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NASA Revives Plan to Put Nuclear Reactors on Mars

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Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#41

Post by xorfish »

avar wrote: post #35
xorfish wrote: post #28

Earlier quoted context omitted.

Pl-238 is very expensive to produce. We are talking millions/kg.

That's a trivial cost when we're talking about sending things to Mars. The Curiosity rover has around 5kg of Pu-238. NASA estimates that restarting production will cost $6M/kg[1]. The total cost of the MSL program is 2.5 billion[2]. That's $30 million out of 2.5 billion, or 1.2%. NASA has also been buying Pu-238 from the Russians at around $1.5 million/kg[3], which would be $7.5 million for Curiosity, or 0.3% of the…

The cost wouldn't be trivial for powering a mars colony.

I'm sure the demand for a colony would scale pretty fast to 100kW or more. Now we are talking about Billions.

So I think that your original point that cost for Pu-238 is not an issue for a colony is wrong.

Small reactors are a much better option as a single ton of fuel could supply a colony with a few MW for decades. You just have to make sure that the largest part is less than 37 tons so it can be transported with a Long March 9.

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#42

Post by [deleted] »

petre wrote: post #24
cortexio wrote: post #15

I'm getting kinda sick of the media putting more & more non-sense in our heads instead of actual news. This is pure fantasy. They can't build nuclear reactors on Mars! The only reason why they write this article is because the topic "Mars" generates large amounts of views. News shouldn't be a bussiness :(

They don't have to build it on Mars. A kilowatt scale nuclear reactor is small and also safer and more portable. The Russians have already sent nuclear powered satellites into space.

[deleted]

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#43

Post by Symmetry »

davedx wrote: post #39

I looked into some numbers on this, comparing theoretical costs of nuclear power with a solar PV solution on Mars. Kilopower (NASA's research project for a Martian nuclear fission reactor, from the article): 7,200 kg for 40 kW. [1] ISS solar arrays: 14,515 kg for ~100 kW in Earth orbit. [2] If we assume 40-50% Earth solar insolation on Martian surface, the ISS PV array probably isn't far off 40 kW output on Mars Conc…

A robotic rover can afford to shut down during the night but humans aren't able to do that. So you need to average out the power generated over the day night cycle and add mass for enough batteries to store daytime power for use at night. Last I did the calculations that roughly doubled the weight. So more like a factor of 8 than 2. But still, power generation won't be the majority of the mission weight so it's not a slam dunk.

On the moon it would be. Half-month long nights mean you'd need a lot more batteries if you're making a permanent settlement and aren't at one of those spots on the south pole where you can always see the sun traveling along the horizon.

EDIT:

I think solar panels have gotten a lot lighter since the ISS went up and when I last did the math nuclear and solar were a lot closer.

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#44

Post by motoboi »

davedx wrote: post #39

I looked into some numbers on this, comparing theoretical costs of nuclear power with a solar PV solution on Mars. Kilopower (NASA's research project for a Martian nuclear fission reactor, from the article): 7,200 kg for 40 kW. [1] ISS solar arrays: 14,515 kg for ~100 kW in Earth orbit. [2] If we assume 40-50% Earth solar insolation on Martian surface, the ISS PV array probably isn't far off 40 kW output on Mars Conc…

Maybe you forgot to account for batteries?

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#45

Post by xorfish »

baybal2 wrote: post #37
xorfish wrote: post #31

Earlier quoted context omitted.

Enriched uranium has a very high energy density. 20% enriched Uranium would contain 16TJ/kg. So a 4MW u-battery would use around 8kg fuel per year.

>Enriched uranium has a very high energy density. 20% enriched Uranium would countain 16TJ/kg. I did not count in burnup ratio. A simple thermal neutron reactor can only use <1% of fission energy in its fuel.

I'm pretty sure that conventional reactor split around as much fuel as the U-235 content.

For conventional reactors it is around 3% and you are left with around 3% fission products.

Natural uranium has around 0.7% U-235. But I0m pretty sure that you would enrich the uranium befor you send it to mars. The 16TJ/kg is for enriched uranium with 20% U-235 content.

Anyway, energy density of nuclear fuel is extremly high. Even if you pay 10000 USD/kg for the transport of fuel to mars, you'd pay around 1 cent/kwh for the transport.

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#46

Post by avar »

xorfish wrote: post #41
avar wrote: post #35

Earlier quoted context omitted.

That's a trivial cost when we're talking about sending things to Mars. The Curiosity rover has around 5kg of Pu-238. NASA estimates that restarting production will cost $6M/kg[1]. The total cost of the MSL program is 2.5 billion[2]. That's $30 million out of 2.5 billion, or 1.2%. NASA has also been buying Pu-238 from the Russians at around $1.5 million/kg[3], which would be $7.5 million for Curiosity, or 0.3% of the…

The cost wouldn't be trivial for powering a mars colony. I'm sure the demand for a colony would scale pretty fast to 100kW or more. Now we are talking about Billions. So I think that your original point that cost for Pu-238 is not an issue for a colony is wrong. Small reactors are a much better option as a single ton of fuel could supply a colony with a few MW for decades. You just have to make sure that the largest…

My original point was that dredmorbius's comment that Pu-238 is in low supply wasn't referencing some law of nature, but a political decision that could be changed.

I said they were a "bad idea for general power generation", so I'm not suggesting that they be used to power a Mars colony, but rather that the reasons not to do so don't include Pu-238 being in low supply.

We also have a low supply of rockets & other infrastructure to colonize Mars, but we can simply decide to make them.

Still, I think any extrapolation of current numbers to say that Pu-238 would be categorically unsuitable for such a purpose is probably premature. Nobody's tried to produce it on a truly industrial scale, which would bring costs down. It has a half-life of around 90 years degrading at 1%/year, so once you produce it it'll power the colony for a long time.

It's also around 6% efficient at generating electricity[1], but 100% efficient at generating heat, which is a huge part of energy requirements on Mars when it comes to human habitation. The Curiosity rover generates 120W of electricity but 2000W of heat.

1. https://physics.stackexchange.com/questions/34203/mars-curio...

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#47

Post by nkrisc »

krasin wrote: post #13
simias wrote: post #10

Earlier quoted context omitted.

I agree with your sentiment but let's face it, sending humans to Mars is as much PR as it is scientific research (maybe even more). Look how we ended up on the moon in the first place. If NASA wants to get the funding it has to make it as marketable as possible. If there's a big push back from the general population it will be hard to convince the politicians to invest billions in an unpopular project with no short-t…

On a related note, I very much like the fact that "The Martian" movie uses RTG as a life saving device and the best car climate control ever. It helps with the public perception that it's not that dangerous.

Generally I agree with you, but I don't know if it's wise to promote the unintended use of a device by a fictional character as a last hope in a dire survival situation as the bar for what's "safe". Regardless of whether it's actually safe, showing me it's safe enough to sit near in a situation where one would probably die anyway isn't exactly comforting.

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#48

Post by mikejb »

danpalmer wrote: post #11
tiku wrote: post #9

Earlier quoted context omitted.

I don't thinnk it was the fear of the general population, because what influence do we have on dangerous endeavors? If the scientist can do it safely, they could just do it. It must have something to with the state of technology and not being able to do it safe until now.

I disagree. Nuclear reactors have been very safe for a long time now, but between high profile incidents with old reactors, the link with nuclear weapons, and misinformation, the public perception is that they are unsafe.

"very safe" might be true (your interpretation of 'very' might vary), but it is a low chance/high price kind of thing. I live in Bavaria, and hunters here still need to take precautions due to Chernobyl, some 31 years later.

Re: NASA Revives Plan to Put Nuclear Reactors on Mars

#49

Post by batushka »

davedx wrote: post #39

I looked into some numbers on this, comparing theoretical costs of nuclear power with a solar PV solution on Mars. Kilopower (NASA's research project for a Martian nuclear fission reactor, from the article): 7,200 kg for 40 kW. [1] ISS solar arrays: 14,515 kg for ~100 kW in Earth orbit. [2] If we assume 40-50% Earth solar insolation on Martian surface, the ISS PV array probably isn't far off 40 kW output on Mars Conc…

Better windmills :D This green energy hoax barely sustains communities on earth, why would sane someone risk on Mars? Mission needs reliability - we have nuclear power sources reliably working for decades, powering bigger things than calculator.
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