Disposable Debris Collector Sat.

Consider a small satellite comprised of essenitally a hollow cylindrical body, closed on one end, and a simple thrust vectoring system for mobility. The cylinder is filled with an increasingly dense gradient of what amounts to clay or some sort of self-healing ballistic gel. The densest material would lie on the closed end, with the less dense, self healing material near the open end. After being released into an Earth orbit of your choosing, the satellite uses a combination of GPS and radio signals broadcast from ground stations to manouver into an orbit in front of a piece of orbital junk at a relatively similar, though slower velocity. Result, space junk enters open end of sat. at a reasonable velocity, penetrates into the ballistic gel, and is trapped. The ballistic gel heals over the wound caused by capturing the piece of debris, and the satellite moves on to next piece of junk.

NASA tracks anything larger than a softball, so it is reasonable to consider such a satellite remaining in orbit for some time to catching various pieces of orbital debris. If properly constructed (i.e. few heavy metals and other really hard to burn off materials), the sat. could simply be instructed to re-enter the atmosphere and safely and completely burn up over the ocean, along with it's payload of junk.

If you are really anal about tracking position of the sat. vs. oncoming junk you could give the sat. other devices such as LIDAR or some form of radar and computer aided thrust control to help posisition it properly, as well as make it's fuel supply refillable to facilitate longer orbital periods.