ISS Mobile Transporter Back On The Job

Spacewalking astronauts Piers Sellers and Michael Fossum were high-altitude repairmen Monday, as they worked on the International Space Station's Mobile Transporter rail system... putting a cart back on the tracks and, in the process, dealing with problems of their own.

NASA reports that Sellers' backpack -- a critical piece of equipment should his tether to the station itself come loose -- kept trying to float away on its own. The problem was in a faulty clamp; Fossum finally fixed the problem by improvising a tether between Sellers and the pack itself.

Fixing that rail cart has been a priority, as it is necessary for completing the space station. Without it... the heavier materials needed for continued work on the ISS would be impossible to haul around... and now that the shuttle's are back on the job again... the schedule is very tight.

At the start of their six hour, 47 minute spacewalk, Sellers and Fossum also installed a spare thermal control system pump on a stowage platform outside the station.

With the second spacewalk of STS-121 now in the books, the crew onboard Discovery can look forward to a relatively light workload Tuesday... before Sellers and Fossum once again trek outside the orbiter, to test out materials future astronauts may use to repair glitches in the shuttle's heat shield on future missions.

The two astronauts are scheduled to begin that spacewalk Wednesday morning.

FMI: www.nasa.gov