New solar array drive motor installed on station
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: January 30, 2008
Working smoothly through a 35-minute pass through Earth's shadow, station commander Peggy Whitson and Dan Tani removed a faulty solar array positioning motor today and replaced it with a spare unit. If the replacement motor works as expected, the array can be moved from side to side like the station's other solar panels to maximize electrical output, clearing the way for launch of the European Space Agency's Columbus module aboard the shuttle Atlantis on Feb. 7.
The original motor, known as the bearing motor roll ring module, or BRRM - pronounced "broom" - failed Dec. 8 amid iniitial attempts to launch Atlantis. The shuttle flight was derailed by problems with fuel tank hydrogen sensors and station managers ultimately decided to stage today's spacewalk ahead of the next shuttle launch attempt to boost the lab's power output.
The work was carried out during orbital darkness to minimize the threat of any potentially dangerous electrical shocks. The array attached to the motor generates a regulated 160 volts of electricity at more than 210 amps when in full sunlight. Four of five cables were connected to the new BMRRM before the astronauts had to back way as the station passed back into sunlight. The final connection will be made during the next eclipse period beginning around 8:25 a.m.
After all the cables are plugged in, flight controllers will verify the health of the new motor while Whitson and Tani turn their attention to stowing the old motor and beginning additional inspections of the station's right-side solar alpha rotary joint, or SARJ.
The starboard SARJ is designed to rotate the outboard arrays like a giant paddle wheel to keep them face on to the sun. Last fall, engineers stopped the right-side SARJ because of concern about higher-than-expected vibration levels. Subsequent inspections revealed metallic contamination and damage to the bearing race ring at the heart of the gear-driven joint. Engineers have not yet determined what is causing the damage or what might be needed to fix it. Today's inspection is intended to collect additional data.
Given the ongoing SARJ trouble, replacing the faulty BMRRM, an unrelated problem, was critical for generating the power needed to support the addition of the European and Japanese research modules.