September 3, 2012

New ISS Spacewalk Planned For Wednesday

Lee Rannals for - Your Universe Online

A new unexpected spacewalk is set for early morning on Wednesday for astronauts aboard the International Space Station.

Expedition 32 Flight Engineers Sunita Williams of NASA and Akihiko Hoshide of the Japan Aerospace Exploration Agency will be taking a stroll outside the orbiting outpost to attempt to complete installation of a spare power unit on the space station's truss.

The two will head outdoors for the second time in six days to complete the installation of a Main Bus Switching Unit (MBSU).

"Following a thorough review of preparations, the International Space Station Mission Management Team, including all international partners, agreed to press ahead for the follow-up spacewalk," NASA said in a statement. "A final readiness review by station program officials will be conducted on Tuesday, Sept. 4."

The two spacewalkers previously had to remove a faulty MBSU from its slot in the S-zero truss on August 30, but were unable to secure a space unit to the station.

NASA has been working to troubleshoot the problem that prevented the space MBSU from being installed.

"The most probable cause is likely a combination of a slight misalignment in the positioning of the spare unit for its installation prior to bolting and possible damage to the threads of the receptacle posts on the S-zero truss to which the MBSU must be bolted in place," the space agency said.

It said the MBSU-1 had been showing "intermittent bit flip errors," which are known as circuit reconfiguration confirmation errors.

An analysis indicated there was a component hardware failure internal to the MBSU, which caused the problem.

"Although the unit continued to provide power without interruption before its removal on Aug. 30, and had not been a threat to the health or safety of the crew, station, or continued research, mission managers decided to remove and replace the unit," NASA said.

The space station has four MBSUs, and they are the primary electrical power routing devices on the laboratory.

NASA said the spacewalkers have been spending the weekend reviewing procedures and fabricating a series of tools to add to their arsenal for the cleaning and lubricating of the MBSU's bolts and the S-zero truss post receptacles.

If the unit cannot be bolted into place during the upcoming spacewalk, the astronauts could bring the unit inside the station for further analysis and troubleshooting, according to NASA.