A spaceport in orbit
Ken Tapping, June 12, 2013
Anyone who has fought their way up hundreds of stairs to get to the top of a mediaeval building will have a full appreciation of gravity. Going upwards involves working against it, and that takes a lot of energy. This has been the main problem in our exploration of space. Everything we put into space has to be lifted from the surface of the Earth, which takes large amounts of fuel, costs a lot of money, and subjects the astronauts and spacecraft to a bruising experience. Most of the fuel for any ground-launched space mission, to anywhere in the Solar System, is burned in the first fifteen minutes.
Part of the solution is to start our missions from Earth orbit. Ever since our first dreams of exploring space, there has been the idea of having a space station orbiting the Earth, which would be the starting-off point for space missions to explore the Solar System and beyond. The spacecraft would be built in orbit and launched from orbit.
One approach is to obtain materials and possibly components from the Moon. The Sun shines unimpeded on the Moon’s surface, so there is a reliable energy supply, and the absence of an atmosphere and weak gravity means it will be easier to move materials from there to the construction site. We could of course build our spacecraft on the lunar surface, but for most space missions, fighting the Moon’s gravity would be the mission’s biggest task, so it would be nicer to avoid that problem too, and launch from Earth orbit.
Another possibility being discussed for obtaining raw materials is that of mining the asteroids. There are many millions of these in the Solar System, mostly orbiting between Mars and Jupiter. These range in size from dust to bodies up to a thousand kilometres in diameter. Some are mostly ice, others rock, and some of them contain useful metals.
Robot miners could work on them, sending us the result. Of course sending lumps of metal weighing hundreds or thousands of tonnes in our direction poses certain safety issues we will need to address. Another possibility is to divert suitable asteroids towards Earth, parking them in Earth orbit. This also poses safety issues, even bigger ones.
Mining makes a lot of tailings and dust. On the Moon there is no atmosphere to blow it around, and enough gravity to pull it down. The weak gravity of any asteroid small enough for us to move to Earth orbit will not be enough to hold down dust and mining debris, so it will end up orbiting the Earth as a new form of space junk, posing navigation hazards to astronauts and spacecraft.
This does not mean that obtaining raw materials from the Moon and the asteroids is something we should not do, or that manufacturing components for our spacecraft on the Moon or in Earth orbit is impractical. These are all challenges we can meet.
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