NASA said today that it has decided to push back the final launch of the space shuttle Endeavour until at least May 16. This is the third delay since the shuttle's April 29 launch was scrubbed due to problems with its hydraulic systems.

The shuttle Endeavour atop pad 39A shortly after a launch scrub was announced on April 29. NASA said today it would delay the launch until at least May 16.

In a release, NASA said that Endeavour will launch no earlier than May 16. After the April 29 scrubbing, the agency targeted May 2, then May 8, and now mid-May at the earliest. NASA managers have got to be worried that each subsequent delay is threatening the space shuttle program's last-ever launch, that of Atlantis, which is currently slated for June 28.

NASA said it will hold a press conference Monday to update the public on the status of repairs to Endeavour's hydraulic systems. "Kennedy [Space Center] technicians are continuing work to resolve an issue in a heater circuit associated with Endeavour's hydraulic system that resulted in the [April 29] launch postponement," NASA said in a release today. "Technicians determined the failure was inside an aft load control assembly, which is a switchbox in the shuttle's aft compartment, and possibly its associated electrical wiring."

The agency acknowledged that it has yet to uncover the underlying cause of the switchbox failure, but said its technicians are substituting hardware that might have been the problem. "This weekend, technicians will install and check out new wiring that bypasses the suspect electrical wiring connecting the switchbox to the heaters," the release stated. "They will also run the heaters for up to 30 minutes to verify they are working properly and complete retesting of the other systems powered by the switchbox."

While NASA is currently targeting May 16 as the earliest possible date for launching Endeavour on its final mission, the agency said that there are launch opportunities available until May 26. It did not address what would happen if Endeavour cannot be launched until after May 26, but presumably that would mean that the Atlantis mission would have to be pushed back.