Make a catcher for space junk, whether a bag of of ice, a ball of pumice, or a big chunk of memory foam. Make another one. Put the pair in orbit, with a cable between them, and start them spinning about their common center.
The gist of this idea is that the position of the bola balls can be varied by simply winding the cable in and out. Obviously, the distance from center will be changed, but so will the speed of rotation.
If, say, a piece of space junk will be passing 400 meters from center of rotation, the weights should be cranked in to 800 meters apart. In addition, the pull-in will affect the rotation speed and, through careful timing, the angular position of the weights, and allow for one weight/ball to intercept the junk.
The two balls can then cover all the area within the sweep of the cable, with no expenditure of reaction mass. The only cost is the solar power to run the winder motor.
This assumes some good tracking of the space debris, and some planning time for each intercept. And, one hopes, a way to predict where the impact of the debris will move the space bolas for the next intercept.
The bola pair can be moved about by a rocket motor in the cable's center. Or by carefully dribbling mass from the balls at the right time ... which will create more space debris ...-- baconbrain, Apr 21 2013 //The only cost is the solar power to run the winder motor.//
It seems to me that you could use a regenerative approach here. Pulling them together will take power because the motor will be pulling against the centripugal force of the rotating balls, but when you release them further apart, you can use the motor as a generator and convert the energy back to electricity from angular momentum.
So the solar panels just need to top up the energy lost to heat in the motor and the control electronics.-- Wrongfellow, Apr 21 2013 If the bolas are roughly in the same orbit as the approaching debris, then you might be able to do a real sneaky timing trick.
You seem to have described the "catcher" equipment as also being the bola masses, but here I'm saying they should be separate, and can slide along the cable between the bola masses. Two such catchers will make this notion work much easier than one.
You compute the closing velocity of the debris, and you set your bola masses just far enough so that the place where the cable is, where the debris is about to intersect, is moving at just about the same velocity. Also, you get one of the catcher gadgets to move to the intersection point (and the other moves the other way, toward the other bola mass, to keep things balanced).
So, when the debris arrives, the catcher gadget snaps shut and snags it. Now you can add the mass of the debris to one or both of the bola-masses, and wait for more debris to arrive.-- Vernon, Apr 21 2013 Bun just for the novelty.-- AusCan531, Apr 21 2013 random, halfbakery