With Atlantis mission, shuttle's last days draw nearer

After a two-month delay, the space shuttle Atlantis and its six-member crew are set for launch Friday evening on an 11-day mission that is vital to completing the International Space Station.

This trip is the third to beef up the station's ability to provide electric power to European and Japanese laboratory modules, slated to begin arriving later this year. If all goes well, the work will put the station on track to receive a final set of solar panels and batteries next July and to support a crew of six, rather than three, in 2009. By July 2010, the station should be complete.

That timetable, though, brings a bittersweet recognition that Atlantis, Endeavor, and Discovery are fast approaching their collective curtain call. Completion of the space station means an end to the shuttle program, and for veteran NASA engineers who've worked on it for most of their careers, it's reminiscent of parting with Ol' Betsy.

"It's a little bit like taking your old car that you really have enjoyed ... and trading it in on a new one," says Wayne Hale, the shuttle's program manager. "The space shuttle is such an incredibly capable vehicle, and so many of us have spent so many years working on it. We're going to be very sad to retire it. But ... there are certain things about the space shuttle that we just can't make better" or safer.

The ramping down is already apparent. Workers at NASA's Michaud facility in New Orleans are welding and adding foam insulation to the last bullet-shaped external fuel tank, which feeds the orbiters' voracious main engines. In Canoga Park, Calif., workers are building the last one of those engines. Charts displaying orbiter assignments show a large blank for Atlantis after September 2008. When that mission ends, NASA will ground the orbiter and cannibalize it for spare parts.

President Bush's Vision for Space Exploration calls for a new set of rockets and capsules designed to send astronauts to the moon and perhaps to Mars. Moving on to the Constellation program "is very exciting," says Mr. Hale, citing "some new bells and whistles and new capabilities."

For Michael Suffredini, NASA's space station program manager, the concerns are a bit more pragmatic. "We'll miss the payload capacity," he says. The shuttle's cargo capacity is much greater than anything else currently launching to the space station, he notes. Indeed, two of the last three shuttle missions are contingency flights to bring vast quantities of supplies to the station in case other countries can't provide sufficient freight capacity on their spacecraft.

Still, the shuttle show is far from over. Hale notes that more shuttle flights remain than all of the lunar-landing missions that the Apollo program mustered. The pace is picking up, too. In 2005, NASA launched one mission, marking its return to flight after the Columbia accident in February 2003. Last year, the agency lofted three missions. This year, it scheduled five, although Atlantis's launch delay has whittled that back to four. Five are slated for next year.

Although this latest mission aims to increase the space station's ability to generate electricity, it also has a certain aesthetic element to it. "With this flight, we hope to see more symmetry" in the station's configuration, says Floyd Booker, the missions launch-package manager. After astronauts installed a similar set of solar panels last September, the orbiting outpost looked like an H with one leg missing. As a practical matter, this means the station's attitude-control system has to work harder to keep the outpost properly oriented.

Atlantis was originally scheduled to launch in March. But a severe thunderstorm moved across the launch site at the Kennedy Space Center, pelting it with golf-ball-size hail that damaged foam insulation at the top of the fuel tank. NASA had to haul the shuttle back into the cavernous Vehicle Assembly Building to fix the foam.

"We're really excited to be at this point after a long and arduous spring," said Leroy Cain, launch-integration manager at the Kennedy Space Center in Florida, at a prelaunch briefing Wednesday.

The delay prompted NASA to use this flight to exchange US space station crew members ahead of schedule: Sunita Williams – who has served as flight engineer aboard the station since December, setting a record for space walks by female astronauts and becoming the first astronaut to run the Boston Marathon in space (on a treadmill) – will return, to be replaced by Clayton Anderson.

After Friday's launch the Atlantis crew will spend two days circling Earth at ever greater distances to catch up with the station. Using an extension to the shuttle's robotic arm, they'll also inspect the craft for damage to the orbiter's heat-resistant tiles. Damage to Columbia's heat shield during launch led to the craft's destruction on reentry in 2003, killing its crew.

Once Atlantis docks to the station, astronauts using the orbiter's robotic arm will pluck a $376 million truss segment bearing the solar panels from the cargo bay and hand it off to the station's robotic arm. The station crew will use the arm to gingerly install the nearly 18-ton truss on an end of the station's girder-like backbone.

During the first of three planned space walks, mission specialists Jim Reilly and John "Danny" Olivas will hook up power cables from the truss and prepare the panels for deployment. The panels, which unfold like a gargantuan road map, will stretch 240 feet from tip to tip when fully extended. It will take two more space walks to prepare the new solar panel to rotate so that it can track the sun as the station orbits and to install an external vent valve for the new oxygen-generating system delivered last July.