TAG | Jan. 30th spacewalk to fix ISS solar motor seems successful |
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| by William Atkins | |
| Thursday, 31 January 2008 | |
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ISS Expedition 16 commander Peggy Whitson and flight engineer Daniel Tani brought out a new motor earlier today, which NASA hoped would fix one of two failures that have weakened the power assembly system on the International Space Station, and threatened to forestall further construction of the station. Early in the spacewalk, the two NASA astronauts removed a 2.5-foot container (a beta gimbal assembly housing) that encased the old motor. With the Sun hidden behind the Earth, the two astronauts then removed the fasteners that held down the defective motor, and disconnected its cables. Then, they installed the new motor in its place. They were working in darkness because if sunlight (or any form of artificial light, say from a flashlight they might be carrying) were to fall on the solar array, 160 volts (200 amperes) of electricity would be going through the cables that the astronauts are disconnecting and connecting, along with the chance that the astronauts might accidently touch a hot spot on the solar arrays. As of about 9:30 a.m. CST (which is Houston time in Mission Control at the Johnson Space Center, where ground controllers are directing the spacewalk), NASA is reporting the initial testing of the new 250-pound electric motor shows it is working properly. It has already tilted about three degrees, showing initially that it can perform its new job. The astronauts were a little bit over 5.5 hours into their spacewalk when this first test occurred. The old motor stopped working in early December 2007, which compounded a problem that occurred about three months earlier when a solar alpha rotary joint (SARJ) on the right (starboard) side of the main power truss had to be turned off. With the new solar tilting motor installed, the astronauts are now working on the other power-generating problem outside of the space shuttle—the SARJ. The jammed starboard joint is supposed to continuously rotate 360 degrees to automatically keep the solar arrays on the right side of the shuttle pointed in the direction of the Sun. However, it was earlier found to be malfunctioning. Later, it was discovered by Tani, while in a spacewalk, to be full of metal shards, which supposedly somehow causing it to malfunction. NASA is still unsure the original of this problem.
The SARJ is being now inspected by the astronauts. They removed the blanket-like thermal covers that encase sections of the joint. They will photograph the bearings and other parts of the joint.
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