The U.S. space shuttle Discovery has been moved to the launch pad in advance of its planned liftoff in late May or early June. The roll out is a major maneuver in the two-and-a-half-year-long effort to return shuttles to flight after the orbiter Columbia's disintegration. Discovery and the two other remaining shuttles have undergone extensive safety modifications. But, officials at the U.S. space agency, NASA, warn that no upgrade can guarantee against another disaster.
When Discovery takes off to rendezvous with the International Space Station, it will be with many thousands of enhancements to upgrade its hardware, improve NASA's ability to track and inspect it in flight, and attempt repairs in orbit if necessary.
"We have looked from end to end at the shuttle and tried to make improvements across the board so that it will be safer than it ever has been," said Deputy shuttle program manager Wayne Hale.
"We've had 20,000 people, very dedicated, working on the space shuttle to return it to safe flight, people who sacrificed their weekends, their evenings, their holidays to get us back to safe flight," he said.
NASA's focus has been on preventing pieces of hard insulation foam covering the shuttle's huge external fuel tank from shedding during liftoff and damaging the orbiter. A small piece cracked Columbia's wing, allowing extremely hot atmospheric gases to penetrate and doom the shuttle during the searing heat of re-entry. The foam prevents the frigid liquid hydrogen and oxygen fuel from causing ice buildup on the tank. It has been removed from the location it broke off on Columbia's tank and replaced with heaters. Elsewhere, its application has been improved.
But Mr. Hale says despite the effort, NASA cannot entirely eliminate the chance a foam pellet would cause havoc.
"There is still going to be the possibility that a golden BB could get us," said Wayne Hale. "We have done a huge amount of work to reduce the debris environment, but it's my understanding that we're still going to fly with some risk."
As a result, NASA has increased the number of cameras that observe shuttles at every stage of ascent. About 100 cameras will document debris shedding. They are positioned around the launch site on a ship at sea, on observation aircraft, and on the shuttle and the external fuel tank itself. Radar will be used for night launches. In addition, a new camera at the end of a mechanical arm can inspect the surface in orbit.
The shuttle's wings also have new sensors to measure debris impacts and any increase of heat.
If damage does occur, Discovery astronauts would take a spacewalk to repair the shuttle's surface with caulking or plugs. They will practice such techniques on their next mission. If the damage is too extensive to fix in orbit, deputy space station program manager Bill Gerstenmeier says the astronauts could move into the station for up to 45 days while ground technicians prepare a second shuttle to rescue them, although room aboard the station would be tight and facilities strained.
"It's something that you don't want to go do, but in a survival sense, it's executable," said Bill Gerstenmeier. "It's a reasonable plan that's available if it's absolutely needed. Again, I think the conditions won't be good on the station, but it's better than the alternatives and overall I think we're prepared to go execute if we need to execute."
As NASA prepares to resume shuttle flights, it is also starting to formulate plans to retire the fleet. Agency officials say they have begun examining ways to cancel contracts from shuttle suppliers, close certain work sites, and redirect or eliminate some of the work force.
Shuttles have been the main logistical support for the space station, but President Bush has ordered NASA to decommission them by 2010 after station construction is finished. He has directed the agency to switch its focus to developing new spacecraft and technologies to send humans back to the moon and beyond.
The U.S. astronaut currently aboard the station, Leroy Chiao, says the loss of the shuttles would not affect the supply of the outpost because Russian spacecraft can fill the void, as they have during the shuttle launch hiatus. In addition, a new European supply craft will be available next year.
"We've got several different options to resupply the station, and I'm confident we'll have that capability," said Leroy Chiao.