Station power problem threatens next mission

The starboard solar wings on the International Space Station have been parked as a result of contamination detected during the second of five spacewalks planned for Discovery's stay at the outpost.

Managers and engineers are concerned that the contamination -- which appears to be metal shavings -- might get caught up in a giant rotary joint that enables the solar wings to turn like a Ferris wheel, constantly tracking the sun to maximize electrical output.

The wings, however, are unable to generate electricity at peak capacities in the parked position.

Station flight engineer Dan Tani spotted the metal shavings during a spacewalking inspection earlier today. Managers added the inspection to the to-do list after engineers over the past several weeks detected increased current levels and vibrations in the solar wings. The current levels and vibrations were an indicator that something might be interfering with the rotation of the 10-foot-wide, wheel-like joint.

NASA engineers are scrambling to analyze the problem in an attempt to pinpoint the source of the contamination, clean-up metal shavings and return the solar wings to normal operation. Discovery's astronauts might be asked to do additional inspections or troubleshooting work before the shuttle departs the outpost in early November.

In the meantime, engineers are trying to determine whether enough power will be available to prepare the station for the long-anticipated arrival of the European Columbus laboratory. The newly arrived U.S. Harmony module must outfitted with a conical shuttle docking port and moved to the front of the U.S. Destiny science lab before Atlantis and Columbus can be launched.

Liftoff now is planned for Dec. 6 and NASA only have one week to get Atlantis and the European lab launched in the current calendar year. The sun angle on the station between Dec. 14 and Dec. 30 will make it impossible to generate enough power and heat-dissipating capability for both the outpost and a docked shuttle during that time. The next launch opportunity would come around Jan. 2.

The current situation raises the stakes for an ongoing bid to move a set of solar wings to the port side of the central truss. It's unlikely NASA could proceed with the launch of Columbus if the stowed wings on the P6 solar array truss cannot be unfurled during a spacewalk scheduled for Tuesday.