Shuttle engine leaks still a mystery

NASA contractors aim to reinstall two of shuttle Discovery's three main engines Friday, but engineers still aren't exactly certain why they failed leak checks after they were initially installed in the orbiter late last month.

Amid subsequent tests, no leaks were found in either the engines or the maze of plumbing that makes up the orbiter's main propulsion system.

Consequently, engineers think the leak is related to metallic seals that are put in place between the engines and the orbiter during engine installation.

Made of a high-strength nickel alloy known as Inconel, the interface seals are located at the point where engine low pressure fuel and oxidizer turbopumps connect to the orbiter's main propulsion system.

NASA's plan is to reinstall Engine No. 2 and Engine No. 3 with new seals. Then leak tests will be repeated.

If the interfaces are tight, the engines will remain in the orbiter with Engine No. 1, which passed leak checks after it was installed last month.

If they leak again, the engines still will remain in the orbiter so that routine launch processing can continue. In that case, the leak investigation would continue and corrective action would be taken at a later date.

The interface seals can be accessed through the orbiter's rear engine compartment, so any repair work could be done in either the Vehicle Assembly Building or at the launch pad.

The leak investigation and the ultimate resolution to the problem will be taken up by senior program managers during the Flight Readiness Review for Discovery's upcoming mission to the International Space Station.

NASA still has not set an official date for the launch, but the agency hopes to get the flight under way during a window that extends from May 3 through May 23.