NASA is holding to its March 2005 Space Shuttle return to flight date, despite deciding to replace the rudder speedbrake actuators on the three surviving orbiters. The US space agency decided to fit new actuators after discovering wrongly installed gears in two of the units removed from Discovery.
The split-rudder speedbrakes on the Shuttle are operated by four mechanically driven actuators, originally supplied by Hamilton Sundstrand. NASA removed the units for inspection after discovering corrosion in a similar actuator on Discovery's body flap. X-ray inspection revealed a gear in the lower actuator had been installed in reverse. A similar defect was found in a spare unit due for installation in Discovery.
Pointing out that Discovery has flown 30 times since 1984 with the wrongly assembled actuator, NASA says a failure was only likely under the high stress of an emergency landing at Kennedy Space Center, Florida after an aborted launch.
Nevertheless, the agency is to install four unflown spare actuators in Discovery, while Hamilton Sundstrand believes it has components available to make at least two, and possibly four, new actuators for Atlantis. If required, components from Endeavour will be used to complete the set, and new actuators manufactured for the third orbiter.
Re-installation of the actuators, which will take "several months", NASA says, is pacing the Shuttle return to flight.
Source: Flight International