The space shuttle Discovery's flawless touchdown at the Kennedy Space Center in Florida Monday marks the end of NASA's recovery from the Columbia tragedy and paves the way for the agency to resume building the International Space Station.
Over the next 12 to 18 months, NASA is loading its space shuttles with space-station elements that will push the orbiters to their cargo-carrying limits. The complexity and packed pacing of spacewalks that shuttle astronauts and the station crew will have to perform are unprecedented, NASA officials say.
It's all in the name of putting the infrastructure in place to support the final elements – European and Japanese laboratory modules and a full crew of six – before the shuttle program ends in 2010.
"The operations we plan over the next 12 to 18 months are the most complicated things we've done in the history of manned spaceflight," says Paul Hill, the mission-operations manager for the space-shuttle program.
For the moment, however, NASA managers are savoring the success of Discovery and its six-member crew.
Discovery delivered 500 metric tons of supplies and equipment to the station. By contrast, all of Russia's vital resupply missions after the Columbia accident in 2003, when the shuttles were grounded, delivered some 290 pounds of food, clothing, and other gear. In addition, spacewalking astronauts swapped out a balky piece of hardware associated with a small rail-car-like transporter astronauts will need to use during construction. They bolted a spare cooling pump to the station's exterior, which station crew members can install later.
"I can't think of a better mission in recent history," space-station program manager Michael Suffredini said during a weekend briefing.
Discovery's flight also has demonstrated that NASA appears to have solved the worst of its problems with foam insulation, which can break loose during launch. A suitcase-size chunk of foam weighing just under two pounds damaged Columbia's heat shield and led to its destruction and the death of its seven-member crew in 2003.
The current flight was the second of two aimed at testing on-orbit inspection and repair techniques for the tiles and carbon-composite materials that make up the shuttle's heat shield. The most unusual defects the inspections found turned out to be bird droppings.
Overarching goals for the opening phase of construction are to make sure the station can generate enough electricity for the additional modules it will host, to have the docking capacity it needs, and to have sufficient cooling capabilities. Along the way, astronauts will rearrange existing solar panels along the station's exterior and rewire the station's electrical systems.
At one point during this initial phase, the shuttle and its robotic arm will gently tug one set of multiton solar panels free of its current position at the center of the station, then drag it to its final location at the end of a truss, where it will be reinstalled.
The coming construction missions have been planned for years, delayed only by the Columbia accident. NASA and its contractors have taken advantage of the hiatus to upgrade hardware and give crews extra training time to prepare for this final push.
"Everybody comes up with new things we can go off and do here on the ground that will save us time on orbit," says Brad Cothran, director of station integration operations for Boeing, the prime contractor for the station elements that the US is providing.
For example, engineers and technicians at the Kennedy Space Center spent six to nine months installing and testing a wireless network for sensors on key structural elements that will provide information on the structural health of the station. Initially, NASA had planned to install that system on orbit. The result: "That's going to end up saving the program a lot of precious EVA time," Mr. Cothran says, referring to extra-vehicular activities, or spacewalks.
Here at the Johnson Space Center, mission planners also have been poring over mission-activity schedules to find ways to keep from overtaxing astronauts and station crews, adds John Curry, the lead flight director for Discovery's next mission in December. Some of these changes include eliminating the rigorous exercises that astronauts perform just before spacewalks and giving them extra time to relax prior to a space-walk – called "the camp-out protocol" for EVAs.
Barring another orbiter accident, the biggest concern for Mr. Hill is what he terms "infant mortality ... that we finally have some major piece of equipment that fails. Those are the types of things we can't control."
Every major component so far "has worked right out of the box," he says. But the failure of a newly installed component "would throw a monkey wrench into everything else we plan to do," he says.
It's unlikely that NASA would delay the shuttles' retirement to compensate. "There's no double-supersecret plan to fly other flights," Hill adds. "The no-kidding NASA policy is that we intend to stop flying the shuttle in 2010."
Still, the goal is worth the risk, he concludes. "We're on the cusp now. The shuttle's back in action. We're going to do these really hard assembly flights in the next 18 months. Then we're going to start using this thing and getting the bang for the buck that we'd intended to get."