Fusion drive when?

[Exoscientist]

 Elon Musk suggested on Twitter that a much larger Starship might be able to travel to other star systems. His phrasing there is not the best since a chemical propulsion system, such as the Starship is, couldn't make such a flight. But many different proposals have been offered over the years to accomplish it. Surprisingly, one method that of using a fusion drive may be possible near term. The reason why I say it may be possible near term, within decades, is because of how rapidly the various different approaches to fusion power are progressing. Practical fusion power might be reached within a decade. For the fusion drive, it would then have to be made lightweight enough for a space propulsion system. That's not a guarantee but I think it should be doable within decades of the fusion power being reached.

 See one proposal discussed here:

 

 Robert Clark

[Terwin]

Well, depending on you definition, might have been Ikaros in May of 2010(first solar sail)

[tater]

5 hours ago, sevenperforce said:

The ever-useful Project Rho has a whole page dedicated to realistic fusion designs. The Firefly Starship is a particularly nice design. It's a true interstellar cruise spacecraft powered by Z-Pinch D-D fusion.

Z-Pinch fusion has the advantage of being useful in the near-term. We should be able to do it with only a little more theoretical work, really. You don't have to have a self-sustaining fusion reaction since you are doing it in pulses.

Not wanting to just steal his link, I reposted his reply, instead.

I have a buddy who follows fusion stuff closer than I have, I'll see what links he has and look at them at some point.

Edited March 20 by tater

[sevenperforce]

The name of it isn't coming to me at the moment, but I believe there is a version of Z-Pinch that would use a fission reactor to charge a capacitor that would then dump into a metal ring to create the collapsing magnetic field. The capacitor and metal ring would all be sacrificial and would be composed of a high amount of lithium to seed the fusion reaction. You'd have a magnetic nozzle, also powered by the fission reactor, to point the escaping plasma in the correct direction. Basically a really tiny pure fusion Orion.

Not useful for power generation on Earth because it's technically net-negative in terms of the ability to generate usable power, but very suitable for spacecraft propulsion. Good for going to Mars and back.

[darthgently]

21 minutes ago, sevenperforce said:

The name of it isn't coming to me at the moment, but I believe there is a version of Z-Pinch that would use a fission reactor to charge a capacitor that would then dump into a metal ring to create the collapsing magnetic field. The capacitor and metal ring would all be sacrificial and would be composed of a high amount of lithium to seed the fusion reaction. You'd have a magnetic nozzle, also powered by the fission reactor, to point the escaping plasma in the correct direction. Basically a really tiny pure fusion Orion.

Not useful for power generation on Earth because it's technically net-negative in terms of the ability to generate usable power, but very suitable for spacecraft propulsion. Good for going to Mars and back.

I'm picturing sweaty space sailors in the ring-capacitor magazine ramming ring-capacitor rounds into the chamber and locking the bolts closed like WWII 88 loaders now

[sevenperforce]

1 hour ago, darthgently said:

I'm picturing sweaty space sailors in the ring-capacitor magazine ramming ring-capacitor rounds into the chamber and locking the bolts closed like WWII 88 loaders now

They would be sweaty all right. The neutron radiation dose in proximity to an operating D-D fusion generator becomes lethal after approximately one fifth of a second.

[AckSed]

4 hours ago, sevenperforce said:

The name of it isn't coming to me at the moment, but I believe there is a version of Z-Pinch that would use a fission reactor to charge a capacitor that would then dump into a metal ring to create the collapsing magnetic field. The capacitor and metal ring would all be sacrificial and would be composed of a high amount of lithium to seed the fusion reaction. You'd have a magnetic nozzle, also powered by the fission reactor, to point the escaping plasma in the correct direction. Basically a really tiny pure fusion Orion.

Not useful for power generation on Earth because it's technically net-negative in terms of the ability to generate usable power, but very suitable for spacecraft propulsion. Good for going to Mars and back.

That'd be the Pulsed Magneto-Inertial Fusion: https://www.scientia.global/dr-john-slough-fuelling-the-next-generation-of-rockets-with-nuclear-fusion/

I remembered this because the D-D Fusion Magneto-Inertial Reactor is a key card in High Frontier 4 All, and a favoured way to build a rocket. (If you're a rocket nerd, you need to play this boardgame.) The Appendix helpfully listed the specs (0.1 Hz firing rate, Q of 200, 510MW_th and the person responsible, John Slough, though its version uses a "350kW solar-powered initiator".

Edited March 21 by AckSed

[Watermel00n]

I think we'd be seeing fusion drives before NTRs because the general public thinks fission bad fusion good (i mean a NERVA full of uranium fuel rods raining down doesn't sound very nice)

[farmerben]

They would probably use a chemical rocket in the atmosphere and start the nuclear reactor in space.  Uranium before fission is not too bad.

[Nuke]

my guesstimate is before fusion power. and sicne the drive wont be break even, idk what kind of power requirements we are looking at. there are some pretty low tech fusion methods. one in the uk i always forget the name of, they literally shoot at fuel cubes with a big gas gun. their research is mostly optimizing the kinetic targets. something like that with a proton-boron fuel. if you can make it go brrrrrrrrrrrrrrrrrrrrrrrt into a magnetic nozzle, you might have something and something that wouldn't require a lot of power to operate. pretty much just the superconducting magnets in the nozzel, and a few actuators/valves/igniters, etc. pretty much orion's less bombastic little brother.

17 hours ago, sevenperforce said:

The name of it isn't coming to me at the moment, but I believe there is a version of Z-Pinch that would use a fission reactor to charge a capacitor that would then dump into a metal ring to create the collapsing magnetic field. The capacitor and metal ring would all be sacrificial and would be composed of a high amount of lithium to seed the fusion reaction. You'd have a magnetic nozzle, also powered by the fission reactor, to point the escaping plasma in the correct direction. Basically a really tiny pure fusion Orion.

Not useful for power generation on Earth because it's technically net-negative in terms of the ability to generate usable power, but very suitable for spacecraft propulsion. Good for going to Mars and back.

the fission reactor is the thing that seems to be missing. both the us and soviets have flown actual reactors before, but never really saw a need to perfect the technology. i think all are still in orbit. there is kilo power which i haven't been following, but idk how far they are from a test article. with a decent power plant, nuclear-electric can really take off. fusion gets us another order of magnitude or two  of isp. still quite a ways from an interstellar mission. you can probibly sidestep the need for the reactor for a test article, but an actual mission to the outer system will likely need it.

Edited March 21 by Nuke

[StrandedonEarth]

1 hour ago, Nuke said:

i think all are still in orbit

Definitely not "all." One Soviet nuclear sat (Kosmos 954) crashed in the Canadian Arctic in 1978

[AckSed]

Helion is developing its reactor that uses field-reversed confinement with magneto-hydrodynamic pickup, and iterating on engineered prototypes with realistic expectations, which is a huge win. I think it's the closest to true fusion right now. But it and its banks of capacitors are the size of a building.

Here's the thing. A superconducting magnetic coil is an energy storage device, or SMES. It's not great on volume, it's kind of heavy, but the energy it stores and the current is amazing. Further, it's being used today, mainly in smoothing out power delivery in chip fab plants.

Hand-in-hand with most developed fusion reactors are... superconducting magnetic coils. We already have comparatively lighter and smaller coils from MIT's SPARC project. I say 'comparatively', but the test magnet is 9.6 metric tons.

Even if Helion or the other reactors coming out don't work out as a reaction drive, what if they were combined in some near-future ship? FRC reactor charges the coils, coils discharge into a Z-pinch drive.

It'd be an absolute pig, but we have a reusable heavy-lift vehicle coming online in a few years.

There'd be advantages to a charged superconducting magnetic coil as well, like maintaining an active storm shelter.

[farmerben]

I wonder what happens when a tokomak quenches all at once.  The magnetic field in the inductor cannot change instantly so the activity of the plasma must spike.

[AckSed]

29 minutes ago, farmerben said:

I wonder what happens when a tokomak quenches all at once.  The magnetic field in the inductor cannot change instantly so the activity of the plasma must spike.

The plasma will hit the sides and burn some shielding. The inductor's field would drop rapidly and be expressed as heat in the coil; it'd probably burn out. The plasma's temperature might be impossibly high, but the total thermal energy is relatively low. Part of the reason they are so damn difficult to build is that you have a very slippery snake of plasma and you're containing it with, essentially, magnetic rubber bands. Soon as you lose containment, it squirts out the gaps.

If you're thinking Z-pinch = short in coils = fault will crunch/heat tokomak plasma so much it will explode, no. You have to design this ability to compress to fusion temps/pressures in. It's also not trivial.

We are learning that we can make coils that can survive a quench with minimal violence, too. I'll repost what I posted in Science News: https://news.mit.edu/2024/tests-show-high-temperature-superconducting-magnets-fusion-ready-0304

Quote

Whyte says, “Basically we did the worst thing possible to a coil [a quench], on purpose, after we had tested all other aspects of the coil performance. And we found that most of the coil survived with no damage,” while one isolated area sustained some melting. “It’s like a few percent of the volume of the coil that got damaged.” And that led to revisions in the design that are expected to prevent such damage in the actual fusion device magnets, even under the most extreme conditions.

 

[kerbiloid]

As here is a lot of well-educated Kerbal herders with statistical charting software at hands, maybe build some timeline regression diagrams of energy available to humans, of speed available, of energy source density available, , etc.?

Then by looking at it, we would have a clear picture.

[Nuke]

6 hours ago, StrandedonEarth said:

Definitely not "all." One Soviet nuclear sat (Kosmos 954) crashed in the Canadian Arctic in 1978

forgot about that one. lol.

[Nuke]

7 hours ago, AckSed said:

Helion is developing its reactor that uses field-reversed confinement with magneto-hydrodynamic pickup, and iterating on engineered prototypes with realistic expectations, which is a huge win. I think it's the closest to true fusion right now. But it and its banks of capacitors are the size of a building.

Here's the thing. A superconducting magnetic coil is an energy storage device, or SMES. It's not great on volume, it's kind of heavy, but the energy it stores and the current is amazing. Further, it's being used today, mainly in smoothing out power delivery in chip fab plants.

Hand-in-hand with most developed fusion reactors are... superconducting magnetic coils. We already have comparatively lighter and smaller coils from MIT's SPARC project. I say 'comparatively', but the test magnet is 9.6 metric tons.

Even if Helion or the other reactors coming out don't work out as a reaction drive, what if they were combined in some near-future ship? FRC reactor charges the coils, coils discharge into a Z-pinch drive.

It'd be an absolute pig, but we have a reusable heavy-lift vehicle coming online in a few years.

There'd be advantages to a charged superconducting magnetic coil as well, like maintaining an active storm shelter.

i honestly dont think one of these startups is going to beat iter to the punch. i used to think polywells were going somewhere until they weren't (they seem to have abandoned experimental approach and are now working with computer models, quietly, and not putting out any papers). seems while fusion startups try to find funding, iter is dropping in coils, some of the biggest superconducting coils humanity has ever seen.

none of these are drives though. i figure the "asymmetrically leaky reactor" type drives will be a ways out. but those will be able to run steady state and provide power, which is what you will need for manned missions in the outer solar system and beyond. or just keep the reactor closed and use plasma thrusters (but you could do that with fission and nothing new need be developed). the technically fusion drives will come first, since you just need to funnel fusion products down the tail pipe.

[PakledHostage]

7 hours ago, AckSed said:

Helion is developing its reactor that uses field-reversed confinement with magneto-hydrodynamic pickup, and iterating on engineered prototypes with realistic expectations, which is a huge win. I think it's the closest to true fusion right now. But it and its banks of capacitors are the size of a building.

 

Helion has managed to secure itself a lot of positive press coverage, but this "not so fast!" video by ImprobableMatter is relevant:

 

[StrandedonEarth]

As far as fusion power goes, there’s also General Fusion, but I don’t think that’s easily convertible to a direct Fusion Drive…

[insert_name]

There's this which claims to be a fusion augmented electric plasma thruster

https://interestingengineering.com/space/nuclear-fusion-powered-electric-propulsion-drive

[kerbiloid]

First they need to light up B+H, unless they want to ride a neutron bomb.

[Exoscientist]

12 hours ago, kerbiloid said:

As here is a lot of well-educated Kerbal herders with statistical charting software at hands, maybe build some timeline regression diagrams of energy available to humans, of speed available, of energy source density available, , etc.?

Then by looking at it, we would have a clear picture.

 Good point. Fraser Cain did an interview with advanced space propulsion researcher Andrews Higgins about possibilities for interstellar flight.  About 14 minutes in, Higgins makes the point extrapolation of global energy usage suggests sometime in the 23rd century we might be at the energy level needed for interstellar flight. So Star Trek got it right he notes.

 

 But I actually don’t think it will be that long. I think it will be on the order of decades, at least for sending small probes, because of the fact both nuclear fusion and space solar power are rapidly approaching.

  Robert Clark