Two Russian cosmonauts headed into open space today to install a new solar panel, a mission that could culminate months of repairs on Mir's damaged power supply system.
The cosmonauts were expected to spend about six hours on the outside of the orbiting station.
The solar panel is stored on the exterior of Mir, and the cosmonauts will unpack it and mount it on the Kvant module, one of six modules that make up the sprawling station.
If the mission is successful, eight of Mir's 10 solar panels will be working normally. The ninth is operating, but at less than full capacity, and one was damaged beyond repair in a June crash with a cargo ship. The accident knocked out four solar panels and cut Mir's power supply almost by half.
The world's most experienced spacewalker, Mir commander Anatoly Solovyov, and fellow cosmonaut Pavel Vinogradov removed an old solar panel Monday, and today's effort was to complete the operation.
U.S. astronaut Dave Wolf was monitoring controls inside Mir and planned to switch on the solar panel after it was installed. His Russian colleagues will remain outside to make sure the panel unfolds properly and to wedge it open manually if necessary.
The crew also fixed a problem with Solovyov's spacesuit, which failed to transmit data on oxygen supply and other safety indicators, causing a two-hour delay of Monday's spacewalk.
The problem was not in the spacesuit itself, but in a transmitter aboard the station, Mission Control spokeswoman Irina Grishnyakova said. The faulty communication block was replaced, she said.
Monday's spacewalk went ahead despite the malfunction and was successful.
But when the cosmonauts headed back into Mir, the hatch between space and Mir's docking chamber failed to seal.
The docking chamber is walled off from the rest of the station, so its partial loss of pressure has not affected other parts of Mir or changed plans for today's expedition, Grishnyakova said.
When Solovyov and Vinogradov return to the station after the spacewalk, they will close the hatch and then try to restore the airtight seal by installing 10 clamps.
The station has had enough energy to carry out normal flight since the first successful repairs in August, but Russian space officials say more power is needed to resume regular scientific experiments.
For Solovyov, 49, today's excursion is the 14th of his career, more than anyone else. Vinogradov, on his first Mir flight, makes his fourth spacewalk.