Monday, April 20, 2009

Solar power... in SPAAAACE!

Recently there's been some discussion of space-based solar power. Basically you whack a bunch of solar panels up there with a big mylar sheet to concentrate the light, then you beam the power back to Earth. Sounds cool, yeah? Well...

Apart from the obvious cost difficulties (it's about $10,000/kg to get something into space), this faces many practical difficulties, too. To be able to beam back to a single station, the satellite would have to be in geosynchronous orbit - about 36,000km up. Getting it up there takes a lot more energy than to low earth orbit where we put the space station and the like. At first that looks like just a cost issue, but it underpins many of the technical issues I outline below.

The first issue is that if you have a 1km2 mylar sheet, the solar wind (the stream of particles it blasts into space along with its heat) and the very light it's designed to capture will blow the satellite out of position over time. The solar wind is such that people have actually planned spacecraft which use it to travel around the solar system. You can have manouvering rockets on board to counter this, but that uses up fuel - and you have to get the fuel up there, too, a few times over the several decades lifetime of the satellite.

Secondly, the Earth has a magnetosphere, that is its magnetic field shields it somewhat from high-energy particles from the Sun. Craft high up don't have that protection (which is one of the problems with long-range spaceflight, both manned and unmanned) and so would need to be heavily shielded (increasing the non-productive weight to put up there), or else would occasionally get blasted and destroyed. Repairs would be difficult to say the least.

Thirdly, beaming the energy back to Earth is difficult. As anyone who's ever had an electric torch knows, light spreads out. You can tighten the beam somewhat, but still over thousands of kilometres it'll spread out. So either your receiving station is really huge or else you lose a good chunk of the energy; if you're losing the energy anyway, why bother putting the station in space, the whole purpose of which was to get more energy than you could on the ground?

Fourthly, the building of the thing would require several launches, and assembly in space. The International Space Station was planned for 12 years before the first modules were launched into orbit, and has been in construction for 10 years, still not finished - and it's only in Low Earth Orbit, not the geosynchronous orbit this thing would require.

Fifthly, geosynchronous orbit is already pretty crowded. Basically it's the plum spot for communications and spy satellites. It's one thing to whack another table-sized sat up there, it's another to put a 1km2 satellite up there. Or hundreds of them, as we'd need. 

The first and fifth points combine to make a maintenance nightmare. At orbital velocities of kilometres per second, the tiniest speck of dust becomes deadlier than a bullet. It whacks into the mylar sheet and makes a hole. Then the solar wind pulls on the sheet and tears that little hole into a big long rip. Much less or no power is produced by the thing. Then your power satellite is pushed more on one side than the other, and starts spinning.

You better have a lot of spare fuel on board, and a crew ready to head up there and repair it. You can't just chuck the old mylar sheet away, that's 1km2 of rubbish floating around in orbit at several kilometres per second, other satellite owners - especially those owning other power satellites - won't appreciate that kind of litter. So you have to roll it up. Fancy rolling up a 1km2 sheet? Do you know how to? Nope, neither does NASA or anyone else, no-one's had to do it before.

So even if the launches were completely free, there are a lot of technical obstacles in the way of this kind of satellite.

Seems a lot easier to build the thing on the ground. I mean, does the Earth really lack big empty spaces for us to build power stations in? Not Australia, that's for bloody sure.
And so in conclusion, here we see another example of the modern religion of Science! That's different to plain old science, which is just the study of things to figure out how they work; the believer in Science! has blind faith that it'll save us like a Messiah. "They'll figure something out," the believer says, meaning "the Lord will provide." By which reasoning I should go ahead and leap off a cliff because I'll figure out how to fly before I hit the bottom. Maybe - but probably not. 
It's really a lot easier to go with what we definitely know works, and works well: reduce, reuse, recycle, in that order, combined with a mix of geothermal, hydroelectric, solar photovoltaic, solar thermal, tidal and wind, railways,   walkable towns and cities, eat less meat and more plants, and don't buy so much junk.
Science is needed for all that, Science! isn't. 

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