CAPE CANAVERAL, Fla. - Spacewalking astronauts ventured outside the International Space Station Monday, tackling construction work deemed critical to the most expensive building project ever attempted in orbit.
Clad in cumbersome spacesuits, mission specialists Robert Curbeam and Tom Jones floated into shuttle Atlantis' cargo bay about 11 a.m. EST (16:00 GMT) and then began scaling the 17-story international outpost.
"I think it's a great day to go do a spacewalk," shuttle pilot Mark Polansky told his crewmates as they headed out into open space.
The prime job at hand: Moving a shuttle docking port from a temporary storage spot on a station truss to the forward end of the U.S. Destiny science laboratory, where it will serve as parking place for future outpost assembly crews.
NASA officials say the move is crucial to the $60 billion station construction project, a joint effort of 16 nations on four continents.
The station's only other shuttle docking port is located directly below the 16-ton Destiny lab. If construction crews had to park at that port on upcoming flights, additional segments could not be mounted to the outpost because the lab would block the way.Consequently, the failure to move its twin to the front of the lab would force NASA to reorder a series of 40 more U.S. shuttle and Russian rocket flights still required to finish the growing station, which eventually span an area nearly as large as two football fields.
"If you can't dock where you intend to, it generally messes up the assembly sequence pretty badly," NASA lead flight director Bob Castle told SPACE.com during a news briefing Sunday.
"So we would have to fly another flight - or the next flight would have to take on a significant change and have to go finish the job - if we fail to get it done."
The criticality of the move, meanwhile, is not lost on either Jones or Curbeam.
"That's where all the shuttles will be docking for a long time," Curbeam told SPACE.com in a preflight interview. "I want to say for the next two years, they all dock there. That's a long time."
~Shaped like a big cone, the docking port was plucked from the end of the station's Unity module with the shuttle's robot arm and then latched to an outpost truss Saturday.
Robot arm operator Marsha Ivins pulled off the initial move with a spacewalking assist from Curbeam and Jones, clearing the way for the Destiny lab to be fixed to the end of Unity, a pressurized passageway to other parts of the station.
The trio set out Monday to do essentially the same job in reverse as the station's resident crew - Bill Shepherd, Yuri Gidzenko and Sergei Krikalev - continued to outfit the interior of the newly arrived Destiny lab, which was delivered to the outpost by the shuttle crew.
With the joined shuttle-station complex flying high above Earth, Ivins grappled the docking port with the 50-foot (15-meter) robot arm as Jones prepared to loosen the latch holding it to the truss.
Curbeam, meanwhile, was ready to remove protective covers from a berthing mechanism at the front end of the lab so that Ivins could slowly swing the port into place.
The spacewalkers had one other crucial job on their to-do list Monday: Installing a specially designed grapple fixture on the outside of the lab. The pin-like fixture must be put in place so that a Canadian-built construction crane can be mounted to it during a mid-April shuttle mission.
Starting four days, 16 hours and 46 minutes after the shuttle's launch from Kennedy Space Center, the spacewalk is the second of three planned for the Atlantis mission.
The final excursion - which is scheduled to get underway about 10:18 a.m. EST (15:18 GMT) Wednesday - will involve stowing a spare communications antenna outside the outpost.
Atlantis remains scheduled to depart the station Friday after a final farewell and hatch-closing ceremony set for 7:18 a.m. EST (12:18 GMT) that day. The shuttle and its crew are due to land at KSC at 12:52 p.m. EST (17:52 GMT) Sunday.
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