Geoffrey Forden, an MIT physicist and expert on the Chinese space program, was recently interviewed by John Johnson Jr. of the LA Times on the topic of the recent proliferation of space junk from China's missile test last year ("China Added to Space Debris" April 16, 2008). The news item caught my eye with the new-to-me and very impressive sounding word "supercriticality." Apparently that is what happens when space junk collides in a cascade of impacts. It is apparently very, very bad. Space is becoming cluttered to the extent that clutter will beget clutter, and in time it won't be...