A mobile rail cart is on the move at the International Space Station today in advance of a risky bid to make spacewalking repairs to a damaged solar wing.
Built by the Canadian Space Agency and known as the Mobile Transporter, or MT, the rail cart is moving toward the middle of the station's central truss from a work site near its far left end. The 97-foot move is taking place at a speed of five feet per minute.
Perched atop the rail cart is the station's 57.5-foot crane. It will grapple an orbital inspection boom in Discovery's cargo bay before handing it off to the shuttle's robot arm.
That move will be made to maintain a power stream to the boom's laser sensors and camera, which still must be used to inspect Discovery's heat shield prior to atmospheric reentry next week. Otherwise they could freeze up and fail.
Later today, the rail cart will be moved back to a work site at the port end of the truss. Then early Saturday, the inspection boom will be snatched up by the station arm so it can be used as a work platform for the spacewalking repair work.
The end result will look like this:
The new sequence reduces from 12 to eight hours the amount of time power is not being routed to the boom, increasing the probability that its sensors will survive for the shuttle heat shield scan.
The spacewalk is scheduled to begin at 6:28 a.m. EDT Saturday. Discovery mission specialists Scott Parazynski and Douglas Wheelock will team up for the excursion.
Station flight engineer Dan Tani and Discovery mission specialist Stephanie Wilson are the outpost crane operators. Discovery pilot George Zamka and commander Pam Melroy are the shuttle robot arm operators.
You can watch mission operations unfold live here in The Flame Trench. Simply click the link below the top image to launch our NASA TV viewer and round-the-clock coverage of NASA's 120th shuttle mission, the 23rd devoted to station assembly and maintenance. Refresh this page for periodic updates.
The timing of the highly choreographed spacewalk preparations can be found in the latest version -- Rev K -- of the NASA TV schedule: tvsked_revk.pdf.
A more detailed timeline and messages beamed up to the joined crew of shuttle Discovery and the station can be found here in the Flight Day 11 Execute Package: FD11exec.pdf.
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