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Nuclear Conversion for Starship

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Re: Nuclear Conversion for Starship

#91

Post by bobthespaceguy »

asdff wrote: post #88
Animats wrote: post #45

That's a useful analysis. Nuclear power gives you more energy, but you're still limited by how much reaction mass you can carry. The plans that work look like early 1960s NASA plans - build infrastructure in orbit, assemble nuclear power interplanetary craft in orbit, nuclear power is from planetary orbit to planetary orbit only. That was Wernher von Braun's "Man Will Conquer Space Soon" plan.[1] The Apollo program,…

It makes you wonder though, should you set up such space based infrastructure, is it even worth publicizing lest you trigger an arms race?

I think advancing science sometimes comes with risks. I would welcome a friendly arms race for better access, but who knows what would actually happen.

Re: Nuclear Conversion for Starship

#92

Post by moffkalast »

lostlogin wrote: post #44
idlewords wrote: post #38

Earlier quoted context omitted.

The Project Orion design (shoot hundreds of fission bombs out the back and ride the shock wave on a reaction plate) is surprisingly practical, and probably our only way to get humans past Mars. It's just kind of terrifying.

Yup, it’s scary. “A moderate-sized nuclear device was estimated, at the time, to produce about 5 or 10 billion horsepower.” https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...

Finally, the gigahorse.

Re: Nuclear Conversion for Starship

#93

Post by matheusmoreira »

Kim_Bruning wrote: post #47
therein wrote: post #16

Earlier quoted context omitted.

One of the core teachings of Kerbal Space Program.

However, in KSPI [1]: Consider the combination of a nuclear lightbulb with compressed air as the reaction mass: Surprisingly good midpoint qua TWR and ISP! If you install a compressor you can get some pretty interesting SSTOs out of it. Whether these would work IRL is a different question, of course. [2] Nuclear lightbulb is of course highly theoretical, but scientifically/engineeringly plausible at the least. [3] [1…

It's that close flyby of the sun that always gets me.

Re: Nuclear Conversion for Starship

#94

Post by nickik »

idlewords wrote: post #15
politician wrote: post #7

I think we'll see nuclear propulsion for Starship variants that receive fuel rods in orbit and are not designed for reentry. Interplanetary logistics between Earth/Moon/Mars orbits.

Name me a country willing to give Elon Musk control of fissile material, however indirect.

If SpaceX was willing to do the work and put in the investment they could absolutely get access to fissile material. The US government evaluates things based on regulations and not who is popular on twitter.

Re: Nuclear Conversion for Starship

#95

Post by [deleted] »

fsloth wrote: post #59
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 spec…

[deleted]

Re: Nuclear Conversion for Starship

#97

Post by nickik »

mcpackieh wrote: post #51
daveslash wrote: post #20

Earlier quoted context omitted.

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…

> The biggest issue for the nuclear waste disposal idea is that it doesn't make any economic sense.

No the biggest issue is that its a stupid idea in the first place. Nuclear waste is fine and perfectly reasonable to handle here on earth with close to zero chance of actual danger.

Re: Nuclear Conversion for Starship

#99

Post by ben_w »

klyrs wrote: post #87
ben_w wrote: post #81

Earlier quoted context omitted.

Shooting just electrons out the back of your ship is fine for the brief period before your ship gains a positive electric potential comparable to the net potential those electrons experience due to the inside of the particle accelerator you were using, after which your ship's own field is a major source of drag. If your ship has a positive electric potential of over 1.044 MeV[0], you also start getting positron-elect…

Twin beta+ and beta- engines?

First, you have a way to store an absurd quantity of positrons. For a sense of scale, without shielding the electric fields, 1 picogram of positrons (or electrons) confined within a 10 cm radius is going to trigger positron-electron pairs formation, thanks to free electrons in the area responding to the surface potential.

Second, AFAICT if you can do that then you're either going to want to use them as an energy source to propel your cheap reaction mass even harder than a fission rocket would, or you're going to want to react them with electrons to make a photon rocket.

Re: Nuclear Conversion for Starship

#100

Post by moffkalast »

ben_w wrote: post #81
klyrs wrote: post #54

Earlier quoted context omitted.

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

Shooting just electrons out the back of your ship is fine for the brief period before your ship gains a positive electric potential comparable to the net potential those electrons experience due to the inside of the particle accelerator you were using, after which your ship's own field is a major source of drag. If your ship has a positive electric potential of over 1.044 MeV[0], you also start getting positron-elect…

Don't ionic thrusters typically solve this problem by also emitting oppositely charged particles from a thin rod behind the motor? Maybe that still causes drag, but overall the main problem is that while the ISP is high, the thrust is almost non-existent.
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