NASA scrubbed the launch of space shuttle Columbia for the third time after discovering a leak as liquid hydrogen and liquid oxygen were being poured into the fuel tank Wednesday.
The decision was made after 10 times the normal amount of hydrogen was found in the shuttle's aft compartment, said shuttle director Robert Crippen.The launch crew immediately began trying to trace the leak. No new launch date was set.
NASA canceled the first launch attempt in May after sensors detected an unusual buildup of liquid hydrogen during fueling in the aft compartment and around a valve in plumbing between the orbiter and external tank. The second scrub was last week because mission control had trouble communicating with one of the four telescopes in Columbia's cargo bay.
``I think we got fooled by the fact we had two leaks,' Crippen said. ``I think this leak has been there all along.'
Crippen said there was no leak this time in the connecting link between shuttle and tank. The aft compartment, where the explosive hydrogen was found, contains the shuttle's main engines.
Thursday's attempt would have been the 36th shuttle flight and the first in four months.
Wednesday's troubles were the latest blow to NASA's image. The highly touted Hubble Space Telescope failed to operate as advertised because its mirrors were ground wrong; the shuttle Atlantis developed a hydrogen leak similar to Columbia's and NASA controllers had intermittent problems contacting the Magellan space probe which is orbiting Venus.
``The shuttle's business is flying, and we're sitting on the ground,' Crippen said. ``I guess all I can say is that the shuttle is a very complicated vehicle. It flies in environments that are very strenuous and we have to be able to assure that the vehicle is safe to fly.'
Space shuttles rely on two sources of power to get into orbit. Two solid fuel rockets burn for two minutes to get the vehicle off the ground. At the same time - and continuing for eight minutes - the orbiter engines burn a combination of liquid oxygen and liquid hydrogen.
The shuttle's 154-foot-long tank holds 385,000 gallons of liquid hydrogen which is cooled to 423 degrees Fahrenheit below zero, and 144,000 gallons of liquid oxygen at 297 degrees below zero.