Hey, a robot could attach small disposible sun sails to the smaller stuff (the stray nut or bolt), do the dive and ion drive back for the medium stuff, and for the larger stuff, use the ion drive to move it to a stable common orbit with Other Things - a Cosmic Junkyard area. Maybe even tie it all together.

There has also been some (unsuccessful, if I recall) experiments with using tethers for orbit change. This project could explore that further, maybe with a separate robot, and once the technology was viable, it could be used to collect the junk. This is all significant AI challenge or a great place for students to place practical celestial mechanics, under proper supervisor, of course. Yes, I am assuming the problems are non-trivial. But so would a bolt through the helmet of a space walker. The image of a cracked Space Shuttle window from a paint chip is haunting.

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I came for the astronomy but I do love the physics!