Space station astronauts fixing motor on 1/30/2008 spacewalk

William Atkins
Tuesday, 29 January 2008 22:11

Science - Space

ISS Expedition 16 commander Peggy Whitson and ISS flight engineer Dan Tani will be working in space on Wednesday, January 30, 2008, to replace a faulty motor at the base of one of the space station’s starboard solar arrays.     

The two spacewalking astronauts will have to dance around the Sun, however, because they can only work during 33-minute time intervals—while the Sun is being blocked by the Earth.

If the Sun is shining on the solar array, high power levels will pass through the arrays from the collection of sunlight, which would be a likely threat of shock to the astronauts if they were to come close or touch the arrays.
The pair of NASA astronauts is hoping to replace the motor in one 33-minute interval. If they don’t complete the job, then they will have to wait for about one hour, until another night-side 33-minute interval comes about.

The International Space Station makes one orbit about the Earth in approximately 91 minutes at its altitude of about 184 nautical miles (341 kilometers) above the surface of Earth.

After they replace the motor, additional power will be generated by the station’s solar arrays.

Currently, the positioning motor is down-and-out due to several earlier electrical short-circuits in its system. Consequently, the solar arrays connected to the motor have been unable to continuously follow the Sun in order to collect sunlight that is used to generate electricity onboard the orbiting station.

Specifically, the 250-pound (113-kilogram) motor controls a beta gimbal joint that pivots around one of the two starboard solar arrays. The faulty motor is being replaced by a backup motor that was delivered to the space station on an earlier flight.

If time permits during the spacewalk, Whitson and Tani will also inspect the solar alpha rotary joint (SARJ) on the right (starboard) side of the main power truss. Tani discovered earlier that metal shavings had collected around the gear. NASA engineers are still trying to figure out a fix to this problem.

The ten-foot (three-meter) diameter SARJ is the main rotary joint that allows the solar arrays to rotate 360 degrees in order to track the Sun. One SARJ is located between the P3 and P4 truss segments (P is for "Port") and the other SARJ is positioned between the S3 and S4 truss segments (S is for "Starboard").

NASA will broadcast the International Space Station Expedition 16 crew's fifth spacewalk live on NASA TV beginning at 4:00 a.m. Eastern Standard Time (EST), or 0900 GMT, on Wednesday, January 30, 2008. The spacewalk is scheduled to begin at 5:20 a.m. EST or earlier, if the astronauts are ready.