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What is a steam powered spacecraft?

asked 2016-05-07 10:20:32 -0600

Rob Mueller gravatar image

Recently Deep Space Industries, inc announced that they would be developing small steam powered spacecraft using water mined form asteroids as propellant. How does this work? Is the Isp good enough to be effective for space propulsion between planets in the solar system?

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answered 2016-08-24 00:28:56 -0600

DrPhiltill gravatar image

There are several ways to use steam to propel a spacecraft. One is to heat water in a tank then simply vent the vapor through a nozzle into the vacuum of space. Because space is at zero pressure, this is by definition always less than the critical pressure, so as a result the water vapor (steam) will choke at the speed of sound in the nozzle and then accelerate to supersonic velocity. Simple!

The next more complicated system is to heat the water vapor in realtime as it enters the rocket nozzle. This will cause it to go even faster as it exits the nozzle so it provides more thrust. In the simpler version of a steam rocket, you blow steam through the nozzle but by the time it comes out the end of the nozzle it's a mixture of water droplets and water vapor, or it might even contain snow. A steam rocket can be a snow-blower in space. However, if you superheat the steam just as it enters the nozzle, then it does not condense into droplets or snow as it blows out into space. However, this is a much more complicated rocket because it must deliver heat into the steam at a very high rate, so therefore it requires a very large power system on the rocket.

The next more complicated system is to electrolyze some of the water into hydrogen and oxygen. This essentially stores energy during the electrolysis process in the form of chemical energy. When you cause the hydrogen and oxygen to mix in the rocket engine and then burn, they produce water vapor again along with all that liberated chemical energy, which appears in the form of heat. This superheated water vapor then rushes through the nozzle just like before to create thrust. This is the type of engine that the Space Shuttle used, so in a certain sense it was a steam rocket. It was shooting into space on a flame of water. However, we do not normally call an engine a steam rocket when it combusts the hydrogen and oxygen to make the steam. Usually a steam rocket is when the propellant already starts out as water and we use some other method to make it into hot steam. I only mentioned this combustion engine to show that it is actually quite common to use water for rocket propulsion.

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answered 2016-08-24 00:53:55 -0600

Flipper gravatar image

No. This is a waste of resources. Water (H2o) is the most precious commodity that we could have on board a spacecraft or on Mars. You won't find abundant amounts of water on an asteroid. Steam power is incredibly inefficient in this capacity unless there is NO other option of propulsion.

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answered 2016-08-24 14:06:31 -0600

DrPhiltill gravatar image

I respectfully disagree. We are getting significant amounts of water from asteroid minerals (hydrated clays), and steam rockets get about 160 sec specific impulse, which is really not that bad. There are cases where the simplicity is desirable, like hopping on Europa using surface ice for the steam.

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Asked: 2016-05-07 10:20:32 -0600

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Last updated: Aug 24 '16