Live data from Hacker News

Nuclear Conversion for Starship

toughsf.blogspot.com

41–50 of 155 posts

Re: Nuclear Conversion for Starship

#41
post #18

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.

Did you read to the end? That's the idea he ends up with: only use nuclear propulsion for space-to-space travel where you don't care as much about shielding.

I make no claims about my reading comprehension. That last bit seemed too narrow to me. Once you have all the bits in orbit, shielding doesn’t seem too onerous. Is the claim that even space-space shielding + reactor is too heavy to be worth the advantage of the nuclear drive?

Re: Nuclear Conversion for Starship

#42

Earlier quoted context omitted.

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

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.

> As a weapon of mass destruction, it's hard to beat relativistic impact.

> relativistic impact

You... er, realise they're not actually starships, right? At the speeds they go at (or would go at if they could take off without exploding) there is no significant relativistic effect.

Re: Nuclear Conversion for Starship

#43

The summary of this methodical and enlightening article from an excellent source for mathematically backed science fiction / space travel is: No. Nuclear is not worth it for starship, as the added engine weight limits the additional delta V and the additional challenges of handling nuclear material.

The no accompanies the short explanation of a nuclear planetary transfer vehicle that never lands on earth. A lot of conceptual work has been done on these designs, and Andy Weir’s The Martian features one.

Nuclear powered space tugs is a particular rabbit hole I’ve spent too much time on.

See, for example, this Boeing design: https://www.projectrho.com/public_html/rocket/spacetug.php#b...

Re: Nuclear Conversion for Starship

#44
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

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...

Re: Nuclear Conversion for Starship

#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, at US$20 billion, was the economy version. To the moon and back, no space station, no permanent infrastructure in space.

[1] https://www.youtube.com/watch?v=Sz7njI0wEIw

Re: Nuclear Conversion for Starship

#46

The design is not advanced enough, they should be thinking of https://en.wikipedia.org/wiki/Fission-fragment_rocket So here is my science fiction theory: fusion will never be possible, but fission already is. So in the galactic civilization, rare uranium is the most valuable resource since it enables interstellar travel. Uranium is only produced in the collisions of neutron stars, so we are lucky to have any. We shou…

> We should not squander our uranium for power generation.

I think we might have enough.

"He noted that fast breeder reactors, fueled by naturally-replenished uranium extracted from seawater, could supply energy at least as long as the sun's expected remaining lifespan of five billion years"

https://en.wikipedia.org/wiki/Uranium_market#Available_suppl...

Re: Nuclear Conversion for Starship

#47
post #16

Earlier quoted context omitted.

Nuclear rockets are useless for launching things into orbit. They don't have the thrust-to-weight ratio to get off the ground. Nuclear rockets are useful because they have high specific impulse which means using less fuel for thrust.

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] https://forum.kerbalspaceprogram.com/topic/173818-181-1122-k...

[2] https://xkcd.com/1244/

[3] https://en.wikipedia.org/wiki/Nuclear_lightbulb

Re: Nuclear Conversion for Starship

#48

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...

George Dyson (Freeman's brother) wrote a book on it that is fantastic reading.

Re: Nuclear Conversion for Starship

#49

Earlier quoted context omitted.

I'm going to go out on a limb and say Niger, CAR, Palau, etc don't have access to highly enriched uranium.

Who says it has to be highly enriched to start? https://en.wikipedia.org/wiki/List_of_countries_by_uranium_r...

Well, there's a reason Niger hasn't nuked us yet and isn't flying rockets to Mars.

Re: Nuclear Conversion for Starship

#50

Earlier quoted context omitted.

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

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.
Post reply on HN