sgsguru | A Really Big Sponge (Reply)

Wednesday night, there was a meeting/book signing with a bunch of SF authors at Reitier's Books in downtown DC. Much fun.

Somebody brought up the issue of space debris. We've left a lot of junk in orbit, and it can cause real trouble if it hits something. Worst case is if Satellite A hits Discarded Booster B, creating a cloud of debris that hits Satellites C-K, creating more debris ... Result, no more satellites. The problems are:

Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.
We don't know what all is out there. We keep track of the big stuff, but little things like paint chips are problems, too.

Some numbers -- at low earth orbit velocity, a kilogram of mass has about 49 MJ of kinetic energy. That's a bit more than ten times the energy of a kilogram of TNT. Those paint chips have more energy than ten times their mass of TNT.

How to get rid of it? One person suggested a big net (presumably after reading Varley's Gotta Sing, Gotta Dance). That would work for big stuff; stuff that we can track and send a little "tugboat" satellite after (let the ion engine guys have some fun!). But that leaves the small stuff -- and there's a lot more small stuff than big stuff.

So we use a sponge.

Seriously. Send a tank of monomer and a tank of gas into orbit and blow up a big cloud of open-cell foam. We'd want an elliptical orbit with a low perigee so the orbit will decay fairly quickly, and figure the rest of the orbital parameters to sweep an appropriate area. How big a sponge? I'd think there'd be no particular problem getting one that's miles across.

When a paint chip or whatever hits our sponge, it'll get pushed closer to the sponge's orbit. Hitting one foam bubble won't do much, but going through a big chunk of sponge (many bubbles) should transfer quite a bit of momentum. After a time, the whole thing will re-enter the atmosphere.

Low energy collisions are even easier. The chip just sticks to the foam.

Side effect -- it should be really pretty from the ground.