Endeavour Now Scheduled To Land November 30

Astronauts Shane Kimbrough and Steve Bowen (shown below) began the fourth and final planned spacewalk of the STS-126 mission to the International Space Station about 20 minutes ahead of schedule, switching their spacesuits to internal battery power at 1:24 pm EST on Monday.

During the planned six hour and 30 minute activity, the spacewalkers will complete the installation of trundle bearing assemblies on the starboard Solar Alpha Rotary Joint (SARJ), and clean and lubricate the port SARJ.

That joint has been the focus of activities on the first three spacewalks of Endeavour’s mission to the station. It has been used sparingly since increased power consumption and vibrations were noticed in September last year. A test of the joint rotating in the mode to automatically track the sun will be done early Tuesday morning to judge the repair work

In addition to repairs to the SARJ, spacewalkers will also install a camera on the Port 1 truss and attach a Global Positioning System antenna on the Japanese Experiment Module Pressurized Section.

The spacewalkers exited the station shortly after receiving word from NASA their visit to the ISS has been extended by 24 hours. Endeavour will now undock from the station Friday, one day later than planned, and will return to Earth Sunday afternoon.

NASA extended the mission to give crews onboard the ISS some more time to troubleshoot the off-and-on Urine Processor Assembly (UPA), part of a new water reclamation unit installed onboard the station. NASA reports the UPA ran for almost three hours Sunday -- the longest successful operation to date -- and processed about a gallon of liquid, after modifications by Expedition 18 Commander Mike Fincke and Endeavour Mission Specialist Don Pettit. The system then shut down.

On Monday, Fincke will install two bolts in the UPA's distillation assembly to further reduce vibration. Mission officials believe those vibrations are causing problems for the UPA's motor assembly... and hope the added measures will relieve the problem, so to speak.

If the UPA remains uncooperative, NASA will need to fly a new motor to the ISS... potentially delaying the planned Summer 2009 deployment of the first six-person crew onboard the ISS. The water reclamation unit is vital to supporting an expanded crew complement.

FMI: www.nasa.gov