But the above number is energy to accelerate 100kg, which is about the same as one person with some minimum amount of personal effects. Multiply that by your 10K people, and you get 4 x 10^20, so the energy just to accelerate the people is about 100 times your calculated food costs for 100,000 years. 1% seems a reasonable ‘rounding error’.
And why 100K years? At 0.1c, that’s travelling 10,000 light years. No one is presuming a trip that far with no pitstops. Our first attempt will probably be less than 100 lightyears, so maybe 1000 years of travel.
Then add the energy needed to accelerate everything else the ship carries, and the ship itself. A rounding error on the rounding error, by that point.
Reasonable. I hadn’t picked up on the 100kg initially.
Although with error bars that would make me nervous about even fractional amounts.
Recognize too of course that barring sudden realization of an imminent supernova generation ships are not likely until after humanity has inhabited other portions of the solar system with lots of technology developed in the process.
There could even be a long term selection process for those with lower metabolism and smaller mass able to thrive in lower oxygen maybe higher carbon dioxide environments.
In most strategies of this kind, generation ships are envisaged as travelling much slower than 0.1c. If they travel at 0.01c (taking a thousand years to get to the nearby star Tau Ceti) the amount of energy required to support a closed ecological life-support system would be increased by at least a factor of ten. But the energy needed to accelerate and decelerate would be reduced by a factor of around a hundred. That means the energy required to support the population for a thousand years would start to be a significant fraction of the total energy budget. And that is for one of the closest stars.
I’ve never really considered generation ships to be a particularly useful strategy - they require very large amount of energy overall, even if they travel slowly. But they do have the advantage of taking a large and complex environment on the voyage - probably a useful thing when the travellers arrive at the destination system to find that there are no easily habitable planets (which will almost always be the case).
We’re going to have to start using a spreadsheet! Everyone is talking about different trips. Different durations, accelerations, different numbers of people. Hell, now we’re even talking about only sending short people! Every choice affects the relative energy needs of every other option.
This is actually one of the things the ISS is doing - researching things like growing food in space (they actually have grown a tiny bit of food up there, like lettuce), recycling water, and so forth. To a lesser extent some of the Antarctic research stations are also doing similar things, as well as giving us knowledge about how groups isolated for extended periods of time in limited space do or don’t work well. The progress is small and incremental, which doesn’t make the eager-beavers happy.
If we can’t even make a viable Moon colony - even one that needs periodic inputs from Earth - then there’s no way we can make generation ships. Rescue from the Moon is possible (although very difficult). Rescue from a generation ship is not.
Biosphere doesn’t get much love, and I think that’s a shame. The originators knew that it would most likely “fail” but the point was to learn from how it didn’t work. The media hyped it up, but people actually involved in the project didn’t really think we’d get it right the first time. We did, in fact, learn quite a bit what not to do from those attempts, as well as a few things that worked.
While the first go round with Biosphere II did require inputting food and oxygen, the second experiment did not need either of those showing that there was some improvement. Some small-scale experiments are still performed there, including one studying how soil developments from something like sterile volcanic rock.
Really, Biosphere II is exactly what is needed - a laboratory to study ecological questions in a setting where rapid rescue is possible. Is it a perfect test bed? No. We don’t have a perfect test bed for this sort of thing.
One thing we have discovered is that this sort of science is hard work and tedious. It’s not as sexy as penis-shaped sub-orbital rockets that let rich civilians a taste of black sky at noon and a bit of micro-gravity.
I’m not sure what else we’d be using other than nuclear propulsion (anti-matter is a sexy SF concept, but there are all sorts of problems with even getting a substantial amount of anti-matter, much less doing anything with it).
But, aside from that - there’s research being done in incorporating radiotrophic fungi into radiation shielding for, say, a Mars colony. Might also be a thing for space habitats. Not sure how much energy could be harvested from such a system, and whether or not such fungi would “play nice” with the rest of an enclosed ecosystem, but it has the interesting prospect that you might be able to grow some radiation shielding to size when you get to a new location and not have to bring the whole thing, just some seed stock.
My point was not to slag off the Biosphere efforts. You’re right it is hard work and tedious. And this ties into my actual point… if you want to colonize Mars, and you’re serious enough to name a date of (say) 10 years from now, then your next-generation biosphere project on Antarctica should have started 5 years ago. Yet Musk isn’t even talking about it now.
That’s how you pick out the frauds from the Mars fantatics (hint - all of them are frauds).
Hogs can get a lot of human diseases. Much better to run the bodies through some sort of vegetable and/or fungal matter first. If pigs are desired as part of the system, then feed that matter to the pigs.
Whether pigs should be included on a generation ship is one of the questions that requires ecological experimentation – and this particular question also brings up sociological questions, as there may be humans involved whose religion forbids eating them. By the time the ship’s a few generations out religion is likely to be changing; but at least so long as the crew is recognizably human religion’s likely to still be an issue (and may be afterwards, depending on what the species changes are.)
Yes, there are people doing some work on this. And that sort of thing is one of the reasons to think those people are serious, and seriously understand the problems.
And you’re right that it’s hard work and tedious – and by its very nature takes many years to get results. Because something appears to work for six months doesn’t mean it’ll necessarily work for six years. If something appears to work for six years, that doesn’t necessarily mean it’ll work for sixty; let alone six hundred, or six thousand.
We’re not even anywhere near the point at which it would be suitable to find out whether successful pregnancy, and then successful rearing to adulthood, could be done under specific circumstances. And that stage is going to require a minimum twenty years all by itself – and that would be assuming no problems come up, which seems unlikely.
(That work needs to be done even if what’s being proposed isn’t generation ships, but seed ships. We’d need to know whether the suggested AI’s actually could raise the kids, and whether people so raised could set up a functioning society – considerably more than 20 years to figure that one out, even once the uterine replicators are designed and functional and the AI’s supposedly ditto; all that in addition to the ecological work needed to check whether we coulld keep them alive. You’d need to run your society into three generations at least in order to tell whether it was working.)
I agree, but I think a lot of that is their own fault. It was presented badly and expectations were too high. It wasn’t offered up so much as a work in progress/science experiment as a finished solution - at least to the public and the press. There was also a lack of transparency. When they had to supplement supplies, rather than announcing ‘Here’s what we’ve learned - we need more ~whatever~’, supplies were sneaked in. This led to bad feeling about the project as far as the public was concerned.
In reading this thread another thought occurred to me, would a generation ship loose energy through heat? Space is cold, right? A ship with humans in it for, say a couple hundred years, would need to be warm inside. Would the heat that radiated out into space have an overall negative balance on the ecosphere inside? If so, would there be any way to prevent it?
Insulation. The closed ecological life-support system would produce a certain amount of heat over time, which could be calculated; to retain that heat, you just need to add enough insulation on the outside to balance the waste-heat from the life support and food production, as well as all the bodyheat of the humans (and any livestock and pets, etcetera). A nice thick layer of insulation would also help to protect against cosmic radiation.
Note that you don’t want to make the insulation too efficient, or the temperature of the ship will rise and the inhabitants will cook. Although it would be relatively easy to extend a few radiators if the ship starts to overheat.
Yep, at some point, entropy wins, and waste heat ends up as waste, and needs to be removed. But that will be at the tail end of the most elaborate recycling system ever devised, most likely. We’ll push back against entropy in every way we can, and get as much use out of every joule as possible.
We will need radiators, though. Due to the square/cube law, the larger your ship (and a generation ship will be very large) the smaller the surface area is relative to the volume. Roasting everyone aboard is a bigger threat than freezing (unless all life support systems have already failrd).
Could you explain this better, please? I understand that an enclosed system will generate heat and need to be bled off, but will the heat loss not result in a negative mass loss as well?
FYI, I read this but it’s a little above my pay grade.
The only method to lose heat without losing mass is black-body radiation. When you look at a piece of iron in a forge, and it’s glowing red-hot, that light is energy leaving the iron; if your iron was floating in a vacuum, that energy would still be getting out of the iron.
Red hot iron is visible to the naked eye because it is putting out so much of this radiation at the right frequency, but so do you (that’s what infrared goggles see). So would a spaceship; radiators let you maximize surface area and temperature in a small space to maximize efficiency.
Most of the problems you have to solve to create a vessel capable of travelling to a habitable planet around another star are the same problems you have to solve to be able to live in space indefinitely without a planet. In other words, once we can travel to live on other planets, we no longer need to.
