Inside the Orbiter Processing Facility at the Kennedy Space Center, NASA technicians are readying the space shuttle Discovery, which is expected to be launched next March. Discovery will be the first shuttle to go into orbit since the loss of Columbia in February 2003, and the space agency has redesigned the vehicle to reduce the risk of a similar catastrophe. Yet not all the recommended fixes will be in place at the time of the first flight, limiting the kinds of missions the spacecraft can tackle.
First and foremost, NASA will remove the foam insulation from the metal struts connecting the shuttle to its external fuel tank; a 1.7-pound chunk of this foam fell off during Columbia's launch and punched a hole in the shuttle's wing, allowing superheated gases to flow into the craft on reentry. And in case foam peels off from another part of the external tank, NASA has put sensors in Discovery's wing panels to detect debris impacts and will install a digital camera for viewing the tank after it separates from the shuttle during the ascent.
Other safety steps, however, have proved harder to implement. In its August 2003 report, the Columbia Accident Investigation Board urged NASA to devise ways to inspect the shuttle while it is in orbit and repair any serious damage that is discovered. The space agency began work on a sensor system located at the end of a 50-foot-long boom that would be attached to the shuttle's robotic arm. Equipped with a laser ranger and a television camera, the system is designed to capture three-dimensional images of the reinforced carbon-carbon panels on the shuttle's wings. But a recent report by the Return to Flight Task Group, which is monitoring NASA's progress, said the inspection effort faced "enormous challenges" because of the tight schedule for developing the sensor system. The plans for repairing damage are also incomplete: although the astronauts will be able to fill cracks in the wings and plug holes up to four inches wide, they will not be able to fix a gash as large as the six- to 10-inch breach that doomed Columbia.
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As a stopgap, NASA is preparing alternative measures that do not require as much technology development. Before Discovery docks with the International Space Station, the shuttle's pilot will flip the craft so that astronauts in the station can take photographs of the heat-shield tiles on the shuttle's underside from 600 feet away. The crew members may also conduct space walks to get a closer look. If they find a hole that cannot be fixed, the Discovery's crew will remain in the station until the arrival of the shuttle Atlantis, which could be launched on a rescue mission within 45 days. The station should have enough supplies to support the astronauts for that long, assuming there are no breakdowns in critical systems such as oxygen generation or carbon dioxide removal.
Because NASA will rely on the station as a safe haven for shuttle crews, agency director Sean O'Keefe has canceled a planned 2006 mission to service the Hubble Space Telescope, which is expected to cease operating by 2008 if its batteries and gyroscopes are not replaced. (Hubble and the station travel in very different orbits, making it impossible for the shuttle to visit both.) Instead O'Keefe gave the go-ahead in August for a robotic mission to install new batteries, gyroscopes and scientific instruments to Hubble, at a cost estimated between $1 billion and $1.6 billion (about three times as expensive as a shuttle mission). But a robotic mission to Hubble might not prove successful, because much new technology needs to be developed, according to a July National Academy of Sciences report.
Ironically, limiting the shuttle to space station flights might actually be riskier than fixing the Hubble. Robert Zubrin, an astronautical engineer who heads the Mars Society, notes that the risk of fatal impacts with micrometeors or man-made debris is much lower during a Hubble mission because the shuttle can be oriented to minimize its vulnerability. (While docked at the station, the craft's belly is exposed.) And finishing the assembly of the station will require at least 25 shuttle flights, whereas repairing Hubble would entail only one.