1.   The panel struck an engine nozzle as it fell away.

2.   The roll program tells the engine nozzles how much to gimbal, or swivel, to aim the shuttle properly, Herring said.

3.   There is also a two-dimensional pitch-vectoring main engine nozzle.

4.   This shutdown does not necessarily threaten the safety of the shuttle crew, but hydrogen gas can be released through the engine nozzle.

5.   Similar devices are being used to give fighter planes greater maneuverability by changing the direction of their engine exhaust nozzles.