Antiproton/Uranium microfission

Winchell Chung today hath diggen up ICAN II. This was a fusion torchship idea but the idea's core is fission.

As we recall from Bikini Atoll, fusion demands high energy even to get started - which gets worse if we don't want neutrons and haven't sussed out spin. Edward Teller solved that little problem by blowing up a fission bomb to get the fusion fusin'. Teller was making bombs though, not anything good. People trying to get around the AEC looked into chemical explosives but the chemistry was theoretical in 2009 and here we are now.

Suppose where we WILL be is in space, trying to be constructive not destructive. [UPDATE 7/27] Although I am not here considering lowering NuScale power-generation; we're doing Orion or NERVA here. - or sparking a larger reaction...

Say we move the ship to ELL2, aiming to spark some fusion there. The problem with that is the same Every Gram Counts problem we've been enduring since Tsiolkovsky launched his first firework. Chemical reagents for the big bang, assuming it's not total unobtainium, will be, like, heavy, man. Looking to the nucular realm the Uranium-235 also isn't great: 52 kilos to criticality. U-233 "thorium" is lighter: 233/235 as much per atom but more to the point, only 15 kg critical. UPDATE 2/28: Curium-247 is half even that.

Over the 1990s, came a proposal to cut the critical mass. Ship less uranium with... an antiproton (pdf). Yeah, antimatter is expensive to make. But we might pay that down on launch savings. Antimatter itself can be scooped from cosmic radiation in the high Van Allen.

I note that as launch costs per kilo have plummetted, I haven't found much interest in the microfission notions (hate to say, "meme"). If we were ever to fire a torchship from Earth orbit - much less from Mars or Luna - we may as well send up the heavy metals, for it. We might even store up solar energy in some massive orbiting capacitor and light the fusion candle from that. No need for nukes, there; just silicon panels. UPDATE 2/6: Although given Lawson this would likely be a tritium drive which has her own problemata.

I think, though, may come a time and place where the uranium gains in expense again. As to who needs to carry around their own tinder for a fusion reaction: that's for de-celeration, to a hitherto unsettled planet or 'stroid, I do think.

Then and there, it may come cheaper just to make an antiproton or three, saving precious metal. That manufacture is done as close to the sun as you can get, where energy is cheapest. Classically authors have given over Mercury for this but I'm thinking Venus Hilda.