Astronauts aboard the International Space Station are preparing for a crucial spacewalk today to reroute the outpost's power system.
The Discoverycrew, which arrived at the station on Monday for a week-long stay, needs to rewire the station's electrical system to use power produced by new solar arrays installed on the station in September.
The Earth is reflected in the visor of astronaut Christer Fuglesang of Sweden as he replaces a faulty TV camera on the exterior of the International Space Station this week
The rewiring will pave the way for laboratories built by Europe countries and Japan to be attached to the space station beginning next year.
The shift to the new arrays will increase power for the station by roughly half, Kirk Shireman, deputy programme manager for the International Space Station, said.
Spacewalkers Robert Curbeam and Christer Fuglesang, who completed the first of three planned spacewalks on Tuesday, camped out in the station's airlock last night in preparation for a six-hour foray.
Today, the Nasa ground crew will power down half of the station to allow the spacewalkers to unplug power cables from a temporary power supply and attach them to the permanent system. Nasa wanted to rewire the station in 2003, but the destruction of the space shuttle Columbiathat year halted all shuttle flights for more than two years.
Nasa engineers were not sure if the electrical equipment, which has been subjected to extremes of space thermal cycles for longer than expected, would work once it was connected.
If it fails, the two astronauts will have to quickly fix the problem before they run out of time on the spacewalk. It will be a tense time with little or no backup power if problems arise.
The astronauts also are set to activate part of the station's thermal control system and to relocate a work platform for storing tools and spacewalking hardware.