I think you can do better than radiative cooling though. Maybe my physics is wrong, but I was thinking about an open cycle. You simply process the existing atmosphere, extract the CO2, compress and liquefy it. Meanwhile you store molten salt. When you need power you simply run a heat exchange. You end up with very hot, very high pressure super critical CO2 and you run an open cycle turbine, so the heat is rejected with it. I've no idea of the overall efficiency of the process but you do have the advantage of a lot of stored energy in a relatively small space.
You can, for instance, put [waste heat] deep within the regolith underlying the settlement. So deep that the heat pulse produced by summer's excess electrical capacity (dumped still in the Sabatier process) doesn't reach the surface until the middle of winter when it's needed most. So the regolith itself is acting as a reservoir of heat and a sort of delay buffer to even out the heat flow....And the deep soil is already naturally at a high enough temperature to prevent freezing...
Heat StorageStoring summer heat -- waste or other -- in "deep soil" beneath the hab, for use in winter, is infeasible. Summer heating of surface regolith penetrates only ~ 50 cm, and the heat captured in this very thin surface layer must radiate out before winter. And further down? Consider for example Gusev Crater:This crater is basically equatorial at 14.5o S, and it's low-lying at ~ -2 km. It gets as much heat as anyplace; more than most sites.What's the thermal profile of bedrock at Gusev? Frozen to ~ 3 km depth. This rock is not "naturally at a high enough temperature to prevent freezing". Because it's frozen.Inject heat into that rock down to 500 m depth, through a heat-exchange borehole. Raise the rock temperature by 45 degrees to reach -5 C. Each cubic meter of that volcanic rock, warmed to -5 C, absorbs ~ 110 million Joules. If you heat 10 cm of rock around a 30 cm diameter borehole, that's 7 billion Joules you've put into the ground.
And the ground is still frozen. So you can't recover that heat in winter.Bedrock's a heat sink on Mars. Not a heat store. You'd want to design your hab's heat storage around some other scheme.
Heat StorageQuote from: Robotbeat on 11/29/2016 04:29 amYou can, for instance, put [waste heat] deep within the regolith underlying the settlement. So deep that the heat pulse produced by summer's excess electrical capacity (dumped still in the Sabatier process) doesn't reach the surface until the middle of winter when it's needed most. So the regolith itself is acting as a reservoir of heat and a sort of delay buffer to even out the heat flow....And the deep soil is already naturally at a high enough temperature to prevent freezing...Storing summer heat -- waste or other -- in "deep soil" beneath the hab, for use in winter, is infeasible. Summer heating of surface regolith penetrates only ~ 50 cm, and the heat captured in this very thin surface layer must radiate out before winter. And further down? Consider for example Gusev Crater:This crater is basically equatorial at 14.5o S, and it's low-lying at ~ -2 km. It gets as much heat as anyplace; more than most sites.What's the thermal profile of bedrock at Gusev? Frozen to ~ 3 km depth. This rock is not "naturally at a high enough temperature to prevent freezing". Because it's frozen.Inject heat into that rock down to 500 m depth, through a heat-exchange borehole. Raise the rock temperature by 45 degrees to reach -5 C. Each cubic meter of that volcanic rock, warmed to -5 C, absorbs ~ 110 million Joules. If you heat 10 cm of rock around a 30 cm diameter borehole, that's 7 billion Joules you've put into the ground.And the ground is still frozen. So you can't recover that heat in winter.Bedrock's a heat sink on Mars. Not a heat store. You'd want to design your hab's heat storage around some other scheme.
This is off-topic for this thread.
Quote from: Robotbeat on 11/30/2016 12:14 amThis is off-topic for this thread.Indeed it is. Maybe we need a heat thread? Don't make the mods hot under the collar.
There was a FISO conference recently on fission vs solar power for Mars:http://spirit.as.utexas.edu/%7Efiso/telecon/Rucker_12-7-16/
Quote from: Russel on 11/25/2016 08:26 amI think you can do better than radiative cooling though. Maybe my physics is wrong, but I was thinking about an open cycle. You simply process the existing atmosphere, extract the CO2, compress and liquefy it. Meanwhile you store molten salt. When you need power you simply run a heat exchange. You end up with very hot, very high pressure super critical CO2 and you run an open cycle turbine, so the heat is rejected with it. I've no idea of the overall efficiency of the process but you do have the advantage of a lot of stored energy in a relatively small space.You're describing an open cycle gas turbine, and replacing the natural gas flame by a nuclear reactor with an internal molten salt loop. The volume flow required of very low pressure Martian atmosphere will be gigantic, and the change in pressure required to get significant heat exchange from the molten salt heat exchanger very high. If at all possible, the compressor would be extremely heavy, with a formidable number of stages. If air holds 1 kJ/kgK and has a density of 1 kg/m3, so 1 KJ/m3K, then Martian atmosphere holds 0,01 kJ/m3K. Supposing your gas enters at -50 and leaves at 200C, then to remove 10 MW of heat, you need a volume flow of 10 000 kW / 0,01 /250 = 4000 m3/s. that's a lot of air flow, 8 000 000 cfm.You're much better off melting ice and using that in an open cycle to cool your reactor.I expect reactors cooled by radiation would only be used in the very early phases of colonisation, if at all, as hot water is a great by product on Mars. It will depend how easily water can be mined on Mars.In a sense, once you use a reactor to melt water, the entire base becomes a large radiator :-)
Quote from: lamontagne on 11/08/2016 01:13 pmSand settles. But Hydro has run into trouble in countries with a high erosion rate, as the reservoirs get sanded in.So hydro is not trouble free either (and out of the running on Mars anyway).QuoteSolar and wind farms are typically overbuilt by a factor of 3 on Earth, due to clouds and weather. I.E. their availability is 30% (not to mention night time). Would sand storms be worse than this? Do they cut sunlight by 60%? I think solar is adequate, but that nuclear might be simpler, if it was available.Try a factor of 5 overbuild as it's claimed a sandstorm cuts sunlight by 80%. You need a second system and it should not be dependent on the weather.
Sand settles. But Hydro has run into trouble in countries with a high erosion rate, as the reservoirs get sanded in.
Solar and wind farms are typically overbuilt by a factor of 3 on Earth, due to clouds and weather. I.E. their availability is 30% (not to mention night time). Would sand storms be worse than this? Do they cut sunlight by 60%? I think solar is adequate, but that nuclear might be simpler, if it was available.
There is another FISO presentation on small fission power source for manned Mars and deep space missions dated February 1st by Lee Mason.FISO presentation slidesIt appears that some sort of prototype reactor will be tested in Nevada this year. See slides 28 through 30.Also the table on the lower right of slide 25 indicate that a 5 kWe KiloPower system could fit in a Red Dragon with a modified nose hatch.
Quote from: Zed_Noir on 02/06/2017 06:22 am...This is very impressive. They've kept up the momentum and they've got the funds together for what looks like a full up test. Page 6 "flight like U-Mo core, Sodium heat pipes, Stiling power conversion" all in a vacuum. It looks like the only subsystem missing is the final radiator. The Kilopower team has done an amazing job of forming links to other organizations and using what would be viewed as very limited resources to get close to delivering a highly usable result. Given how long people have talked about space power reactors and how close they are to full up testing I will be looking forward to their work at NSS later this year.One note of caution. Although it looks like you can put a Kilopower module inside a Red Dragon I don't think it can work inside one and I think they expect human crew to deploy it, especially the radiator. If I'm wrong or it can be set up for auto deployment then we could be looking at a reactor on Mars sooner rather than later, but that's a pretty big shift. ...
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