Already patent pending...
Had a thought about this (ahem) several years ago...
Internal iron core electromagnet (14kg) with a field strength capable of attracting ferric materials to it or attracting the satellite to the material. Surrounding this core would be approximately 9m to 12m of expanded gel material in flexible polymer sphere. A boom (think long PVC pipe) would house retractable solar panels for recharging the battery for the magnet, as well as motor module for acceleration/re-entry, through a conduit in the bag.
When deployed (preferably in waves of single satellites against fields of debris), the gel is activated by bi-chemical release into the sphere. The chemicals expand, mix, and form the gel.
The gel is spongy enough to absorb the impact of materials as they encounter the node. Either the gel will completely encapsulate the material, or slow it down to the point of rapid degradation of its orbit (think ballistics jelly and bullets). The ferric core will also help bring it to a slower speed (and quicker re-entry). Larger objects encountered that make it through the gel and contact the core would merely increase the mass of the electromagnet, increasing its field strength. The key is the simplicity of the onboard systems; it is expected that the ferric core will take great shocks from impacts that reach it; it is just a mass of iron core with wires wrapped around it. All electronics are internal to the core, and shielded; as they are in a relatively stable field (ie. not moving through magnetic flux lines), the logic should not be affected.
This device would be relatively inexpensive (compared to most any other artificial satellite), easily mass produced, able to collect the very large percentage of material that is *not* magnetic, and light to launch (compared to the several ton comms gear). The design is also completely scalable to larger versions for either large debris fields or larger targets.
Estimated life span would be 3 months, at which time it would be expected that enough debris was collected by that one, and allow it to burn up or collect for processing at a rendevous orbit... getting a few of these together in one space with the magnets on, and you have a self collecting depot. :)
Just think of the "junk" from other countries picked up and collected for the next manned collection mission... How much should I charge the NSA for that? :)