Space

From the little I've followed on this topic, any kind of kinetic space junk cleanup (meaning physically touching or capturing the junk) is going to be very very limited in effectiveness for the majority of the junk. For really large things, like an entire satellite still intact, it can make sense, but these are very few of the space junk pieces in orbit today.

The problem is two fold: Space is huge and the junk is very far apart. There are hundreds of thousands of pieces of space junk (mostly small).

The most promising approach to address the majority of the junk is a "directed energy" method. This would be using something like a laser to slightly push space junk into lower orbits where the thin air will slow it over time and it would fall back to Earth.