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The US government is taking a step toward space-based nuclear propulsion

arstechnica.com

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Re: The US government is taking a step toward space-based nuclear propulsion

#81

Post by pixl97 »

avar wrote: post #47
somenameforme wrote: post #7

Earlier quoted context omitted.

I think the obvious concern would be failure scenarios. There will always be failures in space technology. As space expands exponentially (as it is likely to do so in the future), failures will become relatively regular. So the obvious question would be what would happen if a nuclear rocket, with reaction in process, crashed to Earth. Or even if it broke up in the atmosphere.

> Or even if it broke up > in the atmosphere. The atmosphere we've already detonated over 500 nuclear weapons in?

Mostly about the ocean it would typically fall into in the most common failure shortly after launch scenario.

Re: The US government is taking a step toward space-based nuclear propulsion

#82

Post by pixl97 »

version_five wrote: post #53
asu_thomas wrote: post #35

Earlier quoted context omitted.

[flagged]

It's funny because it's this, turning inward and waging war on ourselves after there wasn't an obvious enemy anymore that's responsible for the decline the upstream comment was talking about. Post WWII through the 90s saw massive increases in global standard of living, 2020's the west has gone back to religious squabbles over absurd ideological things. Watchmen had a similar idea.

Post WWII understood how terrible war was. Post 90s those that experienced it in mass were going extinct. We forgot what fascism did to the past and too many are embracing it again.

Re: The US government is taking a step toward space-based nuclear propulsion

#83

Post by FirmwareBurner »

zaptrem wrote: post #38
asu_thomas wrote: post #35

Earlier quoted context omitted.

[flagged]

Investment in space has historically led to a disproportionate return in economic growth.

Probably because there is no oil in space and nobody to sell ads to.

Re: The US government is taking a step toward space-based nuclear propulsion

#84

Post by secondcoming »

Is Anthony Zuppero involved? [0]. He is/was a scientist who wanted to build a rocket that could travel the Solar System [1]

[0] https://www.theregister.com/2009/11/15/zuppero_solar_system/

[1] http://www.neofuel.com/inhabit/inhabit.pdf

Re: The US government is taking a step toward space-based nuclear propulsion

#85

Post by rgmerk »

rich_sasha wrote: post #59
version_five wrote: post #55

The basic idea is straightforward: A nuclear reactor rapidly heats up a propellant, probably liquid hydrogen, and then this gas expands and is passed out a nozzle, creating thrust. But engineering all of this for in-space propulsion is challenging, and then there is the regulatory difficulty of building a nuclear reactor and safely launching it into space. Can anyone give a eli5 explanation of what makes this better…

The propellant is important for its bulk (some mass to shoot out the back) and it's energy. In a chemical rocket, the propellant provides both the bulk and the energy. As it happens, there isn't that much energy in chemical propellants per kg, but the rest of the engine is light enough that these things can fly to orbit. In a nuclear rocket, the energy comes from a nuclear reaction and the gaseous fuel only provides…

Are you sure about that? Some of the nuclear thermal rockets tested way back in the 1960s were very, very powerful.

That said, it’s hard to imagine that they’ll ever be used for launches from the Earth’s surface. Mars, maybe.

Re: The US government is taking a step toward space-based nuclear propulsion

#86

Post by cheese_van »

rbanffy wrote: post #73
vkou wrote: post #61

Earlier quoted context omitted.

Broad optimism? Science hype? Are we living in the same country?

One thing I learned from the outside, the US - like any large country, BTW - is wildly diverse in pretty much every aspect.

It's almost intuitive if you consider the distance from Bangor to LA is pretty much the same distance as Madrid to Moscow. Think of the diversity between Madrid and Moscow. Bangor to LA won't take you through an equal amount of diverse cultures, the US is a single country after all, but the diversity is certainly there.

Re: The US government is taking a step toward space-based nuclear propulsion

#87

Post by ben_w »

gibolt wrote: post #20
ben_w wrote: post #16

Earlier quoted context omitted.

Depending on the design, failure during launch can be anywhere from "meh" to "basically high-altitude Chernobyl" — random actinide decay products (and plutonium fuel) are bad, unreacted uranium fuel is mostly a heavy metal hazard rather than a radiation hazard. (Could be worse, but the Orion drive is currently illegal by treaty and hopefully nobody is dumb enough to use that in Earth's ionosphere anyway).

The nuclear payload could be treated similar to humans, with eject systems and soft landing built in. The fuel will only be needed for a lighter craft in deep space. Getting it up with a high reliability rocket (like Falcon 9) significantly decreases risk.

> The nuclear payload could be treated similar to humans, with eject systems and soft landing built in.

In principle yes — even just on the grounds that enriched fuel is expensive — but it's a hard thing to prove in advance, hence all the times humans died in a space mission one way or another.

Re: The US government is taking a step toward space-based nuclear propulsion

#88

Post by ridgeguy »

lazide wrote: post #72
ridgeguy wrote: post #64

Earlier quoted context omitted.

It's the high temperature and the lower exhaust molecular weight. Specific impulse (Isp) is how much force you get from each mass unit of propellant you exhaust. So an engine with Isp = 300 gives 300lbs force for every pound of exhaust gas mass. IIRC, Isp scales as the inverse square root of exhaust molecular weight. So a pure (molecular) hydrogen exhaust would have a molecular weight of 2. A pure H2/O2 engine would…

The real limiting issue tends to be materials in the reactor - at some point, every known material is a liquid or a gas and the reactor stops being an ongoing concern. Usually reactors run cooler by several orders of magnitude, as this is referred to as a ‘meltdown’ and people get snippy about the releases of radiation and expensive cleanup crews, etc. Space is more forgiving and has fewer HOA types, so they can go c…

Yeah, the materials issues dominate design basics. They've looked at HfC and HfCN as nuclear engine materials (m.p. ~3950°C), pretty exotic.

I feel like if designers would drop their effort to wring out the last increment of Isp from nuke engines and reduce temperatures to ~2000°C, it would give faster development. There are many materials that can live in 2000° hydrogen for >100K hours.

There's an old Rand study that showed H2 would give an Isp >1100 at 1 atm chamber pressure (!), temp ~2000°C, exhaust pressure 10e-4 atm. Seems worth exploring.

Re: The US government is taking a step toward space-based nuclear propulsion

#89

Post by ben_w »

asu_thomas wrote: post #35
mdorazio wrote: post #2

Finally! This is one of the few fission uses I'm genuinely excited about. Nuclear-thermal just makes so much sense for in-space propulsion of large vessels compared to chemical rockets.

[flagged]

The people making these aren't any good at building houses.

The lack of housing is, IMO, a failure of government — material costs for homes are surprisingly low compared to everything else — but even then, housing policy is a different department to the space stuff.

Re: The US government is taking a step toward space-based nuclear propulsion

#90

Post by tiffanyg »

Aw man, forget all that noise. Bring back "Project Orion"*, baby!

If we're not gettin' out our (NASA-approved) Huarache sandals, "waxing down" our pusher plate, and surfing "the pocket" of those sweet nuclear detonations in the near future, then, I'm afraid our species is utterly consigned to the category of "posers"!!

See, Kilgore knew how to put this kind of (heavier) ordnance to good use:

https://youtu.be/8XJYnKhI_x0?t=1m06s

... and it don't get heavier than nuclear for us, currently!

* https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

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