The Associated Press
CAPE CANAVERAL, Fla. Ÿ An overheated fuel cell forced NASA to scrub the launch of space shuttle Endeavour just hours before liftoff yesterday, delaying the already belated science mission by one week.
One of Endeavour's three electricity-generating fuel cells failed early yesterday morning, before NASA had even begun to fuel the shuttle. Technicians were able to restart the power plant, but it overheated again.
Shuttle managers called off the launch at 3:30 a.m., just after the five astronauts woke up to prepare for their scheduled 11:04 a.m. liftoff.
Shuttle operations director Bob Sieck said the fuel cell will be replaced, allowing for a launch attempt Thursday.
Until the fuel-cell trouble, NASA officials were most worried about thunderstorms that threatened to delay liftoff.
Endeavour was supposed to blast off in early August, but the shuttle had to undergo unprecedented launch pad repairs after NASA discovered singe marks on O-ring seals in the solid rocket boosters of two other shuttles. Technicians replaced the thermal insulation surrounding the Endeavour O-rings, located in nozzle joints.
The Challenger disaster in 1986 was blamed on a leak of hot gas through a different set of O-rings.
Sieck said yesterday that the latest mission ''has had more than its share of hardware and weather woes.''
''You have to look at it philosophically when you're in this business,'' he said. ''There are times when the hardware's going to stick its tongue out at you. You find the problem, you fix it and you get on with what the mission is all about.''
Engineers believe a valve on the fuel cell may have gotten stuck, said Pat Simpkins, chief of NASA's fuel-cell branch. The valve had been used for 1,700 hours, well below the limit, he said.
Beeswax interspersed with copper flakes is used to move the plunger that operates this valve. It's unlikely, though, that beeswax is to blame for the failure, Simpkins said.
The fuel cell heated up to 184 degrees Fahrenheit, 24 degrees above the limit.
Fuel cells, located beneath the cargo bay, burn liquid hydrogen and oxygen to generate electricity throughout a shuttle flight. Each unit weighs 255 pounds and is 40 inches long, 15 inches wide and 14 inches thick.
Fuel cells are critical: The failure of even one in orbit would force NASA to order a shuttle and crew back to Earth as soon as possible.
The National Aeronautics and Space Administration has replaced a fuel cell only once before at the launch pad, on Challenger in 1983.
During the 11-day mission, the five-man crew is supposed to release and then retrieve two science satellites, and perform a spacewalk to test tools and procedures for building an international space station.
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