Aw, Jude, you stole my idea.
It is the year 2300. The stratosphere has been so cluttered with satellites, derelict spacecraft, and meteor debris that the Earth is completely enclosed in a geosynchronous shell. This layer of "space junk" has gotten so bad, in fact, that, in some places, it has started to eclipse the sun.
Worse, due to collisions between some of the objects, the orbits of some of the satellites and spaceships have started to decay, with the result that bits and pieces of debris have started to fall back to earth with increasing frequency. At first this phenomenon was largely ignored by the media; however, as more and more buildings and more and more people were hit by falling detritus the nations of the Earth started to wake up. Additionally, it was discovered that many of the remnants were dangerously radioactive. Clearly, something had to be done about the problem.
An emergency council of the world's best and brightest scientists was hastily assembled. Most of the space junk, it was discovered, still had limited functionality and could actually be controlled to a limited extent on common radio frequency bands. While the space objects fell at a uniform rate, they could be rotated on an axis or even pushed in a certain direction.
Most of the objects were very large, they noticed, and tended to assume geometrical shapes. During the course of his experiments, a Russian astrophysicist noticed that, if the objects could be manipulated into forming a solid line, the semi-functioning power cores would magnetically fuse, forming a harmless, inert composite that could be safely salvaged. Unless this happened, however, the individual pieces would continue to remain dangerously radioactive.
Additionally, some scientists theorized that if too many of the objects accumulated in one location, without being converted to inert scrap, they would reach a critical mass, resulting in a thermonuclear explosion that would make Chernobyl look like Fourth of July fireworks. Time was rapidly running out. Could the Earth be saved, or was this mankind's final hour?