Washington, DC - Expedition 46 Commander Scott Kelly and Flight Engineer Tim Kopra of NASA are preparing for a previously unscheduled spacewalk outside the International Space Station on either Monday, Dec. 21, or Tuesday, Dec. 22. The pair will move the station’s mobile transporter rail car so it can be latched in place ahead of the Wednesday, Dec. 23 docking of a Russian cargo resupply spacecraft.

The mobile transporter -- used to position the station’s robotic Canadarm2 -- stalled on Dec. 16, just four inches (10 centimeters) from where it began its move, while flight controllers in the Mission Control Center at NASA’s Johnson Space Center in Houston were attempting to reposition it robotically. The cause of the stall still is being evaluated.

A start time for the spacewalk has not yet been set, but NASA Television coverage will begin 90 minutes prior to the start of the excursion, which will be conducted out of the U.S. Quest airlock. The station’s mission management team is targeting Monday for the spacewalk, but will meet again in a readiness review Sunday, Dec. 20 to make the final decision.

This will be the 191st spacewalk in support of space station assembly and maintenance, the third in Kelly’s career and the second for Kopra, who just arrived at the station Dec. 15. Kelly, who is nine months into a one-year mission, will be designated extravehicular activity crew member 1 (EV1) wearing the suit bearing the red stripes, and Kopra will be extravehicular activity crew member 2 (EV2) wearing the plain suit.

The ISS Progress 62 supply spacecraft is scheduled to launch at 3:44 a.m. EST Monday from the Baikonur Cosmodrome in Kazakhstan and dock at 5:31 a.m. Wednesday to the Pirs docking compartment.

For NASA TV streaming video, schedule and downlink information, visit:

http://www.nasa.gov/nasatv