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NASA Wants to Send Nuclear Rockets to the Moon and Mars

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Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#71

Post by baybal2 »

NohatCoder wrote: post #64
simonh wrote: post #37

Earlier quoted context omitted.

You do what you would on a terrestrial reactor, and shut down the reactor e.g. by using control rods, or pulling out fuel rods to shut down the chain reaction. These wouldn't be simple radiothermal devices, but proper actively managed reactor cores. Having said that you absolutely would need active cooling even in a 'shut down' state, probably by circulating a cooling fluid to radiator fins. You might use the same fl…

Absolutely not, in space you have the option of jettisoning the core, carrying coolant for a controlled shut down is a waste of weight. You might even go as far as having 4 disposable cores, one for each acceleration stage.

Brilliant solution man.

Additional nuclear fuel, unlike the popular belief says, will not be taking any much significant weight. A critical mass of plutonium is only 10kg, and you will likely have it reduced with moderation and reflectors.

If you have to keep disposing heat away from a powered down, but still residually active core, you will have to keep a no joke mass of radiators just for that.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#73

Post by yellowapple »

mlindner wrote: post #58
logfromblammo wrote: post #13

Earlier quoted context omitted.

The risk is that in a catastrophic launch failure (read: exploded rocket), the radioactive materials could be dispersed downrange. The solution--if that's really a problem--is to use the same escape systems used for crewed launches to eject the nuclear fuel with a parachute and emergency beacon, and keep it all inside a durable shielded container until the craft needs to start up the nuclear engine.

Except that's not a big problem. A non-activated reactor just contains enriched uranium. Uranium is dug out of the ground and you can buy it on amazon and chemically concentrate it yourself. It's safe to hold and handle (wash your hands afterwards so you don't eat particles) and store in your house even. (In the US this is all legal.) Reactors only become dangerous after you activate them and short lived isotopes are…

> Uranium is dug out of the ground and you can buy it on amazon and chemically concentrate it yourself.

Well now I know what I'm putting in all my nieces' and nephews' stockings this year: https://www.amazon.com/Images-SI-Uranium-Ore/dp/B000796XXM/

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#74

Post by baybal2 »

Robotbeat wrote: post #16
api wrote: post #3

Earlier quoted context omitted.

I don't know for certain but I'm fairly sure that the idea is that you don't activate the reactor until it's in space. Before a reactor is turned on the fuels are less radioactive. It's once you turn it on that radioactivity increases dramatically and you get all the nasty decay products and such. So not zero but not as much as you might think. Personally I don't like the idea. Environmental concerns are real, but th…

Why is this downvoted? This is informative and (in my opinion) basically correct. And while I agree that in the near term, refueling via chemical rockets is a far cheaper (and even higher performance) way of solving this problem, I do support the research because someday we'll want to go even beyond refueling of chemical rockets. When you get REALLY high transfer times between Earth and Mars, the higher Isp makes a s…

> Why is this downvoted? This is informative and (in my opinion) basically correct.

I once wrote that Chernobyl had no chance to explode in a nuclear explosion in rebuke to some guy called Moxie Marlinspike. I had -4 for the next few days on all my posts, and somebody even bothered to find my work email, and futilely tried to troll me and my colleagues into deleting my rebuke for a week.

"That" demographic is definitely there, and working in a "tech" occupation does not preclude a person from being a part to it these days.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#75

Post by logfromblammo »

mlindner wrote: post #58
logfromblammo wrote: post #13

Earlier quoted context omitted.

The risk is that in a catastrophic launch failure (read: exploded rocket), the radioactive materials could be dispersed downrange. The solution--if that's really a problem--is to use the same escape systems used for crewed launches to eject the nuclear fuel with a parachute and emergency beacon, and keep it all inside a durable shielded container until the craft needs to start up the nuclear engine.

Except that's not a big problem. A non-activated reactor just contains enriched uranium. Uranium is dug out of the ground and you can buy it on amazon and chemically concentrate it yourself. It's safe to hold and handle (wash your hands afterwards so you don't eat particles) and store in your house even. (In the US this is all legal.) Reactors only become dangerous after you activate them and short lived isotopes are…

Reactor fuels or RTG cores are a bit more dangerous than ore.

A properly designed reactor requires the fuel to be in the core to sustain a chain reaction, and neutron activation of other elements in the reactor does not occur until the reaction has started. Thus, a rocket explosion would not cause a criticality event. The worst that would happen would be dispersion of nuclear fuel to a place where someone might handle it without its transport-safety shielding. Which still wouldn't be that bad.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#76

Post by wbl »

cr0sh wrote: post #52
BAReF00t wrote: post #22

I’m disappointed. I expected a project-Orion-type interstellar solution. Not a measly ”twice as fast as conventional“ water kettle. Also, no word about what they will acually use. Because classic uranium is a quite limited resource actually. It has been said to run out even before fossil fuels. Also, why not a fusion rocket? Given that we know how to make fusion bombs. Because until we find a massive amount of anti-m…

> Because until we find a massive amount of anti-matter I honestly hope this never occurs, or we never are able to contain/store such a mass for any real length of time. Because if we can do it, it will be used for a weapon. Seriously - I can't even imagine what - for instance - one kilogram of anti-matter coming in contact with regular matter - the amount of energy that would be released...it staggers the imaginatio…

Antimatter bombs emit mostly gamma radiation and so are unlikely to efficiently couple it to air. You would need a tungsten or lead (or even uranium) coupler to absorb the gamma radiation and heat up to drive the explosion.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#77

Post by dogma1138 »

NohatCoder wrote: post #64
simonh wrote: post #37

Earlier quoted context omitted.

You do what you would on a terrestrial reactor, and shut down the reactor e.g. by using control rods, or pulling out fuel rods to shut down the chain reaction. These wouldn't be simple radiothermal devices, but proper actively managed reactor cores. Having said that you absolutely would need active cooling even in a 'shut down' state, probably by circulating a cooling fluid to radiator fins. You might use the same fl…

Absolutely not, in space you have the option of jettisoning the core, carrying coolant for a controlled shut down is a waste of weight. You might even go as far as having 4 disposable cores, one for each acceleration stage.

Not sure why this is being downvoted jettison the core would likely be the go-to solution you can put into a stable orbit or even set on course with the sun and let it burn off...

There is no much need for a complex control mechanism in fact keeping those core as orbital modules on mars would likely allow you to skip many of the complications of having a complex control system to prevent a run away effect and modulate power output no one really cares if the core would go critical even at low orbit on Mars as there is so much radiation there from natural sources anyhow.

If the core goes critical mid way then either have a fallback core or just jettison it and wait for a rescue mission.

The vessels would likely have enough supplies for such occasions and as far as risk to the crew goes nuclear propulsion in space is much less dangerous than chemical propellants that can actually explode.

With a nuclear core you can safely vent hydrogen and xenon to space not worrying that much about radiation or long term contamination the cores can be more or less exposed with large fin stacks for radiative cooling.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#78

Post by dogma1138 »

DoctorOetker wrote: post #26

what happens at the end of such a trip, when the propellant is exhausted, and can no longer evaporatively cool the core? it has to contain enough propellant to come back to Earth orbit to refuel the propellant coolant? even if the core is throttled to its lowest levels, it will still produce heat in the vacuum of space? or will radiative cooling balance the remaining production of heat?

Most likely it would be a very simple core without power throttling or control at all and will be used as a disposable booster and jettisoned once the acceleration phase is complete.

Another core can then be used for deceleration and disposed off as well before entering earth orbit where for the final orbital insertion a much smaller chemical rocket can be used.

Alternatively you don’t get back to earth at all but rather back to the moon where you could jettison the core even on the surface during final approach without giving much thought to radiation.

Then use moon to earth transit via chemical rockets.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#79

Post by teslaberry »

nuclear thermal propulsion should start right here on planet earth with the shipping industry. biggest low hanging fruit EVER when it comes to reducing oil useage AND reducing cost of refueling AND reducing particulates, sulfate n02 and c02 emissions. oh yea, and it's cheaper!!! .
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