Mission Specialists Piers Sellers and Mike Fossum turned their spacesuits to battery power to officially start the spacewalk at 8:17 a.m. CDT. After they configured their tools and safety tethers, they moved to the S0 Truss and installed a blade blocker in the zenith Interface Umbilical Assembly to protect the undamaged power, data and video cable. Then they rerouted that cable through the IUA so the Mobile Transporter rail car could be moved into position on the truss for replacement of the Trailing Umbilical System containing the severed power and data cable during a spacewalk Monday.
The remainder of today’s spacewalk was devoted to testing the combination of space shuttle robotic arm and Orbiter Boom Sensor System as a platform for spacewalking astronauts to make repairs to a damaged orbiter. Sellers got into a foot restraint on the OBSS, almost 100 feet from where the shuttle arm is attached to the payload bay sill, and performed a set of motions designed to see how the arm/OBSS handled the forces generated by those movements; Fossum stood nearby and reported his observations of the arm/OBSS’ movements.
Then Fossum joined Sellers on the end of the OBSS for another round of demonstrations, with measurements again taken by a load cell mounted under the foot restraint. For the last measurement the arm maneuvered Fossum into position so he could push against the end of the P1 Truss.
Sellers, wearing the spacesuit with red stripes, and Fossum, wearing the white spacesuit, re-entered the station and started pressurizing the airlock at 3:48 p.m., concluding the first of three spacewalks planned for the mission. Today’s EVA was the fourth of Sellers’ career, and the first for Fossum.
Pilot Mark Kelly served as intravehicular crewmember, keeping the spacewalkers on time and relaying information from Mission Control in Houston, while Mission Specialists Lisa Nowak and Stephanie Wilson and Expedition 13 Flight Engineer Jeff Williams operated the shuttle robot arm and Discovery Commander Steve Lindsey monitored their activities while transferring water onto ISS.
During the EVA ISS Commander Pavel Vinogradov and Flight Engineer Thomas Reiter unloaded cargo from the Multipurpose Logistics Module. Today’s transfers included a new oxygen generator, to be installed in the Destiny laboratory in the coming months, and a Minus Eighty Degree Laboratory Freezer for ISS, which will provide low temperature storage for lab supplies and for experiment samples awaiting return to Earth.
Delivery of cargo from the MPLM onto ISS will be the centerpiece of activity on orbit Sunday, and the second of two spacewalks will take place Monday morning at 7:13 a.m. CDT.
Also Saturday, Mission Managers reported clearing for entry all but one area of the orbiter’s thermal protection system that engineers had been looking at closely. The remaining area, a protruding gap filler near the external tank umbilical doors, needs further analysis, according to Steve Poulos, Orbiter Project Office Manager. The outlook was favorable for clearing that area, as well, Poulos said, but image analysts will be working through the night Saturday to finish looking at it.
Overall, the spacecraft thermal protection system had relatively few “dings” and Chairman of the Mission Management Team John Shannon said that Discovery was by far the "cleanest" in terms of damage to the heat shield.