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Re^12: "Practices and Principles" to death

by tilly (Archbishop)
on Mar 05, 2008 at 22:22 UTC ( #672297=note: print w/replies, xml ) Need Help??

in reply to Re^11: "Practices and Principles" to death
in thread "Practices and Principles" to death

Re-read it. The Hohmann Transfer Orbit is a 2 shot circular to circular transfer. First you turn it elliptical, then you turn the elliptical circular. I discussed only doing the first shot, which would turn the circular orbit into an elliptical one. I was therefore discussing the idea of what it takes to turn a circular orbit into an elliptical one that grazes the atmosphere.

About matching speeds. With work you can match orbits very precisely. But the point I was making is that if you have, say, a 10 cm piece of metal in orbit next to your spacecraft, it is easier to take that piece of metal and store it in your spacecraft for later disposal than to suddenly knock it out of orbit.

However doing this means taking a spacecraft and maneuvering it to match the junk. Every piece of junk you try to maneuver to takes a lot of energy, energy means fuel, and fuel means cost. This is no big deal if you're going to the ISS or servicing a satellite because that docking maneuver is the whole point of the trip. However you generally don't have resources to do a whole lot of those maneuvers. And it is truly cost prohibitive to dock individually with every dropped screw that is up there.

About low thrust. First, that is relatively low thrust. But you still need just as much energy in the end. Unless you use the chaotic nature of orbit to wind up getting repeated net gravity boosts from the Moon and the Sun to move. This would potentially let you do your rendezvous much more cheaper per rendezvous, but at a cost of only picking up one piece of junk every year or two. Amortized over several decades, this might be reasonably cost effective. But to make a dent in the existing problem you would need a flotilla of these garbage satellites, and you'd need a long time. There remains the question of who would design and build these satellites, or what their incentive would be.

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