NASA and NASA-contractor mission control personnel at the Johnson Space Center, Houston, Texas, were quick to investigate the problem caused by one of the power channels of the P4 solar array electrical system. It was decided that a “glitch” (malfunction) to a direct current switching unit caused the problem.
The direct current switching unit controls the distribution of power from the solar array to various hardware locations such as the battery systems. Two communication systems, some science facilities, control moment gyroscope # 2, various lights, and a few heating units were affected by the power loss. As designed, redundant systems took over for the primary systems while the matter was being investigated.
The P4 solar array electrical system is part of the P3/P4 truss assembly on the space station. Together, the P3 and P4 (P stands for Port side) segments contain a pair of solar arrays, a radiator, and a rotary joint. The P3/P4 truss assembly was installed during the STS-115 mission by the Space Shuttle Atlantis crew, which was launched on September 9, 2006.
Within twenty-four hours, mission ground controllers had restored power to almost all the affected systems and equipment. At that time, they were still trying to determine why the initial glitch occurred, and if it was only an isolated incident.
NASA personnel indicated that the ISS crewmembers were in no immediate danger from the power failure. The crewmembers aboard the International Space Station (ISS) at the time of the incident are U.S. commander Michael Lopez-Alegria, Russian flight engineer Mikhail Tyurin, and U.S. flight engineer Sunita Williams.
As of February 8, 2007, the following is a listing of the major statistics on the International Space Station: http://spaceflight.nasa.gov/station/isstodate.html.
For information on the last three spacewalks by the ISS astronauts, go to: http://www.itwire.com.au/content/view/9409/1066/.