Shuttle Fleet Grounded Again
Falling foam still too much of a risk
28 July 2005--The space shuttle Discovery blasted off its launchpad at the Kennedy Space Center in Florida Tuesday morning, finally returning the U.S. shuttle fleet to flight, following a two-and-a-half-year grounding in the wake of the Columbia disaster. But the celebratory atmosphere was soon tempered when newly installed cameras on the Discovery's huge external tank revealed a chunk of foam, about 70 by 30 by 20 centimeters, peeling off the tank during the ascent to orbit.
Though this foam did not strike the Discovery, in February 2003 a slightly larger piece of foam from an external tank struck the leading edge of Columbia's left wing, and the resulting 25-cm hole allowed superheated air to enter the Columbia, destroying the spacecraft during reentry. Consequently, much of NASA's efforts since then were aimed at ensuring that large pieces of foam could not come off the tank. With the apparent failure of these efforts, yesterday evening NASA ordered the rest of the shuttle fleet to be grounded again--indefinitely.
The external tank cameras also revealed that one of the heat-resistant tiles near the Discovery's front wheel well was dinged during lift off. But a closer analysis with another new piece of shuttle technology, a three-dimensional imager mounted on the end of an extension boom attached to the shuttle's robot arm, is not expected to reveal significant damage. Discovery should be able to make a safe landing on schedule on 7 August.
The successful launch of the Discovery, with its international crew of seven, was critical to the United States' ambitions in space. Even though NASA has been at pains to recast the shuttle as an experimental vehicle conducting test flights, it needs the remaining shuttles--Discovery, Atlantis, and Endeavor--as workhorses in the assembly and supply of the International Space Station. John Elbon, vice president and program manager of the ISS for Boeing, NASA's prime contractor for the station, explained before the launch, "we've had our fingers in the dyke, keeping the station patched together, and now we'll be able to make forward progress again."With that progress stalled once more, the future of U.S. participation in the ISS is in doubt. In 2006, the Russians will start demanding money for seats on their Soyuz spacecraft, the only means to reach the ISS with the shuttle out of commission. However, U.S. law prohibits NASA giving the Russian space agency any cash directly, raising the specter that U.S. astronauts may wind up without a ride to the ISS. [See "Saving the Station," October 2003, IEEE Spectrum, for a discussion of alternatives for completing and staffing the ISS]
Quite apart from the issue of completing the station, or sending up U.S. astronauts, there is the difficulty of maintaining the station, as is, without the shuttle. Discovery will be bringing valuable parts and supplies to the station that could not be brought up on the automated Russian Progress cargo ships that are regularly sent to the station.
Two new automated cargo ships planned for launch in 2006 and 2007 by Europe and Japan respectively will help ease the supply problem, but almost as important as delivering cargo to the ISS, the shuttle hauls things away. Although some garbage produced on the station can be stuffed into cargo ships, these ships burn up in the atmosphere after they leave, making them unsuitable for items such as the results of experiments that have to be returned to Earth. Discovery is bringing up about 1000 kilograms of material in the Italian-built cargo pod, dubbed Raphello, which is mounted in its payload bay. But it will bring back almost 2500 kg.
It is difficult to imagine how NASA will fix the external tank's foam-shedding problem without considerable analysis and testing, but even if the space shuttle fleet could be returned to flight tomorrow, Discovery's mission marks the beginning of the end for the shuttle. NASA's management is anxious to replace the aging shuttle fleet with a proposed Crew Exploration Vehicle, which will form the cornerstone of the agency's plan to return to the moon. The first manned flights of the CEV are planned for 2014, and NASA hopes to retire the shuttle by 2010, if it is not forced to permanently ground this troubled model of spacecraft today.