Shuttle launch delayed to July

NASA is delaying its next space shuttle mission to July to replace faulty fuel sensors inside the external tank.

The space agency had been targeting May 10 for the second flight since the 2003 Columbia accident. However, the schedule already was tight and the external tank fuel sensors were just one of several technical hurdles to clear before liftoff.

NASA shuttle program manager Wayne Hale announced the delay this afternoon after two days of meetings about the issue. This was not an easy decision, Hale says.

The four suspect sensors measure the liquid hydrogen in the bottom half of the external tank. One of the sensors gave unexpected readings during an electrical test before the tank was shipped from its New Orleans factory to the Kennedy Space Center in Florida late last month. NASA engineers have been debating what to do about the problem ever since.

The sensors provide a backup way of making sure the shuttle's three main engines shut down after reaching orbit.

If multiple sensors fail in flight, the engines could cut off early and force the shuttle commander to attempt a risky, never-before-tried emergency landing. Another possible consequence: the engines could continue to run dry, without propellants, potentially causing an in-flight explosion.

The same type of fuel-depletion sensors caused NASA to delay its first attempted return to flight mission last year. The agency ultimately launched without knowing what caused some of the sensors to give intermittent readings during tests.

Swapping out the four sensors, which are located inside and near the bottom of the 15-story tank, could take three to four weeks. The launch team at KSC already was working with no slack time in its schedule between now and a mid-May liftoff.

That left the agency with little choice but to delay to the next available launch window, which stretches from July 1 and July 19. The limited launch windows (a couple weeks at a time about every other month) are a product of a new safety requirement to launch shuttles only during daylight hours to make sure cameras get clear pictures of the shuttle and possible debris.

A July launch, in theory, would still allow the space agency to attempt up to three launches this year.

Among other problems facing the team: the 11th-hour replacement of Discovery's robot arm after it was inadvertently damaged by workers. Ultrasound inspections found a small crack inside the crane-like robot arm, and it is being shipped back to the manufacturer in California for repairs.

NASA also is waiting for results of wind tunnel tests to determine whether changes to the external tank's foam insulation are safe. The test results were to be analyzed in April, leaving little time for additional modifications, if needed, before a May flight.

Hale says that the extra six weeks or so will provide some additional time to deal with those other issues.