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Endeavour crew completes fifth and final spacewalk BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: July 27, 2009 
Astronauts Thomas Marshburn and Christopher Cassidy staged a 4-hour 54-minute spacewalk today, the fifth and final excursion planned for the shuttle Endeavour's space station assembly mission. The spacewalkers installed two Japanese television cameras on a new experiment platform, fixed an insulation problem on a Canadian robot and re-wired a gyro control circuit. They also completed a variety of minor "get-ahead" tasks after flight controllers decided there might not be enough carbon dioxide absorbent available in Cassidy's spacesuit to complete deployment of a cargo storage mechanism on the right side of the station's main truss. That task will be carried out by station astronauts or a future shuttle crew. "Great job, outstanding EVA," Japanese astronaut Aki Hoshide radioed from Houston after Marshburn and Cassidy floated back into the Quest airlock module. "We're all very happy to work with you, it's a privilege. Thanks and congratulations on five EVAs." Said lead Flight Director Holly Ridings: "Today was a great day." "With the completion of our fifth spacewalk, that really marks the end of an amazing list of objectives that have been successfully finished during this mission," she said. Through five spacewalks, along with near daily work with three robot arms on the shuttle and the space station, the astronauts attached a sophisticated experiment platform to the Japanese Kibo lab module, installed three experiment packages, replaced aging solar array batteries and mounted critical spare parts on the station's main truss. With today's installation of two television cameras on the Japanese Exposed Facility experiment shelf, or porch, the astronauts completed the assembly and outfitting of the three components making up the Kibo lab complex. "Congratulations, you guys just completed the JEF assembly," Hoshide called from mission control. "Well, that is a big deal," David Wolf replied from the shuttle-station complex. "You guys have a fabulous space agency and it's an amazing laboratory, both internal and at vacuum. It's been a privilege to work with you to complete it." Commander Mark Polansky and his crewmates - pilot Douglas Hurley, Canadian flight engineer Julie Payette, Wolf, Cassidy, Marshburn and returning space station flight engineer Koichi Wakata - plan to undock from the International Space Station on Tuesday and land back at the Kennedy Space Center on Friday to close out a marathon 16-day mission. "We've had our challenges and as a team," Ridings said. "We've all worked together to overcome those challenges and complete what looks like a very, very nominal mission almost exactly like we planned it." During his first spacewalk last week, Cassidy, a former Navy SEAL, used up more CO2-absorbing lithium hydroxide than expected, forcing flight controllers to order an early end to the excursion. During his second spacewalk two days later, CO2 levels rose only slightly and he was able to complete a full-duration seven-hour 12-minute spacewalk. But for today's EVA, Cassidy and Marshburn used a different type of CO-absorbent called METOX, a "rechargeable" compound that is slightly less effective than lithium hydroxide. An analysis of Cassidy's usage early in the spacewalk raised concern he might run into problems by the end of a full-duration EVA. "Consumables, METOX for Tom is seven (hours) plus zero zero, METOX for Chris is five plus three zero. Those are non-conservative numbers," Hoshide radioed. "When we did the math on the ground, with the 15 minutes out for cleanup, we're past the bingo time for the PAS deploy. Just wondering what you guys think." "We'll declare bingo. Simple," Wolf replied from orbit. The payload attach system - PAS - mechanism on the starboard truss must be deployed before a November shuttle mission delivers spare parts and equipment that are scheduled to be stored at that location. It's not yet clear whether the crew of a late-August shuttle mission will inherit the deployment or whether the station crew will have to take it on. "We had a lot of discussions before this EVA, we were very concerned with how much consumables we would have," lead spacewalk officer Kieth Johnson said later. "So we built a timeline with a full set of activities, hoping to get to those. But we knew if we went at the last task we had assigned without enough time we could get caught in the middle of it. "And so at a certain point in the EVA, we had to make a decision as to whether or not we were going to do the payload attach system deploy. ... Unfortunately, because of the consumables, we had to back up our bingo time and we made the decision at that point not to go do the payload attach system." Ridings said the decision might appear conservative to outsiders, but it was the right call given the past problems with Cassidy's suit, earlier trouble with similar attachment mechanisms and the arrival Wednesday or a Russian Progress supply ship. "When you do the task, you're actually taking structural pieces of the truss apart," she said. "You've got to get the platform out and you've got to get it put back together. We've got a Progress coming less than 48 hours after the end of the EVA today and if you get yourself in a configuration where those beams are not structurally mated to the truss, then it's not a good idea to dock vehicles. "When you think consumables, which we were tracking a little bit conservatively just based on our previous experience on this mission, plus the Progress in just a couple of days ... it made a lot more sense to be a little conservative. On paper, that task (PAS deploy) was going to take an hour and 30 minutes. The only two we've done, we've had trouble with both of them. ... We did the calculation, we had about an hour and 40 minutes. That was too close to go and do the activity." Today's spacewalk began at 7:33 a.m. EDT and ended at 12:27 p.m. It was the 130th spacewalk devoted to station assembly and maintenance since construction began in 1998, the 11th so far this year and the fifth for Endeavour's crew. Total station spacewalk time now stands at 810 hours and 36 minutes, or 33.8 days. Endeavour's total through five spacewalks is 30 hours and 30 minutes.
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