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Nuclear Conversion for Starship

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Re: Nuclear Conversion for Starship

#51

Post by mcpackieh »

daveslash wrote: post #20
misterbishop wrote: post #11

Aren't SpaceX launch explosions big enough already?

I don't know why you're downvoted. I think it's a legitimate question. When I was in high school I asked " Why don't we just shoot our nuclear waste into the sun? ". As an adult, Kerbal Space Program has taught me that it's incredibly difficult to lose the orbital velocity and get things into the Sun! But the answer my teachers told me was "Well, even if rockets have a 99.5% success rate and a 0.5% failure rate, and…

A rocket explosion is unlikely to pulverize solid nuclear fuel or vitrified nuclear waste. It would most likely fall, intact or in large pieces, into the ocean which is a pretty good place for it anyway. If it blows up over Florida that's worse, but the worst case scenario is that it reenters earth's atmosphere at near-orbital speeds over a populated area and burns/breaks up. Then you have a situation like Kosmos 954, where the radioactive material is spread over a large area and is consequently much harder to clean up.

The biggest issue for the nuclear waste disposal idea is that it doesn't make any economic sense. It's better to dump it into the ocean, or down a mineshaft, or even just to let it sit in storage near the power plant for decades. But with nuclear fuel for rovers, satellites or rockets the rewards could outweigh the risks, and so this is sometimes done.

Here's a NASA doc that goes over the risks of launching plutonium into space for their Mars rovers. To summarize, it's not really a big deal: https://rps.nasa.gov/resources/81/mars-2020-launch-nuclear-s...

> The General Purpose Heat Sources (GPHS) inside the MMRTG is designed specifically to prevent such an occurrence. The fuel inside each GPHS is surrounded by several layers of protective materials, including the type of tough material used in the nose cones of missiles designed to survive fiery conditions during re-entry into Earth’s atmosphere. In addition, the radioisotope fuel is manufactured in a ceramic form (similar to the mate- rial in a coffee mug) that resists being broken into fine pieces, reducing the chance that hazardous material could become airborne or ingested.

Re: Nuclear Conversion for Starship

#52

Post by paulsutter »

>So will going Nuclear be worth it?

>The short answer is no

>If we need the full performance advantage of nuclear propulsion, we should design a spaceship that is intended for it from the get-go. It never lands, only going from orbit to orbit, so there is no need for heat shielding, flaps, high thrust engines, thick steel structure or aerodynamic shaping requirements.

Re: Nuclear Conversion for Starship

#53

Post by idlewords »

andrewla wrote: post #36
CarVac wrote: post #27

Earlier quoted context omitted.

For specific impulse. When you have unlimited power, you want the lightest possible molecular mass exhaust for the best total delta V.

I need to play Kerbel Space Program. I have absolutely no intuition about this sort of thing. Some intuition around orbital mechanics from my physics days but rocketry is a bit of a mystery.

For me it helped to remember that the term that matters in the rocket equation is exhaust velocity, not momentum. You want to be shooting the lightest things you can out the back of the rocket, at the highest speed.

Unfortunately with chemical rockets, the energy source and reaction mass are the same thing, so you're kind of stuck with whatever burning your fuel gives you. But when you can separate reaction mass from energy source (like in nuclear or electric rockets), hydrogen is always the best bet.

Re: Nuclear Conversion for Starship

#54

Post by klyrs »

CarVac wrote: post #27
andrewla wrote: post #23

I only skimmed the article; but as I understood it the liquid hydrogen here is being used strictly as ejecta. It is not being combusted, the way that it is used in the space shuttle boosters. If that is the case, liquid hydrogen seems like an awful substance -- hard to produce and transport, hard to store and the mass required to support keeping it is not insubstantialy, all for a mass density of ~70g/L. Why not just…

For specific impulse. When you have unlimited power, you want the lightest possible molecular mass exhaust for the best total delta V.

So, since beta radiation is even lower mass... just put a block of nickel-63 into a magnetic lens?

Re: Nuclear Conversion for Starship

#55

Post by euroderf »

idlewords wrote: post #50
euroderf wrote: post #21

Earlier quoted context omitted.

NK, "if" he has enough cold hard cash.

"I'll trade you Twitter for six critical masses" doesn't have the appeal of a year ago.

Yeah rilly. I mean, what can you possibly accomplish with a measly two critical masses.

Re: Nuclear Conversion for Starship

#56

Post by Kim_Bruning »

Skunkleton wrote: post #2

First I am reading about nuclear engines applied to Starship. I wonder if it would be more practical to launch the reactor, fuel, and propellant into orbit using conventional rockets. Later a mission could pick up this Nuclear rocket engine and use it as a sort of booster while not inside a strong gravitational field. Ofc that doesn’t sound like Starship at all.

That was (part of) the original plan, post Apollo program. Somehow it got stripped down to to just a space shuttle. :-(

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

Re: Nuclear Conversion for Starship

#57

Post by renewiltord »

idlewords wrote: post #31
jaggederest wrote: post #28

Earlier quoted context omitted.

Starship and the booster already collectively carry 70 kiloton-tnt-equivalent masses of liquid methane and oxygen. As a weapon of mass destruction, it's hard to beat relativistic impact.

That's like saying they carry 4400 tons of mass-energy, which could destroy the planet.

Would you not realize a lot of damage by just pointing Starship somewhere instead of at the sky?

Re: Nuclear Conversion for Starship

#58

Post by Kim_Bruning »

andrewla wrote: post #36
CarVac wrote: post #27

Earlier quoted context omitted.

For specific impulse. When you have unlimited power, you want the lightest possible molecular mass exhaust for the best total delta V.

I need to play Kerbel Space Program. I have absolutely no intuition about this sort of thing. Some intuition around orbital mechanics from my physics days but rocketry is a bit of a mystery.

Yes, absolutely: https://xkcd.com/1356/

Re: Nuclear Conversion for Starship

#59

Post by fsloth »

maxcan wrote: post #9

AFAIK, the only nuclear rocket that makes sense is landing a reactor on an icy comet and using it to shoot super heated steam wherever you want thrust. #seveneves

Project orion was super cool and I warmly recommend the book by similar name by George Dyson (son of Freeman Dyson!) who did a tremendous job of putting everything back together as well as humanly possible for an ops with very top secret components.

Nukes can totally function as the energy for rocket’s impulse. Very small and very directed nukes. The directed explosion plasma wave hits a pusher plate, where very specific plasma physics play out - the plate is not vaporized but merely receives an impulse - and then there are dampers to smoothen the blow.

Half of the interviewed experts were positive it would work and half were skeptical.

So, it’s sort of sad they had to wrap it up due to nuclear test ban before actually being able to run actual tests.

The best part? The bigger it is, the better. We could totally have gigantic nuclear space cruisers that go to Jupiter in like a week (I exaggerate because I forget the exact orbits but with ISP from nukes that bastard goes fast)

Re: Nuclear Conversion for Starship

#60

Post by agent327 »

daveslash wrote: post #20
misterbishop wrote: post #11

Aren't SpaceX launch explosions big enough already?

I don't know why you're downvoted. I think it's a legitimate question. When I was in high school I asked " Why don't we just shoot our nuclear waste into the sun? ". As an adult, Kerbal Space Program has taught me that it's incredibly difficult to lose the orbital velocity and get things into the Sun! But the answer my teachers told me was "Well, even if rockets have a 99.5% success rate and a 0.5% failure rate, and…

Why would you dispose of such a useful material by attempting to shoot it into the sun? Sure, there is some danger associated with storing it, but it's not as if nuclear material is the only hazardous substance on the planet, and with the rest of it we seem perfectly ok with just sticking it in a hole somewhere. Nor does nuclear material, by itself, represent a danger of civilisation-ending proportions (only if you build a bomb out of it, and that is quite a significant operation that can only be conducted by people that know what they are doing. In other words, it won't explode if left by itself.).
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