Shuttle engines pass leak checks

Two of the three main engines that will help propel Discovery into orbit on NASA's next shuttle mission passed leak checks this week after being equipped with new interface seals.

Engine No. 2 and Engine No. 3 failed leak checks after initial installation into Discovery in late January. The engines were removed from the ship so engineers could investigate the situation. Engine No. 1 passed its leak tests and remained in the vehicle.

Subsequent tests showed no leaks in either the two engines or main propulsion system plumbing within Discovery.

Engineers determined the leaks most likely were caused by metal interface seals located at the point where engine low pressure fuel and oxidizer turbopumps connect to the orbiter main propulsion system.

New seals were shipped to Kennedy Space Center and inspected last week. Four that most closely met engineering specifications were used when the two engines were reinstalled. Successful leak checks then were performed.

Three of the four seals were slightly thicker or thinner than specification. Engineering analyses will be carried out to make certain the shuttle is safe to fly with those seals.

The analyses will be conducted along with an examination into another issue.

During a routine inspection, technicians found a minute (0.08 milligram) metallic shaving in the oxidizer prevalve filter screen associated with Engine No. 1.

The prevalve is located in a 12-inch main propulsion system feedline that regulates the flow of liquid oxygen into the engine. A similar piece of debris (1.1 milligrams) was discovered in a liquid oxygen prevalve screen within the main propulsion system of Endeavour.

Engineers are trying to determine if the debris could ignite in flight, triggering an engine fire. Technicians could replace the screen or try to vacuum out the shard. Or engineers could determine it is safe to fly Discovery as is.

NASA has not set an official target date for launch of Discovery on its second post-Columbia test flight. The agency still is hoping to launch the mission during a window that extends from May 3 through May 22.