Half a croissant, on a plate, with a sign in front of it saying '50c'
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This would work fine, except in terms of success.

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Mercury vapor nuclear engine for Mars

Heat mercury and turn turbine with it.
  [vote for,

How to generate power on Mars? Solar panels are fine to rove around a few kg of robot, but what about energy intensive things: concentrating gases, shaping rocks for construction, and the like? One remedy for scarce resources is abundant power.

There is nothing to burn on Mars so it will have to be nuclear. There are those slow nuclear reactors like on the Soyuz but the output is nothing compared to a nuclear steam turbine. Steam requires water and water is precious on Mars. Steam engines reclaim the water but water is squirrelly and it is easy for it to escape.

I propose that a "steam" engine using mercury as the working medium would be well suited for martian use. Mercury offers the following advantages.

1. Vaporization at higher temperature. Cooling rate is faster when temperature differences are greater. An engine relying on phase change must get the working fluid back to liquid. Higher temperature vaporization means more rapid cooling / conversion back to liquid.

2. Very low volatility means less risk of atmospheric loss from evaporation or sublimation; on Mars this would be an important consideration when handling water.

3. Volume increase on phase change should be comparable to water.

4. Unlike water, mercury does not expand on freezing and so poses less risk of expansion-related damage to machinery and containers.

5. Water has a propensity to dissolve salts, which then corrode/ precipitate and otherwise damage machinery. There might be airborne salts on Mars. Salts are insoluble in mercury.

As a sidenote considering dust: I am thinking of the cleaning power of water. Part of how it works is to dissolve dust, but the kinetic interaction between fluid molecules and loose contaminants (dust) is a big part of cleaning. Fluid scrubs things.

Water used for cleaning is contaminated by the particles it carries away. Mercury would offer the same kinetic interaction and stay clean, liberated dust particles floating to the surface to be skimmed away.

bungston, Jul 12 2015


       There is something of a long-range desire to terraform Mars, so that you can walk about without a pressure suit. This Idea would make the task more difficult --lots of mercury to remove from the environment!
Vernon, Jul 12 2015


       " I am thinking of the cleaning power of water "
normzone, Jul 12 2015

       Hey, won't a large portion of life support systems on Mars be dedicated to scrubbing CO2 sequestration?   

       Near the poles the temperature at night plummets to minus 195 degrees F (minus 125 degrees C).
Carbon Dioxide changes from the gas to solid phase (dry ice). At atmospheric pressure, sublimation/deposition occurs at -78.5 °C (-109.3 °F).

       Would there not be an ideal zone somewhere on Mars that would let us use the sublimation of Carbon Dioxide to power generators?   

       I am trying to picture a sublimation engine driven by sunrise. I suppose a big chamber with a gradually rising piston as it fills with CO2, geared down to spin a generator? Then same thing in reverse as it condenses at night.   

       I do not have an intuitive feel for CO2. Or phase changes in general. For example - is the volume of gas in a cylinder greater than that volume of CO2 as a solid? I cannot imagine that would be allowed but maybe.
bungston, Jul 14 2015

       Would there be a Mars vapour nuclear engine for Mercury?
MaxwellBuchanan, Jul 20 2015

       From what I've read, pressurized CO2 (in proposed LFTR reactors) can approach the viscosity of water, making very small and efficient turbines possible. Since the atmosphere of Mars is CO2, maybe it would make sense to use it as a working fluid?   

       Of course, nuclear need not be the only option. Once we can make PV panels locally on Mars, or at least support structures for massive rolls of such brought from Earth, solar might be a better option. Mars only gets about 60% of the solar power we get, but perhaps the temperatures would help increase average efficiency, and networks of superconductive power transmission lines might actually be possible due to the much lower cooling effort required to reach superconductivity.   

       Sublimation engine: cool idea. Actually, it makes me wonder if a working fluid, like He, could be cooled enough during the night to freeze large quantities of CO2. The He would be circulated through a device that insulates it from surrounding IR, and allows heat to dissipate in the direction of space. The CO2 ice could then be used in a sublimation engine, drawing ambient heat from the atmosphere to change phase. I guess it's the opposite of solar power -- dark power.
TIB, Jul 20 2015


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