The rocket's second stage failed to complete its second planned burn. As a result, Orion 3, which was manufactured by Hughes Space & Communications of El Segundo, Calif., achieved an orbit well below the planned final altitude.

The most likely scenario appears to be that the combustion chamber burst owing to a rupture, probably a failure of a seam along one of four joints in the reinforcement structure.

Investigators noted two unexplained shocks. The first came 4.5 seconds after the initial firing of the rocket's second stage, which was built by Pratt & Whitney. That burn was successfully completed without further incident. Then, 3.5 seconds after the engine reignited for a second burn, the rocket was jolted with a much larger shock.

The engine came to an abrupt stop and the rocket started tumbling through space. Nearby equipment registered a sudden increase in temperature as hot gas exploded from the combustion chamber. Then, temperatures dropped as cryogenic rocket fuel escaped.

The leak was probably caused by a faulty reinforcing structure of the combustion chamber inside the rocket upper stage's RL-10 engine. The fault probably was the result of a new manufacturing process.

The RL-10 engine, built by Pratt & Whitney, is used in the third stage of Boeing's Delta 3 as well as in Lockheed's Atlas and Titan rockets.

• Delta 3 (1998-08-27)
• Boeing mishaps report

Launch failures chronology