in near Earth orbit using only materials from Earth. However, obtaining the fuel may be another matter, in particular for the starships requiring helium3 to power their fusion reaction. This isotope of helium is only available in the large quantities required from the atmosphere of the gas giants (the present production on Earth is less than 10 kg per year). The methods proposed for extracting helium3 are described elsewhere. This chapters concerns itself with the physical and virtual transportation infrastructure required for this fuel production, and touches on the more general possibilities of an interplanetary transportation infrastructure.

DeltaV

The main obstacle to interplanetary travel is reaching space itself. But beyond the problem of getting out of Earth’s gravity well, the difficulty becomes, not the energy, but rather the time required to travel between the planets. Using economical Hohmann transfer orbits, we can see from the deltaV map that reaching the Moon, Mars, Venus or Geostationary orbit all require about the same velocity change; around 4 km/s. And that reaching Saturn, Uranus, Neptune or even Pluto can be done using about 18 km/s of deltaV. The most difficult planet to reach economically is Jupiter, due to the intensity of its gravity, that requires 33 km/s of deltaV.

However, when we look at the Express line, even for a powerful vehicle capable of producing 80 km/s of deltaV, the time required to get to Uranus is about 1 year, Neptune, about 2. Setting up homesteading and infrastructure in such a context takes time, inevitably.

Interplanetary transfer

Tsiolkovsky rocket equation is also used here.

Dv = Velocity change (m/s)

Dv = ve*ln(Mo/Mf) and Mo=Mf* e(Dv/Ve)

Ve = Exhaust velocity (m/s)

mo= Initial mass (kg) = Fuel, payload and vehicle structure

mf = Final mass (kg) = Payload and vehicle structure

If we use electrical propulsion to create the deltaV, it is interesting to note that the energy cost is not very high. For all of the transfers at 80 km/s seen in the deltaV map, the energy use is the same: about 260 kWh per kg of cargo. At an electrical cost of 10c per kWh and a drive efficiency of 60%, that’s 56$ per kg of cargo for anywhere in the solar system. A fraction of this for the moon or Mars.

The main cost is not the transfer trip itself, but the cost of the construction for the interplanetary ships as well as their design and development. The other major cost being the cost of moving the fuel for the ships up from Earth’s surface.

Due to their advantageous deltaV requirements, there are real economic opportunities in obtaining fuel from the Moon or Mars for high Earth orbit, rather than moving the fuel up from Earth itself.

Thus, for an interplanetary civilisation a three tiered infrastructure might be put in place:

1- Chemical propulsion to low orbit, for the Moon, Earth or Mars.

2- Solar electric for transfer to high orbit, particularly for the Earth.

3- Solar electric (or nuclear electric) to Mars or Venus and Nuclear electric to the outer planets.

Interplanetary cargoes

The most common type of vessel in an interplanetary infrastructure will be some form of automated cargo ship.

The history of space exploration has shown that remotely controlled vehicles are capable of very complex operations, and there is no reason to expect this to change in the future. Interplanetary ships will operate in contexts that are much simpler than the ones that, already today, are being navigated by the autonomous cars of Tesla or Google. Without the need for an habitat, interplanetary cargoes can be relatively simple ships, and the loss of such a ship will not be a tragedy.

The candidate technologies for such interplanetary cargoes are numerous. However, nuclear electric stands out as a technology with low requirements, a higher level of technological readiness and interesting operational costs.

A typical nuclear cargo would require nuclear reactor(s), energy converter(s), some structure and controls and a cargo bay.

By the time the Starship is built, the nuclear electric drive might be replaced by a form of direct fusion drive. Not really for cost reasons but for faster trip times, in particular for ships with crews and passengers. The testing of early form of Starship fusion drives might make versions of these available for interplanetary travel.

In fact, if nuclear electric vehicles can be used to transport an adequate fuel production facility to a gas giant (Uranus for example), the Starship itself will provide the most economical and rapid way of travelling through the solar system. The starships presented here reach Uranus in just about 1 year using 40 tonnes of propellant or less. If a fission electric vehicle had arrived a decade before and set up a fuel production and storage facility, the starship could fuel up there for its interstellar trip. This scenario is explored in detail in the fuel acquisition section.

Any subsequent trip in the solar system could be done by a spaceship similar to an interstellar probe, but carrying no more than a few hundred tonnes of propellant. As already mentioned, fusion drives would probably be problematical in low orbits near to the planets, and certains types of drives might produce so much radiation that they could not be used near orbital installations. So some form of space tug would still be required to reach these vehicles.

Crewed Interplanetary ships

Robot construction will likely make great progress in the coming decades. However, it is expected that human intervention will be required for many of the complex and untested tasks required for the construction of the starships. Teleoperation is limited in range, providing another reason to bring humans up to, or at least near to, the starship construction sites. Human presences adds important requirements. Radiation protection for humans is needed for any trip in space. For long term trips, heavy shielding will be required for solar storm and Galactic Cosmic Rays (GCR). Crewed ships would also be likely to have a rotating section for artificial gravity, unless medical discoveries allow the crew to live for long periods without gravity. Experience and research over the last decades in the ISS has shown that lack of gravity leads to loss of muscle mass, de-calcification of the bones and eyesight problems. A rotating living area should solve these problems, although this has yet to be demonstrated in practice.

Starship construction and supply requirements

The construction and supply requirements for a fusion Starship differ mainly according to the fuel used. Two broad categories stand out, the ships using only deuterium and those required He3 as well. Starships using only deuterium, such as Firefly, do not require an interplanetary infrastructure at all. The production of the deuterium required should initially be much more economical on Earth than on the gas giants, simply due to the cost of transporting a large production facility to those planets. The idea of using deuterium from Mars is an intriguing possibility, and is explored in the fuel acquisition chapter, but hardly a requirement.

For He3 powered ships, such as Daedalus, the minimum interplanetary infrastructure required are robot vehicles capable of transporting the fuel production facility to the gas giants, and at least one crewed ship capable of reaching them in a reasonable amount of time. The minimum amount of He3 fuel brought back from the gas giants is about 60 tonnes, that would be used to power the starship for an initial shakedown and a refueling trip to the gas giant. See the Fuel acquisition chapter for details.

Orbital Construction Facility / Space Dock.

The primary facility will be the orbital construction facility- or space dock – a large structure which will enable the spacecraft to be assembled adjacent to it or inside it. The facility does not need to be in Earth Orbit, but may be in Lunar Orbit or even at an Earth-Moon Lagrange Point. Ultimately, it might be advantageous to have the construction facility at Uranus or another gas giant, in particular for ships fuelled with Helium3. The location will depend on whether the majority of the resources arrive to be assembled from Earth (the Maximum Earth, Minimum Space Architecture), or if the resources arrive from a range of locations in space (all the other space systems architectures), e.g. Earth, Moon, Near Earth Asteroids, Main Belt Asteroids etc.

Structurally, the construction facility will likely take the form of a long boom or multiple booms, an encircling structure or an enclosing structure, depending on whether in space construction experience has shown by that point what the most suitable construction facility form would take. An enclosed structure prevents components from floating away, but to enclose such a large volume as that required for a starship concept would require a very large space dock indeed.

Propellant Processing Facility

The propellant pellets used for the starships using ICF propulsion systems will need to be manufactured prior to loading into the spacecraft's propellant tanks. It is anticipated that, due to the nature of the pellets, this processing will take place off-planet, and because of the composition of the pellets, mostly solid deuterium and He3, likely further out from the Earth than Geostationary Orbit. As they are expected to be extracted from Uranus or one of the other gas giants, a close orbit above one of the gas giants is the most likely place for a pellets fabrication facility.

In Situ Resources Utilization

Originally proposed by Robert Zubrin for his Mars Direct proposal(), ISRU has recently been adopted by NASA as the best way to reduce the cost of a Mars mission(). SpaceX bases its Interplanetary Transportation System on ISRU, as presented by Elon Musk in September 2016 () and september 2017().

In Site Resources Utilisation replaces the transportation of the fuel for the return leg of the two way trip to another planet by the construction of a local fuel production facility. This installation extracts fuel from the target planet or moon and stores it to supply fuel for the return flight. This reduces the need for fuel transportation significantly.

The interplanetary vessel could use 4 x 40 km/s burns, rather than 4 x 20 km/s burns, for example, to halve travel times. Local fuel production will be required for the vehicles that move fuel up from the atmosphere of the gas giants as well. It would not be logical to bring this fuel from Earth.

Even the fuel available in Earth orbit might better be sourced from the Moon or from Mars than from the Earth itself. Simple chemical launchers from the Moon could provide Nitrogen and Hydrogen to interplanetary ships and power themselves using propellants such as methane or aluminium and oxygen. These would, in a sense, be solar powered, since the power to extract and prepare the propellant would probably come from solar cells on the Moon or Martian surface.

Space Tracking Facility.

By the time the starship launches, it is anticipated that a significant, in-space, deep space tracking and communications infrastructure will have been established. This will include large space based antenna farms, and quite possibly autonomous tracking and communications arrays dispatched in advance to the solar focus points, out at a distance from the Sun of about 550 Astronomical Units, and at a locations suitable to receive the transmissions from the probe. Cis-lunar space is also a likely emplacement.

Given the use of spider fab technology to fabricate the antennas for the spacecraft at its destination, the same technology could be used to build a very large antenna farm in cis-Lunar space. Any one of these antennas could also be used to provide very high bandwidth communication with in-system ships, reducing the requirements for transmission antennas by providing tremendous reception capabilities.

Functional analysis for the Interplanetary Infrastructure

Objective: To be the most capable and cost effective interplanetary cargo transportation and construction infrastructure, using the minimum extrapolation from current technology.

It should be clear from the analysis bellow that the technology for the Interplanetary infrastructure is far from ready. Although there are no specific showstoppers, there has been little work done on actual systems for an Interplanetary infrastructure beyond the ISS and communication satellites. For the 100 year time frame of the project, there is ample time to develop the required technology. The SpaceX proposals() are probably the most likely sources of progress in this regard.

References

1- The impact of SSTO introduction on interstellar starship construction, Richard Osborne

https://drive.google.com/open?id=0B52GlVTiDp1ARktIWldFQlliZWM&authuser=1

^1,2 The ESA Ariane 6 and US Vulcan are classified in this table as “Pseudo-reuseable”, since the efforts towards re-usability made by ArianeSpace for the Ariane 6, and ULA (United Launch Alliance) for the Vulcan, are relatively weak and cumbersome, compared to those of SpaceX, Blue Origin and Reaction Engines. If the reusable versions of the Ariane 6 and Vulcan do enter service however, following the space industry's risk averse approach, such launchers would likely then remain in service for similar timeframes to the Atlas and Delta launchers.

³ Whilst the Russian Proton launcher is included, it should be noted that in time, it will be phased out in favour of heavier lift variants of the Angara launcher, with current forecasts for its retirement from service of the 2025-2030 timeframe.

⁴ For completeness, as well as US and European concepts, three Russian concepts are included; two expendable launchers, the Amur-5 and Yenisey-5, and the semi-reuseable MRKS-1 – an upscale of the Baikal launcher concept, with first stage winged fly back boosters. Considerable development was undertaken on the Baikal, including a full scale mock-up which was demonstrated at the Paris Air Show. This work has continued with the MRKS-1 concept.

⁵ Insufficient details are available as yet (2016) as to the reuseability potential of the Blue Origin orbital launcher. Whilst it is planned to have a reusable first stage, it would be wrong to speculate on this as a given feature. Hence its categorisation in the table above as potentially suitable. Its engine development (the BE-4) is proceeding well however, and is likely to be ready by the scheduled completed date of 2018, which, allowing for vehicle construction and integration, could see an actual vehicle ready for launch in 2020-2021.

⁶ The SpaceX ITS architecture of a large booster with an entirely recoverable second stage was presented by Elon Musk at the September 27th 2016 International Astronautical Congress: ‘Making humans a multiplanetary species’.

⁷ In the timescales ascribed to this mission, it is highly likely, that the air breathing Single Stage To Orbit SKYLON spaceplane or a derivative of it, will be in service.

(8) Aerospace projects review, EV1N4, produced and distributed by Scott Lowther, is a great source for all historical information regarding space development in the US. A series of articles was devoted to exploring all the information made public about the Orion program.

()Quicklaunch website. The Quicklaunch project was an attempt to finance the construction of a space gun. As per 2016, Quicklaunch development is in hiatus as it cannot compete against recoverable vehicles.

Radiation calculation site

Tethers unlimited

Reaction Engines ltd

Ad Astra Vasimir moon tug paper

Bigelow aerospace

Fairing standards, reference SpaceX manifest, Ariane and Delta IV user’s manual

Japanese space agency 50m sail project

(x)https://www.nist.gov/pml/x-ray-mass-attenuation-coefficients

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