NASA to shift gear in shock discovery

NASA is to replace braking mechanisms on all its space shuttles in a bid to avert another catastrophe after discovering some of the gears were installed backwards.

Shuttle programme manager Bill Parsons launched an investigation into why the rudder speed brake gears all old original parts in the shuttle tails were never inspected in more than two decades of flight. If one of the improperly installed gears had been in a high-stress position, it would probably have led to the spacecraft's destruction at touchdown, he said.

"Bottom line is, it was not good," Mr Parsons said.

The rudder speed brake guides and slows the shuttle as it comes in for landing. If even one of the four sets of gears jams, the spacecraft could not land safely.

The reversed gears found recently in Discovery were in the least stress-prone position and never failed. But one of the replacements a spare set also installed backwards would have ended up in a more high-stress location in the tail. All the rudder speed brake gears in NASA's inventory are being X-rayed to see if they were properly built, and to look for rust and micro-cracks, already spotted on some gears.

Parsons said new or refurbished gears should be installed in time for shuttle flights to resume next March, after a two-year grounding following the Columbia tragedy in which seven astronauts were killed during reentry.