Indian American astronaut Sunita Williams and International Space Station Commander Mike Lopez-Alegria moved a step closer to space walking records with another seven-hour 11-minute stroll.
Venturing out at 7.08 pm IST on Sunday on the second of an unprecedented three space walks in nine days, the duo returned to their home in space through Quest airlock at 2.19 am IST on Monday, US space agency NASA said.
They are scheduled to take a third space walk on February 8 taking Williams' to a total of four, the most ever by a woman. She has to date logged 22 hours 36 minutes outside the space station, including her first 7-hour 31-minute walk on December 16 and the second 7-hour 55-minute walk on February 4.
Lopez-Alegria too will set an astronaut record on February 22 when he takes a fourth walk with Russian cosmonaut Mikhail Tyurin taking his total to 10.
On a slightly longer-than-planned space walk on Sunday, flight engineer Williams and Lopez-Alegria hooked up a new cooling system to pave the way for installation of European and Japanese modules beginning this year. But in attaching a second pair of ammonia cooling lines to the station, they encountered a few problems including minor ammonia leaks.
Once exposed to the frigid cold of space, ammonia freezes, creating snowflake-like particles that might have touched the astronauts' spacesuits. "It was a very, very slow leak," said space station flight director Derek Hassmann.
NASA wanted to prevent ammonia from getting into the station's air, where it could pose a respiratory risk. So in addition to using the sun to gently bake off any hazardous particles on the suits, Williams and Lopez-Alegria waited a few minutes inside the station's airlock while ground control teams monitored sensors for signs of contamination. Finding none, they came in.
Earlier, after hooking the cooling lines, Williams brought tools and cables to the forward end of the lab, where Lopez-Alegria joined her. Together they worked on fixing a new cable that will allow specially equipped shuttles to tap into the station's electrical system rather than use their own limited supplies of chemicals to generate power.
The space duo did not have enough time to finish the cabling work. But they photographed a solar panel that is scheduled to be folded up during a station assembly mission next month as part of the most ambitious station assembly work ever attempted without a US space shuttle crew present.
Problems retracting an identical panel during the last shuttle mission in December prompted NASA to extend that crew's stay at the station for an unplanned space walk to help fold up the balky wing. The extra day in orbit ate into supplies normally reserved for weather-related landing delays. Engineers are tweaking plans for folding up the second panel in hopes of avoiding similar problems.
Once operational, visiting shuttles will be able to stay about three days longer at the outpost. NASA intends to try out the new gear during shuttle Endeavour's mission, now scheduled for June.
Managers shifted tasks normally handled by visiting shuttle crews to the resident station astronauts to free as much time as possible for the shuttles to haul and install the station's remaining laboratories, modules and trusses before the fleet is retired in 3-1/2 years.
Starting from scratch, it takes about 100 crew-member hours to prepare for a space walk. By doing them a few days apart, considerable crew time can be saved by not having to repeat some of those preparatory steps.