Shaking on space station rattles NASA
Vigorous vibrations caught on video during orbital reboost last month

A faulty rocket command sequence aboard the international space station caused the 300-ton structure to shake back and forth vigorously for two minutes last month, during what was supposed to be a routine, gentle orbital adjustment. Space experts in Houston and Moscow have spent the last two weeks searching for the cause of the shaking and doing a damage assessment.

The thrashing of the long solar array wings reached a degree "five times greater than allowed," one source told msnbc.com in an e-mail. Another source said the swaying was the "biggest I've ever seen... Outside the certified limits of ISS structure…"

The extent of the damage or structural weakening induced by the shaking is "very much still in work," a third source said in an e-mail. The attach points of the long booms, and the docking interfaces between pressurized modules, are particularly susceptible to accumulated flex-induced fatigue. In the latter case, loss of pressure integrity is a potential consequence.

This source said two "million-dollar questions" had to be answered soon. First, data gathered from accelerometers and stress sensors on the structure must be analyzed to see how bad the overloads were. Second, why were the Russian commands for the automated rocket burn approved without adequate simulation and testing?

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