(click photo for hi-res version)

Using Space Shuttle Discovery’s Remote Manipulator System/Orbiter Booster Sensor System (RMS/OBSS) for maneuvering, astronauts Piers J. Sellers (red stripes) and Michael E. Fossum, STS-121 mission specialists, work on the S0 Truss of the International Space Station. The 7 hour 31 minute spacewalk was the first of three scheduled EVA sessions for the STS-121 mission. Photo Credit: NASA

[Quote:]

In a high-drama spacewalk on Monday, a pair of NASA astronauts overcame an issue with a loose jet pack to make crucial repairs to the International Space Station.

The jet packs are designed to whisk astronauts back to safety should they float away from the ISS and into space. But once Mike Fossum had helped his partner Piers Sellers secure the jet pack, the two completed their work preparing the ISS for the expansion planned during future shuttle missions.

The astronauts replaced a key system that sends power and commands to a railcar attached to the station’s truss. The truss acts like a backbone to the station and supports its power-generating solar arrays.

The station’s robot arm moves on the railcar to access hard-to-reach areas, making the railcar critical for the installation of more solar arrays and truss segments.

“If we didn’t get this successfully changed and checked out, then we couldn’t proceed with the next mission, which is right on our heels,” says ISS lead flight director Rick LaBrode. The next shuttle is currently scheduled for a lift-off on 28 August.