Two of eight launch pad hold-down bolts on the right- hand solid rocket booster (SRB) of Space Shuttle STS 92 Discovery failed to separate completely during the launch on 12 October.
It was the first time in 100 missions that two bolts had been affected - although 11 missions have suffered from a single bolt not separating. The bolts are released by firing explosive charges at SRB ignition to shatter nuts which hold the bolts in place.
NASA says the failure was not serious. But a bolt remaining fixed to the base of an SRB and the failure of any of the nuts to shatter, could cause momentary instability at lift-off, possibly enough for the thrust of the SRBs to tip the Shuttle off course - the scenario that NASA most fears.
The STS 92 launch was the 100th by a Space Shuttle. The first Shuttle launch was made on 12 April 1981. One Shuttle launch, Challenger SIL, failed in January 1986 with the death of seven crew.
NASA administrator Dan Goldin, has revealed that although the Shuttle is now a much safer vehicle than it was when first launched, the probability of a major failure in the system is still 1:200, compared with a commercial airliner reliability factor of 1:1,000,000.
Despite a Ku-band antenna failure which meant docking with the International Space Station (ISS) without radar, and an electrical failure in the Space Vision system used by the remote manipulator system operator, the STS 92 Discovery mission has succeeded in joining the Z-1 truss and a new docking port to the space station. During the mission, astronauts performed extra-vehicular activity (EVA) on four occasions.
The new docking port will be first used by the Shuttle STS97 Endeavour when it arrives in November to erect the first US solar arrays in a temporary position on the Z-1 truss.
With the addition of the Z-1 truss and the docking port, the ISS now weighs 80t.
Source: Flight International
