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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

#81

Post by kwoff »

dogma1138 wrote: post #77
NohatCoder wrote: post #64

Earlier quoted context omitted.

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 modulat…

"set on course with the sun and let it burn off" - https://laughingsquid.com/why-it-is-more-difficult-to-crash-...

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

#82

Post by simonh »

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.

So you would not build in mechanisms to moderate the heat output of the core, and have it generating at full power constantly? Ok, what state is the core in before you want to fire the engines? Suppose you want to burn to leave Earth, and agin to slow down at Mars, what happens to the engine core on the coasting period of many months in between? If you're carrying several disposable cores, if there's no way to moderate their output how do you store them safely when not in use and switch them on? Also, whole propulsion cores are lighter than the cooling system for a single core? Really?

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

#83

Post by sq_ »

ceejayoz wrote: post #69
sq_ wrote: post #67

Earlier quoted context omitted.

Interesting. I'm kinda down on Artemis overall, as it seems like the whole thing is getting bogged down in political maneuvering, as usual. NASA keeps saying it's more than boots on the ground, but all the plans they announce seem to be boots on the ground or overly complicated paths to the surface meant to please contractors. This gem of a line from this week's Orbital Index kinda sums up why I'm preparing for disap…

I'm skeptical of any human exploration plans NASA has beyond 2-4 years or so. Anything more and the next President winds up nixing it to put their own stamp on things. My money's on a commercial program like they one they've been doing for ISS resupply.

> My money's on a commercial program like they one they've been doing for ISS resupply.

Fully agree. If I had to bet right now, I would guess that SpaceX will get humans to the moon before NASA does. They’re moving so quickly on Starship and seem extremely determined to prove their new rocket.

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

#84

Post by NohatCoder »

simonh wrote: post #82
NohatCoder wrote: post #64

Earlier quoted context omitted.

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.

So you would not build in mechanisms to moderate the heat output of the core, and have it generating at full power constantly? Ok, what state is the core in before you want to fire the engines? Suppose you want to burn to leave Earth, and agin to slow down at Mars, what happens to the engine core on the coasting period of many months in between? If you're carrying several disposable cores, if there's no way to modera…

A core is just nuclear fuel with enough other parts that it can be handled. Of course there needs to be a control mechanism for adjusting the output, you just can't use that for eliminating heat output. Once the core has been turned on there is decaying fission products producing heat, that is why you can't turn off a nuclear power plant in an instant, and why you might want to get rid of the core. Unused cores can be stored with few special precautions as the unspent fuel decay too slowly to be a major hazard.

The ship would carry one small nuclear reactor, and several tons of coolant/propellant. The only way the cooling system is actually going to keep up is by ejecting the hot coolant into space, which is also what creates thrust. You can't recycle the coolant as there is no efficient way to cool the coolant.

In effect, if you don't want to dispose of the core you have to keep the engine on consuming coolant/propellant, depending on a lot of factors that may or may not be viable.

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

#85

Post by simonh »

NohatCoder wrote: post #84
simonh wrote: post #82

Earlier quoted context omitted.

So you would not build in mechanisms to moderate the heat output of the core, and have it generating at full power constantly? Ok, what state is the core in before you want to fire the engines? Suppose you want to burn to leave Earth, and agin to slow down at Mars, what happens to the engine core on the coasting period of many months in between? If you're carrying several disposable cores, if there's no way to modera…

A core is just nuclear fuel with enough other parts that it can be handled. Of course there needs to be a control mechanism for adjusting the output, you just can't use that for eliminating heat output. Once the core has been turned on there is decaying fission products producing heat, that is why you can't turn off a nuclear power plant in an instant, and why you might want to get rid of the core. Unused cores can b…

>You can't recycle the coolant as there is no efficient way to cool the coolant.

Alright, this is the crux of the problem. Yes you can, the ISS has huge radiator panels in it's shadow for thermal management. The shuttle also had radiator panels in the bay door structure, they were so crucial the vehicle had to re-enter soon after closing the doors to avoid excessive thermal buildup. This is a known solved problem. And that's on vehicles that aren't carrying any nuclear power systems, and just have to contend with solar radiative heating.

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

#86

Post by NohatCoder »

simonh wrote: post #85
NohatCoder wrote: post #84

Earlier quoted context omitted.

A core is just nuclear fuel with enough other parts that it can be handled. Of course there needs to be a control mechanism for adjusting the output, you just can't use that for eliminating heat output. Once the core has been turned on there is decaying fission products producing heat, that is why you can't turn off a nuclear power plant in an instant, and why you might want to get rid of the core. Unused cores can b…

>You can't recycle the coolant as there is no efficient way to cool the coolant. Alright, this is the crux of the problem. Yes you can, the ISS has huge radiator panels in it's shadow for thermal management. The shuttle also had radiator panels in the bay door structure, they were so crucial the vehicle had to re-enter soon after closing the doors to avoid excessive thermal buildup. This is a known solved problem. An…

The ISS doesn't have a heat budget anywhere close to that of a reactor core, you'd need to carry a much larger radiator construction, just for this job. Extra cores cost way less weight.

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

#87

Post by BAReF00t »

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…

Well, if we found it, it would already be contained unless accessed by definition.

Also, magnetic fields could definitely contain it, as is already done.

We can already make anti-matter, as it't essentially the process of making matter bounce off, using a photon, in such a way that it reverts its time direction. Or, in classical view: Turn a photon into a particle/antiparticle pair. The problem is, of course, that it first takes those shitloads of energy, that it would release later.

And to actually find anti-matter in nature, you would most likely have to turn into anti-matter yourself, travel back in time, and somehow survive the big bang without touching anything, to come out the hypothetized other side where time is reversed and anti-matter expanded to. Or try to get inside a black hole, and revert your direction of motion (as time and space are reversed in there). Both not yet technically available, to say the least. ;)

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

#88

Post by simonh »

NohatCoder wrote: post #86
simonh wrote: post #85

Earlier quoted context omitted.

>You can't recycle the coolant as there is no efficient way to cool the coolant. Alright, this is the crux of the problem. Yes you can, the ISS has huge radiator panels in it's shadow for thermal management. The shuttle also had radiator panels in the bay door structure, they were so crucial the vehicle had to re-enter soon after closing the doors to avoid excessive thermal buildup. This is a known solved problem. An…

The ISS doesn't have a heat budget anywhere close to that of a reactor core, you'd need to carry a much larger radiator construction, just for this job. Extra cores cost way less weight.

But if you don’t have mechanisms to moderate those cores output, they’ll be blazing away all the time. You can’t get away from the fact you need a way to moderate the reaction, including For ‘spare cores, which you at least need a mechanism to activate, and you need an active cooling system.

And on top of all that, even with reaction mass cooling the core when it’s active, that not going to be enough to capture all the generated heat.

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