The U.S. space agency NASA says Tuesday wiring problems with fuel sensors have forced it to postpone the May launch of the shuttle Discovery until at least July 1.
NASA officials say the sensors monitor fuel levels in the external tank. Known as ecosensors, the devices tell engineers when the liquid hydrogen fuel is about to run out. Space Shuttle Program Manager Wayne Hale said the wiring problem could lead to false readings.
"After a lot of work, there is now some body of evidence that would indicate it's possible for the sensors to read, erroneously, dry when the tank is not, in fact, dry," said Wayne Hale.
Hale said vibrations caused during the transport of the tank could have caused the problem. He said NASA engineers are taking no chances.
"We are taking the step of removing the external tank cutoff sensors from the bottom of the liquid nitrogen tank on the tank we're going to use for the next shuttle flight," he said.
Hale said replacing the tanks could take up to three weeks.
The new external fuel tank is covered with softer insulating foam than its predecessors to reduce the chance of detaching insulation damaging the shuttle during lift-off.
A chunk weighing about one kilogram came off the orbiter Columbia during launch three years ago, piercing a wing. The damage led to the deaths of seven astronauts when the shuttle disintegrated during the searing heat of re-entry.
NASA grounded the shuttle program for two years, as it tried to solve the problem by eliminating some foam and applying it better in other places. But more pieces broke off Discovery's fuel tank last July, causing another stoppage of flights.
NASA hopes to launch three shuttles this year to resume assembly of the International Space Station. President Bush has ordered the agency to finish the space station construction and disband the shuttle fleet by 2010. NASA is expected to develop a successor to the shuttle for missions to the moon by 2020.