Modal test of Shuttle engine nozzle

A structural failure occurred on the main propulsion test stand at NSTL causing a hydrogen fire and damage to the engines to be used on the Orbiter Columbia. Scattered accelerometer measurements indicated very high response levels at 254 hertz and 311 hertz. The Engine Office at MSFC asked the Dynamics Test Branch to try and find out what caused the failure. All three nozzles were sent to Huntsville for testing. Modal test data revealed very quickly how the failure occurred in the steerhorn and also pointed out two other structural problems. A complete set of data is presented along with a narrative explanation of the steps taken to identify and verify the structural problem.