Astronaut Steve Swanson at work during the second spacewalk of the STS-119 mission.
Spacewalks, space junk and dodgy plumbing
24 Mar 2009
The STS-119 mission of space shuttle Discovery to the International Space Station approached the halfway point with Sunday's spacewalk to prepare the complex for future assembly flights and arrival in the fall of a new cargo-carrying spacecraft—Japan's H-II Transfer Vehicle.
Steve Swanson and Joe Acaba floated out of the Quest airlock for the six hour, 30 minute spacewalk, completing the highest priority tasks that included preparing a worksite for new batteries that will be brought up on the STS-127 mission of Endeavour. They also installed a Global Positioning System antenna on the pressurised logistics module attached to the Kibo laboratory.
During installation of a cargo carrier attach system, a misaligned bracket proved too difficult to reposition and the crew was called off to pursue other tasks, including taking photos of station heat radiators.
With the 122nd spacewalk devoted to station assembly and maintenance complete, astronauts now have spent more than 768 hours outside the station. Swanson completed his fourth spacewalk and Acaba, his first.
Replanning efforts are underway to review tasks for the third spacewalk planned for Monday. Acaba and Ricky Arnold are scheduled to conduct that spacewalk.
Astronaut Joseph Acaba at work on the outside of the space station.
Inside the station, station Commander Mike Fincke and shuttle Mission Specialist Sandy Magnus activated the newly installed distillation assembly component of the Urine Processor and claimed its initial operation seemed to operate with less noise. But it soon became apparent that it wasn't operating properly and, despite several hours of trying to get it to work, in the end mission control instructed the astronauts to call it a day.
"The troubleshooting steps we just did to try to resolve this problem with the UPA (urine processing assembly) were no joy," said Rick Davis in mission control. "We are going to stand down from UPA activities for today so that we can get everyone looking at it to come up with some additional ideas."
"He [space station commander Mike Fincke] had begun configuring the urine processor assembly for a wet run with that distillation assembly this afternoon," said NASA spokeswoman, Nicole Cloutier-Lemaster. "He had been making those configurations throughout the morning and working with the ground team, noticed that they had a slower-than-expected flow rate in those tanks.
"The ground team has been working with (Fincke) on some different steps to try to identify the cause of the lower-than-expected flow rates and have initiated a couple of commands from the ground, as well as some steps from on board involving the hoses and the quick disconnects."
Also on Monday, the crews were given some off duty time ahead of continued transfer work and preparations for Tuesday's (Sydney time) spacewalk.
Dodging space junk
Potential damage from a collision with space junk is a perennial problem for the station and shuttle. Parts of the station are equipped with shields to protect vital components, but such shields are only effective for very small impacts.
Over the weekend, concern was raised that a 10cm-long piece of debris from a Chinese rocket would come very close to the station. Mission controllers therefore decided some action was required, and chose to use Discovery's thrusters to change the orientation of the station. This would increase its drag in the tenuous upper level of the Earth's atmosphere, slowing it down and altering the altitude of its orbit somewhat.
Why is this woman smiling? NASA astronaut Sandy Magnus will be coming home at the end of the week, having spent four months aboard the space station.
Adapted from information issued by NASA.
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