http://www.ft.com/cms/s/0/0644ee74-2cef ... z3BarrLjK4Lockheed Martin seeks to clean up space junk
The title says enough to get the gist without infringing on the copyright of an article that says a lot of nothing. Lockheed doesn't have a plan to rid us of space junk, but they did get a big chunk of change to track the junk. But only some junk. The easy junk. The junk the size of a grapefruit.
Which is good. Knowing where it is helps us avoid running into it.
But, they have no plan to rid us of it.
It doesn't take a grapefruit-sized piece of space junk to ruin a mission's day.
Consider: An astronaut on the space station takes a shit. That turd is then ejected into space. It retains the same orbital velocity (algebraically summed with the ejection velocity of a few feet per second) as the space station. And there it sits (relatively), just waiting for a passing vessel to run into it. Thus ends that vessel.
Look at a map of the space junk they can actually track ...
And multiply those dots by about 100 and you have a better picture of the real existing hazard.
Okay, but as of now it is still not really major hazard. It looks dire but the odds of running into something substantial are still pretty slim (though it does happen).
But we're only 50 or so years into this. What happens in a 100 more years? It WILL eventually be a big concern.
We need to
1) De-orbit what we orbit (if you orbit a pound you must de-orbit a pound).
2) Don't create debris; de-orbit your shit (literally and figuratively).
3) De-orbit the existing debris (and that is the tough part).
The problem is that the minimum energy required to de-orbit a pound of junk equals the energy expended in orbiting that pound of junk from the top of the atmosphere to wherever it is. The [relative] velocity must be reduced such that its orbit falls below the wisp zone (or, I suppose, increased such that it exits the system altogether).
Here's one plan I've seen, loosely described:
Consider a orbiting sheet of Kevlar 10 miles on a side travelling perpendicular to the earth's plane in X orbit in a direction opposite the earth's rotation (which is head-on to most debris). A piece of debris strikes the sheet and punches through. The velocity is thus reduced by some value, lowering its orbit. But so too is the orbit of the sheet (Newton, et al). Energy must be expended to keep it in its sweeping orbit.
Where does that energy come from?
As I think about it, maybe that isn't the biggest problem. It can start the sweep at a high orbit and by the time its orbit is reduced to re-entry velocities, it is swiss cheese, it's mission done, time to launch its replacement.
But how many Kevlar sheets do we need to make a dent? Better get bigger sheets.
It is a hard problem.
Get started now.