Nasa officials have scrubbed today's launch of the space shuttle Atlantis after sensors on the main hydrogen fuel tank failed critical tests. The launch has been postponed until at least 4.09pm (21.09GMT) Friday, while engineers attempt to fix the problem.
The Atlantis mission is set to deliver the European Space Agency's long-delayed science lab Columbus to the International Space Station.
In tests this morning at the Kennedy Space Center, two out of four sensors indicated that the shuttle's main hydrogen fuel tank was full when it was actually empty. "If that were to happen in orbit, the engines would continue to run dry and that would be catastrophic," said Alan Thirkettle, ESA's programme manager for the space station.
Similar sensor glitches have blighted launches since they resumed after the loss of the space shuttle Columbia during re-entry in 2003.
The sensors are part of a safety system that ensures the shuttle's main engine does not switch off too early or too late. At least three must be working perfectly before the shuttle can be cleared for launch. In flight, an onboard computer shuts the engines down when a majority of the sensors declare the main fuel tank to be empty.
"This is the kind of thing that can happen in countdown. It's a complicated vehicle and we'd much rather go late and right than on time with doubts. Yes, we are disappointed, but this will be a temporary disappointment," said Thirkettle.
Engineers are not only checking the sensors, but also surrounding circuitry for faults. Earlier this morning, engineers discovered a minor leak in equipment used to fill smaller liquid hydrogen tanks aboard the shuttle. The gas is used to power fuel cells that provide electricity during the voyage.
The delay could have knock-on effects for the mission, which officials are keen to extend from 11 days to 13. If the shuttle is kept on its launchpad for too long, some of the hydrogen already pumped into the fuel tanks will evaporate, and the fuel cells will not be able to generate electricity for the extra two days.
