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NASA needs time to have more checks and tests in resolving the technical problem that suspended the planned Wednesday launch of Discovery, the US space agency said late Friday afternoon.
It said it is also trying to have a launch before the end of July or extend the current launch window for five days.
Shuttle program deputy manager Wayne Hale said this at a news conference after a NASA management team meeting.
The current July launch window runs until July 31. The next launch window is in September. The engineers are working quickly and over weekend.
If they find what caused the launch glitch, they are near fixing it, Hale said.
A future launch date pins on how fast the engineers could work out a solution and there will be a launch four days after fixing the technical problem, he added.
A sensor designed to warn about a low level of liquid hydrogen in the shuttle external fuel tank failed to work properly in the pre-launch test Wednesday and caused the delay of the first shuttle flight of NASA since the 2003 Columbia disaster.
There are four sensors working for different purposes installed at the bottom of the tank. As a NASA rule, a launch requires the normal operation of all of them.
A similar sensor problem occurred in the April tanking test. But a May test saw all sensors working properly.
After that, Discovery was returned to the assembly building and replaced with a new and safer model of tank.
NASA officials had said they just could not understand the sensor problem normally. The US space agency is now having 12 engineering teams around the nation at work to look at every aspect of the launch glitch to find out the cause.
One of the possibilities is that modifications in the tank design NASA had made to improve flight safety caused the sensor problem, which NASA said only emerged after the Columbia disaster.
Earlier in the afternoon, NASA spokesman Allard Beutel said NASA has currently no plan for a rollback of Discovery from the launch pad to the vehicle assembly building.
NASA had made many shuttle safety improvements over the past two and a half years. The efforts included major modifications in the tank design, and the installation of an extra heater along the feedline of liquid oxygen to prevent ice buildup on the tank when the tank is filled with super cold liquid oxygen and hydrogen fuel.
The measures were intended to reduce the risk from insulation foam and ice breaking off the tank on liftoff and damaging the shuttle.
The Columbia tragedy was blamed on a suitcase-sized insulation foam that fell off the external fuel tank on liftoff and harmed Columbia's left wing, leading to the shuttle's disintegration during re-entry.
However, NASA engineers found in the April tanking test that any ice breaking off the tank on liftoff could do bigger harm if it smacked into the shuttle. Safety concerns then had delayed the launch from mid May to July.
The task force reviewing NASA's return-to-flight preparations had concluded that despite the progress in many aspects, NASA has failed to meet three of the 15 recommendations raised by the Columbia accident investigation board.
It said NASA has not eliminated the debris risk, failed to sufficiently toughen up the shuttle's shell, and remained incapable of orbit repairs.
After its own review of preparatory work, NASA had decided that the level of risk was acceptable, and that it would go ahead with the launch.
As the hurricane season has begun, NASA had feared that unfavorable weather could block the launch on Wednesday. However, the weather that day had turned to be good.
(Xinhua News Agency July 16, 2005)
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