NASA Wants to Send Nuclear Rockets to the Moon and Mars

[DoctorOetker]

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?

[simonh]

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 fluid as the propellant or might not. In the former case sure, you wouldn't be able to use all of it as propellant.

[Symmetry]

With a nuclear thermal rocket generally you do 90% of your burn all at once to maximize the Oberth effect then you shut down the reactor. But you've still got secondary decays going on for a while so you slowly use the remaining 10% of the propellant to cool the engine while getting a bit more thrust.

[dogma1138]

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.

[dclowd9901]

Why do you believe they haven't/aren't already thought/thinking about these things and solving them? Or are you just genuinely curious?

[sq_]

> which will almost certainly be used on any crewed mission to Mars.

This is interesting. I hadn't seen anything about NASA plans to get humans to Mars requiring nuclear-thermal propulsion. Does NASA even currently have a serious plan for Mars missions with the whole Artemis thing going on?

[ceejayoz]

They branded Artemis as part of a larger "Moon to Mars" plan, with logo and all. https://www.nasa.gov/moontomars/

[Arrezz]

How big is the added risk of toxic waste? I'm not sure how much waste is produced in relation to propulsion energy given but it must be quite small? And I imagine that during travel in space you could just dump that waste out into space considering the vastness of it all.

[Symmetry]

Whenever you're splitting Uranium atoms the results will tend to be radioactive. The results will build up in the fuel over time and eventually make the reactor stop working. Conventional reactors breed a bit of plutonium too as U238 captures neutrons but most aerospace reactors want to be as light as possible and so use highly enriched Uranium. So after your trip the engine will be quite radioactive but, as you point out, there's a lot of space and outside Earth's atmosphere and Van Allen belts it's moderately radioactive anyways.

Thankfully nuclear reactors aren't particularly radioactive until you turn them on, which is a big improvement on the radiothermal generators, RTGs, that we sometimes use in probes headed for the outer solar system where solar panels don't work. It's during launch, before this part gets turned on, that you have a risk of crashing and losing the reactor somewhere on Earth.

[api]

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 those aside it's likely more expensive than multiple refueling flights with big conventional rockets. These would be expendable and very costly to research, develop, fuel, and launch, whereas for the same cost you could probably put stages in orbit and send fuel up to them with reusable tankers. Like hydrogen this is another example of NASA chasing the sexiness of high performance in a pure sense (high iSP etc.) without doing a total cost analysis.

In general SpaceX and Blue Origin have the right approach.

[logfromblammo]

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.

[scohesc]

I would imagine the engine would be fairly inert if it's not activated until in orbit.

I could see issues if the craft all of a sudden loses its orbit with an radioactive engine burning up in the atmosphere spewing radiation (although I'm sure we get bombarded with way more from the sun potentially?)

Maybe if during launch something goes catastrophically wrong and blows up mid-air like a bomb of sorts?

[t0mbstone]

How does one convert nuclear heat energy into directional energy for propulsion purposes?

[rmckayfleming]

Take a look at this: https://en.wikipedia.org/wiki/Nuclear_lightbulb

[new_guy]

Links dead.

Edit: available through outline https://outline.com/nbpE5n

[anon234345566]

so things got really serious and we need to get out there as fast as we can

[stickfigure]

Anyone else just get a JSON 404 page from this link?

    {
        statusCode: 404,
        error: "Not Found",
        message: "Not Found"
    }

[ksaj]

I got that error from another article linked to Wired from HN the other day. After a short time, I clicked again and all was fine.

Something wonky is going on there, since it probably shouldn't even be 404 unless they keep deleting their articles and then resurrecting them shortly thereafter (which would be just a little weird).

[u801e]

I tried it just now and was able to see the article. On another note, why do they include the HTTP status code in the JSON body? Isn't it already present in the status line of the HTTP response?

[toxican]

They admitted to encountering the literal definition of UFO -- "Unidentified Flying Object", which in no way at all proves or even suggests alien activity. If you want to get annoyed with the media, direct it at them convincing people that "UFO" = aliens

[everdev]

Unidentified != Alien

[wfbarks]

For the first time, period. Doesn’t look like we had one 60 years ago...

[ceejayoz]

We did: https://en.wikipedia.org/wiki/NERVA

Tested successfully (on the ground) in the 60s.

Real pity about its cancellation, too. It was considered for the "Grand Tour" that the Voyager probes wound up doing; they could've sent nearly 30x the spacecraft mass with NERVA rockets.

[autokad]

I don't have time to verify the video at the moment, but I believe this is them testing said engine 60 years ago: https://www.youtube.com/watch?v=GmxPRCyR-Co

[bra-ket]

this is great! check out project Orion https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

[inamberclad]

It's much more likely to look like NERVA than Orion.

https://en.wikipedia.org/wiki/NERVA

These types of engines have already been run: https://www.youtube.com/watch?v=eDNX65d-FBY

[BAReF00t]

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-matter, this will be the next best thing for a loong time. The only limiting factor would be a human body's ability to withstand G forces.

[Robotbeat]

All of those things are harder than a nuclear thermal rocket. Got to walk before you run. And a fusion reactor is actually likely to be much heavier than a fission one (at least in the near term).

They're using Low Enriched Uranium for this design. We have plenty of uranium (resources are huge, but no one bothers to prove them into reserves until the price is right), and not much is required for this project.

Don't be disappointed by the first step in a journey not taking you immediately to the destination.

[cr0sh]

> 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 imagination. Today's fusion weapons release only a fraction of their potential energy; anti-matter conversion would be 100% (roughly):

https://en.wikipedia.org/wiki/Antimatter_weapon

"Using the convention that 1 kiloton TNT equivalent = 4.184×1012 joules (or one trillion calories of energy), one gram of antimatter reacting with one gram of ordinary matter results in 42.96 kilotons-equivalent of energy (though there is considerable "loss" by production of neutrinos)."

So...one kilo of anti-matter would be equivalent to 42 megatons - which is close to yield of the Tsar Bomba:

https://en.wikipedia.org/wiki/Tsar_Bomba

...but in a much more compact package. 50 kg of antimatter - which would be feasible for current launch systems, and comparable in size to current warheads:

https://en.wikipedia.org/wiki/W80_(nuclear_warhead)

Well - that's a 2 GT weapon...while I'm sure such a thing has been considered as to it's effects...I honestly don't know what that would be. Best guess might be that one such warhead could easily take out a good portion of say, the west coast (of the United States)?

Ultimately - we are not ready in any manner - socially, morally, politically - as a species to wield that kind of power responsibly. Honestly, even nuclear weapons fall into that assessment, despite recent history - I'm honestly not sure how we have gotten this far without a major nuclear war occurring.

Sadly, though, I know that my conjecture (in which I am not alone, I hope) will not do anything to stop the research - right now, though, the cost to produce anti-matter (let alone contain it) is so high as to make even a small mass cost an exorbitant amount of money. I sincerely hope there isn't any breakthrough on that front.

I honestly think we, as a species, are not ready for it (that isn't to say none of us are - but those who would be responsible with such "stuff" are likely very few - I know I am not one of them).