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I'm allowing for approximately 150 years of technological advancement. This is in Earth's future, so I want to be realistic based off of what we are capable of now and projections for declining resources in the future. The space station is orbiting Earth, but at a distance, and doesn't rendezvous with the surface, so it can't refuel. Would solar power be adequate to sustain life support and other systems?

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  • $\begingroup$ Hi Marina, and welcome to Worldbuilding! If you've got a moment, feel free to check out our tour and the help center to learn more about what we're all about here. Have fun! $\endgroup$ – Dubukay Jul 23 '19 at 2:26
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    $\begingroup$ @Marina "Rendezvous with the surface" seems like a rather odd phrase for "land on Earth and take off and rendezvous with the space station". I am only used to "rendezvous" being used in astronautics for a meeting in space, not for landing on the surface of a large world. $\endgroup$ – M. A. Golding Jul 23 '19 at 16:24
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    $\begingroup$ There's no technical reason you couldn't build the space station with enough radioactive material to run RTGs for 150 years. $\endgroup$ – Carl Witthoft Jul 23 '19 at 19:04
  • $\begingroup$ How large is the space station? Is it just a bit larger than the ISS, or is it in the range of an O'neil cylinder, or even larger? $\endgroup$ – Michael Richardson Jul 23 '19 at 21:55
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    $\begingroup$ "indefinitely" is such a strong term. Past the lifetime of the Sun? Past the heat death of the Universe? Past the time the last protons decayed? Past the time the last black holes evaporated? $\endgroup$ – vsz Jul 24 '19 at 5:03
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I can think of at least four power sources:

1) Solar Power, which is used in the International Space Station. Solar panels are, however, vulnerable to micrometeorites and fast ionized particles in the solar wind, but it would be possible to have microrobotic repair systems.

2) Catching He3 from the solar wind for fusion power. Since this He3 is ionized, it is possible to catch it with a magnetic field, similar to how a Bussard ramjet would catch ionized hydrogen (which might also be used, though pure hydrogen fusion is more difficult than He3 fusion). A magnetic field would be less vulnerable than a solar panel, and it might even protect the space station itself from fast ionized particles.

3) Using a giant wire loop to harvest energy as the station moves through the Earth's magnetic field (as described in David Brin's short story "Tank Farm Dynamo". This, however, has the side effect of slowing the station's orbital speed, leading to a slowly deteriorating orbit. Hence, it would only work in combination with something like a solar sail that adds speed to the orbit at the same rate. This solar sail could double as a solar panel, with the vulnerabilities mentioned above.

4) Power beamed from the surface as microwaves (assuming there is still a civilization on Earth). Microwaves have been suggested as a way to beam solar power from orbit to the Earth's surface, so would obviously also work in reverse. A microwave rectenna would be far less vulnerable than solar panels.

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    $\begingroup$ If using a giant wire loop then you could balance power gain with momentum gain. Need power? Shed momentum. Got excess power (from solar if available)? Reverse the polarity and rise!!! $\endgroup$ – Joe Bloggs Jul 23 '19 at 12:42
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    $\begingroup$ @JoeBloggs: Yes, that would do the trick - but to use power in reverse polarity to balance the orbit, you would need at least as much power as you get out of the loop. If you have that much power from another source, it is probably better to dispense entirely with the loop, unless it has other uses. $\endgroup$ – Klaus Æ. Mogensen Jul 23 '19 at 12:48
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    $\begingroup$ Indeed, but if the power supply fluctuates or occasionally needs shutting down (1 and 2 could both fall into that category) having a loop available for either orbital corrections or power generation is a pretty solid idea. $\endgroup$ – Joe Bloggs Jul 23 '19 at 14:51
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    $\begingroup$ @KlausÆ.Mogensen A "reactionless" drive for a space system to do station-keeping is a great use of the loop. $\endgroup$ – Yakk Jul 23 '19 at 17:49
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    $\begingroup$ Less-serious (but no less-renewable) energy sources include sarcasm, angst and dad jokes $\endgroup$ – Punintended Jul 23 '19 at 21:05
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In terms of energy, solar is the way to go.

All the energy stored chemically and kinetically in all the planets, comets and asteroids together pales in comparison with the energy stored and provided by the sun.

If you haven't already familiarized yourself with the Kardashev scale, now is a good time. This is a paper from 1964, widely popular in science and sci-fi. One of the conclusions here is that if you are near a star, you should go solar - if you are using any other power source, you are likely primitive.

However, do take note of Shadowzee's answer - your energy source may be abundant, but nothing else will be. If you require continuous human occupation of the station you need to either constrain the timespan of the mission, or handwave where the food and water are coming from. Also the air slowly leaks away into space - in real life, a resupply mission usually includes some amount of atmospheric gases as well.

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    $\begingroup$ Yet, per m^3, it isn't much. The square meters just add up. In a space station, you only got so many square meters. $\endgroup$ – Yakk Jul 23 '19 at 17:50
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No. It's not about being able to have enough energy. There would simply not be enough resources available for a closed system like a space station to sustain itself. They would need to recycle their air, water and waste perfectly to ensure the system could sustain itself. They would not be able to support a large number of additional life, like children due to the limited resources or expand their living structure.

Parts wear out, things need to be fixed, you need to go outside. Things will be wasted. And since they can't recover them from the surface they are doomed once they run out of supplies eventually.

So power is the least of your worries. You need raw materials. Protection from micro comets. And some form of entertainment and exercise on board so your astronauts don't go mad with boredom.

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  • $\begingroup$ I think she meant in terms of energy only. $\endgroup$ – Renan Jul 23 '19 at 2:57
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    $\begingroup$ Maybe combine solar power and asteroid mining $\endgroup$ – John Jul 23 '19 at 3:15
  • $\begingroup$ @Renan Its a space station orbiting Earth that doesn't rendezvous with the surface. If they cannot get Fuel from the surface, pretty safe to assume they also can't get other resources, since its going to take a spaceship load of fuel to ship it up to them in the first place. $\endgroup$ – Shadowzee Jul 23 '19 at 4:38
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    $\begingroup$ -1 Because, while you make a good point, you don't attempt to answer the question as stated. $\endgroup$ – bendl Jul 23 '19 at 12:41
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    $\begingroup$ @Marina If your tech is futuristic enough, it might be possible to convert raw energy into matter to sustain the space station. But I don't think any space station in orbit would be large enough to support such operations. It would need to be huge to be able to absorb enough energy/material to support an operation like this. $\endgroup$ – Shadowzee Jul 24 '19 at 0:40
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If the space station is designed and built 150 years in the future there is a strong probability that fusion power will be perfected by then.

Presumably the water supply on the station will be extra large and will have more water than is needed for other purposes, so that from time to time some of the water will be broken down into hydrogen and oxygen and the hydrogen will be sued a a fusion fuel for the fusion power generator.

Presumably the space station will also also have giant solar panels for electricity, and maybe a giant mirror to focus sunlight to heat water for a steam turbine to generate electricity, so the station can use either solar power or fusion power or both at the same time.

And possibly your "space station" is actually a space habitat, a sort of space city with a population of thousands. If you are not familiar with concepts of space habitats you might want to learn about them. And if that space habitat was provided with space ships when it was built, it may sometimes send expeditions to rendezvous with asteroids and comets to bring back raw materials to be used by the habitat's 3D printers to make objects and replace matter lost from the habitat.

The amount of energy and thus fuel needed to rendezvous with an asteroid or comet tens or hundreds of millions of miles away and return with cargo might be far, far less than that needed to land on Earth just a few thousand miles below and take off again with supplies for the space station.

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    $\begingroup$ I was thinking about fusion power for the station. Then I realized that, in all likelihood, and based on current and historical fusion development, practical fusion power will probably be about 20 years away... no matter when the station is built. $\endgroup$ – Laughing Vergil Jul 23 '19 at 16:41
  • $\begingroup$ You jest, but it's only been 80 years since fusion power began to be researched. Since then amazing leaps in the technology have been accomplished, even if the ultimate goal has not yet been achieved. It's reasonable to say that in 150 years we'd have at least something resembling fusion power. Especially given the current push for cleaner and renewable energy. $\endgroup$ – Miguel Bartelsman Jul 23 '19 at 19:18
  • $\begingroup$ @MiguelBartelsman We even managed to get energy-even with fusion. That's far from economical or practical, but it clearly shows the massive progress that has been made since the first Tokamak sixty years ago. Each next generation is massively better compared to the previous - the main impediment is that they are complex, hard to build devices that cost a fortune for "mere" research. The hard part is building something that's better than fission (cheaper, cleaner, better PR...) :P $\endgroup$ – Luaan Jul 24 '19 at 8:40
  • $\begingroup$ I imagine after 150 years, direct photovoltaic conversion will be more efficient than concentrated solar power. $\endgroup$ – forest Jul 24 '19 at 10:04
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Fission would be perfectly viable in 150 years. We have existing systems that fit onto submarines and military ships now. Assuming realistic physics, fission will give you all the power you need or could want, up to the limits of how well you can afford to cool your reactor in space. I would assume active cooling, where heat is pumped into the radiators, not just passive cooling.

The basic objections on Earth and in the modern era to fission can be broken into two categories: Technological, which can probably be overcome in 150 years, and questions around handling waste. But if we're in space to that extent in 150 years, handling waste is easy. Earth may not be full of places we feel like we can stick waste, but space is. Space is already an irradiated wasteland, we can't really make it worse in that regard. Plus, we should not assume in 150 years that the same social attitudes are in play; if a space civilization literally depends on generating power to survive, they may have somewhat different opinions than those people on Earth who can afford to turn off all their machines and go stand outside, where clean water literally falls into their mouths if they wait long enough. That's not how it'll work in space.

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    $\begingroup$ Where you would gather fissile material in space? $\endgroup$ – L.Dutch - Reinstate Monica Jul 23 '19 at 18:25
  • $\begingroup$ @L.Dutch, (ignore my earlier comment; I grossly misread this answer) fissile material is everywhere where heavier materials are found... I.e., in moons, asteroids, and meteoroids. If there is any sort of in-situ resource utilization program, there will be fissile material in about the same quantities as found on Earth. $\endgroup$ – Ghedipunk Jul 23 '19 at 19:10
  • $\begingroup$ @Ghedipunk, they don't refuel, per OP statement. And purifying fissile material takes a whole lotta of energy and equipment $\endgroup$ – L.Dutch - Reinstate Monica Jul 23 '19 at 19:20
  • $\begingroup$ Re, "active cooling." A nuclear reactor doesn't make anything but heat. That's great if all you want is to heat your meals and keep the station from freezing at night. But, if you want anything else from your reactor—energy to run the water recycler, electricity for computers and communication, or the ability to actively cool anything—then you're going to need a heat engine that extracts useful energy from the natural flow of heat from the reactor to a heat sink. $\endgroup$ – Solomon Slow Jul 24 '19 at 0:58
  • $\begingroup$ I am assuming with "150 years of technological advancements" that anything that we could do in the 1940s is something a space station could feasibly put together. As for the fact you need more gear to make the fission power plant put out electricity, the first fission-powered submarine was commissioned in 1954. I didn't think that was something that needed to be pointed out, as it's been a solved problem here in the real universe for longer than most of us have been alive. It's not like it's an impossible amount of gear; basic versions of it fit into a 1950s submarine. $\endgroup$ – jerf Jul 24 '19 at 18:22
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Solar Thermal is the future

Don't forget solar power is not limited to photovoltaic collection. A water-based solar thermal plant which focuses unlimited solar energy using simple light-weight reflectors can generate massive amounts of mechanical energy which can be used to power low-tech electricity generating turbines as well as machinery such as hatches and tools. Since your station is isolated its water supply would have to be closed-loop which would not be a problem for internal steam circuits. Leakages of non-toxic water would simply be recollected by the environmental systems. Steam circuits would require heat radiation elements which could simply combine with the stations climate control coolant loops. In an extreme emergency steam could also be used as a propellant to alter the station's orbit.

Steam power technology isn't sexy so it rarely makes it into sci-fi milieus. But in reality it would be a smart use of simple physics for space-based colonies.

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