On the eve of NASA's return to flight, a falling window cover dinged a couple of tiles on the shuttle Discovery — but the space agency said engineers made a quick fix to keep preparations on track for Wednesday's scheduled launch.
Less than two hours after NASA Administrator Mike Griffin declared that Discovery was "go for launch," engineers at the launch pad discovered that a foam-edged, plastic cover had come off one of the cockpit windows, fell 60 feet (18 meters) and hit a protruding engine pod on the left side of Discovery's back end, the agency said in a written statement.
An assessment determined that the cover had damaged two of the shuttle's high-temperature tiles, and that a repair could be made quickly by switching out the metal panel to which the tiles were attached, Discovery vehicle manager Stephanie Stilson told reporters. She said a spare panel was installed and checked — and although the replacement was slightly out of alignment with the surrounding tiles, inspectors gave the OK for launch.
"This is a minor repair for us," Stilson said.
Overnight, NASA engineers would inspect the rest of the shuttle and make calculations about whether the falling panel, which weighs less than 2 pounds (1 kilogram), might have damaged the shuttle's structure, Stilson said. But she voiced confidence that the countdown would proceed toward launch at 3:50:53 p.m. ET Wednesday.
The biggest uncertainty had to do with weather in the area around Florida's Kennedy Space Center. Forecasters rated the chance of acceptable weather at 60 percent, a slight downgrade from the previous estimate of 70 percent.
Griffin said he was "hoping the weather gods are kind for tomorrow." If weather forced a postponement, NASA could try again Thursday. Further launch opportunities are available until July 31, and then again starting in September.
Following up on Columbia
Discovery's top mission is to test safety measures that were put into effect after the catastrophic breakup of the shuttle Columbia in February 2003. That tragedy killed all seven of Columbia's astronauts and brought the rest of the shuttle fleet to a standstill while NASA and an independent panel investigated the accident's cause.
Investigators concluded that Columbia's left wing was hit by a piece of flying foam insulation from the external fuel tank, opening up a hole in the left wing. Sixteen days later, during atmospheric re-entry, hot gases entered that hole and destroyed the shuttle from within, the investigators said.
Since then, the shuttle and its fuel tank have undergone scores of upgrades. More than 100 cameras will watch Discovery's launch and ascent for any signs of damage, and during the 12-day mission, astronauts will try out new procedures for inspecting the shuttle in orbit. Spacewalkers will test three methods for fixing damage to the shuttle's protective skin, using sample materials.
Griffin said he was confident the safety concerns raised by the Columbia accident had been adequately resolved. "There is nothing that we know of that we have not addressed," he said.
At the same time, he acknowledged that risks still remained. "Can there be something out there that can bite us? The answer is yeah. ... This is a very tough business," he said.
On Monday Wayne Hale, head of Discovery's mission management team, reported that some "loose ends" still needed to be tied up before the go-ahead was given for launch. Some of those pending issues involved questions about test readings from fuel tank sensors, standards for winds in the upper atmosphere at launch time, and paperwork for the repair tools to be tested during the mission.
Those technical issues were discussed during what Griffin called a "very interesting" meeting of the mission management team at midday Tuesday. Without going into specifics, the administrator said all the loose ends were "amply put to bed. ... We're in good shape."
Earlier in the day, test director Jeff Spaulding said preparations at the launch pad were on schedule. A support structure surrounding the spaceship is to be pulled away Tuesday night, and if the schedule goes according to plan, Discovery's external fuel tank will be filled starting at about 6 a.m. Wednesday.
Launch weather officer Kathy Winters said rain showers were likely to sweep over NASA's Kennedy Space Center at midday Wednesday, just hours before space shuttle Discovery's appointed launch time. "We may actually have to go 'red' during the countdown," she said, referring to a no-go condition.
However, Winters and other shuttle team members were hopeful that the skies would clear in time for the launch.
In addition to the safety tests, Discovery is to bring 28,000 pounds of payload to the international space station, including a replacement navigational gyroscope and a storage platform that will be installed during two of the mission's three spacewalks.
The third spacewalk will be devoted to the testing of repair tools, including a caulking gun and a daub-on applicator that could fill half-inch-wide (centimeter-wide) cracks in the shuttle's protective skin.
Griffin acknowledged that the experimental repair tools packed aboard Columbia didn't have "any substantial repair capability," and he said "it'd be a very interesting question as to whether we'd even want to try that" in the event of a serious breach.
A "more logical" move would be for the crew to seek refuge on the space station and await rescue, he said. NASA has drawn up an emergency plan to send up a second shuttle crew aboard Atlantis within about 40 days to pick up Discovery's astronauts and bring them back. A similar rescue plan is in place for the next shuttle mission as well, but Griffin said NASA couldn't set up such dual-shuttle scenarios indefinitely if the agency wanted to finish construction of the space station by 2010 as scheduled.
NASA's vision for space exploration calls for retiring the shuttle fleet in 2010 and developing a new spacecraft for pushing on to the moon, Mars and beyond. Advance reports have indicated that Griffin favored a shuttle-derived system for the shuttle's successors, but he declined to discuss his views on that subject until after Discovery's launch.
The administrator said NASA's return to flight was an essential step in NASA's space exploration strategy. "Obviously it is utterly crucial for NASA, for the nation, for our space program to fly a safe mission," he said.
Griffin said Discovery's mission paid tribute not only to Columbia's astronauts, but to other space explorers as well: "Every space launch we do is a tribute to all those who have gone before — those who have died, and those who have lived."
He specifically cited the loss of three astronauts in the 1967 Apollo 1 fire and the 1986 Challenger explosion. "Going back even further to 100 years of aviation, the safety systems that we who fly have learned and know are written in other people's blood," said Griffin, who is a pilot as well as a rocket scientist.
In a statement, the families of the Columbia astronauts praised NASA's efforts and said "the exploration of space must go on."
"We hope we have learned, and will continue to learn, from each of these accidents, so that we will be as safe as we can be in this high-risk endeavor," the families said.