Astronauts from the Space Shuttle Discovery this afternoon will work as weightless electricians to permanently upgrade the International Space Station's power system. In the first of two planned spacewalks, Mission Specialists Robert Curbeam and Christer Fuglesang will spend nearly 6 hours adjusting equipment that will bring the ISS's newest solar arrays on line for use by the station's systems and prepare for more arrays to be added next year, the U.S. space agency said in a prepared statement.

In preparation for the operation, NASA's ground control will power down half of the ISS's electrical subsystems. Today's spacewalk will be followed by another on Saturday that will, if successful, complete a long-planned process to shift the space station away from relying on an interim power supply to one that will provide the electricity from solar panels to sustain all the energy needed to add the modules and components necessary to complete the ISS as originally designed.

"This is the major milestone," said John Curry, NASA's lead flight director for the space station. The international space agencies involved in the project would be able to increase the number of crew members aboard the space station and proceed with expansion plans, Curry said. "Now you're limitless."

The pair of spacewalkers, aided by Flight Engineer Sunita Williams at the controls of the robotic arm on Discovery, will also today try to relocate two equipment handcarts, which would clear the way for the station's mobile transporter rail car to move down the station's rail system mounted to the superstructure. This will enable other astronauts, from next spring's STS-117 mission, to complete work on the so-called S1 truss, which supports thermal controls, communications equipment, and outboard cameras.

NASA also said it was considering what to do about a balky solar array attached to the station's port-side P6 truss. It stopped midway through its planned retraction yesterday, during preparation for the current spacewalks. The array was retracted sufficiently to allow the new P4 solar arrays to begin rotating last night, an operation that was completed without incident, the space agency reported. In their current state, the P6 port array and the P4 arrays have more than 16 feet of clearance from one another. Should they remain as they are, the partially retracted arrays pose no issue for the shuttle's undocking or any planned station activities until a Soyuz relocation flight set for April 2007.

Besides Curbeam, Fuglesang, and Williams, the crew of Discovery's Mission STS-116 consists of Commander Mark Polansky, Pilot William Oefelein, and Mission Specialists Joan Higginbotham and Nicholas Patrick. In addition, Flight Engineer Thomas Reiter of the European Space Agency will return aboard Discovery after a five-month stay on the space station (and Williams will take his place on the ISS). They are scheduled to return to Earth next Tuesday, 19 December.


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