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November 01, 2007

Spacewalks Delayed

Power is the priority. So Thursday's spacewalk, that had originally been to check out a new shuttle tile repair method (something called T-RAD) and then changed to a check of the starboard SARJ, is now going to be a repair of the P6 array. But Mission Control needed time to work out the procedures, and the crew needs time to go over them. So the spacewalk has been postponed until Friday at the earliest.

The array is working at 97 percent power. Because the thin solar blanket has a tear in it, it has been locked in place, and is not fully extended. (Ironically, this is the side that has a working SARJ.) The concern is that the stress/flexing induced by rotating the array could increase the damage. One option I heard discussed is to fold that section shut, and then extend the array. It will be interesting to see what the repair entails.

The starboard SARJ repair has been postponed to an unspecified date--meaning it will not be done by the STS-120 crew. As ISS Program Manager Mike Suffredini noted before, the power loss from not being able to rotate the starboard arrays is not an issue until next spring. It is more important to get the P6 array repaired.

Hopefully, the repair can be completed on Friday. If so, the shuttle will undock on Monday and land Wednesday. If not, another spacewalk may be added, presumably on Sunday.

The spacewalk that had been planned by the station crew (to disconnect the PMA in preparation for moving Harmony to its permanent location) for Friday, and then postponed to Saturday, is being moved to after the shuttle leaves. If another spacewalk is required for P6, then the shuttle will probably leave on Wednesday and land Friday. What this means to the timeline for the STS-122 in December is not yet clear. That flight has already been postponed from December 6 to 7.

The space station is the first to use a distributed power system: with the arrays on a truss providing power to multiple modules. In this sense, it is the first space "utility" ever built. So there is a definite silver lining to the problems we've encountered with this first system. We now know what to expect in terms of lifetime degradation of the arrays. We know it is difficult to fold up and move older arrays. They tend to tear when redeployed. We also now have a way for our spacewalking repairmen to coax arrays into their boxes, and are working right now on a way to fix a tear and clean out a clogged joint. With these skills neatly tucked into our space utility plans, we can be much more confident in building a future space solar power station to provide electricity to Earth.

So let's hope for no more torn gloves or arrays, and that all goes smoothly on Friday. But if it doesn't go as planned, we will still have learned some valuable lessons that will benefit us all in the future.

Marianne Dyson
NSS member

Posted by m_dyson at November 1, 2007 01:20 AM



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