Power options for a Mars settlement

[biosehnsucht]

No mention yet of solar + flywheel. For storage during long dust storms, seems like a high-reliability, high-density, overall easy option compared to large quantities of batteries, stored heat or stored fuel. No risk of leaks, fires, hopefully little chance of RUD. Additionally it could provide bursts of high current for things like welding, hot water, ovens, without causing a brownout.

That's a good point, regular batteries (regardless of chemistry) aren't the only way we can store energy.

Flywheels (as you said), compressed gas (CO2 is plentiful, can compress it, store it, then run it back through a turbine to generate power), and even simply burning ISRU-collected CH4/LOX in a methane ICE or turbine of some kind (assuming your ISRU generation and storage is beyond your MCT refuel needs - assumes you aren't bringing Hydrogen with you anymore but harvesting it locally from water or other sources and in sufficient quantity, since until then that will be a major ISRU fuel constraint).

Flywheels are probably easiest - you could even ship them without their weights, just empty containers in a circle/tube/whatever, and fill them with Martian 'dirt'. Would need a way to balance them but there's probably some easy ways to do it such as having either stick-on weights like balancing a car's wheel or simply adding and removing material from the containers. Either way, you can basically take a wheel balancer you'd find at the tire shop and use it's balance detection mechanism for giving instruction on fine tuning the balance.

[Vultur]

Then there's the strategy of turning off non-essential power-using activities.

You could keep a reserve of water, etc. long enough to last through any dust storm so that you could turn off the water purifiers EDIT: during storms.

Finally, a dust storm wouldn't reduce the output of solar to zero - it seems the MERs worst reduction was ~80% - and such a storm wouldn't prevent base personnel cleaning the solar cells manually.

If it's that "small" a reduction, plants in a Martian greenhouse might not need supplemental lighting even during a dust storm - 1/5 of normal Martian sunlight is something like 1/15 of normal Earth sunlight, which I think is still more than gets through thick clouds on Earth. And plants grow fine in heavily cloudy regions on Earth.

A key issue for all designs is what if the LV crashes and dumps it in the sea.

This is indeed the key issue, and is the reason why PV for Mars wins, wins, and wins.

What do you both imagine might happen if it dumps in the sea?

It's a political concern, not a matter of "real" risk.

Realistically, probably nothing would happen. Water is very good radiation shielding - and radioactive stuff isn't nearly as much of an ecological problem as people think anyway (since ecosystems - unlike human public health - don't care about individual outcomes but only populations).

[launchwatcher]

No mention yet of solar + flywheel. For storage during long dust storms, seems like a high-reliability, high-density, overall easy option compared to large quantities of batteries, stored heat or stored fuel. No risk of leaks, fires, hopefully little chance of RUD. Additionally it could provide bursts of high current for things like welding, hot water, ovens, without causing a brownout.

A relatively recent case of a power flywheel RUD is described here:

http://www.timesunion.com/local/article/Flywheels-fail-at-energy-project-2227225.php

Pictures of the externally-visible aftermath are here:

http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon-power-frequency-flywheel-plant/

[john smith 19]

It's a political concern, not a matter of "real" risk.

Realistically, probably nothing would happen. Water is very good radiation shielding

It's also a very good neutron moderator potentially pushing a marginally sub critical design over the edge into going critical and starting a chain reaction, giving a long lived radiation source, if not an outright nuclear explosion.

Personally that's why I like molten lead or lead alloy designs. On a crash there's no way for the water to penetrate inside the cooling channels, as they are filled with solid alloy.

- and radioactive stuff isn't nearly as much of an ecological problem as people think anyway (since ecosystems - unlike human public health - don't care about individual outcomes but only populations).

True, but it represents another complex system that has to be designed, tested and certified before you can move to a settlement.

[john smith 19]

A relatively recent case of a power flywheel RUD is described here:

http://www.timesunion.com/local/article/Flywheels-fail-at-energy-project-2227225.php

Pictures of the externally-visible aftermath are here:

http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon-power-frequency-flywheel-plant/

Interesting stuff.

Note while these are quite small for Earth use they might be quite large for Mars use. It's impressive a unit failed but the flywheel released its energy by shattering, leaving a fine powder. A potential fire and inhalation hazard, but not an explosive one, as you would see if a complete fly wheel flew through the air, scything everything in its path.

[Mongo62]

It's a political concern, not a matter of "real" risk.

Realistically, probably nothing would happen. Water is very good radiation shielding

It's also a very good neutron moderator potentially pushing a marginally sub critical design over the edge into going critical and starting a chain reaction, giving a long lived radiation source, if not an outright nuclear explosion.

But the reactor would NOT be "marginally sub-critical". It would not be remotely close to criticality during launch, and could not become critical without a no doubt careful procedure only done once it is located at its permanent location on Mars. For example, having the fuel pellets carried in several separate flights, such that no single collection of pellets can approach criticality, even if they are all mashed together into one lump.

[philw1776]

No mention yet of solar + flywheel. For storage during long dust storms, seems like a high-reliability, high-density, overall easy option compared to large quantities of batteries, stored heat or stored fuel. No risk of leaks, fires, hopefully little chance of RUD. Additionally it could provide bursts of high current for things like welding, hot water, ovens, without causing a brownout.

A relatively recent case of a power flywheel RUD is described here:

http://www.timesunion.com/local/article/Flywheels-fail-at-energy-project-2227225.php

Pictures of the externally-visible aftermath are here:

http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon-power-frequency-flywheel-plant/

Reading your excellent citations shows how FEW KiloWatt HOURS are stored and accessible per flywheel.

[launchwatcher]

A relatively recent case of a power flywheel RUD is described here:

http://www.timesunion.com/local/article/Flywheels-fail-at-energy-project-2227225.php

Pictures of the externally-visible aftermath are here:

http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon-power-frequency-flywheel-plant/

Reading your excellent citations shows how FEW KiloWatt HOURS are stored and accessible per flywheel.

Yup, it's more of a short-term buffer to cover the minutes it takes for another generator to spin up.   I don't think they make sense for long-term power storage.   

On Mars, having the ability to burn spare ISRU-generated methane+oxygen to cover solar power deficits during dust storms would make a lot more sense; the only additional mass required would be some number of methane-burning engines and generators and associated electrical switch gear.

[john smith 19]

But the reactor would NOT be "marginally sub-critical". It would not be remotely close to criticality during launch, and could not become critical without a no doubt careful procedure only done once it is located at its permanent location on Mars. For example, having the fuel pellets carried in several separate flights, such that no single collection of pellets can approach criticality, even if they are all mashed together into one lump.

Those are design decisions. Fast or epithermal spectrum reactors are believed to be more compact as they have no volume dedicated to moderator. However they need enrichment because the capture cross sections for U and Pu are lower at higher energies.

So what's marginal at a fast spectrum becomes much less marginal IE supercritical when immersed into a large pool of moderator, especially if that moderator floods into the coolant channels, as it will for a gas or room temperature liquid.

I like the reactor option. It's a closed system, excellent power density, independent of outside weather conditions.

But with USG procurement it's going to be eyewateringly expensive with a very small market. That's important because compact --> highly enriched and the USG is going to be very wary of any private entity holding

About the only things I can think of to lower that cost are trying to get commonality between the fuel elements for thermal and power reactors, as (currently) NASA seems to be putting some more money in NTR than power generation.

[sewebster]

I believe the energy density for flywheels is similar to batteries, so while they might be useful, they don't help for something long term like a dust storm any more than (more) batteries would.

[jpo234]

Highly speculative: I wanted to connect two dots: Nuclear power for Mars and Elon Musks recent talk with the Secretary of Defense.
If I wanted a highly reliable and compact nuclear reactor, I would look at the A1B https://en.wikipedia.org/wiki/A1B_reactor. And then I would try to talk to the man in charge...

[guckyfan]

Are you saying Elon Musk summoned the Secretary of Defense not the other way around?

 

P.S. I don't think Elon Musk can get that technology from the Navy.

Edit: I also don't think a technology developed for Navy use with unlimited cooling water available would be suitable for Mars. I may be wrong on this one.

[jpo234]

Since the talk was at the Pentagon, he obviously did not summon Ash Carter. 

But I think that the US Navy has the deepest knowledge on how to run compact nuclear reactors. If the A1B is unsuitable, there might be other designs. I would suspect that a boomer can't use all that much cooling water, if it wants to run ultra silent.

[mvpel]

Navy reactors were magnificent works of technological art two decades ago when I was taking my ASVAB; I wonder what they must be like these days. The specs of the A1B are remarkable.

Remember, Bechtel is a "private company" too.

I think that nuclear power on Mars, like it or not, is really going to be the difference between a camping trip and a second branch of human civilization.

[Robotbeat]

Navy reactors were magnificent works of technological art two decades ago when I was taking my ASVAB; I wonder what they must be like these days. The specs of the A1B are remarkable.

Remember, Bechtel is a "private company" too.

I think that nuclear power on Mars, like it or not, is really going to be the difference between a camping trip and a second branch of human civilization.

At-scale solar farms would also work, but I agree nuclear power is quite attractive on Mars surface. The big problem is heat exchange.

[mvpel]

At-scale solar farms would also work, but I agree nuclear power is quite attractive on Mars surface. The big problem is heat exchange.

Here's a concept from about a dozen years ago that uses lithium heat pipes for heat exchange, and cesium thermionic cells for power conversion, delivering 1.2MWt and 100Kwe:

The Martian Surface Reactor: An Advanced Nuclear Power Station for Manned Extraterrestrial Exploration

[Robotbeat]

At-scale solar farms would also work, but I agree nuclear power is quite attractive on Mars surface. The big problem is heat exchange.

Here's a concept from about a dozen years ago that uses lithium heat pipes for heat exchange, and cesium thermionic cells for power conversion, delivering 1.2MWt and 100Kwe:

The Martian Surface Reactor: An Advanced Nuclear Power Station for Manned Extraterrestrial Exploration

...and has a total mass of several tons. It /might/ be better than solar from a specific power perspective if you include mass of batteries (thin films are better and with state of the art batteries, could be better than nuclear), but not much.

The radiators look like they're in the multiple ton range for 1.2MWth (100kWe).

No, I think you'd want nuclear at several megawatts electric. And not thermionic or thermocouples for heat conversion buy a turbine.

If you're going to bother with the hassle of going nuclear, then don't mess around. Do at least 1MWe.

[mvpel]

Good point... Doesn't BFR intend a hundred tons to the Martian surface? "Go big or stay home."

Supercritical CO2 turbines are rather interesting technology - you can use the Martian atmosphere as your turbine's working fluid.

[Tyber1]

While nuclear would be useful for starting a colony, I think nuclear energy should be reserved for temporary projects like starting colonies, deep space travel and outer solar system mining. It's easy to forget because it's so plentiful but nuclear power is a non-renewable energy source.

[Lar]

While nuclear would be useful for starting a colony, I think nuclear energy should be reserved for temporary projects like starting colonies, deep space travel and outer solar system mining. It's easy to forget because it's so plentiful but nuclear power is a non-renewable energy source.

Um?  It depends on your fuel. Breeders won't run out of fuel for a very very long time. I don't see this as a serious show stopper.