Spacecrafts that harvest ice are not out of the ordinary, there’s even research being conducted about steam powered spacecrafts (steampunk spaceships anyone??). But I want to engineer a ship that uses water in ALL its shapes and forms for power, not just for propulsion. With futuristic tech available like a completed fusion reactor how would this hydro powered ship make the most out of the available water including its components?

I’d like to know more about the cycle of water in the ship so I can better depict the inner workings of the spacecraft. It’ll be interesting to see a complex water cycle in a spaceship.

Edit: The ship is designed for long lasting exploration and will most likely carry passengers, or can be modified to do so. Core elements of the ship include the fusion reactor, cooling systems, turbines, a hydroponic or vertical farm and the ships electronics like the autopilot and batteries. Thanks to electrolysis hydrogen and oxygen are also available to make the most of the resource. Additional water is harvested from commets and debris but the ship should be able to recycle its water. Water circulates throughout the ship and should have as many uses as possible.

  • $\begingroup$ Do you mean you want everything possible powered directly by steam or flowing water, or do you mean a steam-powered nuclear generator making power that runs the ship, PLUS water propulsion? $\endgroup$
    – DWKraus
    Commented Aug 30, 2021 at 23:40
  • $\begingroup$ @DWKraus Yes. I want water to be used in as many systems of the ship as possible. $\endgroup$ Commented Aug 30, 2021 at 23:43
  • $\begingroup$ what i the purpose of your ship, a warship is going to have very different needs from a transport or generation ship. $\endgroup$
    – John
    Commented Aug 31, 2021 at 2:01
  • $\begingroup$ @John Very well. I’ll edit the question to include the specific details. $\endgroup$ Commented Aug 31, 2021 at 7:56

4 Answers 4


Just your everyday fusion-powered ion rocket. Harvest the water/ice, extract the hydrogen through electrolysis, then fuse the hydrogen in your fusion reactor to create copious amounts of energy. The remaining oxygen could be used onboard, or expelled through the ion propulsion system. Use any excess water for cooling (a big problem with nuclear reactors), then expel the steam for additional thrust. Honestly, you probably have little need to capture additional water for your crew, UNLESS your crew is growing in number during travel. Otherwise, just keep it in a completely separate system from the power system.

Edit: OP updated post to emphasize a desire for complexity. This isn't typically good engineering practice, but can make for good storytelling. In that case, in addition to the above schema for propulsion and power generation, consider the following "water cycle":

  1. Harvest water from environment. (If ice, wait for it to melt onboard, cooling the ship.)
  2. Purify water. Put it in a "cool pure water" tank.
  3. Separate some of the cool pure water into hydrogen and oxygen, using the hydrogen for fusion as outlined above and the oxygen for ion propulsion, as outlined above. (Oxygen is not the most efficient ion to expel (too light), but if you have an excess, you might as well use it. The helium produced in fusion would be even worse, but could be used similarly. Using these eliminates the need to carry additional ions to expel.)
  4. Run more of the cool pure water past the nuclear reactor, turning it to steam. (This will also cool the reactor, preventing overheating.)
  5. Use steam to run turbines, generating electric power. Store the steam temporarily in a "pure steam tank."
  6. Cool some of the steam into hot pure water in a cooling chamber. (Structure: A strong tank with cool water running in pipes through it. The warmed coolant water will run out to thin fractal panels on the outside of the spaceship, where they will emit black-body radiation into space, thus cooling the coolant again.)
  7. Further cool any unused hot pure water back into cold pure water, returning it to the "cold pure water".

Filtering: So now, in addition to electricity and thrust, we have sources of steam, hot pure water, and cool pure water, which any equipment, system, or person on board can tap into. These provide the sources for the hydroponic farms, everyday plumbing, steam hammers, cleaning, etc. When the water gets dirty, it's purified and added back into the cool pure water tank. Of course, these filters will need to be cleaned with water, so there will (unfortunately) always be waste water. The cool waste water should be heated by the ship's cooling system (heat transfer), then to steam by the reactor, and expelled out the back and sides of the ship as high-impulse thrust (very good for turning quickly). This, together with the constant conversion of hydrogen to helium in the reactor, is why the spacecraft must keep harvesting water.

Cooling: As mentioned above, radiative cooling is a good bet for general cooling. Pump cool pure water through the ship, gathering heat, then through the radiative cooling fins (think metal ferns with water running through the veins). As the fins emit black-body radiation into space, the water will cool again, and heat will leave the ship. If there is excess waste water, additional cooling can be attained by heating it to steam and expelling it for thrust, as mentioned above.

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    $\begingroup$ And also the jacuzzi. And some of the oxygen can be used to make ozone to keep the jacuzzi clean because otherwise your people could get that jacuzzi rash. No-one wants to grow your crew in number with someone that has got jacuzzi rash. $\endgroup$
    – Willk
    Commented Aug 31, 2021 at 0:42

Behold: the nightmarish abomination known as the nuclear saltwater rocket. Also, have a Robert Zubrin paper on it.

Salts of nuclear fuels are mixed into water, which is then run through an open-cycle reactor (i.e. exposed to the outside, as opposed to self-contained like existing reactors) and shot out for thrust.

It is incredibly radioactive, and you don't want to use it near anything with a biosphere or potentially hydro/atmosphere, but water is a pretty common thing in the universe, as opposed to, say, methane.

Also, if you want water to be used in as many systems as possible, fill the habitation spaces with it. It lets whatever crew there are survive acceleration much better than if said spaces were filled with air, IIRC, and it's much better at blocking radiation.

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    $\begingroup$ I am a simple man. I hear about a nuka-cola powered rocket, I gotta go play Fallout. $\endgroup$ Commented Aug 30, 2021 at 23:44
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    $\begingroup$ That sounds like the water won't last very long. Am I wrong or is it mass inefficient as hell? $\endgroup$
    – Henry Shao
    Commented Aug 30, 2021 at 23:49
  • 1
    $\begingroup$ @HenryShao According to Atomic Rockets, one such design has a specific impulse of 6,728 seconds - more than some modern ion drives - and a thrust equivalent to about a third of a Saturn V's first stage. projectrho.com/public_html/rocket/enginelist2.php; control-F and type in "nuclear salt water". $\endgroup$
    Commented Aug 30, 2021 at 23:54
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    $\begingroup$ Although this only addresses the thrust part of a steam-power steampunk starship, I gotta admit it's pretty fun! Everything else could be powered off the cooling system that keeps the ship from overheating due to the waste heat bleeding out where it shouldn't. But how to COOL that steam without losing water via venting? Maybe pump the heat into the sheathing water for the engine? $\endgroup$
    – DWKraus
    Commented Aug 31, 2021 at 0:01
  • 2
    $\begingroup$ @DWKraus The point is that the water ISN'T cooled - it's basically liquid nuclear fuel that gets pumped through the core of a fission reactor crossed with a rocket engine. Pumping heat into the fuel tank would be a bad idea, since it should be as cold as possible before it enters the reactor, since expanding fast gives it speed. Water-cooled radiators, though, are a doable thing. Also, this doesn't just address the thrust part; filling the habitation spaces full of water was also mentioned. $\endgroup$
    Commented Aug 31, 2021 at 0:05

Microwave rockets

The first point is that technology is simple to operate and maintain which is important if you are millions of miles from home.

Water is used as the reaction mass and a compact, sealed nuclear reactor (molten salt or other design) provides electrical power, although solar cells could be used instead for missions out to about as far as the asteroid belt and still be relatively efficient.

Water is pumped into a 'reaction' chamber lined with very powerful high efficiency microwave emitters (both aerials or masers would work). The water is instantly ionized and expelled out the rear of the ship to produce thrust. In theory the ISP is about twice that of the best available chemical rocket fuel.

The best bit though is that while water is an excellent fuel for such a rocket in theory it can use a wide range of fuels (like methane). In fact virtually any common compound that can be extracted from mined ice could be liquefied and pumped into the ships fuel tanks on the proviso that the masers/aerials are designed to be tunable to the absorption frequency of the compund involved. Again this should be a relatively simple engineering problem since in the real world both devices can tuned to different frequencies.


How about a black hole powered ship?

It is an insanely complex system of ridiculously small black holes doing total conversion, exotic matter batteries, anti-matter thrusters, fusion reactors, and steam engines that step down temperature from the hellscape near the black hole.

Steam, water, helium, oxygen and hydrogen come out of the huge, nearly black box engine block, and ice and water are fed in.

The front of the ship is an iceberg, which is used as both shielding and fuel. The steam turbines dump heat into it, melt it, and pump the resulting water back into the "water tank" between the habitable area and the (ridiculously radioactive) engine core. The engine core consumes the water tank.

The engine does atomic chemistry, so various elements can be provided by it. It is somewhat expensive, as stable isotopes are not always dominant in what it produces.

The Carbon cycle is key; removing CO2 and extracting the carbon is high value. O2 is less useful, as it isn't good fusion fuel.

So this ship has a huge iceberg suspended over a habitat, which is on top of an ocean. Under the ocean is a huge engine reactor block consuming water and doing exotic physics to propel the starship between solar systems. Steam tubes come out from the ground, and the people in the ship consume it; this melts the forward iceberg (from the bottom), which replenishes the ocean, which the engine drinks.

In the habitat, the near-unlimited steam is used to power the needs of the people there. It is a nice medium-density power source - not so crazy that it is fatal for the crew. More exotic deliveries can be asked for to the ship's computer (like "we need more iron") and are delivered at much slower rates.


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