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Nuclear Conversion for Starship

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Re: Nuclear Conversion for Starship

#131

Post by ben_w »

flashback2199 wrote: post #121
ben_w wrote: post #111

Earlier quoted context omitted.

The comparison between the two is almost exactly the same as the comparison between a fart and a hurricane: 16 orders of magnitude, give or take. Space is really hostile.

Ok if it's not taking off or landing from earth then sure

Even then. The sun is always a big ball of dangerous radiation, even despite things like the ozone layer. A nuclear rocket taking off isn't something you want to be near, but even literal Chernobyl wasn't as deadly in total as skin cancer was just in the year the reactor exploded.

Re: Nuclear Conversion for Starship

#132

Post by credit_guy »

This is seriously underselling what US nuclear rocket program of the '60s [1], by calling everything that came after "modern". That program was the only one that built something, everything else was speculation on paper.

The obstacles faced by the NERVA project were immense, and the iterations achieved spectacular improvements in record time. That project that lasted for less than one decade and was done on a shoestring budget is not quite the equal of the Manhattan project, but it's not much below it. It achieved the highest density of power generation by maybe a factor of 100 compared to any other reactor in history.

All that stuff was pretty much lost. NASA is trying to revive this, but it will not have legs. We simply don't have the same pool of talent to recruit from. In the 60's there were lots of scientists and engineers that had first hand experience building nukes and nuclear reactors. Now this country has not built a reactor in 3 decades, with the exception of Vogtle.

[1] https://en.wikipedia.org/wiki/NERVA

Re: Nuclear Conversion for Starship

#133

Post by SECProto »

idlewords wrote: post #120
SECProto wrote: post #113

Earlier quoted context omitted.

> The Project Orion design [...] is surprisingly practical, and probably our only way to get humans past Mars. I don't think this is the general consensus. It is seen as one of the only ways to get humans out of the solar system, but other nuclear rockets[1], and even chemical options[2], could get humans to eg the Jovian moons[3] with TRL's much higher than Project Orion. [1] https://en.wikipedia.org/wiki/NERVA [2]…

It's not just about propulsion, but radiation. The radiation environment in space is awful and you need thousands of tons of shielding to effectively screen a crew from cosmic rays. Moreover, because of secondary radiation, partial shielding from energetic cosmic rays is worse than none. A unique property of nuclear pulse propulsion is that the engineering gets easier the more massive the spacecraft. That leaves lots…

> That leaves lots of room for radiation shielding and consumables, and makes it the only halfway practical choice for multi-year missions into the outer solar system.

I disagree, one of the types I referenced is cyclers, which are specifically good for the same kind of reason. NERVA is another alternative that becomes similarly easier as you scale it up. All three types would need in-space assembly, so no big issues with any of them that way.

Don't get me wrong, Orion is cool (and the only way to conceivably run an interstellar mission with known technology/physics), but it isn't necessary (or even desirable imo) for interplanetary missions, at least as far as saturn anyway.

Re: Nuclear Conversion for Starship

#134

Post by flashback2199 »

ben_w wrote: post #131
flashback2199 wrote: post #121

Earlier quoted context omitted.

Ok if it's not taking off or landing from earth then sure

Even then. The sun is always a big ball of dangerous radiation, even despite things like the ozone layer. A nuclear rocket taking off isn't something you want to be near , but even literal Chernobyl wasn't as deadly in total as skin cancer was just in the year the reactor exploded.

This is super useful information to me because I was born yesterday and am just hearing about the sun now from you for the first time.

Re: Nuclear Conversion for Starship

#135

Post by klyrs »

ben_w wrote: post #107
klyrs wrote: post #105

Earlier quoted context omitted.

I proposed nickel-63 for my electron source. Let's say, aluminum-26? And, yes. The idea is patently absurd. But I'm waiting on a ridiculously long compile.

If you're getting them from radioactive decay, it works , but those examples are 63 and 26 times heavier than just using hydrogen as your reaction mass in the first place :)

Hah, good ole rocket nerds, the general thrust of my concept here is not novel!

https://www.projectrho.com/public_html/rocket/enginelist2.ph...

Re: Nuclear Conversion for Starship

#136

Post by idlewords »

SECProto wrote: post #133
idlewords wrote: post #120

Earlier quoted context omitted.

It's not just about propulsion, but radiation. The radiation environment in space is awful and you need thousands of tons of shielding to effectively screen a crew from cosmic rays. Moreover, because of secondary radiation, partial shielding from energetic cosmic rays is worse than none. A unique property of nuclear pulse propulsion is that the engineering gets easier the more massive the spacecraft. That leaves lots…

> That leaves lots of room for radiation shielding and consumables, and makes it the only halfway practical choice for multi-year missions into the outer solar system. I disagree, one of the types I referenced is cyclers, which are specifically good for the same kind of reason. NERVA is another alternative that becomes similarly easier as you scale it up. All three types would need in-space assembly, so no big issues…

It requires something like several hundred g/cm^2 of polyethylene for adequate GCR shielding. So back of the envelope, if the crew compartment is a cube 10 meters on a side, it requires 500g x 6,000,000 cm^2 = 3,306 tons of plastic to shield. I'm not aware of any non-nuclear-pulse design that can carry around that kind of heft. Just how big are the cyclers you mention allowed to get?

Re: Nuclear Conversion for Starship

#137

Post by sigilis »

idlewords wrote: post #136
SECProto wrote: post #133

Earlier quoted context omitted.

> That leaves lots of room for radiation shielding and consumables, and makes it the only halfway practical choice for multi-year missions into the outer solar system. I disagree, one of the types I referenced is cyclers, which are specifically good for the same kind of reason. NERVA is another alternative that becomes similarly easier as you scale it up. All three types would need in-space assembly, so no big issues…

It requires something like several hundred g/cm^2 of polyethylene for adequate GCR shielding. So back of the envelope, if the crew compartment is a cube 10 meters on a side, it requires 500g x 6,000,000 cm^2 = 3,306 tons of plastic to shield. I'm not aware of any non-nuclear-pulse design that can carry around that kind of heft. Just how big are the cyclers you mention allowed to get?

You would assemble such a craft in orbit. Some of the proposed designs for nuclear pulse propulsion conceive of a spacecraft of truly astounding proportions. The wikipedia article on Project Orion mentions an Alpha Centauri bound design that would be 20km in diameter and 10Mt in mass.

However, now that I think about it, cyclers would only need to use the NPP engines (bombs) to get into their cycling orbits, so you might be able to get away with accelerating them while unmanned. You could design such a craft with much less radiation shielding, but still include enough to prevent cosmic rays from killing (or more accurately, increasing their cancer risk) the passengers giving such a craft a significantly larger fraction of usable mass for other purposes. Initially accelerating a Mars cycler with unmanned landers with supplies and materials for an initial colony with humans to follow could be an interesting design.

All of this is more expensive than anyone is willing to pay for, even if there was an appetite for the nuclear proliferation risk of making and then putting a thousand compact bombs on a spacecraft. Not even mentioning the risk of the bomb carrier rockets exploding and causing a 100x Broken Arrow situation.

It is for this reason that I must urge the government to immediately fund the writing of several novels about how this can go wrong and right for me to read.

Re: Nuclear Conversion for Starship

#138

Post by SECProto »

idlewords wrote: post #136
SECProto wrote: post #133

Earlier quoted context omitted.

> That leaves lots of room for radiation shielding and consumables, and makes it the only halfway practical choice for multi-year missions into the outer solar system. I disagree, one of the types I referenced is cyclers, which are specifically good for the same kind of reason. NERVA is another alternative that becomes similarly easier as you scale it up. All three types would need in-space assembly, so no big issues…

It requires something like several hundred g/cm^2 of polyethylene for adequate GCR shielding. So back of the envelope, if the crew compartment is a cube 10 meters on a side, it requires 500g x 6,000,000 cm^2 = 3,306 tons of plastic to shield. I'm not aware of any non-nuclear-pulse design that can carry around that kind of heft. Just how big are the cyclers you mention allowed to get?

It requires the shielding no matter what the transportation method is. If one wanted to build a cycler, conceptually it is somewhat similar to staging a lunar mission with rendezvous in low earth orbit. The construction methodology would be something like the following:

1. Build the base structure of cycler in earth orbit, then transfer it into the orbit you want (i.e. earth-jupiter intersecting). This would be structure, engines, shielding. This might require a couple dozen nuclear thermal boosters, or maybe it has to be phased over two launch periods and assembled in the cycling orbit

2. Assemble in earth orbit everything you want for a manned mission (food, water, landing craft, astronauts)

3. Rendezvouz that material with the cycler on its next orbit (I don't know the timing for earth-jupiter - maybe 12 years after step 1). This is a comparatively small effort, as the shielding and habitable space was already taken care of with step 1

4. live your life for the year or whatever the transfer is

5. Take your landing craft from the cycler to Europa surface

Different crews can hop on the original cycler by repeating steps 2 to 5. Conceptually you would want multiple of these cyclers coming and going, so that a crew can arrive on Europa on cycler A and return on Cycler G, only spending 5 years on Europa instead of 12. Their advantage is that the big heavy mass (sheilding) only has to be launched once, and can be used repeatedly, indefinitely.

Re: Nuclear Conversion for Starship

#139

Post by adrianN »

dylan604 wrote: post #125
sandworm101 wrote: post #109

Earlier quoted context omitted.

You couldnt do it without publicizing. Space stuff is big and loud. Space itself is transparent. Doing big secret stuff in space is extrodinarily difficult.

You can't hide that your about to do something in space because launches are loud and obvious. However, once in space, you can absolutely hide what you are actually doing. We still don't really know what the Air Force Space Plane does while in orbit.

We might not know, but how about China?

Re: Nuclear Conversion for Starship

#140

Post by adrianN »

rockemsockem wrote: post #128
bluescrn wrote: post #80

Nuclear doesn't work with Elon's approach to development. You can't blow up multiple nuclear rockets within the atmosphere just to learn what needs fixing for the next attempt. Then again, it's looking like the whole 'fail fast' approach is over anyway, with Starship grounded by red tape. A full-stack Starship failure is seemingly too big/dramatic/risky to get away with doing repeatedly, especially admidst the politi…

Nuclear rockets are good in space, not in atmosphere and they aren't radioactive until you turn them on. You test in space. Also that isn't "Elon's approach to development" that's just how everything good has ever been made. Also if you plan to fail then you usually wind up failing more safely than if you don't plan to fail.

If they blow up while being transported to space they usually are radioactive too.
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