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Another attempt at station reboost possible Monday BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: December 1, 2006 Russian rocket scientists believe they understand the cause of an aborted rocket firing Wednesday to raise the orbit of the international space station. An attempt to complete the reboost maneuver, designed to ensure the shuttle Discovery can reach the outpost throughout its upcoming launch window, is expected Monday, officials said today, after adjustments to control software. At the Johnson Space Center in Houston, meanwhile, engineers have reset an open circuit breaker in a critical solar array control system after tracing a glitch earlier this week to a software problem. While the remote power controller, or RPC, is working normally, additional attempts to activate the new array motor control software have been unsuccessful. The software is intended to automatically detect and fix motor-gear tooth misalignments in the mechanism used to rotate the station's new solar arrays so they can stay face on to the sun as the station circles the globe. As it now stands, the mechanism is sound, full redundancy is available and there will be no impact on Discovery's Dec. 7 launch. But barring a quick software fix, any motor-gear tooth misalignments that might occur during Discovery's mission, when the solar alpha rotary joint begins operating full time, will require time-consuming ground commanding to resolve.
A planned 18-minute 22-second reboost attempt Wednesday was cut short three minutes and 16 seconds after ignition of thrusters on a Progress supply ship docked to the aft port of the Russian Zvezda command module. Even with the aborted burn, FD-3 opportunities are available Dec. 7, 9, 11, 13, 15-22, 24 and 26, the end of Discovery's launch window. Russian engineers now think the burn terminated early when control software detected unexpected sideways "yaw" motion in the station. The motion was caused, engineers believe, because of the station's current unbalanced configuration. With a new set of solar arrays on the far left-side of the station's main power truss, the lab's mass is not symmetric about the direction of motion. Engineers now believe they can safely relax the yaw limits built into the rocket control software and that the station will remain in an acceptable orientation throughout the planned 21-minute rocket firing Monday. If the burn goes well, FD-3 docking opportunities will be available every day between Dec. 7 and Dec. 23 and on Christmas day if required.
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