Author Topic: Power for a Mars colony  (Read 172589 times)

Offline Russel

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Re: Power for a Mars colony
« Reply #420 on: 11/25/2016 08:26 am »
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.

Offline lamontagne

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Re: Power for a Mars colony
« Reply #421 on: 11/25/2016 01:49 pm »
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'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  :-)

Offline Russel

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Re: Power for a Mars colony
« Reply #422 on: 11/26/2016 04:13 am »
Well the original idea was to use concentrated solar and have a large storage. Nuclear could be a source of heat but the problem being dealt with was storage.

I wasn't thinking of Martian air directly heated and run through a turbine. I was thinking of CO2 stored in liquid form and used later Hence the power needed to process the CO2 initially could be lower and it would tolerate intermittency. The power you get back could be an order of magnitude higher. So we're talking peak power demand as well as storage.

Again I don't know how to do the thermodynamics but the stored CO2 would be more or less at ambient and you'd raise it to something like 700K before the turbine.

I've no doubt the front end (fans/filters) for a useful plant would be large. However this is also meant to be integrated with an atmospheric processing plant that is also interested in Nitrogen, Argon, Oxygen and water. That would require going through a large mass and in essence the CO2 would be otherwise by-product.

Offline LMT

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Re: Power for a Mars colony
« Reply #423 on: 11/29/2016 06:58 am »
Heat Storage

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...

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.
« Last Edit: 12/14/2016 06:30 pm by LMT »

Offline john smith 19

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Re: Power for a Mars colony
« Reply #424 on: 11/29/2016 08:16 am »
Heat Storage


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.
It's nice to have a few facts and numbers for a change. 
Quote
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.
Something to keep in mind
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Offline Robotbeat

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Re: Power for a Mars colony
« Reply #425 on: 11/30/2016 12:14 am »
Heat Storage

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...

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.
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Offline Lar

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Re: Power for a Mars colony
« Reply #426 on: 11/30/2016 01:50 am »
This is off-topic for this thread.
Indeed it is.  Maybe we need a heat thread? Don't make the mods hot under the collar.
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Offline LMT

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Re: Power for a Mars colony
« Reply #427 on: 11/30/2016 10:47 am »
"When you come to a fork in the road, take it."
-Yogi Berra

This is off-topic for this thread.
Indeed it is.  Maybe we need a heat thread? Don't make the mods hot under the collar.

So is heat exchange for habs OT in a thread talking about habs, or OT in a thread talking about heat exchange?   I'm just following y'all's requests here.

New thread?  Old thread?  Either is fine, but with a smile, fellas.   :)
« Last Edit: 12/14/2016 06:29 pm by LMT »

Offline john smith 19

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Re: Power for a Mars colony
« Reply #428 on: 11/30/2016 11:50 am »
I'd say thermal management for any power source is fairly on topic in a thread about power for a Mars settlement.

Outside of fuel cell or direct nuclear conversion (IE Beta battery systems) all power systems will need a cold sink. The upside on Mars is there's plenty of cold to go around.  :) and many of htem would be more useful that just heating up a river or ocean, as here on Earth.

BTW that also includes PV systems. Depending on the outside "air" temperature and the efficiency of the cells some kind of back face radiator arrangement may still be necessary . 
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Offline gosnold

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Re: Power for a Mars colony
« Reply #429 on: 12/10/2016 10:38 am »
There was a FISO conference recently on fission vs solar power for Mars:
http://spirit.as.utexas.edu/%7Efiso/telecon/Rucker_12-7-16/

Conclusions are:
Better to split fission in several 10kWe units compared to a single 40kWe unit.
For an ISRU demo solar and fission are roughly equivalent performance-wise (solar has a slightly lower mass).
For crew ISRU, fission is better and significantly lower mass  than solar, but solar could work too in some cases.
« Last Edit: 12/10/2016 10:47 am by gosnold »

Offline john smith 19

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Re: Power for a Mars colony
« Reply #430 on: 12/10/2016 11:27 am »
There was a FISO conference recently on fission vs solar power for Mars:
http://spirit.as.utexas.edu/%7Efiso/telecon/Rucker_12-7-16/
A nice round up of the options and trade offs.

As an enabling technology the Kilopower concept (using the KRUSTI technology) looks a winner. It's very scaleable, offers good redundancy is and capable of other uses. a 10Kw unit could run a decent ion drive to Pluto and power a substantial instrument suite on arrival.

The downside for Mars is the doubled HEU inventory. That said the 40KW unit looks like a technological dead end. Big, clumsy and needing a lot of startup power (so you'll need a development programme for that 5Kw array anyway)

Note however this is for LOX only ISRU. NASA has still not committed to full fuel production from Mars water as yet.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline A_M_Swallow

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Re: Power for a Mars colony
« Reply #431 on: 12/11/2016 01:37 am »
We will need a nuclear fuel for the Kilopower fission reactors that can be made in under 2 years and does not weigh more than say twice as much as plutonium.

Offline Asteroza

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Re: Power for a Mars colony
« Reply #432 on: 12/27/2016 03:53 am »
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'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  :-)


I'd just like to point out that there are supersonic ram compressors for CO2 compression that can do 10:1 compression per stage in a very compact arrangement (see RamGen, currently associated with Dresser-Rand). Trick is whether you can keep heat of compression below power system molten salt output temps (doable). You should be able to operate the HX in CO2 supercrticial temps/pressures then blowdown to atmosphere. Considering the turbine would be exhausting to low pressure, even with recuperators you'll have a real beast of a machine there.

DoE and other government labs are doing supercritical CO2 power cycle work (partially in support for molten salt nuclear reactors) that are progressing the knowledgebase for supercritical CO2 regimes.

Offline Zed_Noir

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Re: Power for a Mars colony
« Reply #433 on: 02/06/2017 06:22 am »
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 slides

FISO presentation audio


It 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.

Offline envy887

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Re: Power for a Mars colony
« Reply #434 on: 02/06/2017 03:02 pm »
Sand 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).
Quote
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.
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.

Propellant production will require much more than 5x the minimal base power consumption for quite some time, so the solar arrays would be more than big enough to maintain power in a dust storm.

Offline john smith 19

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Re: Power for a Mars colony
« Reply #435 on: 02/09/2017 07:42 pm »
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 slides

It 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.
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.
[EDIT Been listening to the audio. Full up test is for NNSS in September 2017. Good to know they are already planning for Kilopower II going to 10Kw and ISRU  The bill for this is $20m. In perspective RTG's are listed as costing about $200m each, largely due to the problems of getting Pu mfg restarted, as opposed to the HEU, which I presume is left over from decommissioning nuclear warheads]
[EDIT at about 50mins in Rand Simberg asks what the incremental costs is. The estimate is around$70--80m, with the fuel being free. IE worst case 40% of an RTG using Pu.  I'll note heat output will run a long time and heat output is likely to be a key resource for a human base or settlement]
« Last Edit: 02/09/2017 09:38 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Zed_Noir

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Re: Power for a Mars colony
« Reply #436 on: 02/10/2017 09:00 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.
...

The Red Dragon is just transport to Mars surface in the near term, for a smallish KiloPower module in my view.

Maybe you can raised the KiloPower module up on an internal lift through the nose hatch to deployed the radiator array. . Which will reduce the work needed to set up a fission power module on Mars. Just hook the KiloPower module with power output and control cables after the Red Dragon lands.

P.S. If use as a power station on Mars. Red Dragon => Electro Dragon  ;D

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