Spacewalkers tread lightly amid dock dangers

James Oberg NBC News space analyst

Hard experience has taught Russia and the United States not to take space dockings and undockings of the robot freighter Progress lightly.

In 100 missions over 30 years, the freighters have always succeeded in docking with the space station, but sometimes requiring dramatic second or even third attempts or with assistance of cosmonauts during emergency spacewalks.

During one undocking and redocking test in 1997, an off-course Progress smashed into the hull of the Mir space station, creating a crack and very nearly killing the three men on board.

Such near-calamities explain the extreme caution with which Russian space planners have approached a mechanical docking snag on their Progress M-58 supply ship, now docked with the international space station. It must undock smoothly in early April to clear the way for the arrival of a new crew aboard a Soyuz spacecraft.

A spacewalk Thursday morning is planned to ensure a smooth undocking six weeks from now. Russian cosmonaut Mikhail Tyurin and American spacewalk record-holder Michael Lopez-Alegria will take a collection of U.S. and Russian tools to the back end of the station and try to clear the snag.

Jammed antenna wouldn't budge
"It really is unknown what the vehicle will do if it separates (with the snag in place)," said Richard Labrode, U.S. space station lead flight director. "That's the main concern."

Labrode said that while the snag most likely would break loose safely if the undocking had to be attempted, it's still a risk no one is willing to take.

The snag occurred when the supply drone arrived at the international space station in October. A guidance antenna on a forward-facing swing-arm did not retract as planned before contact. The antenna came in contact with the station next to the docking port, lodging under a handrail installed there for crew access.

During a scheduled spacewalk the following month, Tyurin and Lopez-Alegria tried to manually tug the antenna loose, but couldn’t budge it. Mission Control in Moscow decided to try again on another spacewalk using better tools.

Ground teams have gone over the procedure back on Earth and sent up videos of how it should go the second time around.

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