A potentially dangerous hydrogen leak occurred as Nasa fuelled Discovery for lift-off yesterday, resulting in yet another delay for the space shuttle's final voyage.
It was the latest, and most serious, problem to befall Nasa's oldest and most travelled shuttle in the past week. The launch has now been postponed until 30 November.
Midway through the fuelling yesterday, flammable hydrogen gas began leaking from the attachment point for a vent line on the external fuel tank. A similar problem delayed two shuttle missions last year.
Managers halted the countdown two hours after fuelling began, and before the six astronauts had boarded the shuttle. Discovery's final mission was already four days late because of technical problems and poor weather conditions.
Allard Beutel, a spokesman for Nasa, said engineeers had hoped the craft would be ready for another lift-off attempt on Monday, but that more time was now needed to fix the leak.
Monday would have been the last opportunity before the end of the month for Nasa to send the shuttle to the International Space Station. After Monday, it would have been in danger of overheating while docking because of the solar angles.
Discovery will carry supplies and a humanoid robot dubbed Robonaut, or R2 – the first to go into orbit.