BioEd Online

NASA officials have decided to press ahead with a scheduled 4 July launch for the space shuttle Discovery, despite the fact that a small piece of insulating foam fell from the shuttle's external fuel tank yesterday, 3 July.

A roughly 7.5-centimetre-long triangular piece of foam weighing just 2.6 grams fell from a fuel line used to load the main external tank with liquid oxygen.

That could be a potential worry. During space shuttle Columbia's launch in 2003, a 700-gram piece of falling foam ruptured part of its wing, causing the shuttle to break up on re-entry.

Mission managers are watching Discovery's tank carefully, but say they do not think it will deter them from a launch at 14:38 EDT on America's Independence Day.

John Shannon, the deputy manager of the shuttle programme says that the piece of foam was half the size necessary to be considered a threat during launch. "This is not unexpected, and it would not have caused any damage," Shannon told reporters in a Monday press conference.

Third time lucky?

The piece of foam was the latest setback for the Discovery launch, which has already had two prior attempts scrubbed due to bad weather.

NASA officials say they think the foam problem arose, in part, because the team had to load and unload the frigid liquid oxygen several times from the main fuel tank for these attempted launches. The thermal stress caused the foam to crack, mission managers say, and rainwater freezing in the crack pried the bread-crust-sized piece from the tank.

The foam did not fall from the so-called 'ice frost ramps' that have been the subject of earlier controversy for the mission. In mid-June, two mission managers (a top safety official and chief engineer) gave the shuttle launch a 'no go' vote because of worries over this insulating foam. NASA administrator Michael Griffin overruled them, saying that, even if foam struck the shuttle, it would be possible to shelter the mission astronauts on the International Space Station until a rescue could be planned.

Team managers are now watching to see whether fresh ice forms in the crack. But they have concluded that the loss of foam so far should not lead to abnormal heating or larger foam chunks falling from the orbiter during launch, says the associate administrator for shuttle operations, Bill Gerstenmaier. "There's no loose foam in there, it all looks fine and the structure is in good shape," he says.

By the rules

The team is behaving responsibly, says John Logsdon, director of the Space Policy Institute at George Washington University in Washington, DC, and a member of the investigation board for the 2003 accident. "They're doing what they're supposed to be doing," he says. Nevertheless, the latest incident underscores the frailty of the shuttle system. "It's a fundamental design flaw to have the crew carrier below all this foam," Logsdon says.

The Discovery mission will bring an extra crewmember and supplies to the International Space Station. It is one of 16 more flights needed to complete the facility, a schedule that may prove hard to meet if Discovery continues to be delayed.

Even if the foam problem proves minor, there is a 40% chance that the launch will have to be scrubbed once more because of weather, according to NASA meteorologists. Afternoon thunderstorms are common during the humid southern summers, Shannon notes: "This is Florida in July."

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