Spin polarisation

Gerrit Bruhaug and Ayden Kish may have solved our fusion-rocket problem: The Benefits of Spin Polarization for Fusion Propulsion. h/t Winchell Chung.

The issue we've had around here is the neutron problem. If you want to ignite the fuel (and if you want a cheap fuel), you want Deuterium-Tritium. That sprays neutrons all over the place. There's also "aneutronic" Helium-3 but it is expensive, and doesn't ignite so well. And in practice that process sprays some neutrons too. (BTW, ignore the LOLworthy bit about neutrons being "ionizing". Although, once they've made an isotope unstable... that can be ionising.)

On February I got wind of directing the neutrons. There's a term for that: spin-polarisation. Bruhaug and Kish have crunched some numbers. It cuts down on the anti-neutron shield - and that's not all! The exhaust velocity is higher, so there's your I_SP - awesome for getting out to the Jupiter-and-beyond range.

Spin-polarisation even lowers ignition requirements. The authors point out this brings Helium-3 back into play. Better, I think, it may allow to ignite the fuel from an orbiting solar-energy concentrator, rather than using some chemical or nuclear detonator which we then have to keep from detonating (or getting robbed). Best done at the Venus orbit I think.

I've flagged that tritium has a half-life so is storable only over a timescale of months (although, if your storage facility is good enough - possible if you're not in actual transit - you do get to save the He-3). Chung flags that nucleons depolarise, also. Especially if there's a magnetic field from outside. That's going to be an issue in Near-Earth Orbit, and near Jupiter - so, the space station to launch these ships will need to be in some Libration halo, Mars, Callisto, SVL2 maybe.

A KICK OUT THE DOOR 9/4: Neutrons excepted, the results of fusion should be a plasma - rapidly moving. Is it worth our while for VASIMR to run out the ions that bit faster? Asking for Ebrahimi.