Low Probability Events

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.