Direct Drive Centrifugal Fusion has achieved 25 MW for parts of demonstrations in the lab. The ISP is 60 times too high for an optimal Mars mission and the thrust is 60 times too low. They have received a Limitless Space Institute grant and are working towards improving their system to become practical for rapid in solar system transits and eventually for interstellar missions.
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Aluminium is cheap?
Asteroid mining is a biggie. Find one chunk with a decent amount of gold, and it would pay for a lot. Find a chunk with tons of gold and it could pay for everything. Then there's other minerals too.
There is a different engine design for fusion- fission- hybrid propulsion, called PUFF.
Fusion is an excellent source of the sort of high energy neutrons that cause immediate, not delayed, fission in U238, the more common isotope. That's why fusion bombs have U238 casings. So you might be able to mix some U238 into the hydrogen flowing down the center, and get a boost.
The problem is that high Z atoms make the plasma dramatically more lossy, so that if even a little of it got into the fusing plasma, it would kill the fusion reaction. But that's another reason it would be good in the center bypass flow, it would make THAT flow much less transparent to the heat radiating from the plasma around the circumference.
I wonder if you could breed enough Tritium in the shielding around the reactor to make it worth trying.
I've wondered about the feasibility of beaming power to a rocket, to use directly in a traveling wave accelerator, coupling the transmitted power directly into the reaction mass without having to convert it in any way.
Sure, if you're just barely below breakeven, it wouldn't necessarily be awful. But the amount of power flowing through a decent high ISP rocket like this is so high, that if you have to supply even 10% of it with a separate power source, that's a REALLY big power source.
Deuterium, Plutonium any of the *ium family will do fine 😉
Less than break even means pulsed power but hotter plasma because of the fusion reaction. So it is basically VASIMR with self heating plasma.
Don’t underestimate the potential for tourism to bootstrap development. If Starship delivers on its promise of mass, reliability and cost, then orbital hotels will become very economic for developers and tourists on even modest incomes (once in a lifetime trip). But it doesn’t stop there. If access to LEO is that cheap, and with water on the moon, the incremental cost of reaching lunar hotels becomes negligible once you’ve set up your mining infrastructure and launched your reusable earth-lunar transports. Lunar tourism would be a different experience to LEO tourism, so those who’ve done LEO would become customers for the moon later. After that, and with the addition of these new technology drives, comes Mars, Venus cloud cities, Jupiter and Saturn moons… the opportunities are endless and enough to kick start the infrastructure for accessing these locations for other purposes.
We shouldn’t underestimate the potential speed the Earth-moon scope I described could develop. Capital is plentiful for tourism development once access to LEO is safe and falls to the levels SpaceX is targeting with Starship. It could be a proverbial gold rush similar to the development of mass tourism once jet aircraft made travel accessible for middle incomes.
It's not strictly necessary, but without it, you're just talking about Vasimir that's incidentally radioactive, and yet still needs a power source.
I still don't have a straight answer on this: is breakeven necessary for rockets?
The reason why it might not be is that essentially all you need for super high Isp is high exhaust velocity. Well, a fusion reaction can make some really fast little particles. Who cares if it took net energy to run the fusion? Just have a little fission reactor pumping out a few MW.
Or am I wrong?
This makes me wonder about this kind of propulsion versus something like beamed power propulsion. Looking at distances in AU and km/s, seems like either gives us transition to Mars in ~3 days and to the outer Aneta in ~5 years. But, this would probably let us transport larger loads at greater speeds. Does that sound right? O.o
The boiling point of Uranium is about 4000C. For Thorium it's about 4800C. That's how hot your exhaust might get. That gives you a pretty good specific impulse.
I wonder if this can pull from early research into spinning molten uranium space nuclear rocket research, in terms of systems/materials? Still, this is a neat solution.
currently? he's probably thinking the satellite industry and space exploration.
future? more exploration and the holy grail, asteroid mining, which has huuuge potential.
What actual economic activity are you referring to?
Or just add in some deuterium. Some of that might even fuse, further increasing the performance.
I'd say that's actually a fairly cool concept, if they can actually achieve breakeven.
The more actual economic activities we actually have in space, the more likely truly revolutionary technologies will start being deployed and used.
Few things sadder than seeing rocket engines that are never used for spaceships (ahem, Nerva, VASIMR?).
But this is a slow revolution. We really need to develop space launch capabilities and the space economy, to get to the point where it makes sense to just launch these new wondrous engines to their grand debut.
You can always boost thrust and decrease ISP by dumping something in the plasma exhaust. Nitrogen injection afterburner would work.