The crew of Russia's Mir space station prepared for a spacewalk Friday to test a space glue designed to seal cracks in the aging craft.
Sergei Zalyotin and Alexander Kaleri were to leave the station at 2:40 p.m. Moscow time (11:40 a.m. GMT) and were expected to spend more than five hours in space applying the glue to a special panel imitating the station's hull.
Once back inside, the crew are to study the panel to judge the quality of the protective layer, said Mission Control spokesman Valery Lyndin.
The 14-year-old station started slowly leaking air shortly before the previous crew returned to Earth last August, leaving Mir unmanned before the arrival of Zalyotin and Kaleri on April 6.
Officials say the pressure loss is minor and easily compensated by oxygen supplies delivered by a cargo ship last month. But sealing the small holes is seen as a priority task for the crew in view of plans to extend Mir's lifetime.
During the spacewalk, the crew is also expected to film the parts of the station which are worst affected by aging, study the condition of its solar panels and remove an experimental panel attached to Mir during a previous spacewalk.
The Russian government had planned to dump Mir into the ocean around March because it lacked the funds to keep it aloft, but extended the mission after the Netherlands-based MirCorp provided funds to develop business possibilities on Mir.
MirCorp officials have previously said that they have committed $10-20 million to finance the mission and promised to raise more funds to keep the station in orbit at least through the end of the year. They extolled Friday's mission as the first privately-funded spacewalk.
"Today's spacewalk is another demonstration of how a commercial space station should operate," said MirCorp President Jeffrey Manber. "The cosmonauts have done an excellent job reactivating Mir, and they are now adding a new dimension by taking their work into the full void of space."
The decision to extend Mir's life has annoyed the U.S. space agency NASA, which believes that it diverts scarce Russian resources from a new international space station. The new station is behind schedule because of Russia's failure to launch a key component. The Zvezda service module is currently set to be launched between July 8 and 14.