Direct Acoustic Test of Quikscat Spacecraft 1999-01-5550

A novel direct acoustic test was performed on the Quik- SCAT spacecraft at Ball Aerospace Technology Corporation (BATC) in Boulder, Colorado, in October 1998. The QuikSCAT spacecraft was designed and built by BATC in an accelerated, one-year, program managed by the NASA Goddard Space Flight Center. The spacecraft carries the SeaWinds scatterometer developed by the Jet Propulsion Laboratory to measure the near-surface wind speed over Earth’s oceans. Instead of conducting the acoustic test with the spacecraft in a reverberant room, as is the usual practice, the test was conducted with the spacecraft mounted on a shaker slip-table in a nearly anechoic, vibration test cell. The spacecraft was surrounded with a three-meter high ring of large, electro-dynamic speakers, spaced approximately 1.3 meters away from the two-meter diameter, 900 kg. spacecraft. The thirty-one speaker cabinets were driven with 40,000 rms watts of audio amplifier power. The acoustic specification, with an overall sound pressure level of 135 dB, was achieved one meter in front of the speakers. Many acoustical issues may be raised concerning such a test and how it compares with a conventional reverberant field acoustic test, e.g., the maximum obtainable levels and spectrum, the spatial and frequency uniformity, the efficiency of a normal-incidence direct field vs. a reverberant field in the excitation of structures, and the importance of the spatial coherence of the acoustic field. However, it should be recognized that the conventional reverberant acoustic test is also an inexact representation of the actual flight acoustic environment, which consists largely of progressive waves coming from a select range of angles.