- THE MAGAZINE - WEB EXCLUSIVES A major cause of overtesting of
spacecraft, aerospace and flight hardware during random and
swept sine vibration tests is associated with differences
between the mechanical impedance of the shaker and mounting
fixture, and the standard practice of controlling the input
acceleration to the frequency envelope of the flight data. The
result is artificially high shaker forces and responses at the
resonance frequencies of the test item. These high forces can
damage expensive payloads. To alleviate the problem of
overtesting, it has become common practice to notch the input
acceleration, in order to limit the responses in test to those
predicted for launch into space. In simple terms, to notch means
to reduce the amplitude of the shaker input near the resonant
frequencies of the test item. However, this creates a paradox
because there are multiple resonant points on complex structures
and determining these resonant points on the structure is very
much dependent on analysis, which the