Nasa scrambles to find fault
2005-07-15 10:18
Florida - Nasa raced against time on Thursday to fix its Discovery shuttle and avoid an extended delay in getting the space programme back on track.
After calling off Wednesday's launch, Nasa must get the shuttle into orbit by July 31 or be forced to wait until September 9 for a new launch "window".
Nasa initially said that no new launch could be attempted before Saturday, at the earliest, but by late on Thursday, even Sunday was looking unlikely for another attempt.
Experts have blamed a faulty gauge on the hydrogen fuel tanks for the decision to halt the countdown two hours and 20 minutes before Wednesday's lift-off. The seven crew members, including Japanese astronaut Soichi Noguchi, were already on board Discovery.
Nasa engineers held a first meeting into the causes of the fault early on Thursday before their first examination of the electronic circuitry that controls the sensor and released details later in the day.
The sensor is one of four that sends data on the levels of hydrogen in the main tank, to determine when the three engines should be shut off during the ascent into orbit.
The faulty sensor "showed 'wet' when we sent test commands that should have made it indicate dry to the computers," Wayne Hale, deputy director of Nasa's shuttle programme, told a news conference, explaining what had triggered the alert.
Dry is the "low-level cut off state", said Hale. "One of those four sensors failed that check. That's a violation of our launch commit criteria so we stopped the count."
While keeping an eagle's eye on the sensors, the technicians went ahead and drained the tank in an operation that started on Wednesday night.
Twelve different engineering teams
"When the tank was drained down to the point at which those sensors were uncovered, three - the good three sensors - showed dry." The fourth sensor still showed wet, he said.
However, "after about three hours of reading wet, the sensor changed to dry," presenting the "very worst kind of thing to troubleshoot".
Twelve different engineering teams are in place "to attack" the problem, which he described earlier as an "unexplained anomaly".
Thursday was "largely spent in data review" and "what we are more likely into is several days of troubleshooting".
"Tonight, as our troubleshooting plan comes together, we will probably start to offload the cryogenic reactants for the fuel cells.
"That gives us the safety measure to get into the aft end of the orbiter to try - start - the troubleshooting inside if we decide that's the thing to do.
"Given that work, if we were to get extremely lucky, it is theoretically possible that we could still launch on Sunday," said Hale.
If the problem is serious, Nasa will have to take the shuttle back to its hangar at the Cape Canaveral base in Florida.
Repairs would then take weeks to carry out, and a launch in August is not possible because of the orbit of the International Space Station.