NASA worries about loose ends on shuttle

Busy schedule for astronauts
Discovery's seven astronauts worked alongside the international space station's two crew members on Sunday to transfer tons of cargo to the station.

The job was particularly important because it's been more than two and a half years since space shuttles have resupplied the station. When NASA's shuttles were grounded in 2003, the agency began relying on Russian vehicles to deliver supplies — but some items are too bulky to fit on the Russian-built cargo spaceships.

For example, one of the items that was shipped aboard Discovery is a 600-pound (273-kilogram) replacement guidance gyroscope. The station uses four such gyroscopes to keep the station in its proper position, but only two of them have been working in recent months.

One of the failed gyroscopes has now been reconfigured with the aid of Discovery's crew. The other one will be replaced during a spacewalk, then brought back to Earth along with the rest of the unused equipment and trash being taken out of the space station.

NASA had planned yet another station resupply mission in September, but that flight was put on hold after a large chunk of foam insulation was seen tearing away from Discovery's external fuel tank during its ascent. That means it may be longer than expected before the station gets another shuttle visit. As a result, mission managers extended Discovery's mission by a day so that more goods, ranging from water to laptop computers and a printer, could be left on the station.

Bill Gerstenmaier, the station's program manager, said the extra supplies — plus a Russian cargo shipment scheduled in September — should leave the orbital outpost "in very good shape through the end of the year."

In addition to the transfer activities, three spacewalks are on the agenda. During the first, conducted on Saturday, astronauts tested experimental techniques to repair cracks in the shuttle's tiles or reinforced wing panels. The spacewalk to replace the broken gyroscope is to take place Monday, and the third outing is devoted to installing a cargo platform on the station's exterior. That agenda would have to change if NASA sends the spacewalkers to work on the protruding gap fillers.

Surprised by foam problem
During a series of TV interviews on Sunday, Discovery's astronauts said once again they were surprised to learn that the fuel tank had lost so much foam insulation.

"The biggest emotion was one of disappointment, that all of that work that had been done to make sure that foam would not come off had failed to address one critical area where foam was liberated, and it was a great surprise," astronaut Andrew Thomas said on "Meet the Press."

"We didn't feel it was a threat to us from a point of view of our return home and our entry.  It didn't strike us, but nonetheless we're very, very troubled and very disappointed that such a thing could happen," he said.

NASA's Griffin told NBC that he was surprised as well. "Certainly we were lucky" that the pillow-sized piece of foam from an area called the protuberance air load ramp, or PAL ramp, did not strike the shuttle orbiter, he said.

Before Discovery's flight, engineers had conducted aerodynamic and non-invasive tests focusing on that area of the fuel tank, but decided the best course was to leave the PAL ramp as is. "We goofed on that one," Griffin said.

The space agency will hold off on future shuttle flights until the problem is fully understood and addressed, Griffin said. "We have convened what I've called a tiger team of exceptional engineers within the agency to begin looking at ... what did we miss?  Why did we miss it?" he said.

Thomas questioned whether the decision to leave the PAL ramp alone was motivated by cost pressures or schedule pressures rather than strictly technical factors, but Griffin said he was sure it looked like a "reasonable engineering decision" at the time.

"That decision in retrospect was clearly wrong," Griffin said. "But I am certain it was not made out of schedule or cost pressure justification."

This report includes information from The Associated Press and MSNBC.

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