Power options for a Mars settlement

[john smith 19]

A search of Mars & power did not find an existing thread on this topic, yet it seems quite important.

Any settlement is going to need a substantial power source to run it's ECLSS, ISRU and mfg facilities to expand the settlement.

Lots of people have talked about PV and nuclear options. The actual current SoA for large arrays (from a powerpoint from Jess Sponable on the Evolved DC-X thread) is actually about 7W/Kg. He was working (at DARPA) on blankets pushing 300W/Kg.

The MIT work suggests 6000Kw/Kg thin films are possible, but probably won't survive launch and/or landing.

On the nuclear side the last US nuclear reactor, the SNAP 10a was in 1965 and produced 500W from 30Kw thermal. Upgraded thermo electric modules could bring it to maybe 4Kw. Moving to Stirling engines (demonstrated in the DUFF programme) would give about 8.2Kw, but the reactor design will not meet modern safety rules.

The follow on to DUFF ("KRUSTI") is aiming at a space rated no maintenance reactor in the 1Kw+ range. The largest space power reactors have been Russian designs in the 10Kw range. 

This suggests PV is likely but there is a problem which people don't seem to think about. Mars dust storms can last for weeks, implying the need for huge amounts of battery storage or evacuation back to orbit.

This suggests a 2nd power mode is needed. The obvious one is to use the storm itself with wind turbines. On the upside turbines could be much larger in 1/3 g but the air density is roughly 1/80 that of Earth at sea level, giving radically lower power output per m^2 of swept turbine area.

The key issue with this pair of systems would be a "valley of death" of too much dust to clear off the cells but not enough to spin the turbines.

One idea I've not heard mentioned is using the temperature difference between the air (running +20c/-140c) to the soil, however I'm not sure what the Mars subsurface stable temperature is. On Earth the a number of dried up oil wells generate power by injecting low BP into one well and ducting the outflow from another well into a turbine.

Such systems can generate power in the 100s of Kw range, provided you can find some way to condense the fluid back to the cycle.

[Robotbeat]

We've only discussed this a million bajillion times. Here's one of the latest threads: http://forum.nasaspaceflight.com/index.php?topic=34836.0

Here's another, slightly more general thread that nonetheless immediately began with the power question:
https://forum.nasaspaceflight.com/index.php?topic=34667.msg1195066#msg1195066

[john smith 19]

Thanks for that.

So roughly speaking you're looking for each 100 new people to add between 500KW and 6MW to the power budget.

Just to be clear that's a minimum of 2.5x the size of the ISS PV array and about 1000x the largest reactor the US has ever flown in space, and 100x the biggest the USSR ever flew.

Reactor wise that's on the scale of the units the US Army used to power an Arctic base, per 100 settlers. The units of the NS Otto Hahn (38MW) and NS Savanah (74MW) are starting to look like quite a good size.
Landing such a unit on Mars may be difficult.

I'll also note that played out oil wells on Earth can harvest 500Kw by injecting fluid down one, collecting up the other and running it through a low BP heat exchanger. 

[Vultur]

This suggests PV is likely but there is a problem which people don't seem to think about. Mars dust storms can last for weeks, implying the need for huge amounts of battery storage or evacuation back to orbit.

As Robotbeat said, this has been discussed before, but dust storms don't mean zero sunlight (the solar-powered MERs survived at least one large storm).

If one has sufficiently thin-film cells (low mass per area), just having enough area to provide the needed power at 5%-10% sunlight might be the way to go.

EDIT: fixed quote tag

[JasonAW3]

One would think that you could use some of the waste heat to supplement the heat needed for the colony as a whole.

[alexterrell]

and another idea I raised:
http://forum.nasaspaceflight.com/index.php?topic=39583.msg1491714#msg1491714
....especially valid if SEP tugs are used to get the cargos to Mars orbit.

[john smith 19]

As Robotbeat said, this has been discussed before, but dust storms don't mean zero sunlight (the solar-powered MERs survived at least one large storm).

Survived, as in "not destroyed."

I don't think that's going to be enough for a settlement to wait out such a storm.

If one has sufficiently thin-film cells (low mass per area), just having enough area to provide the needed power at 5%-10% sunlight might be the way to go.

EDIT: fixed quote tag

So you're starting at between 493W and 590W according to Colorado U. in 2016 world record (1st solar CdTe) was 22.1%, giving about 108-130W/m^2

A minimal power level is 500Kw/100 people is 4630 m^2 worst case. So 10x that is 46300 m^2, a square about 216m on a side, per 100 people. At 60Kw/person it's 12x those numbers.

TBF it looks like dust does a lot of scattierng but little absorbing and a figure of 50w/m^2 in a dust storm may be reasonable.

So you'd have to double the minimal size (but at 60Kw/ person that's. 12x bigger)

Assuming 60Kw and 50w/m^ minimum even during a major dust storm that's a square of 22.1% efficient thin film about 334m on a side for each batch of 100 settlers. I do think the "waste" heat from such an array would be quite a useful raw materail for various processes, but it's not clear if that's worth the mass penalty.

[launchwatcher]

As Robotbeat said, this has been discussed before, but dust storms don't mean zero sunlight (the solar-powered MERs survived at least one large storm).

If one has sufficiently thin-film cells (low mass per area), just having enough area to provide the needed power at 5%-10% sunlight might be the way to go.

Presumably the settlement will include ISRU propellant production capability (methane + LOX or whatever); you could burn surplus propellant for electric power and heat during dust storms.

[QuantumG]

Presumably the settlement will include ISRU propellant production capability (methane + LOX or whatever); you could burn surplus propellant for electric power and heat during dust storms.

That reminds me. I often see the argument made that a point failure of a life support system will destroy a colony. The pretty good retort is typically eye rolling and the single word "redundancy". I think there's a little more to be said though: long term storage of LOX in underground tanks shouldn't require refrigeration if done at the appropriate pressure. As such, a surplus can be cheaply built up. So even if your entire oxygen production system went down and you had to wait for a part from Earth before you could get it up again - a worst case scenario - your colony should be able to keep breathing. I imagine there's other problems that would have similar solutions.

[Robotbeat]

More than that. A cubic meter of air at sea level pressure has about 70 grams of oxygen that could be consumed from it before the oxygen level will cause significant hypoxia without exertion, and can withstand about 70 grams of additional CO2 before significant hypercapnia occurs. You inhale about a 1 kg of oxygen per day (some of which is metabolized into water) and exhale about 1kg of CO2. So if the settlement has about 100m^3 per settler (including all pressurized areas), then the settlement could be without ECLSS for a whole week before major problems occur (although you'd want fans to keep the air from going stale, or perhaps people would move to places where the air is not stale).

I think 100m^3 pressurized volume per person is on the low side for a permanent settlement. ISS has about 150m^3 of pressurized volume per crew. But it does show that while you DO need to get ECLSS working eventually, ECLSS doesn't technically need to be working every single day.

tl;dr: If you have 100m^3 of air per person, you can be without ECLSS for about a week before major health problems.

[Impaler]

Indeed, I am always annoyed as hell at Sci-fi in which they say they only have a few hours or air left while standing in a ROOM on their space ship which has enough air in it to last DAYS.  This trope is comes from a lot of old 'hard' writing (Heinlein mainly who loved to show off his disdain for sentimentality by putting someone out the airlock in this situation) but it got really cemented in the general public's mind with Apollo 13 and the whole CO2 scrubber/hack.  People don't realize that the LEM is the size of a phone booth and it still took hours for the air to get even remotely bad with 3 people in it. 

In any kind of long term habitation without evacuation ability it's not the prompt failures or emergencies which get you, it's the slow chronic breakdowns of equipment, festering health, declining morale, and teamwork being supplanted with animosity and isolation that dooms you.  Generally a terrible response to some minor issue either internal or external compounds it and turns it into a catastrophe.  The equivalent of a 90 year old falling and breaking a hip.

[FinalFrontier]

My favorite word one word solution:
Thorium.
FLIBE or NAbe thorium generation plant. Could produce immense amount of power and potentially use ISRU from martian soil to make new thorium for the plant. Tons of potential power production capability because of the extremely high thermal spectrum regime of a thorium reactor (due to liquid blanket reactor physics and operating regimes). Also smaller and lighter weight than traditional reactors, much smaller in fact according to some recent designs such as THORcon.

[john smith 19]

My favorite word one word solution:
Thorium.
FLIBE or NAbe thorium generation plant. Could produce immense amount of power and potentially use ISRU from martian soil to make new thorium for the plant. Tons of potential power production capability because of the extremely high thermal spectrum regime of a thorium reactor (due to liquid blanket reactor physics and operating regimes). Also smaller and lighter weight than traditional reactors, much smaller in fact according to some recent designs such as THORcon.

I suppose if you're going to dream you should dream large.

Practically this is a system with zero operating units (although I think that may change in India and/or China in the next few years)

140 000 000 miles away from Earth is not the distance to discover some of your key operating parts aren't quite as reliable as you thought they'd be. 

[JamesH65]

My favorite word one word solution:
Thorium.
FLIBE or NAbe thorium generation plant. Could produce immense amount of power and potentially use ISRU from martian soil to make new thorium for the plant. Tons of potential power production capability because of the extremely high thermal spectrum regime of a thorium reactor (due to liquid blanket reactor physics and operating regimes). Also smaller and lighter weight than traditional reactors, much smaller in fact according to some recent designs such as THORcon.

I suppose if you're going to dream you should dream large.

Practically this is a system with zero operating units (although I think that may change in India and/or China in the next few years)

140 000 000 miles away from Earth is not the distance to discover some of your key operating parts aren't quite as reliable as you thought they'd be. 

Are you implying that someone would be brave/stupid enough to send a untried/untested reactor to another world?  My impression would be that stuff would, in all likelihood, be rather well tested before it goes anywhere.

[Spaniard]

The MIT work suggests 6000Kw/Kg thin films are possible, but probably won't survive launch and/or landing.

From ISRU point of view, you could send a thin film printer using local materials for the rest of elements.
Only capture surface require some complex and difficult of local extract elements.
The rest could be plastics or aluminium from local resources.

Not for the first colony but it should be ready in after a couple missions later, when all ISRU demostrators was worked well.

Using this way, 6000Kw/Kg even more seems achievable.

[Vultur]

As Robotbeat said, this has been discussed before, but dust storms don't mean zero sunlight (the solar-powered MERs survived at least one large storm).

Survived, as in "not destroyed."

I don't think that's going to be enough for a settlement to wait out such a storm.

Well, they continued to have power, otherwise they would have frozen.

is 4630 m^2 worst case. So 10x that is 46300 m^2, a square about 216m on a side, per 100 people.

That doesn't sound too bad. IKAROS thin films were 25 micrometers thick, so 46300 square meters is 1.16 cubic meters. I believe they were silicon, density about 2300 kg/cubic meter, so that's less than 3 metric tons for the cells.

I don't know how much the power cables etc. would mass, but ... huge areas of thin film are not mass prohibitive, since modern thin films can be really really thin.

(but at 60Kw/ person that's. 12x bigger)

Where does 60 Kw/person come from?

I'd imagine the big power requirement would be the propellant ISRU and life support requirements would be rather small in comparison.

Mars is very cold, but the atmosphere is very thin, so it might not transfer heat as effectively -- the thermal environment might actually be more benign than the near-polar Antarctic research stations. Has anyone run the numbers on that?

Oxygen is going to be a byproduct of the ISRU, and you might be able to get enough oxygen for breathing with plants/algae at very small power consumption (use natural Martian sunlight instead of artificial light - unlike the Moon, the day/night cycle is close enough to Earth's).

EDIT: fixed quote tag

[shooter6947]

Well, they continued to have power, otherwise they would have frozen.

The MERs have ²³⁸Pu-powered Radioisotope Heater Units (RHUs) to provide heating for precisely this reason.  So they could survive with zero power for some period of time and still not freeze because of the RHU power.

[Vultur]

The MERs have ²³⁸Pu-powered Radioisotope Heater Units (RHUs) to provide heating

They do, but...

  So they could survive with zero power for some period of time and still not freeze because of the RHU power.

...I'm not sure they are that capable, because there have repeatedly been concerns of the MER surviving the winter due to diminished sunlight, needing to park on a north-facing slope etc.

So I don't think they can survive zero power.

[john smith 19]

Are you implying that someone would be brave/stupid enough to send a untried/untested reactor to another world?  My impression would be that stuff would, in all likelihood, be rather well tested before it goes anywhere.

Exactly.

And that has not even begun on Earth. 

[john smith 19]

Well, they continued to have power, otherwise they would have frozen.

No. Each rover (in fact most probes) were fitted with a number of Pu radioisotope heaters to keep certain parts of the electronics and mechanics above failure temperatures.

Where does 60 Kw/person come from?

It's from one of the reports in the thread Robotbeat cited at the start of this thread.

I'd imagine the big power requirement would be the propellant ISRU and life support requirements would be rather small in comparison.

I'd agree but those numbers gave a quick snapshot of various groups thinking.

Mars is very cold, but the atmosphere is very thin, so it might not transfer heat as effectively -- the thermal environment might actually be more benign than the near-polar Antarctic research stations. Has anyone run the numbers on that?

Probably, but I don't have them. I will note while you've still got some fluid flow you'll get convection.

Anyone who'se found a draught in a house will now that a small airflow can suck out a lot of heat from a structure.