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Last Updated: Tuesday, 19 July, 2005, 12:31 GMT 13:31 UK
Engineers still chase shuttle fix
Discovery on its launch pad (AP)
Time is running out for Discovery to lift off
The space shuttle Discovery will now fly no earlier than 26 July, Nasa says.

The US space agency's engineers are still trying to get to the bottom of the fuel sensor glitch that scrubbed last week's attempted blast-off.

Discovery has to get airborne by the end of July or it will lose the current window for daylight launches.

"We're still looking for the problem," Nasa's Bill Parsons said. "This team is trying everything it can to launch in the July window."

The technical gremlins centre on one of the four low-level fuel cut-off sensors found inside the shuttle's external tank.

During the countdown last week, it failed a routine pre-launch check. The sensors warn the shuttle computers if the tank is about to run dry, allowing the computers to shut down the three main engines safely.

Shuttle schematic (BBC)
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: To be determined
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda

The shuttle's engine pumps can force half a tonne of propellant per second out of the tank; and were these to run dry unexpectedly, they could overspeed and disintegrate.

"Hopefully in the next 24 to 48 hours, we will find the glitch that has got us all confused or frustrated or pick your adjective, and be able to fix it and go forward," said deputy shuttle programme manager Wayne Hale.

"But I think Tuesday (26th) is probably the earliest day that we would be looking for a launch, even in that optimistic case."

Nasa may decide that to fully understand all the issues it will need to conduct a tanking test. This would involve loading two million litres of supercooled hydrogen and oxygen into the external tank.

Such an operation would likely push a new launch date ever closer to 31 July, the end of the designated launch window.

"There is some debate as to whether we can do the kinds of tests that we would need to do at cryogenic temperatures in a launch countdown and [then] go ahead and launch that day, or whether we need to do a test, de-tank, recycle, [and] think about the data," conjectured Wayne Hale.

"So, that decision is before us, but the last tanking would be no earlier than next Tuesday."

US Space Shuttle Programme Manager Bill Parsons (L) answers questions about space shuttle Discovery  (AFP)
Shuttle programme manager Bill Parsons (l) is hopeful of making the window
If Nasa misses the current window, Discovery would have to wait until September to get airborne.

The long wait results from the need to have the International Space Station (ISS) in the right position in orbit and Nasa's desire to launch during daylight hours so it can photograph all aspects of the ascent.

Discovery's mission will be the first for a space shuttle since the loss of the Columbia orbiter on 1 February 2003.

The delay to Discovery's mission is being used by the crew of the ISS to reposition a Soyuz capsule attached to the orbiting outpost.

Russian cosmonaut Sergei Krikalyov and US astronaut John Phillips were set on Tuesday to take the Soyuz TMA-6 spaceship to a new docking point to make it easier for future spacewalks to get access to the station's exterior.

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