Essay: Interstellar Manned Travel
Speculations on Interstellar Travel
John Engelbrecht Nov 20 2018
Speculations After Hearing Coast-to-Coast A.M. Interviews
web site sites.google.com/site/solderandcircuits/home/more-circuit-design/essay-interstellar-manned-travel
In light of popular-press and T.V. imaginings about living on the Moon or Mars and exploring other planets, I offer some thinking about what interstellar travel by humans would be like. I concentrate on a manned vessel traveling at the speed of the Voyagers. The conclusion is that it wouldn't work. But it is fun to think about why it wouldn't work.
Contents
What Life on the Moon or Mars Tells Us
Going to Another Star System
Deceleration Before Landing
Intergalactic is Out of the Question
Many Generations
Thousands of Generations
Science in Space
Judge Judy Between the Stars
Collisions
Computers On Board
A Web Site
Conclusion
Frozen Embryos
Spiritual Influence
What Life on the Moon or Mars Tells Us
Recent Moon and Mars robots show enough water on the Moon and Mars that a few scientists talk about living on these bodies. But neither prospective home has a magnetic field to shield from solar wind or cosmic rays, or enough atmosphere to dissipate solar wind or cosmic rays, so life would have to be mainly underground. Once a month, for several days, the Moon swings in its orbit toward the Sun and moves beyond the Earth's magnetic field, exposing the Moon to the deadly solar wind and, rarely, the radioactive fury of coronal mass ejections.
$140,000 per pound of anything going from Earth to Mars, but less than that from Moon to Mars because Earth is in a much deeper potential energy hole. From any plants grown on Mars in a pressurized, heated, Earth-like atmosphere, a lot of water is released by the plants and can be condensed from inside the greenhouse. But it all needs to be channeled back to the plant roots. ScienceBlog.com: Volenec: It the plants die, the humans and animals die.
It is known that water ice is near the surface of Mars. Some sources say this ice is abundant. But it is near the poles, and there is a tradeoff, live near the water but there is less sun heat available.
Whatever equipment processes raw sewage to recover all water and reuse all solids will also have to deal with gasses. Some of the gasses are VOC, volatile organic compounds, and most of them are mighty stinky. Equipment will have to process VOC so they don't enter living quarters. Waste heat from the chemistry and motors will be a welcome heat source for living quarters.
I haven't heard about energy sources to sustain a colony. Solar cells would probably work for some years, but solar cells are damaged by radiation. One can find speculation about Helium-3 fusion being an energy source. The Moon's He-3 is accumulated in the lunar soil, and is deposited over long time from solar wind. (In clinics that have accelerators for cancer treatment, the X rays are intense enough that they can't have semiconductors, not even LEDs, near radiation. They have to use incandescent lamps!)
Raising food would consume a lot of energy, not to mention the need for water. (Food-crop plants are not efficient in their use of water, around 90% of water coming in through roots is transpired through leaves and does not go into the grain or fruit. The evaporated water is not lost, it is water vapor coming out of the leaves. But to feed it back to roots, it has to be condensed, and that requires a lot of cooling.) Just think about the news from drought-constrained California in the last few years, where we learn that a single almond requires 1.1 gallons of water (absorbed into the tree roots) and a single tomato needs 3.3 gallons.
There are plenty of stories about people volunteering to colonize Mars, with a one-way trip. How many would actually step onto the transport rocket? Those who board and rocket away from Earth, and land alive on Mars, have to get underground within weeks to escape radiation. What type of primitive, cold, cramped existence would they lead? How meager would be the solar-cell power coming down by wires from the surface? (A person would have to put on a space suit periodically to go sweep dust off the solar cells. He would have to go out into the surface vacuum through an air lock.) How long would it take to locate frozen water? Dehydrated human waste (dried out by exposure to the surface vacuum) would be building up; the food supply all gets eaten and becomes dehydrated waste. Smart women would be asking how many months of bathroom tissue is packed onboard. They would demand that the onboard stock be divided equally among the voyagers, and individual lockers would be checked by their owners before departure and would be locked. As individual stocks shrink, there would be some kind of bargaining, "I'll give you this for 50 squares." There might be a return of discarded vegetable items and such, used in place of tissue, as corn cobs used to be used in outhouses; really, search Internet for 'outhouse corncob.' Similar dickering about food is bound to happen. What about oxygen? How long would it take for the little colony to radio to Earth, "We are bored, depressed, and stressed. The doctor is overloaded. Send us more supplies and another doctor, but don't ever again send any other people." Would there be a protest movement on Earth that blocks large-scale habitation on Mars, merely because Mar's frozen water is taken out for consumption but never replaced? "Save the Mars aquifer!" Speaking of protests, how much air pollution on Earth is caused by a rocket launch? Or is the energy to generate hydrogen and oxygen fuel and oxidizer a bigger factor? "Save the Earth's atmosphere, stop the Mars launches!"
https://engineercalcs.com/living-underground-on-mars-drilling-challenges/ July 6 2020 An engineer who works on giant Earth horizontal tunneling using Tunnel Boring Machines writes about the many challenges of tunneling on Mars. The workers would need to be pressure-suited. Just cleaning the insides of the suits would be a problem. TBMs are really heavy and large. They work for a while, then they stop for repairs and to clear out clogs. Excavated material has to be removed by rail car and dumped on the surface. TBM needs at least 2MW of power. Per megawatt of generated power on Earth, a solar farm needs at least 5 acres. On Mars, the weaker sunlight boosts the area to 1400/600 *5 = 12 acres per MW. If the habitat is nearer a Martian pole, where the frozen water is, the solar cells need to be spread out so they don't shadow each other, and they don't generate power during a Mars night. Would the TBM bearings get worn out from tiny Martian dust? At least Martian dust isn't sharp-edged like on the Moon, because Mars dust storms roll Mars dust around a lot and wear down the edges. https://www.digitaltrends.com/web/martian-dust-is-a-big-problem-for-astronauts-heres-how-nasa-fights-it/#dt-heading-why-is-mars-so-dusty
Look at photos of Earth landslides. You often see big rocks mixed into dirt and mud. Now look at Mars surface photos. You often see a surface littered densely with rocks. Maybe there are so many rocks because dust has been blown away and deposited elsewhere. Would a Mars landing zone have to be chosen for having a smooth surface? Below a smooth surface, are there big, hard rocks that would be hard to tunnel in? How far down is Mars bedrock, and how hard is it?
https://www.scientificamerican.com/article/why-well-never-live-in-space/ "In 1991 eight people entered Biosphere 2 and lived inside for two years...encapsulated environment didn't produce enough oxygen, water or food for the inhabitants...interpersonal conflicts and psychological problems among the residents." "Spaceflight damages DNA, changes the microbiome," problems with circadian rhythms, vision, cancer, muscle and bone loss, immune system, "weakens the heart, and shifts fluids toward the head." Mary Roach's 2022 book, Packing for Mars, points up many severe problems for humans in weightlessness and Moon gravity (17%) and Mars gravity (38%). "The Right Stuff" men went to the Moon and could do it because they were highly motivated and looked forward to returning to Earth and families. People who go to the Moon for a year and live boring lives underground, sheltered from radiation, will not muster the "right stuff" attitude for very long, and will suffer bone deterioration and be invalids if they return to Earth. They might suffer broken bones from the G forces during Earth atmosphere reentry. People who go to Mars would have almost as much bodily deterioration in two years and would likely be stuck on Mars for a long time, their return to Earth dependent on the willingness of Earthlings to finance a return from Mars, plus the Martian dwellers can be supplied with only a trickle of necessities like food and sanitary wipes for hygiene. (Forget hot shower.) A web site categorically says that Earthlings might eke out an existence on the Moon and Mars, with much doubt about raising families to perpetuate colonies, but any other planets or asteroids are extremely hostile and will not be colonized. Web sites propose that only women go to Mars; men-only suffers from testosterone-induced hostility, and mixed men with women, married, might work until death-of-spouse, then unpaired singles will cause big problems. (A web site advises that, away from Earth, sexual relations would need to be completely different from what works on Earth.)
Going to Another Star System
A great debate before departure to another star would be the choice of star. Astronomers would have been studying the closest stars with planets, using spectrographs to learn about the elements in those stars and the subtle red and blue shifts in the starlight that reveal planets. Once a choice is made and the journey commenced, there would be ongoing study of the destination star, and more powerful astronomical tools would reveal additional information. If, after some decades, the destination star turns out to be a poor choice, would Earth let the travelers know that? The travelers wouldn't have fuel to change course to a better choice.
When I look at Internet for speculations about people traveling to planets around other stars, there really aren't many articles. See Wikipedia, Interstellar Travel. There are many problems.
Cosmic rays penetrate all of space, including interstellar. Shielding to protect travelers' DNA would be heavy, and we are thinking about shielding DNA for thousands of generations. (The hydrogen in polyethylene turns out to shield from cosmic rays better than aluminum!) Water tanks, both clean water and water awaiting purification, might constitute good shielding. This means travelers would be packed into small spaces. This is at odds with all movies about space that we see. The movies depict the quarters as being spacious. (Star Trek, The Orville) A web site shows two people in an ISS mockup (on Earth) handling bags of supplies, making a temporary cosmic-ray shield to protect against a solar storm. Timeline.web.cern.ch/timeline-header/146 says that two meters of water shields the same as two km of atmosphere, so even six meters of water shielding would not absorb all the energy of a cosmic-ray shower that bursts out from a cosmic ray striking the aluminum skin of an interstellar vessel. From livescience.... in 2019, Voyager 2 found the levels of cosmic radiation skyrocketed and stayed that way, Voyager 2 had entered a new region of space, beyond our sun's [heliosphere]. The sheath of hot, charged [solar] wind protecting our solar system might not be perfect [keeping out 70% of interstellar cosmic rays] but, as Voyager 2 confirmed, it is part of what separates our home from the ferocious wilderness of space. Considering that manned Mars travel will expose people to about half a lifetime-dose of radiation during a round trip, and frequent over-the-North-Pole flight crews have more cancer, interstellar travelers need lots more shielding than is commonly acknowledged. Cosmic rays that are electron-depleted nuclei are strongly charged, and it may be that a magnetic field around a vessel would deflect this component of cosmic rays, just as the Earth's magnetism protects up to latitude 75 degrees or so. It is likely that radiation-burst detectors would be positioned in living spaces of a vessel, so that travelers would know when a radiation storm is happening.
Mars' radiation is 0 .67mSv per day, galactic cosmic rays. Shielding could be 5m of Martian soil. On a three-year round trip to Mars, including transit time, 10% chance of a fatal cancer later in life. On terrestrial flights, pilots and flight attendants in commercial aviation have more cancer than those who are shielded by the atmosphere.
There is a way to cope with radiation that travels as bursts or clouds. Deploy an array of six ten-pound satellites around the manned vessel, at a distance of two light-minutes (20 million miles). Equip each with a half-watt power source, a radiation detector, and a laser. If a satellite detects a burst of radiation, it signals the manned vessel by flashing a code by laser. The people have a fraction of a minute to move to maximum shielding. Those granted the longest lifetime get the best shielding. (See below, "meritocracy of usefulness.") But for a radiation cloud or beam that travels near the speed of light, there would be almost no warning.
Interstellar space is cold, only three degrees above absolute zero. There would have to be some source of heat to keep the travelers from freezing. It could be that dealing with cold would become the leading preoccupation. Men would grow maximum beards. Women would seek ways to keep their feet warm. The warmest place in the vessel would become a little resort, and that would be the place to have more lighting, too. It could be a reward for those who behave, or it might become a secret place of pleasure for the elite. The warmest place would likely not be a window looking out to space; windows leak heat, and who wants to look out at space when nothing is ever changing, anyway? (Looking with a telescope at variable stars would be the only variation to be seen, and in fact the period of the most obvious variable star might replace the day as a standard for time.) Staying warm is at odds with bathing. Bathing, drinking water that has no residual taste, staying warm, and eating might become the leading lifestyle metrics.
The 2016 interstellar movie, Passengers, depicts a vehicle of proven design (proven by many previous journeys), with 5000 people in hibernation, going 60 light-years distance to an existing colony, and travelling for about 120 years. The movie shows some things that are appealing to the general public, but many things are as unrealistic as Star Trek and Star Wars. Communication back to Earth is halfway realistic. A message to Earth is routinely transmitted but with a warning that it is expensive to transmit so far (which would refer to the energy to send a radio or light message when the energy cannot be directed in a beam less than 20 arcseconds to 20 arcminutes), but the reception time on Earth is related to be 19 years, then there is another 19 years to reply.
The vehicle has a helical shape with a great amount of surface area, which would give fragility, excessive frontal area (exposure to space dust collisions), and excessive heat radiation. But the shape is pleasing to the eye and gives the two awakened travelers a lot of places to explore.
A collision with a ton-mass asteroid or comet shape is depicted as causing a fist-sized puncture through several places in the craft, including the fusion reactor vessel. This is a ridiculous departure from reality. 1) The craft is travelling at about half the speed of light, according to the script, which would be about 100,000 miles per second. You have to just ignore the energy to accelerate to this speed, 200x10^21 joules. This doesn't count the energy to accelerate fuel. 2) The depicted shield, some sort of energy field across the front of the vehicle, might be envisioned for strongly electrically charged obstacles of micron size, but not for uncharged obstacles. The depicted obstacle appears to be a ton in mass, which would give a collision energy of something like 1/2 m v squared (unless the mass is deflected at a tiny angle), about 20x10^18 joules. Compare this to the energy of the 1908 San Francisco earthquake, 5x10^16 joules. Compare to a gigawatt power plant producing 3x10^16 joules per year. (A more realistic way to shield is to send a plow ahead of the manned vehicle; the plow vaporizes smaller obstacles, and part of the plow is vaporized, but some of the vapor will be suddenly decelerated and the manned vehicle will strike the plasma vapor anyway. A plow would give no protection from obstacles evading the shield by coming in at high speed at an angle.) 3) If you plan to detect an obstacle from a distance and steer around it, how big an obstacle can you detect when you are travelling at 100,000 miles per second? Radar or lidar would travel at just double the vehicle speed, and the vehicle would be bearing down on the obstacle while the radar or lidar return signal is coming back. 4) A real puncture would not cause a fist-sized hole through multiple walls of the vehicle. The first contact creates an explosion of plasma, and the size and accumulated mass of the plasma bubble expands with time to create successively larger holes through the vehicle. On Internet, look for "spacecraft shield." Bear in mind that a comet or asteroid with diameter four miles, falling inward to the Earth, deposits so much energy into the Earth that some of the Earth's crust melts.
Patent application, Spacecraft Shield, against micrometeoroids. Vaporize the 100km/s particle and spread the damage over a wider area of underlying shield. From the outside in, bumper, cloud stopper, fragment stopper, atmospheric pressure vessel.
For the majority of occupants of an interstellar vessel, ignorance of the impact threat is better than telling everyone. If there is an impact, the entire vessel is likely to be smashed to bits instantly, and it would only raise fear to train everyone about recovery from an impact. But it would be best to send a message home to Earth once in a while about how things are going.
A Travelers' Guide to the Stars by Les Johnson Not easy, not for the faint of heart [when generations born enroute have no choice in the matter], harsh and forbidding expanse of space. Daunting challenges.
Radiation in the heliosphere, the vast bubble of ions and magnetism that is controlled by the Sun, extends well outside the orbit of Pluto. Outside the heliosphere, the interstellar medium awaits the travelers. Both Voyager spacecraft left the heliosphere, one in 2012 and the other in 2018. They went from hot, low-density plasma to cool, higher-density plasma. https://phys.org/news/2019-11-voyager-interstellar-space-scientists-plasma.html What that means for travelers, I don't know.
Think about body hygiene in terms of willingness to keep oneself clean. That takes discipline. There are always some people who lack discipline. One can imagine bad situations that would happen, being dirty and spreading dirt. Could a large passenger load enter into an interplanetary vessel with no cockroaches or spiders making it on board? Passengers would have to pass a gene screen to avoid genetic diseases making it on board. That probably means couples who are married and who want to go on the voyage both need to pass genetic screening. That may skew the voyagers toward being unmarried, so there may be a high rate of marriage after departing--if marriage is even still a thing on the voyage.
Baby hygiene is a category unto itself. Babies have no interest in being clean. If there is no gravity, imagine the filth that would spread across surfaces and throughout the air, around babies. They would have to be isolated in a particular area, and adults would care for them. That would be a low-status job. The roles of women and men might revert to the old order, women cooking and cleaning while the men work.
Given the importance of alcohol consumption among Earthlings, there would be alcohol brewing and distilling during an interplanetary voyage. Brewing and distilling are energy intensive and require some warmth for fermentation, a bacteria phenomenon. Various food fermentations need up to 114°F, and 118°F for cheese. How would that fit into a long journey with limited resources?
For a colony on Mars, each resident would be allowed an Earth item once every two years and two months. Residents would browse a kind of Amazon and make selections. The selections would be vetted to survive heat, cold, vibration, radiation, and vacuum. Shipping charge of $60,000 per pound would be paid by some benefactor on Earth. There would be no bubble wrap, bubble envelope, or packing paper, all of that is too heavy. Delivery would not be by FedEx or USPS, you would check the box for "rocket." Delivery time would be 20 months, much longer than human travel, because the unmanned space delivery vessel would make multiple close loops around Earth and Venus, building speed at each encounter, the mysterious slingshot effect. "Deliver to" would be a fill-in text box on the order computer, and there would be a selection for back-up recipient, in case the intended recipient dies in the meantime.
For an interstellar voyage, after going past Mars, nothing more would come from Earth, apart from lightweight tools or material that are needed at the last "minute" and would be rocketed to the interstellar vessel, catching up within some years from launch. Women and children on the voyage would have limited shopping; they would quickly know every single item available in the "shops" on the vessel. (There would be conspiracy theories about the secret shops.) When one person doesn't need an item, it would be re-gifted or set back out in a shop. People who do crafting could re-use materials and create new items. But the materials available would increasingly be re-used materials, which could even include bone from the deceased generations. (The on-board warehouse of virgin materials has to feature pure elements, chemical compounds that are hard to synthesize, semiconductors, and metal shapes. A council would dispense materials from the warehouse. They would judge the need compared to how much of the 3000-generation voyage lies ahead. But it is worse than that; upon arrival at a planet, there may be no way of extracting materials from ores and deposits.)
Deceleration Before Landing
If you launch a person toward another star, are you expecting him to go into orbit around some planet, multiple light-years away? If so, the vessel will have to decelerate. That means you have to pack fuel for the deceleration, and you can't afford for any liquid fuel to evaporate for thousands of years. But it also means the mass of the fuel, which far exceeds the mass of the humans and their environment, has to be accelerated to an appreciable fraction of the speed of light. If you are thinking of nuclear propulsion using a radioactive isotope, how many isotopes retain enough reactivity after tens of thousands of years? Perhaps there would be enough energy coming from the planet's star to power an ion thruster, which acts for years at low thrust.
Deceleration upon approach to a planetary system would actually have to be a decision by the travelers. "Do we decelerate at all, given the meager information we have about the planets we are approaching? Maybe it would be better to keep our momentum and search for a better place." The vessel could be built with a small planetary lander; the lander could decelerate with volunteers, and most voyagers would continue without decelerating. How would any one person make up his mind about landing or continuing on through space? Those who land, or orbit, would likely have a prospect of few generations because they would carry few resources. But if they find a habitable planet, they might prosper. At the time that the Landers are being provisioned, there would be contention about how many resources to commit to the Landers, because any resource the Landers take are resources that the Continuers do without.
Those who decelerate for orbiting or landing would commit themselves to deceleration, with no prospect of ever seeing their fellow travelers who continue out into space. Communications between the "Continuers" and the Landers might be sustained for some years, but signals would eventually be lost in noise. As the separation widens, communications would be limited to a dictionary of codes, perhaps 100 codes, with each code sent repeatedly for hours to average out noise. Imagine being assigned the task of writing the dictionary of codes; how many codes would convey success, and how many would convey mishap and disappointment? Among both the Landers and the Continuers, there would be anxiety for years about their decisions, as the Landers approach their destination planet and observe increasing detail using a telescope. What a solemn ceremony would take place at the time of separation.
The larger telescope would remain with the Continuers. After Separation, the Continuers would continue at speed past the target planet, and would relay increasing detail about the nature of the target planet as they reach their closest approach. (The Continuers would streak past the target while the Landers are in their multi-year deceleration.) If Separation happens ten years before the Landers start deceleration (giving ten years to decelerate to orbital speed), the Landers would have been provisioned with the barest information about the planet. Obviously, the vessel should be preceded by a robot observer, Scout, going perhaps 30 years ahead of the manned vessel. The robot would give advance looks at all potential targets so that Landers could be optimally provisioned, supplied with the exact needs but draining minimal resources from the Continuers. A crisis for management and governance would take place concerning Lander provisioning. There would be a political split between Continuers and Landers, each group likely becoming greedy. Perhaps the Landers would engage in a sort of auction with the Continuers, trading off giving the Landers certain provisions in return for the Continuers never seeing the Landers again.
But the Lander situation could get more interesting. After Separation, as the Continuers get closer to the target, their telescopes, and even an atmospheric sampler probe and landing camera, could provide much more detail about the target. If it appears that the target is not going to support life, the Continuers could relay that information to the Landers. The Landers, in their multi-year deceleration phase, might decide to abandon the plan, turn the ion thruster around, and rejoin the Continuers. But this would work only if the Landers jettison mass, or use some mass as fuel. An accountant on the Lander would be figuring the fuel and mass budget all the time, figuring how the Landers could rejoin the Continuers. At some point, the need to shed mass would extend to the living Landers; some would have to be sacrificed, probably used as fuel! And if some Landers actually make it back to the Continuers, the Continuers might radio to the Landers, "We made a contract, you would not be rejoining us. We will take a few of you, and the rest will come on board to be used as resource."
A web site says that the low energy in chemical-fuel reaction, and the need to accelerate the fuel as you accelerate the payload, is a vicious circle with this result: for single-stage rocket, the ratio of payload to fuel keeps going toward zero as you try to get toward 0.0001% of the speed of light. https://www.space.com/40507-interstellar-space-travel-and-science-fiction.html
Both acceleration and deceleration can take advantage of gravitational slingshot, gravity assist maneuver, or swing-by (see Wikipedia). (In the case of deceleration, it isn't obvious that it would work, but look at https://wiki.kerbalspaceprogram.com/wiki/Tutorial:_Gravity_Assist. You have to make a close pass ahead of the massive planet.) This is done routinely by Earth-to-planet spacecraft, and was vital for the Voyager craft which left the Solar System with above-escape-velocity speeds. A trip to Venus or Mercury uses the slingshot technique to decelerate, taking kinetic energy gained from approaching the sun and trading it off to the orbital energy of Venus or Mercury. To decelerate at a terminal star, an interstellar vessel would require a heavy planet orbiting around the destination star. A telescope in the vessel would be required for years before deceleration to pick among candidate planets and plan multiple passes to sufficiently decelerate, to enter a planetary orbit. Computer calculations would be needed, and careful determination of stray gas orbiting the massive planet would be needed so that the decelerating vessel doesn't encounter too much gas pressure and consequent heating. Any rings (like around Saturn and Uranus) would have to be avoided.
My references to thousands of years is from the travel time, thousands to hundreds of thousands of years. A vessel going at the speed of the Voyagers, the fastest objects so far, would take 75,000 years to reach the nearest star. And you are going to pack enough fuel to let the humans decelerate to a planet-orbiting speed? And how many stars have habitable planets, anyway?
Wikipedia Breakthrough Starshot a flyby craft to Alpha Centauri, passing about 80 million miles away and using tiny telescope to photograph any planets, laser communication back to earth, a thin light sail about 16 square meters for laser propulsion away from Earth and as a mirror for the laser back to Earth. At a distance of four light years, there would be little two-way communication to Starshot, and the duration of the flyby would be merely hours, so no chance of people giving commands to Starshot about where to point the telescope.
While an interstellar vessel has not yet reached the halfway point to a destination star, the travelers might think about using their deceleration fuel to turn around and return to Earth, maybe jettisoning surplus mass to conserve fuel. A rebellious few would think about executing most of the travelers so that the rebels have more resources while returning to Earth. But the fuel to return to Earth would likely consume all available fuel and leave no fuel to decelerate to Earth orbit. The rebels could appeal to Earthlings to rescue them, otherwise they would pass by the Earth with no way to decelerate. There would be controversy on Earth about why the travelers are returning and what nefarious actions happened en route. And there would be questions about the physical condition of the rebels and their ability to live in Earth surface gravity.
Intergalactic is Out of the Question
Going to other stars in the same arm of the Milky Way is one thing, and it would be around 1000 times longer to go to another galaxy. So forget the intergalactic thing.
Many Generations
What would it be like to be in the 1,500th generation, halfway to another star? Would there be a tendency to nihilism? What would it be like to perpetually face the possibility of instant decompression due to collision with a 1mm-diameter meteorite? Consider that Star Trek, Star Wars, and Orville visit planets that seem to always have breathable atmospheres and habitable temperatures. That would not be the case for interstellar travel. Just looking at the Sun's planets, only one is friendly to life. What would it be like to get to another star and find that the best planet is like Mars? A big let-down--that would be the persistent thought of planners and the archivist on the interstellar vessel as it reaches a destination. The leaders would need to use propaganda to manage the emotions of the travelers.
When you think about the "habitable zone" around a star, you might get the idea that ETs may be there. But habitable zone really means that the simplest, hardiest, terrestrial-style life could exist there if given the proper atmosphere and nutrition. It says nothing about habitability being prolonged enough for evolution (if evolution exists at all) to happen. Many habitable-zone planets have too much carbon monoxide and carbon dioxide. The outer part of any habitable zone would have liquid water only because of a strong greenhouse effect from dense carbon dioxide. A habitable zone with low carbon dioxide would be a smaller subset of a full habitable zone.
The closest star, Proxima Centauri, produces strong ultraviolet radiation that launches all atmospheric gases away from any planets. Astrobiology.nasa.gov has a web site that says, "It is becoming increasingly likely that the percentage of exoplanets that could support complex life as we know it is very small indeed." And this is from the space agency that gains funding from Congress by promoting the gee-whiz search for life around out Sun. Search Internet for exoplanetHouseOfHorrors.
If the fuel and speed problems could be overcome, how would humans live to orbit a planet around another star? There would have to be multiple generations. But geneticists know that avoiding inbreeding requires care. There would have to be multiple colonies of humans on the vessel, each with a breeding program, and there would be limited cross-breeding between the colonies to keep harmful mutations from proliferating. If you can't choose who you breed with, is that going to cause social problems? An Internet page says that 10,000 to 40,000 people are needed in a gene pool.
Someone (Marin?) says 98 selected people could carry enough genetic variability to rebuild humans on another planet. But he assumes they wouldn't be husband and wife, they would be in a breeding program to maintain the genetics, and they would have no choice about who they are with. It would be assigned, week by week. Offspring would be analyzed for suitability; those deemed non-beneficial would be recycled. Such a cold attitude argues in favor of a larger population on the vessel, where there is more social interaction. Cameron Smith at Portland State, 2014, says 14000 on an interplanetary vessel, and he probably assumes regular families. Eugenics would be the policy. (Eugenics was a popular U.S. policy before it was discredited by Nazi eugenics.)
Conservation of atoms would be a concern for the entire trip. What I am thinking is that there must be no leakage or jettisoning of material. None at all. You have a continuing need for all of what you start with because there is no restocking while underway. Furthermore, if you do budget for some limited jettisoning of anything, you have wasted propulsion energy for whatever you get rid of. On the other hand, jettisoning any mass is that much less mass that has to be decelerated at arrival. But if there are 75000/25 = 3000 human generations, each generation can hardly justify jettisoning more that .001%. That includes any microscopic atmosphere leaks. A vessel would need an "elemental cupboard," materials including most of the known elements, so that on-board scientific development would have all the elements to play with.
The required conservation of atoms has some implications. Intestinal gas must be recycled (search for "volatile organic compounds"). Human and animal development of carbon dioxide must be balanced by plant generation of oxygen. All human and animal waste must be collected and utilized. Stop thinking about a toilet as a place to get rid of nasty stuff--the travelers must reutilize everything that we on earth put in toilets. And all that toilet paper? Each American uses 50 pounds of toilet tissue per year. That wouldn't work in space.
The need to reutilize all the atomic matter in human waste might start with aeration and microbial action just like in sewage treatment plants on Earth. Microbial communities including fungi, bacteria, and microalgae process sewage into substances that are low-hazard and amenable to follow-on usage. "Tertiary treatment" in some sewage treatment plants is an everyday topic and is partly water plants where roots have a remarkable ability to collect harmful substances, but filtering and disinfecting are also important in producing water that is worthy of drinking. Sewage treatment microbes are available on Earth from commercial sources and are shipped in packets or cannisters. On an interstellar vessel, cultivating succeeding generations of living microbes for sewage treatment would be of paramount importance. A mutation in these microbes could have fatal consequences, so multiple cultures would be needed with strict isolation between batches to localize any mutations.
If you check on the toilet habits of people in large parts of the Earth (I know for sure about Arab and India rural places), you find they get along without toilets and tissue. The right hand is the hand of honor and eating, the left hand is the hand of dishonor. You don't touch other people with the left hand, and the left hand remains on the lap during meals. You salute with the right hand. (In some Arab countries, a severe punishment is amputation of the right hand, often done with anesthesia.) The application during interstellar travel is that children born during the voyage would be toilet trained, but in the manner of rural, poor Earthlings. They would grow up knowing no difference. It would be life as normal, without tissue. If this sounds disgusting, you had better learn about this before boarding an interstellar flight.
Think about food. Mammals used for food would have to be rare, and there would likely be no milk. It is more likely that meat sources would be insects, slugs, and worms. There are places on earth where these are eaten. And escargot is snails. So these alternate meat sources might work. As for plant food, grains might be grown, and a little oil comes from grains. But think of how much waste there is with plants. There are roots and stalks. After water is extracted, you have fibrous, hard material left over. It has to be utilized, there is no throwing away of anything, in the long term. Would worms and edible insects eat leftover roots and stalks? Lost in Space depicts delicious meals being served up, but that is not how interstellar or even interplanetary life would be. The 1973 movie, Soylent Green, is about processing dead bodies into nutritious wafers.
How would people get used to eating insects, slugs, and worms? The first generation born on the interstellar vessel could be isolated from any remaining Earth food and would be fed the long-term protein sources. They would know no alternative and might be quite satisfied with insects, slugs, and worms. But books would have to be edited to censor the delights of Earth steak, chicken fingers, and fried shrimp, for at least one generation.
Not much thinking is required to make the preceding paragraph sensible. Take enough Earth food on the interstellar vessel so that two generations of travelers can have an occasional, Earth-style meal. But serve it only to those first two generations, and space out the feasting to less and less frequent occasions. Children born on the vessel will not eat real meat and the other Earth food that requires too much to grow. Most of the food eaten will be the insects, slugs, and worms. If no one tells them about Earth food, the children will not know the difference, and they won't complain. By the time the second generation dies, there will be no complaining about insects, slugs, and worms.
Now, think about trash cans that are used on Earth. If people on Earth don't need something, it often goes in the trash and ends up in landfill. But on an interstellar vessel, nothing can stay trash, permanently. Even dead skin cells that slough off, anything from the throat and nose that gets coughed out, and dust from fabrics would have to be reutilized. Can plants and worms grow in that stuff?
Drinking water and warmth are two mandatory things on board. The first of these, drinking water, can be thought about as we read https://www.nasa.gov/mission_pages/station/research/benefits/water_in_space/. It looks like half the drinking water is sent up by supply rockets. This may be because processed urine and water condensed from humid air retain taste. (Don't forget, collected urine is everyone's urine, you don't have the privilege of consuming your own processed urine.) The web page also says that electrolyzed water, to obtain oxygen for breathing, is only half used, the hydrogen resulting from the hydrolysis can't be burned for energy because that requires too much oxygen! The hydrogen is dumped out into space. (Apparently, enough electrical energy comes from the big solar panels, using hydrogen for energy isn't worth it.) The Sabatier system installed on the International Space Station in 2010 turned carbon dioxide into methane (the oxygen in the carbon dioxide was made available for breathing, and the "waste" hydrogen was joined to the "waste" carbon to make methane, an ideal gas to dump into space if you don't have enough oxygen to burn it).
There is the tricky matter of what to do with deceased bodies. The atomic matter of bodies must be re-utilized; the required conservation of mass does not allow for "burial in space" as there is burial at sea. Probably bones of the deceased would be ground up and used as a calcium supplement. Ligaments and skin would be processed to make gelatin. (Really. Look at https://draxe.com/nutrition/gelatin/ So grandma died last month? Have some gelatin!) You surely do not want the mass of an on-board graveyard to have to be decelerated when it is time to orbit some planet or star. If you recycle all the atoms of the deceased, generations past the first five will have less concrete proof of how many generations have gone before.
I have a feeling that succeeding generations will lose a sense of the passage of time; on Earth, there are anthropologists on T.V. programs who show bones from thousands of years ago, and that gives Earthlings a sense of the passage of time and the passage of generations. The interstellar voyagers past the tenth generation would have no way to relate to this.
Oxygen generation requires light to make plants grow. Where does all the required light come from? Solar cells don't work past 300 million miles from a star; once you are well past the Sun, you literally only have starlight.
If power generation is lost (there would be redundant power systems), the vessel would cool down toward 3 degrees above absolute zero. The first to go would be the meat animals and the crops. Then the people would get colder and colder. At the last, any reserve of oxygen would be consumed by building little fires for warmth.
Considering the many systems that would be required to sustain human life through thousands of generations, any real colony of people launched out toward a star would need to be preceded by large-scale trials in Earth orbit. Human participants would have to be volunteers who are motivated by altruism; years of their lives would pass in orbit while their existence is documented and their mental and physical conditions are monitored and treatments are administered, dealing with disease to start with. If exercising to maintain blood circulation, muscles, and bones is discontinued for an individual, that person would probably be unable to return to Earth, and would be destined to live and die on the experimental orbiting vessel.
During the decades of manned space exploration, into the 2020s, most space humans have been brave individuals who commit to goals and shrug off inconveniences and dangers. But even the bravest of these yearn for a return to Earth, where there are friends and family. This comes out in Mary Roach's book, Packing for Mars. Articles about one-way trips to Mars, with an uncertain chance of ever returning to Earth because a return vessel is just too heavy to get down to the Mars surface*, are probably not dealing with real feelings about arriving onto the Mars surface, living for years under the surface to protect from radiation and cold, and living until death on meager provisions, wondering which of the little colony will be next to die. The survivors, through years of privation, would never be able to have a two-way conversation with anyone on Earth because of the long speed-of-light delay. They would find that Earth cares less and less about them, as time goes on. The short walks up on the Mars surface would get boring because there are no trees or flowers, and the scenery is unchanging and boring. *The mass of a return vessel includes fuel to land onto Mars, close to the habitation that houses the little colony of people, fuel to get back up into Mars orbit, fuel to accelerate toward Earth, and water, food, and oxygen to live through the return. The G force of the deceleration through Earth atmosphere might break several bones in each person because lower gravity on Mars, plus months of weightlessness between planets, inevitably reduces the strength of bones. Exercising does not maintain full bone strength. Packing for Mars says that people suffer from fear, isolation, and loneliness. People get irritated with each other, then get hostile toward each other in these conditions. The unavailability of good hygiene means that people would be stinky all the time, the whole habitat would be stinky. And gritty, dangerous Mars dust would gradually be spread about in the habitat, and there would be a limited quantity of cleaning supplies.
One can read about the mental health of submariners, who lead lives with parallels to interstellar travelers. They are in a closed, artificial, often noisy environment. There is radioactivity to be on the watch for. Many jobs on submarines are critical to the mission, such as waste processing, energy, food, and health. There is a lot of pressure to keep all systems working. The pressure to perform would be more intense on a space vessel. The stress would increase toward the top of the command staff. Depression and PTSD would threaten everyone. There would have to be a way to evaluate the top managers, and replace them if their mental health deteriorates. The threat of being replaced, and doubt and conspiracy theories, could plague the occupants of the vessel. There would be centuries-long remembrance of "this commander kept things running, that commander was oppressive." "Are we training a new generation of leaders who will be better than the previous generation?" "Why are those people eating better than we are?"
The Babylon 5 TV series deals with personal change, loss, oppression, corruption, and redemption. All of these human factors would occur in interstellar travel. A small place in Babylon 5 is a verdant though dim place that people can retreat to for solace.
Depression accounts include anhedonia, hopelessness, feeling of doom and worthlessness, disinterest in personal care, hallucination, phobias, paranoia, psychosomatic disease, anxiety disorders, joint pain, being antisocial and destructive. On an interstellar vessel, there would be worry about being diagnosed as dangerous to the vessel and being condemned to the prison, which would quickly lead to getting recycled as in Soylent Green. U.S. Navy submarine nuclear school instructors routinely "scan students' faces to identify anyone who may be struggling." Nuclear-powered aircraft carriers have come to have psychologists on the staff. Nuclear-trained sailors spend more time in dark, noisy, dangerous places and say they are treated as second-class crew. "Compressed, arduous environment."
Think about hobbies. People on Earth who have free time garden, read, shop, paint, compose music, go to movie, do woodwork. How many of these can be done during thousands of generations on a closed vessel? Composing and playing music could probably work, but using only instruments taken from Earth. When the instruments wear out, they probably get recycled, and no new instruments. Reading by Kindle could make a great library available, and various readers could blog about what they read, through many generations. Gardening might fit with growing food. Just visiting different people and making friends might be a leading preoccupation. Looking at movies might lose interest, because almost all movies are about places on Earth, and Earth would rapidly become ancient history, barely relevant to the travelers. Even science fiction movies about outer space almost always are about going to places, and the travelers, for almost all the generations, would not be experiencing any place. Science fiction might be desirable, though, to keep alive the idea of landing on a planet. And some sort of movie making, using CG, or simulation of planets (Holodeck), would serve that purpose.
With the awareness of U.S. political polarization since 2009, leaders on the vessel would want to steer clear of polarization.
Thousands of Generations
Everyone is familiar with small cave animals that lose pigmentation and eyesight. There would be similar genetic losses affecting interstellar travelers, beginning in dozens of generations and becoming progressively more debilitating as the time for deceleration approaches. If a habitable planet is found, it is likely that the travelers could not deal with gravity or even sustained deceleration.
An interstellar colony of people would have a hard time staying in touch with the long-past human culture of Earth. There would be no contact with Earth, for one thing. At two light-years distance, communications would be at a rate of fractions of a bit per second, even for a thousand-watt transmitter, and the round-trip reply time would be four years. One can imagine that books and movies about the Earth, taken on-board the vessel, would take on the nature of myths. They might be viewed as we Earthlings view sci-fi. The travelers would lose consciousness after twenty generations that relics from the Earth had any significance or represented anything real. Of more significance to the travelers would be simulations of life on planets, and the simulations would become more and more the fruit of imagination, less and less related to life on a planet. Any residents on the vessel who might seek reality would focus on the possibilities at a destination, not on the Earth.
It is possible that the meaning of time would be lost. After leaving the Solar System, there would be no sense of motion. Any one generation would see an unchanging array of stars, and those stars wouldn't even twinkle. The sense of the passage of time might be lost. As a TV viewer sees The Orville, stars are shown streaming past the big windows. This is 40 million times the rate a traveler would actually observe. (The Orville is shown going 30 light years per second, more or less. That is 7.3x1012 miles per second.) For one thing, you can't have big, heat-leaking windows in a vessel that has an meager energy budget, so there won't be much looking out of windows. You could have a camera that would display onto big displays. Over generations, telescope images could be built up of the small amount of parallax seen, the nearest star perpendicular to the path of travel against the distant stars. (Parallax wouldn't be seen from the receding Sun, the vessel is traveling directly away from the Sun.) The images could be played as a time-lapse movie to prove that the vessel is indeed moving. But, just as there are Apollo-Moon-mission skeptics who insist that the Moon missions were staged, with NASA sets for fake astronauts to putter around on, there would be interplanetary vessel skeptics who would insist that the vessel is in orbit around the Earth or Sun, not going toward a distant star.
One of the few advantages of traveling through space would be telescope viewing of all wavelengths, without the Earth's atmosphere absorbing most of the radiation from stars and nebulae. And there would be no light pollution. Before the vessel gets too far from Earth, images from the space-borne telescope could be transmitted to Earth, and Earth astronomers would congratulate the voyagers for their discoveries. But the bandwidth of radio transmission would gradually narrow, and the power to transmit images to Earth would be limited, so the vessel's telescope would become just a plaything for the few on board to dabble in. Upon approach to a destination star, though, the telescope would be the key to learning about planets!
After 1000 years of travel, imagine the darkness that the vessel would be in. The Sun would still be the brightest star, and the Milky Way and bright stars would be prominent. But there would be so little light that the travelers would forget what shadows are. Rarely, on a time scale of 300 years, there would be a supernova that would be a genuinely bright thing. If energy is a limit in the vessel, darkness might be enforced within the vessel, because lighting uses energy. White clothing and white furnishings and walls, and even mirror walls, would reflect light multiple times, boosting the light level available from a given lighting budget. But darkness might be the rule in much of the vessel.
Disagreement among the voyagers would be a big problem. The initial crew would have to be selected to be accommodating people. If reasoned thinking is heritable, the breeding program would have to groom descendants to be accommodating. A major problem would be competition between the low-cross-breeding sub-colonies. There would be tribal conflict. One sub-colony would seek to steal resources from another. "You people make do while we live it up for awhile. You had your prosperous time during the last generation, it is our turn now."
While considering breeding, one might think about natural death at old age. This probably wouldn't be the policy on-board. The policy would probably amount to a "meritocracy of usefulness." Life would be awarded to those who contribute the most, and an end of life would be decreed for those who cause problems, those who have contagious disease, those who have debilitating disease and require a lot of resources to remain living, and those who have outlived their usefulness. There would be a ceremony for end-of-life, but there would be a ribbon worn by those granted extension of life, designating their probable years-to-live. The means of death would be the way that makes it easiest to recycle all the material of the body.
"Healthy living" would be mandated for the travelers. If all occupants of the vessel must be productive and useful, there would be no tolerance for laziness and overweight. Sleep might be regulated, toward the low end of what is healthy. There might be a policy for cross-training, as is done on nuclear-powered submarines, because a more-educated person is a more productive person. Psychologists would regularly investigate the mental health of all but the elite. This would naturally be disliked by the travelers, just as aviators don't like to be examined by flight surgeons; the surgeon isn't there to aid the health of the aviator, just to weed out aviators who develop problems. Does this sound like the novel, 1984?
At times of crisis during mid-voyage, there would be a political push to terminate large numbers of travelers, to let survivors live it up a little. The genetic impetus of having a large breeding population could get ignored. If political poison brings breeding to an end and life style becomes paramount, there would be a mass die-off of the least influential people, and the elite would enjoy several generations of relative luxury (per-capita resources). A middle ground, with less death, could be that the least influential would be operated upon to harvest their limbs for food.
If the majority of people on the journey are preserved through centuries with cryogenics, somehow controlling for no freezer burn, to be unfrozen and waked up near the end of the journey, there would be a temptation among the skeleton crew, those remaining warm and sentient, to harvest a body, now and again, for a cannibalistic feast. After all, there would be 20,000 frozen people, and who would miss a few people, now and then? Two things stand in the way of this practice. 1) The appetite for meat may wane if the main fare at table is slugs, insects, and worms. 2) A frozen body that is to be eaten must first be defrosted, starting from a very cold temperature, and then cooked. Would there be enough spare energy to defrost and cook?
If scarcity of resources becomes the most important thing, most activities on board would fall prey to an accounting system that optimizes the usage of resources. Few people would escape the cold logic of the accounting department. There would be revolutionists who would attempt to revise the accounting system, to change the rationale. The accounting department would tell couples, or just tell women, when to have a baby, because there are limits of resources on board the vessel. In some decades, the ruler or the council would decide that an overall reduction of population is needed; a version of Communist China's One Child Policy would be mandated, but over one generation the geneticists would be watching for an undesired shrinkage of desirable genetic features. The accounting department would have a large say in who can marry who. The department would always be evaluating mental fitness for specific jobs, and many young people would be steered into particular careers that are necessary for survival of the voyage. How would people react to a lack of freedom in regard to who you marry, who you mate with, the job you have to do, the medical treatment that is metered out to you, whether you live toward the outside of the vessel or toward the inside (where the radiation shielding is better), and how long you can live? Soylent Green comes to mind. The accounting department would have authority to mandate that certain people be the guinea pigs for drug testing and other experiments. Looking at toxic politics in the U.S. from 2012 to 2024 (think about The View), it makes one wonder if that type of cultural toxicity could take hold in the vessel and make life so unpleasant that many would lose hope and waste away from depression. Manufacturing antidepressants might be a key endeavor. Could conspiracy theories and rumors make life toxic on the vessel? Older people who become incontinent would likely be terminated because sanitation supplies would be very limited. Out in space, you can't go to Target to buy Depends.
On military submarines on Earth, it is common to have hot bunks, where most of the people have little personal space that is their own; one bunk is used by three different people, and each bunk is occupied 95% of the time. On an interstellar vessel, hot bunking would likely spread to other activities; there would be few places on board where one could really get away from people.
While reading Mary Roach's book, Packing for Mars, one gets the sense that the most interesting thing to do would be "marital relations." Fertility would have to be tightly regulated.
If there are 3000 generations on the way to another star, and if the average population of the vessel is 200, then 600,000 people would be born and die. Or if the population is 20,000 to enhance genetics, the total living and dying would be 60,000,000! Probably, no paper record, and certainly no physical markers (plaques) of the deceased would be maintained. Computer files would be kept, and they would be detailed beyond anything that is done on Earth, so that heritable traits could be traced.
Artificial gravity would be mandatory for the interstellar vessel. This is depicted in 2001: A Space Odyssey and Babylon 5. (In Babylon 5, you never see, outside a window, the consequence of the 5-mile-long vessel rotating: a moving planet, and motion of spacecraft which are orbiting the planet. Or moving stars. They just leave that out.) Without artificial gravity, successive generations would lose their bones. If the interstellar vessel is two globes joined by a passageway, twirling as it hurtles through space, and if both globes are inhabited, the masses of the globes would need to be more or less balanced so that both have similar artificial gravity. Various inhabitants would develop affinities to one or the other globe. There would be favoritism. There would be cliques. There would be rivalry. One globe would try to steal the air of the other and compress it for future use. But there would have to be cooperation because resources in each globe would be needed by both. For example, the semiconductor factory (see paragraph "Computers On Board") would be needed by both globes.
If any of the voyagers could somehow return to Earth, they would all die from new Earth diseases. They would have lost immune-system function and would die like native Americans died when European diseases were introduced.
Compare the number of generations, from the Enlightenment to the present, comparing to the launch of an interstellar vessel to its arrival at a destination star. That is a time factor of 200. Imagine the advances in Earth technology that would happen in the first 1% of an interstellar voyage. But the travelers wouldn't be able to benefit from it. However, Michio Kaku's nanoprobes could be used to overtake a manned vessel and transmit news and advanced science information to the travelers, but only if the travelers stay on the lookout for approaching nanoprobes. Because a nanoprobe wouldn't slow down upon reaching the manned vessel, optimized data transmission rate would have to be programmed in, and the most important data would be transmitted at slower rates to minimize error rates. But nanoprobes launched from Earth, to catch up to the manned vessel, would be subject to changing gravity fields as stars move around, and it wouldn't be certain that a launched nanoprobe would get anywhere near the vessel. After centuries, Earthlings might give up on the interstellar travelers, assuming they would have died, and they would consider it pointless to launch any more nanoprobes. Earthlings launching a nanoprobe would have to look at the launch records of the travelers to know which language to use in the nanoprobe's transmissions. Linguists would need to craft messages in the dialect of the travelers.
Imagine the travelers maintaining a watch, decade by decade, for a nanoprobe. It would be like SETI on Earth. If the travelers detect a nanoprobe, how exciting that would be. After the nanoprobe passes by, there might be depression among the travelers as they wonder if there will ever be any more nanoprobes. How language experts would parse the limited information received from the nanoprobe as it hurtled by! The travelers would have to preserve the knowledge that life on Earth is so much more interesting than life on an interstellar journey; Earthlings would be inclined to lose interest in the travelers and find other things to do with budget.
https://owlconnected.com/archives/could-interstellar-travel-change-language A new paper, called Language Development During Interstellar Travel was created by a group of linguistics professors. They have said that before long, the language spoken on board an interstellar ark would change dramatically from any language that we knew on Earth.
People on board would create their own slang, their own accents, new words, new phrases. And without constant training in how to speak the language on the planet they left behind, they could become extremely difficult to understand. How hard is it to understand the English used by people in Britain in 1000 A.D.? I am thinking Beowulf in literature class in 12th grade.
Coast to Coast AM 4-18-2022 A graduate in business journalism from the Columbia University Graduate School of Journalism, Peter Ward is a British business and technology reporter whose reporting has taken him across the globe. He'll discuss the people and technologies currently attempting to make humans immortal, starting with the birth of cryonics and the feuding subcultures in that field. He acknowledges that a colony of humans on a planet of another star would take a very long time to get there, and cryonics might be a way to pass the time during the voyage.
Science in Space
Humans traveling in space for many generations would lose touch with physics and other sciences. There are limits on the science that can be carried on in zero gravity, with a limited energy budget and a hard constraint on the number of atoms on board.
A science field that would have to be mastered by succeeding generations would be biochemistry. There would be biological crises that would come up, and those on board would have to do the science if they were going to save themselves. Medicine would also have to be mastered by each succeeding generation. Appendicitis and cancer (cancer from cosmic rays, if nothing else) would continue to plague the travelers.
After 1990, more and more scientists reject evolution. JE predicts this will become an avalanche by 2040. Interstellar voyagers would be saddled with outmoded science.
Judge Judy Between the Stars
Among the voyagers, over the many generations, would be some percentage of sociopathic individuals. How would the voyagers deal with them? Could the voyagers afford to let them live, considering that sociopaths could escape custody and sabotage the vessel?
Given that privation would be the lot of interplanetary voyagers, and given that there would be no outdoors to get away from it all, it seems probable that sociopaths would regularly decide that living is not worth it, not for themselves and not for anyone else. These people would be a risk for sabotage and destruction of the vessel. Some means of reserving some power and vessel-to-Earth communication would be needed to let Earth know that sabotage has happened and the voyagers are dead or declining. The message of doom would let Earth know to not try this again.
Sociopaths must be managed within the vessel, there is no way to appeal to Earth. Would decision making on the vessel be democratic or hierarchical, or would decisions be made most fairly by computer algorithms? Considering the political predicaments that countries on Earth get themselves into (Venezuela, Syria with Assad family, communist countries), hierarchical doesn't sound appealing. Is a democracy better? Democratic voting is done by people who mostly don't know much about the complicated issues, and technocrats can make better decisions when there are complications. So are the technocrats going to amount to hierarchy? How do you keep egomaniacs and narcissists from rising to the top and corrupting management? If there is a clear leader in the vessel, how do the travelers deal with aging and dementia? How would up-and-coming young leader-candidates take over from an old guard? Considering the Harvey Weinsteins and Jeffrey Epsteins, how to handle powerful men who want to aggregate young women?
A possibility: sociopaths could be executed and consumed as food. This could be a real, rare treat for the space travelers, if it is deemed to be a moral act.
Collisions
The two Voyager spacecraft have remained functional for 40 years and have gone beyond the orbit of Pluto. The abundance of dust and larger objects that can be collided with falls off a lot between stars. But if a voyage with humans lasts 75,000 years, what is the probability of collision?
Internet says that interstellar dust is no bigger than 0.2 micron. In thousands of years, might it be possible that a larger object would collide? The energy of an impact with an object 10 microns across would be what? E=.5mv2. Mass is about .001kg*10-6/1*10-2)3 = 1*10-12kg. Velocity is about 17km/s (Voyager example). Energy = .1mJ, not as much as I would have thought. But that energy is concentrated in a little spot on the skin of the vessel, perhaps .1mm across, and the areal rate is .1mJ/.01mm2, which for a square centimeter spot would be at the rate of 100W/cm2. This is still manageable by many materials. But if the colliding object is 0.1mm across, there might be a puncture of the vacuum wall of the vessel, and there might be energetic spreading of debris and a shock wave inside the vessel.
How much mass is out there in space? The average across all space, including 1) between galaxies and 2) neutron stars, and maybe supermassive black holes, these being extremes, is only 1 or 2 atoms or nuclei per cubic meter, and most of it is hydrogen and helium. Within galaxies, the density is much higher. "The actual density of hydrogen as it exists in interstellar space is on the average of about 1 atom per cubic centimeter. In the extremes, as low as 0.1 atom per cubic centimeter has been found in the space between the spiral arms and as high as 1000 atoms per cubic centimeter are known to exist near the galactic core." https://hypertextbook.com/facts/2000/DaWeiCai.shtml
Wikipedia "Breakthrough Starshot" each square centimeter of frontal cross-section collides with a thousand particles at least 0.1 micron diameter, per 10 years of travel.
Computers On Board
A long duration of space travel means that electronic devices would all fail and have to be replaced, if the travelers want to retain the vital communications and control functions that electronics give us. The degradation of semiconductor devices is from corrosion of the metals used for connections across chips, and because the P and N "dopants" that create junctions gradually diffuse, and in hundreds or thousands of years there won't be semiconductor junctions any more. (Note that many programmable devices currently in use are guaranteed for only 20 years; beyond 20 years the flash memory loses charge.)
The implication is that travelers would have to run a semiconductor factory, at least once every other generation, merely to keep computers and sensors running. Note that semiconductor processing generates plenty of toxic waste and requires high temperatures. These go against the need to conserve atoms and conserve power. An alternative is to store backup semiconductors away from the living area of the vessel, at 3ºK or 20ºK, with plenty of cosmic-ray shielding.
On-board semiconductor manufacturing to keep computers working would be frozen at some generation of fab technology, like the 22 nanometer node of 2012 on Earth. (See Wikipedia, Semiconductor device fabrication.) The finer-pitch "nodes" of Earth semiconductor fabs could not be handled by a fab on a space vessel, the chemical processing and exotic light frequencies get out of hand.
Memory by Earthlings of the departed interstellar voyagers would be stigmatized by knowledge that the voyagers are "stuck in the past," technologically, while Earth continues to advance. Stigmatization and contempt would be worse, considering that the departed "ambassadors from Earth" are taking an increasingly ancient version of Earth out to the stars. Any Earth funds expended to communicate to the voyagers would be opposed by Earth budget cutters, "who wants to spend money on those old, primitive voyagers? They are on their own." Among the voyagers, speculation about such contempt would make depression worse. It is even possible that improving ability by Earthlings to beam out (in the direction the vessel is going) radio signals and messages to alien civilizations would include messages to "ignore those primitive voyagers from Earth, they no longer represent what Earth is about." The voyagers would receive such messages and feel abandoned, to the extent that the messages would be classified; few voyagers would actually know about the messages.
Actually, vacuum tubes might be a good choice for electronic functions. They work fine in a vacuum, are radiation resistant, and the materials don't degrade very much. Glass envelopes around the cathodes, grids, and plates wouldn't be needed!
A Web Site
https://www.space.com/40507-interstellar-space-travel-and-science-fiction.html Engage Warp Drive! Why Interstellar Travel's Harder Than It Looks By Elizabeth Howell May 07, 2018 Daedelus, Varies.
Wikipedia Starship, Breakthrough Starshot
Drake Equation is less used, of more concern is habitable zone.
Haaretz.com Why the Search for Intelligent Life Beyond Earth is Futile
Science.nasa.gov No existing or planned technology could preserve human life for the tens of thousands of years it might take to reach another star
Conclusion
These problems are evident in mere hours of speculation. Many more problems are obvious to those in various specialty disciplines. It is a sure thing that humans traveling to planets outside the Solar System is not going to happen. A documentary movie depicting various scenarios would be interesting.
Reference
Radius of Pluto's orbit: 5*109 km
Distance to the nearest star: 40*1012 km
Copyright © 2018 John Engelbrecht
JE May 30 2019, Nov 14 2021
Frozen Embryos
Extend the thinking to the possibility of using frozen embryos to "skip" most generations of the 3000 generations that is computed above, and that just to reach the nearest star.
If frozen embryos could be unfrozen and grown to babyhood by robots, that is a way to go to a live crew count of zero during almost all the voyage, and avoid all the resource use that live crew requires.
What are some details that should be considered for this plan?
If power is throttled back to a low level, the whole vessel would get very cold. What mechanism could wake up a power plant, electronics, or robots from 10 degrees or 40 degrees Kelvin?
Near the time that humans would be needed, when a star is approached, one that might have habitable planets, robots would have to unfreeze some number of embryos and grow them to birth weight. There would be no living parent, you would just have babies being raised by robots. There might be videos of the humans of the past. But there would be no nurturing of babies by humans. Would babies survive this? Think of growing up with no mother or father to hold you, talk to you, or discipline you.
Would the child-raising robots still work after tens of thousands of years? (Considering age, chemical degradation, radiation in space.)
Could a person learn language from a robot? What would a new, isolated generation be eating? There would be no animal protein. (Lost in Space TV series shows nice food being consumed with abandon. That's not how it could be on a long space voyage.) How would a robot teach toilet use? If there are to be follow-on generations, either they will be from new batches of frozen embryos or there has to be sexual reproduction carried on by the new crew. Would there be monogamy, or would there be an impersonal breeding program?
Any babies born to the new crew would be a strange burden, with no parents of the grown-from-frozen-embryos to give guidance. Any time there would be a death, how traumatic would it be?
If a batch of babies is growing up, you can imagine that four-year-old boys would be pushing all the buttons they can find, just to find what happens. Any robot that gets in the way of four-year-olds would likely be disabled, or dismantled, by the children. It would just be fun for children. Children would have no way to appreciate the vital functions of the robots.
The vessel would be like a prison to a new generation. There would be no fuel to land on a planet. They would be confined permanently to the vessel, with its meager resources. There would be no communication to Earth. But there might be small probes that would be sent out from Earth in the decades after the departure of the manned vessel; the new generation on the vessel might look forward to probes catching up to them, but what would it matter? This mystery probe is from a civilization many thousands of years old.
There are so many problems with a crew grown from frozen embryos that the plan should be to do everything by robots and send no human crew at all.
Spiritual Influence
Some Earth sociologists consider spiritual and religious ideas to be vital to people. Look how important self-help books are, even in 2021. (They became a category to themselves in bookstores in the 1970s.) Astrology would probably die out on an interstellar voyage, because the planets and the ecliptic would become meaningless. (The ecliptic would still be there because most stars would remain in the same orientation, comparing the Earth view to the traveler view, since the target planet is relatively close to Earth, but there would be no movement of the planets and Moon through the ecliptic.) The meaning of "rising sign at birth" would lose meaning, because nothing rises when you are away from the Sun. Hinduism and Sikhism might be ascendant because of the low consumption of meat. An aspect of Buddhism, letting go of expectations, might be very attractive to the voyagers. Islam would have no way to go on hajj! But praying while facing Mecca might be easy, you just look toward a certain point in the stars. But if the vessel is rotating to give simulated gravity, that would make it tricky to face Mecca. It might work to prostrate at the center of rotation, where there is weightlessness and you can float free of walls and "floor." Christians would have less and less orientation to all the Earthly events of the Bible, that just wouldn't matter any more. The sacrifice of Jesus, fulfilling the Jewish requirement of atonement, would similarly become a (literally) distant memory. Christians might come around to ethics. During preparation for the launch of the vessel, Christians might look at the gloomy prospects for life outside the solar system and decide to stay on Earth. This would leave the vessel in the hands of atheists and people of other religions.
As an Earthling thinks these thoughts, there is competition between Stoics, Epicureans, ascetics, and hedonists. Some web sources claim that Epicurus actually had a good attitude toward asceticism.
2016 Elon Musk of Tesla Motors has an intention for a colony on Mars, a city of a million [mainly those born on Mars]. Speech at Mexico International Astronautical Congress. His motivation is an inevitable extinction event [long-term climate or sudden asteroid] on Earth. A shuttle would take 100 people at a time for $200,000 each, 80 days to Mars. But "the risk of fatality will be high." On "the first missions ... must be prepared to die." His plan has got to be for a buried city to deal with the radiation. The city must have many pressurized vessels underground, sealed by airlocks, so that accidental decompression in one loses only the air in the one vessel.
A colony on Mars would be a prison: Reddit.com Babies born on Mars would lack bones to live on Earth, so would be stuck on Mars.
https://www.centauri-dreams.org/ independent forum for deep space news and ideas propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA and ESA. "I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight." Paul Gilster Various people propose going to one of the Centauri stars in 50 years to centuries. "Each generation of scientists will be handing the probe off to the next generation." A cultural imperative to pass along things of value. The web site lists interesting books.
One of these books, Interstellar Migration and the Human Experience, talks about social, ethical and even legal ramifications. It looks at how humanity has coped with past challenges, such as the settlement of the Pacific islands.
Another book, Interstellar Travel and Multi-Generational Space Ships, addresses the cultural and psychological issues related to long-term voyaging and ponders ‘generation ships,’ in which crew members spend their entire lives on voyages several centuries in duration.
The movie Pandorum starts with an interesting idea. The Elysium carries 60,000 people. Eight years out, a last message comes from Earth: "You're all that's left of us. Good luck, God bless, and godspeed." In this movie, a syndrome is Orbital Dysfunctional Syndrome. There is stress and paranoia. The movie is from Britain and Germany. In the net, it lost money, maybe because it sounds depressing.
How many movie script writers take this way of thinking about interstellar travel and try to develop credible movie plots, plots that deal with reality? Or is a realistic movie about interstellar travel doomed to be pessimistic?