Discovery docks with Mir

HOUSTON (CNN) -- The crew of the space shuttle Discovery, docked with the orbiting Russian space station Mir, was unable Saturday to see a green fluorescent gas being pumped into a damaged Mir laboratory module.

The crew was trying to visually locate the leak caused by a collision with a cargo ship last year.

NASA had hoped the astronauts, as well as Mir's Russian cosmonauts, would be able to spot the gas leaking into space.

"We weren't quite that lucky," Jim Van Laak, deputy manager of the shuttle-Mir program, said at a NASA briefing. "The crew was unable to see any indication of the gas itself."

"That's not too much of a surprise, both because the viewing angle wasn't very good and the lighting conditions were not quite what we hoped for, and also early indications are that the plume of the gas may only be visible up to perhaps a meter from the leak site," Van Laak said.

"We really need to be in very nearly an optimum condition in order to view the actual jet of leaking gas," he said.

The gas -- a nontoxic, nonflammable mixture of nitrogen, the cleaning solvent acetone and the artificial food additive biacetyl -- was carried up in a tank aboard Discovery.

Van Laak said he is still optimistic that the actual leak will be spotted when Discovery undocks from Mir Monday for its return flight to Earth, carrying Andrew Thomas, the last astronaut to live on Mir.

Mir's Spektr module was damaged in the June 25 collision that almost forced the space station's three-man crew to evacuate. The leak is believed to be at the base of the solar panel.

Even if efforts to locate the leak were successful, it's doubtful the Russian Space Agency would repair it, since it plans to let the space station, which is in poor condition, burn up in space by the end of 1999.

The leak tests have been intended as a practice run, in case such technology is needed aboard the future international space station.

When Discovery undocks Monday, Mir will be tilted in an effort to give the astronauts a better vantage point for viewing.

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