Mars and nuclear power

[scottb50]

I would think the best bet would be using the soil rather than the air. You could bury a radiator just a few feet under the surface. <div class="Discussion_UserSignature"> </div>

 

[strandedonearth]

It should be possible to build a craft with dual radiators, one of which is built to double as a heatshield/heat sink for aerobraking (or to cool the heatshield), while the other radiator dumps the heat that the heatshield radiator absorbs. The rest of the time both radiators would be available for heat rejection. Before and after aerocapture is complete, the system would have a lot of redundancy available, so if one radiator springs a leak, the other can pick up the slack until the leak is patched.

 

[scottb50]

I've thought about a combined unit. One side has solar cells the other a radiator/heat shield. In Space it is self oriented and connected to a vehicle or station by a tether.<br /><br />It could also be used as a heat shield for aerobraking into orbit on low priority cargo flights, and as an entry platform to deliver vehicles to the surface of both Earth and Mars. To keep it even simpler the two halves can be separated, no need for solar cells on an atmosphere entry vehicle after all. <div class="Discussion_UserSignature"> </div>

 

[dragon04]

Actually, you might want to bury your radiators in the Martian ice cap within a contained system.<br /><br />All that lovely steam <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[mlorrey]

"A prime example of what would be faced on the moon and Mars is exhibited on the Shuttle. The entire payload bay door inner surfaces are radiators to get rid of heat. Heating is not a problem, cooling is. "<br /><br />On the moon, yes, on Mars, no. The shuttle has to radiate a lot of heat because it is above the atmosphere, receiving about 1.4 times the solar flux we receive on the surface at the equator on a sunny day. <br /><br />Earth normal solar flux on the surface at the equator on a sunny day is still pretty dang intense for anybody but camels. 1.4 times that is broiling. So, in earth orbit, or on the moon, cooling is the main problem, except of course during lunar night, when temperatures are hundreds of degrees below zero, which is when heating IS a huge issue and nuclear power would be essential to keeping one's blood flowing.<br /><br />On or near Mars, however, heating is always an issue. Mars receives .44 of earth normal solar flux, which is about what you get at about 66 degrees north or south latitude: i.e. the latitude that defines the arctic and antarctic circles.... So, once again, nuclear power's cogeneration abilities are essential to the mission application and solar's inability to compete places it at a rather massive disadvantage. Studies cited previously of comparing nuke vs solar only look at electrical loads. They do not look at heating loads for a martian base, and here I believe that nuclear power wins hands down.

 

[josh_simonson]

Since the moon surface is at vaccum if you cover the spacecraft with material that doesn't radiate light very well, then wrap everything in foil such as mylar to reflect it back, you'll get a very good and light insulation. The mylar would also reflect the sunlight away when it's in the sun. <br /><br />Mars' atmosphere can conduct heat away to some extent, but it's pretty thin so it shouldn't require nearly as much heat and insulation as a structure here would.

 

[scottb50]

So, once again, nuclear power's cogeneration abilities are essential to the mission application and solar's inability to compete places it at a rather massive disadvantage.....<br /><br />I think that position is totally unsupported. Solar is not at a massive disadvantage. Sure, the total area of solar panels would need to be adapted to the environment, but adding capability is not a problem. Combine it with my plan to use solar solely to hydrolize water and fuel cells to produce the needed energy makes it a lot more efficient than using solar power directly.<br /> <div class="Discussion_UserSignature"> </div>

 

[henryhallam]

<font color="yellow">Combine it with my plan to use solar solely to hydrolize water and fuel cells to produce the needed energy makes it a lot more efficient than using solar power directly. </font><br /><br />There are significant losses in electrolysis and in electricity production from fuel cells. How is this more efficient than using the power directly?

 

[mlorrey]

Yeah, Scott, you are overlooking the fact that the nuke plant produces ten times as much energy in heat as it generates in electrical power, so while a 100 kw nuke plant is being compared against a 100 kw solar power system, it isn't a fair comparison because the nuke plant produces a megawatt of heat, which the solar plant does not produce and cannot produce, so it cannot supply any fraction of non-existent heat to the mars base for heating requirements, while the nuke can do so.<br /><br />So, lets say the Mars base heating requirements are a load of 100 kw on top of the 100 kw of electricity it requires from whatever power source it uses. Thus, the proper and fair comparison of this 100kw+100kw nuke is to a solar power system that produces 200 kw, which means doubling the mass of the solar power system AGAIN.

 

[scottb50]

Very true hydrolisis uses more power than it provides and there is lose in a fuel cell, the reason it needs cooling. My point is solar energy is free, you add enough solar panels to generate the amount of Oxygen and Hydrogen you need for a given period of time to provide plentiful reserves. The same holds true for the fuel cells, the Hydrogen and Oxygen is turned back to water and then turned back into Hydrogen and Oxygen repeating the cycle. <div class="Discussion_UserSignature"> </div>

 

[scottb50]

The problem with a Nuke is just what you say it produces ten times as much energy total energy as it produces usable energy.<br /><br />I really fail to see your focus on heating, I think getting rid of the heat from electronic and biological sources is more important. <br /><br />If we stay on the same theme you use 10% of the energy to power the electrical requirements another 10% to keep it nice and toasty and have to find a way to get rid of the other 80%. I also think referring to the atmosphere on Mars as a viable heat sink is a red herring. I've driven into the center of the abandoned cooling towers Southwest of Seattle and it takes a lot of area in our atmosphere to remove the excess heat.<br /><br />I don't know about you but I have my computer here in what is designated a bedroom, there are a lot of times I open a window or have a fan running because of the heat. If the house is closed up and the computer is running it is noticably warmer entering the room. Multiply that a few times and you find cooling is more of a problem than heating. <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

Scott, you are not looking at any numbers here. There is no nuke plant soutwest of Seattle, unless you mean the one down near the mouth of the Columbia River, but thats three hours drive away. Commercial nuke plants on earth produce gigawatts of electricity. The sort of nuke we are talking about is much smaller, about 1/1000th the power output that a commercial plant produces, if not a smaller fraction. If you are going to claim it isn't going to work, you need to put up a scientific argument why not, not something based on pure opinion. Show us some numbers based on real world facts. <br /><br />Heat is only a problem with spacecraft when they are in space that exposes them to more than ~1kw/m^2 of solar flux. Mars is not one of those places. On Mars, you have to worry about keeping heat, as it is an arctic climate at the martian equator and worse as you get away from the equator. Having a thin atmosphere with a lot of wind means that it is easier to radiate heat there than in space where there is no working fluid for radiators to transfer energy to easier than mere black body radiation.

 

[scottb50]

It's the one almost completed and shuttdown. I don't remember the name but it's on the way to Ocean Shores from Olympia. <div class="Discussion_UserSignature"> </div>

 

[cuddlyrocket]

"On Mars, you have to worry about keeping heat, as it is an arctic climate at the martian equator and worse as you get away from the equator."<br /><br />Which is why the two Mars rovers have an insulated box containing the electronics with radioactive sources to provide a source of heat.<br /><br />And, of course, heating requirements are greatest at night, when electric heating would need to be supplied by the back-up parts of a solar-power system. (For Martian missions, with presumably an ISRU Methane propellant plant, an internal combustion generator would be far more space and mass efficient than batteries or fuel cells - it also would produce heat directly, like the mini-CHP systems used in domestic settings.)<br /><br />There might not be much in it between a small nuclear plant and solar power for powering and heating a four-man habitat, and the question will probably be decided on the basis of mass v complexity. However, once industrial scale processes are required - like the making of bricks - for a larger long-term base, the large quantities of heat given out by a nuclear plant are likely to tip the balance in its favour (unless you can find a source of high-grade geothermal heat on Mars, but this does limit you to that site).<br /><br />But again, I want to see some calculated figures, not mere assertions. Otherwise we simply end up with a list of factors to be taken into account.

 

[tap_sa]

<font color="yellow">"However, once industrial scale processes are required - like the making of bricks - for a larger long-term base, the large quantities of heat given out by a nuclear plant are likely to tip the balance in its favour"</font><br /><br />What sort of brick making are you talking about here? Sintering/melting sand into bricks? The core temperatures of power generating reactors are quite low and the turbine outlet (=waste heat) are even lower. Rare fast breeder reactors have the highest temperatures, coolant outlet (from core) temperatures at ~550C.<br /><br />The waste heat is great for keeping the habitat warm (although it requires additional plumbing!) but I don't see how it could be used to brick making. There might be some other manufacturing processes though where the waste heat could be useful. <br /><br />BTW solar cells could be used in cogeneration fashion too. At least some cells exhibit better conversion efficiency when subjected to concentrated sunlight, but also poorer performance the hotter they get. It would seem to make sense to use smaller cell area, large concentrating mirror and a coolant loop to carry excess heat away from the cell to serve heating purposes at the habitat. Nighttime heating is a matter of storing heat to a lot of mass during day and releasing it at night. The downside would be pretty much obligatory sun-tracking in the mirror/cell system.

 

[cuddlyrocket]

No, I was thinking more of the way you make mud bricks, perhaps with a polymer additive, which would simply require moderate heating to dry them out. After all, bricks made from soil and water left to dry in the sun were the building materials of the Earth's earliest civilisations, and are still made this way today (though usually straw is added).

 

[nacnud]

Good point, though mud bricks don't like rain that isn't a problem on Mars. How well do they cope with freeze thaw cycles?<br /><br />I do like the idea, expecialy as it gives a habitat the ablity to self repair. As a side note have you seen the ideas for a whole house machine for making buildings.

 

[tap_sa]

The polyethylene bricks sound interesting, good radiation shield. I suspect the polymer is also needed to bind the martian soil into a brick.<br /><br />To make ordinary mud brick requires that the soil is mostly clay. Dunno if or how much there's clay on the Mars. AFAIK formation of clay requires water. Then again MERs proved that there's been a wet period in the past.