Apparently, we were very lucky for a second time. The Columbia disintegration is a tragedy, but it could have been so much larger. The Challenger mission in 1986 was one mission away from one containing a nuclear payload which might have caused extensive radiation poisoning had it been on board. This time, it appears that no nuclear payload was onboard Columbia, but NASA and the Pentagon have plans for many such missions in the near future. Go to the Global Network Against Weapons and Nuclear Power in Space web site for more.