When the Pentagon ordered a Navy ship to shoot down a crippled U.S. spy satellite last February, it claimed the operation was necessary to prevent a harmful fuel from being dispersed in the atmosphere. At the time, critics charged that the Bush administration was using the toxic fuel as an excuse to demonstrate missile-defense and antisatellite capabilities.

Now, there is new evidence that the critics were very likely right.

Astrophysicist Yousaf Butt obtained U.S. government documents showing that NASA's own analysis concluded that the satellite's fuel tank was expected to burn up completely during re-entry—even though NASA probably overestimated the tank's chances of survival. "Despite its optimistic oversimplifications, the released study indicates that the tank would certainly have demised high up in the atmosphere," Butt, a staff scientist at the Harvard-Smithsonian Center for Astrophysics, writes in an article for the Bulletin of Atomic Scientists.

Up to now, U.S. officials had refused to release any of the prelaunch analyses regarding the fuel tank, claiming they contained sensitive information.

Beyond the stated concern about the toxic fuel, U.S. officials also were probably trying to prevent any fragments of the highly classified National Reconnaissance Agency imagery satellite from falling into the hands of U.S. adversaries.

There were some additional inconsistencies surrounding government officials' accounts of the operation. In the days before the launch, several U.S. officials warned that bad weather could delay the mission.