Another Data Point
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Posted
by Frank Morring, Jr. at
11/16/2007 9:36 AM CST
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A quick metallurgical analysis of samples from the fouled solar-array rotary joint that is hampering power production on the International Space Station (ISS) shows the ferrous debris came from the 10-foot-diameter race ring that carries the entire starboard end of the station truss as it windmills 360 degrees to follow the sun.
That complicates planning for getting the mechanism - formally known as the Solar Alpha Rotary Joint (SARJ) - turning again in time to generate electricity for Japan's big Kibo laboratory module if it arrives on schedule in April. If the problem requires a shift to the backup race ring in the joint, it will take "multiple" spacewalks to make the shift, according to Denny Todd, ISS integration and operations manager.
The latest analysis of power levels on the station without the starboard SARJ indicates the port-side solar arrays can generate enough electricity to support planned activities until the Kibo delivery mission next April. That includes two shuttle flights to deliver Europe's Columbus laboratory, the logistics module for Kibo and the multipurpose dextrous manipulator (Dextre) for the Canadian-built ISS robotic arm.
But without a clear understanding of just what is going on inside the SARJ, Todd says, more inspections will have to be done before a repair plan can be drafted. Early betting is on a full inspection of the starboard SARJ by the station crew early next year, followed by repairs during and after the mission that delivers the Kibo logistics module and Dextre in February. If that doesn't work, there may not be enough power to support the Kibo systems following an April delivery.
Station engineers had hoped the samples collected by astronaut Dan Tani from the fouled SARJ would pinpoint the problem and allow repair-planning to begin. But Todd said today the material does not appear to be from the trundle bearings that hold the two halves of the joint together, or from the drive lock assembly (DLA) that turns the geared mechanism.
Even without knowing just what the problem is, mission managers have repacked the space shuttle Atlantis to preposition a spare DLA and some more trundle bearing assemblies on the station to gain flexibility for a repair next year. Atlantis is scheduled to lift off Dec. 6 with Columbus, and Todd said the Expedition 16 crew is making such good progress getting the ISS ready for another docked mission that the timeline currently would support an on-time launch of the STS-122/1E assembly mission.
However, Tani and Expedition 16 Commander Peggy Whitson must perform two very difficult spacewalks on Nov. 20 and 24 to connect the plumbing that cools the new Harmony node where Columbus will be attached, and Todd stressed that station readiness for a launch could slip a little if problems arise.
