Day: February 10, 2008

Mining the Gas Giants

Helium-3 is often seen as a profitable material to “mine” the Lunar regolith for – it’s a potential fusion fuel, but currently a fuel without a market. No current reactors in the works (i.e. ITER) are big enough (!) to burn the stuff, and no 2nd and 3rd Generation Fusion reactors are likely before c.2100, at current pace of development.

BUT let’s assume there was a market – He-3 burns quite well in IEC reactors only a bit bigger than D-T burning IECs, so once Doc Bussard’s Whiffle-Ball is demonstrated a market might appear over-night (5-10 years.) If so, how much is on the Moon? According to this reference there’s 2.5 million tons embedded in the upper layer of Lunar regolith (typically 4-12 metres deep, depending on locale.) Sounds like plenty, but you have to process a lot of moon-dust to get at it – there’s 38 million sq. kilometres of Moon and so just ~ 66 kg He-3 per sq.km, some ~ 8 million cubic metres of regolith to process for just that.

How much is 66 kg of He-3 worth then? Fusing He-3 generates ~ 57 million kW.hr of energy of which about 60-80% can be electricity with the right converters. Call it ~ 60% and 66 kg of He-3 is 2.266 billion kW.hr of power – about $113 million @ $0.05/kW.hr. Using current technology this would be unprofitable, but a few things could be done to improve the economics. For example, Jerome Pearson’s Lunar Beanstalk would eliminate the need for rockets to launch material to Earth, and could deliver ~ 200kg per trip to the Earth-Moon L1 point to be retrieved by low-thrust inter-orbital vehicles for return to LEO. Mining would have to be fully automated, of course, and processing millions of cubic metres of soil per year would be required, but this might not be onerous.

Eventually the supply will run-out. Globally we currently use ~ 15 TW of power, with growth steadily heading up, even with efficiency gains. If everyone used energy like an American or Australian (11 kW/capita) then currently 74 TW would be needed. That’s 74 billion kW.hr per hour, some 649 trillion per year. Some 286,000 tons of He-3 per year. The Moon would be exhausted in a decade. That’s a rather unlikely rate of use, but it does show the Moon’s resource potential is very limited. Within ~ 100 years we would be looking further afield. So where next?

Bryan Palaszewski’s 2006 study for NASA (available via the Glenn Technical Reports Server) looks at the options for mining the Gas Giants. For Uranus and Neptune, which have quieter atmospheres, should be accessible to balloon-borne factories, like the Daedalus report advocates – Bryan actually uses that design for analysis. On Jupiter and Saturn, with greater turbulence, actual aircraft will be needed. What does seem problematic is getting the stuff into orbit as that requires sustained hypersonic flight by the vehicles, something yet to be achieved reliably.

All that could change, at least on Earth, as Alan Bond’s Reaction Engines Limited advocates a hybrid SSTO called SKYLON, and a non-orbital version for hypersonic passenger flight. If SKYLON were developed successfully an immense amount of hypersonic experience would be gained, ultimately allowing mining of the Gas Giants. SKYLON would also enable other power-sources, like SPS, so it’s worth pursuing by itself.

Method of Reaching Extreme Altitudes…

Robert Hutchings Goddard is the father of modern applied rocketry, Konstantin Tsiolkovsky the father of rocket theory. A certain paper of Goddard’s published in 1919 (Summarised in Scientific American in 1920) looked at what kind of rockets were needed to reach altitudes above the atmosphere – and to even strike the Moon with a ton of Victor flash powder…

Extreme Altitudes

…which was mocked by the physics-idiots of the time, but noticed by anyone keen on extraterrestrial journeys. Goddard himself became something of a recluse, working almost alone on liquid-propelled rockets. His best reached 7,500 feet, far short of the immense spans he’d proposed to cross. But his basic ideas were taken up by the Germans, culminating in the V-2 bombardment of Britain and Belgium in 1943.

Did anyone else take notice? The writers of Buck Rogers did – when Buck encounters the Martians, he calls on a certain professor Stoddard to help propel him to Mars. At the same time Edward Elmer Smith, Ph.D, (“Doc Smith” to SF fans) believed so much in Goddard’s efforts that he wrote this little piece in his Spacehounds of IPC

“That’s fine—you can get the idea all x, with that to go on. Let’s sit down here on this girder. Roeser didn’t do it all, by any means, even though he got credit for it—he merely helped the Martians do it. The whole thing started, of course, when Goddard shot his first rocket to the moon, and was intensified when Roeser so perfected his short waves that signals were exchanged with Mars—signals that neither side could make any sense out of. Goddard’s pupils and followers made bigger and better rockets, and finally got one that could land safely upon Mars. Roeser, who was a mighty keen bird, was one of the first voyagers, and he didn’t come back—he stayed there, living in a space-suit for three or four years, and got a brand-new education. Martian science always was hot, you know, but they were impractical. They were desperately hard up for water and air, and while they had a lot of wonderful ideas and theories, they couldn’t overcome the practical technical difficulties in the way of making their ideas work. Now putting other peoples’ ideas to work was Roeser’s long suit—don’t think that I’m belittling Roeser at all, either, for he was a brave and far-sighted man, was no mean scientist, and was certainly one of the best organizers and synchronizers the world has ever known—and since Martian and Tellurian science complemented each other, so that one filled in the gaps of the other, it wasn’t long until fleets of space-freighters were bringing in air and water from Venus, which had more of both than she needed or wanted.

“Having done all he could for the Martians and having learned most of the stuff he wanted to know, Roeser came back to Tellus and organized Interplanetary, with scientists and engineers on all three planets, and set to work to improve the whole system, for the vessels they used then were dangerous—regular mankillers, in fact. At about this same time Roeser and the Interplanetary Corporation had a big part in the unification of the world into one nation, so that wars could no longer interfere with progress.”

…thus Doc Smith had high hopes for Goddard’s efforts in c.1930. The great pity is that Goddard apparently never knew how many “fans” and well-wishers he had. Perhaps, in an alternative world, if Goddard had been more of a self-promoter, more open about his works, then the world would be a very different place today, indeed. Albeit, without “Doc Smith”-style Martians and Roeser Rays.