Nuclear Conversion for Starship
toughsf.blogspot.com
toughsf.blogspot.com
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.
https://en.wikipedia.org/wiki/Orion_(satellite)
https://en.wikipedia.org/wiki/Lacrosse_(satellite)
https://en.wikipedia.org/wiki/National_Reconnaissance_Office
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 politics of Twitter/X.
Sure you can. Russia has blown up multiple experimental nuclear-powered cruise missiles in the last few years [0,1]. It's a political question of tradeoffs, of how much you value technological progress on a particular front.
America hasn't blown up any atmospheric nuclear reactors in this century. America is also unlikely to learn how to build aerospace nuclear reactors in this century.
[0] https://en.wikipedia.org/wiki/Nyonoksa_radiation_accident
[1] https://news.ycombinator.com/item?id=16509396 ("U.S. Has Been Watching Russia's Nuclear-Powered Cruise Missiles Crash and Burn (thedrive.com)")
Why should it? It already knows. Since last century:
https://en.wikipedia.org/wiki/Project_Pluto
In a place called 'Jackass Flats', of all things...(Giggle)
Edit: Or take the https://en.wikipedia.org/wiki/NERVA mentioned here by credit_guy: https://news.ycombinator.com/item?id=38136383
Same place, name is program :-)
Because as I’m sure you know and can see where I’m going with this, you’re already living under an enormous amount of lethal radiation, you and everyone else has been for their entire lives… its called the van allen belts.
But even if he was super-careful about ensuring that restricted information wasn't shared with the new company, I'm sure his political enemies would find ways to have him locked up if he tried that...
#seveneves
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)
“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...
Son. https://en.wikipedia.org/wiki/George_Dyson_(science_historia...
Relatives Sir George Dyson (grandfather) Freeman Dyson (father) Verena Huber-Dyson (mother)[1] Esther Dyson (sister)
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] https://en.wikipedia.org/wiki/Interplanetary_spaceflight#Cyc...
[3] https://en.wikipedia.org/wiki/Exploration_of_Jupiter#Human_e...
A unique property of nuclear pulse propulsion is that the engineering gets easier the more massive the spacecraft. 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.
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.
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.
Not really, each one would be 6 inches in diameter and weight over 300lbs.
RIP New Caird
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.
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...
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.
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...
> 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.
we put humans on a moon, and we've put robots on another planet.
>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.
I suspect at least ten government agencies from various nations all have him/his assets under 24/7 surveillance just to make sure he doesn't do something at least this unwise.
There are in fact a lot of countries that would be thrilled to give Elon fissile material in exchange for investment.
https://en.wikipedia.org/wiki/List_of_countries_by_uranium_r...
[1] https://en.wikipedia.org/wiki/SpaceX_Starship
[2] https://en.wikipedia.org/wiki/TNT_equivalent
[3] It can't explode all at once unless pre-mixed in perfect proportion, of course. What you'd really expect is an awfully big fireball + fire but not the same massive force all at once of a nuclear detonation.
[4] Or 50 terajoules (the ship) and .184 terajoules (TNT), which come out to the same thing, but I find gigajoules both more intuitive and more a more fun BTTF reference.
> 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.
It wouldn't even be like the effect of the planes on the WTC in 9/11, as planes use fuel continuously during flight, whereas spacecraft use almost all of it just to take off.
[0] which implicitly assumes the self-destruct still isn't working right
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 use water? Water is 1000g/L and can be stored without any real effort at all. If all you're doing is shooting it out the rear end of the rocket with as much energy as possible, it's mysterious why you would even consider liquid H2.
> Most significant for our purposes is methane as propellant. It is six times denser than liquid hydrogen, can be stored at 100K, which is compatible with liquid oxygen, and it can be produced using water and carbon dioxide. At high temperatures, it breaks down into hydrogen and carbon, turning it from a 16 g/mol molecule into a 3.25 g/mol plasma. That is how it achieves a specific impulse only mildly lower than what is achievable using liquid hydrogen. Zubrin lists its specific impulse as
>Previous calculations using hydrogen propellant revealed how volume-limited the Starship design was. There was no room for the bulky liquid hydrogen, and getting to orbit meant sacrificing the payload mass and volume advantages that the Starship is built around.
>These could be solved by using denser liquid methane as propellant for the nuclear propulsion system. The Isp will be lower, but the mass ratios become so much better that more deltaV is available overall.
If your ship has a positive electric potential of over 1.044 MeV[0], you also start getting positron-electron pairs forming on your hull.
[0] less in practice, because any electrons you're going to encounter were already moving
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.
And, yes. The idea is patently absurd. But I'm waiting on a ridiculously long compile.
https://www.projectrho.com/public_html/rocket/enginelist2.ph...
- This math is specifically about thermal propulsion; your 17 keV electron wasn't in thermodynamic equilibrium with anything, it's a different sort of problem
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.
Just steer clear of the planet Eve. It's been years and I still haven't been able to leave it.
I think all real-life actually-tested nuclear thermal rockets have used hydrogen as propellant, though use of other substances has definitely been proposed.
In deep space you don't really care about the volume of your fuel tank, so then it does make sense to use something light like hydrogen.
https://news.ycombinator.com/item?id=38086518 https://planetocracy.substack.com/p/mars-cyclers
And if we use them inside of a planet's magnetosphere, we have to think about environmental contamination too.
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 only 1 out of every 200 rockets explodes during launch... then eventually a rocket carrying nuclear waste is going to explode and spread it everywhere"
As others have pointed out: Nuclear rockets don't have the thrust ratio necessary for take off, so presumably they'd be assembled and used in space. My question is: What level of risk does launching nuclear rocket parts/fuel into space pose?
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.
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.
So its safe to fly a new reactor into a stable orbit, if something bad happens you'll scatter some uranium but that's just toxic heavy metal bad, not radiation hazard bad. Just make sure the orbit is high enough to be stable, not like Kosmos 1402.
Or just used as an upper stage! See https://en.wikipedia.org/wiki/Saturn_C-5N, for instance, and a bunch of even more ridiculous Soviet designs.
Amazingly, this project (nuclear third stage for Saturn V) was actually under serious development. This to be used on a rocket stack which had had two major incidents in 13 launches; it really was a very different safety culture back then.
But even without a crash can, it's of less concern to public health than the radioisotopes in coal.
And chernobyl was a giant fission reactor.
What's your point?
Space is really hostile.
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 should not squander our uranium for power generation when we can use solar for that. It's like not using oil or gasoline for heating.. we need it for transportation.
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...