how to restart a fusion reactor in space?

[jedidia]

Let's say we have a fusion-powered spacecraft (not too unrealistic given one to one and a half centuries of time), and the thing goes out on the way for whatever reason.

What would be feasible possibilities for a backup device to provide enough power to restart it?

 

[Kaito]

Let's say we have a fusion-powered spacecraft (not too unrealistic given one to one and a half centuries of time), and the thing goes out on the way for whatever reason.

What would be feasible possibilities for a backup device to provide enough power to restart it?

Well, if it went out, I'd say you'd be SCREWED
as to restart it...maybe a backup nuke to get it going again?

 

[the.punk]

To start the fusion you need a lot of heat!!!
Maybe millions of degrees. You must the atoms so near that the chain reaktion starts. and you also need a lot of pressure.
Because in normal temperaturs the hydrogen atoms are stable and they don't want to fuse.

 

[Sky Captain]

An ordinary backup fission reactor should be enough to provide necessary electrical power to start up main fusion reactor. Basically you need a lot of electricity to power confinement magnets and heat up the plasma to get fusion process going.

 

[the.punk]

An ordinary backup fission reactor should be enough to provide necessary electrical power to start up main fusion reactor. Basically you need a lot of electricity to power confinement magnets and heat up the plasma to get fusion process going.

Yes. That it is. And the heat you need is immense. Because it must be chain reaktion.

 

[Kozak]

Yes. That it is. And the heat you need is immense. Because it must be chain reaction.

No link.

What would be feasible possibilities for a backup device to provide enough power to restart it?

You'll anyways not have the fusion reactor running all the way - there is minimal power scale for it to be in energy surplus. So, a fission reactor will be the main option.

 

[the.punk]

But it is shut down you need a lot of energie to start the reaktion again.
I mean when it is cold. You're right, there is maybe an minimum mode but I mean when it is absolutly shut down.

 

[insane_alien]

it's reaction not reaktion.

and just need strong magnetic fields.

i imagine there would be a large ultracapacitor bank holding sufficient energy to kickstart the reactor(that would have been charged while the reactor was running).

fuelcells, solar panels all these can provide the necessary energy although it needs to be stored so you can release it quicker than you produce it.

as for the heat necessary for the reaction, its not really that much to start it. what you need is temperature. extremely high temperature doess not always mean extremely high heat load. you'll only have maybe a milligram of fuel to heat up.

most of the energy will be deposited in the magnetic confienment system.

 

[jedidia]

An ordinary backup fission reactor should be enough to provide necessary electrical power to start up main fusion reactor.

That's the conclusion I had reached, but it seems such an unefficient setup, mass-wise.

i imagine there would be a large ultracapacitor bank holding sufficient energy to kickstart the reactor(that would have been charged while the reactor was running).

I played with the thought, but I just couldn't imagine a capable enough capacitor, that can a) store enough power and b) release it in a sufficiently short time. However, I know next to nothing about how a capacitor actually works (respectively what kinds of capacitors there are), did you have anything specific in mind?

Another thing that crossed my mind would have been kind of a very effective "combustion engine" that could produce the required energy by burning hydrogen. That would mean that a ship had to carry a certain supply of oxygen for a reactor restart, and I have no idea if the needed energy could actually be produced that way...

 

[TSPenguin]

There are amazing new technologies on the rise for capacitors. There is a good chance that within a few decades all our consumer batteries will actualy be capacitors that hold their charge (nearly) indefenitely, can be charged within seconds and weigh next to nothing. Aerogel is the right way so far, and when we have working mobile fusion reactors, these kind of capacitors should be readily available.

 

[insane_alien]

well, any ship large enough to actually carry a fusion reactor(ITER is going to be several thousand tonnes) will have enough space to carry a capacitor bank capable of storing 50GJ of energy.

not to mention be the time we get to the stage of putting fusion reactors in a spaceship then there will have been tremendous advances in both fusion technology and energy storage.

as for capacitors storing sufficient energy and releasing it quick enough, well they already can and do. its how most fusion reactors are started due to the extreme load that would be place on the power supply if it was simply hooked up to the mains. when you knock out a few square miles of power grid people get upset.

 

[the.punk]

it's reaction not reaktion.

Thanks.

i imagine there would be a large ultracapacitor bank holding sufficient energy to kickstart the reactor(that would have been charged while the reactor was running).

Yes. That is a good idea. But I don't know how we can do this.

fuelcells, solar panels all these can provide the necessary energy although it needs to be stored so you can release it quicker than you produce it.

I think solar panels cannot provide such energie for a start when you out to maybe the outher planets or even interstellar travel. But we could use fission or small fusion backup reactor.

as for the heat necessary for the reaction, its not really that much to start it. what you need is temperature. extremely high temperature doess not always mean extremely high heat load. you'll only have maybe a milligram of fuel to heat up.

Yes. You need temperatur because the hydrogen atoms must come very near so that they can fuse.

 

[insane_alien]

i explained how you can use solar panels for it.

sure, they can't provide the 50 odd GW burst needed but they can charge a capacitor bank at 100kW for a few days and then the capacitors start the reaction. although on a ship large enough to actually hold a functioning fusion reactor you'll likely have more than 100kW available because it will be massive. it's much more likely that the reactor would be left in an idle mode especially if they are out by the outerplanets. it would be more efficient than shutting it down and reverting to alternate energy sources and you're going to need quite a bit of power to sustain the rest of the ship which is going to be massive.

we're not talking shuttle or even ISS sized craft here. you're going to be looking at something the size of a large aircraft carrier. when you need thrust all you'd do is throttle up the reactor and when you don't need to move you just leave it on idel and it produces all your power needs which likely will be quite high compared to today.

 

[the.punk]

Yes. Your right. The ship would be a bid ship. And I also think that wouldn't ahve only on reactor. Maybe some smaller auxiliaries reactors that are fission based or even little fusion based reactors for emergencys.
And than the big main reactor.

---------- Post added at 12:36 PM ---------- Previous post was at 12:35 PM ----------

Maybe the size of Vespucci D.

 

[insane_alien]

no, one big reactor would be more efficient. there would likely be fuelcells as emergency backups (and the oxygen can be recovered once the fusion reactor is back online). you already have masses of weight from a fusion reactor, you don'twant to have to double the size of the things to put a messy fission reactor in. fusion reactors don't do so well when they're small. they can't make enough energy to power themselves nevermind something else. they only really excell when they're big. even theoretically.

 

[RisingFury]

There isn't enough solar power between stars to make use of solar cells. Power produced by them will be next to nothing.


There's only one mission to Jupiter planned with solar cells that I know of, instead of a RTG... and that's because solar cells are finally efficient enough to produce enough power. Still, the surface area will be massive.

But even if you make 100% efficient solar cells with several km^2 surface area and put them between stars, the power output will be close to 0.

 

[the.punk]

There isn't enough solar power between stars to make use of solar cells. Power produced by them will be next to nothing.


There's only one mission to Jupiter planned with solar cells that I know of, instead of a RTG... and that's because solar cells are finally efficient enough to produce enough power. Still, the surface area will be massive.

But even if you make 100% efficient solar cells with several km^2 surface area and put them between stars, the power output will be close to 0.

That I mean.

 

[insane_alien]

yes, but solar cells are not the only solution. fuel cells are the most likely.

 

[the.punk]

When you say fusion reactor are only good when they are big than I think it would be good to have a fission reactor as backup to star the main fusion.


Ah...And what do you mean with "fuelcell" ?

 

[Mindblast]

If you're going to use a Tokamak design you will definitely need some kind of capacitor array as Tokamaks can only be operated in a pulsed way (5 - 10 Minutes iirc). So you need to restart the thing constantly. There is also research being done on Stellarators that can run continuously but they are a more complicated design compared to Tokamaks.
And then there is the Polywell design conceived by Robert W. Bussard and his team that if it works (which is not at all sure yet) could get us fusion reactors much more compact than Tokamaks could ever be and might even open up possibilities for using reactions with very low neutron generation (i.e. H-Boron).