Foam Mishap Won't Delay Shuttle Launch
Tuesday, July 4, 2006
CAPE CANAVERAL, July 3 -- NASA engineers cleared space shuttle Discovery late Monday for an Independence Day launch after technicians used a makeshift inspection probe to show that the loss of a small piece of foam insulation from the external fuel tank did not pose a safety threat for liftoff.
"We're going to continue with the launch countdown," William H. Gerstenmaier, NASA's associate administrator for space operations, told a news conference. An evening meeting of Discovery's mission management team gave the go-ahead "without dissent," he said.
The scheduled launch, the third attempt in a window that lasts until July 19, will take place at 2:38 p.m. Tuesday, barring mechanical glitches or inclement weather such as the storms and thunderheads that prompted two cancellations over the weekend. The launch, if successful, will be the first for the shuttle on the Fourth of July.
Tuesday's launch was thrown into doubt after the launch pad's "ice team" detected a crack late Sunday in insulation on a bracket holding the liquid-oxygen feed line to the side of the external fuel tank. The crack was noticed after the tank had been emptied after Sunday's scrub. Eventually a three-inch triangular piece of foam fell from the site of the crack to the launch platform, where it was picked up by the ice team.
The triangle weighed 0.0057 of a pound, about half the size of any fragment that could do significant damage to the thermal tiles on the shuttle's underbelly, mission management team Chairman John Shannon said early Monday.
Still, the incident marked another problem with the external tank's foam in a series that began in 2003, when foam debris breached space shuttle Columbia's heat shielding during launch, causing the orbiter to disintegrate on reentry. Launch debris during the first post-Columbia flight last July did not damage the shuttle but caused NASA to ground the shuttle fleet for another year.
Engineers for this flight are also closely watching for foam loss from brackets that hold pressure lines and electrical cables to the tank. Sunday's problem had nothing to do with these brackets.
Shannon laid out three criteria used to determine whether Discovery could be launched Tuesday: that the lost foam would not lead to overheating of the tank on the exposed surface during liftoff; that excessive ice would not form on the denuded patch; and that inspectors could take a close look at the damaged area to make sure there were no additional problems.
Gerstenmaier said the first two conditions were easily met because there is "plenty of [safety] margin" for thermal stress and ice formation. But inspecting the damaged area was "probably the biggest issue," he said, because the launch would have to be postponed a day to allow a platform to be set into place so technicians could get a good look.
But "some of our folks down here . . . came up and said, 'We have a technique we've been using to inspect some remote areas, and we'd like to try it,' " Gerstenmaier said. "The team came to the rescue."
Gerstenmaier said the technicians used a device they made -- a camera inserted into an eight-foot length of plastic pipe that could be bent, allowing it to peer around corners and into inaccessible alcoves and niches.
Engineers on the launch pad watched the images as the team moved the camera around the affected area, showing clearly that there was no further foam damage. "They did as good an inspection . . . or even a better inspection than if they had gotten out there on the platform," Gerstenmaier said.