Pyrotechnic Shock Propagation

The following is based on a description from Dennis Kern, NASA/JPL, which Isam Yunis, NASA Langley, referenced in a shock presentation.

Shocks travel through structure as a combination of propagating waves and vibration response, with the vibration response concentrated more in lower frequencies and the waves more in higher frequencies.

The propagating waves will not couple dynamically with the structure. However, they are strongly affected by changes in the impedance of the structure, such as at joints.

Impedance mismatch can significantly attenuate the shock wave, but the wave will bounce off the impedance boundary, causing both amplification and cancellations as a function of phasing.

Launch vehicle and spacecraft systems may be subject to ground tests where their pyrotechnic separation devices are activated in order to measure the resulting shock response. Mass simulators may be used in place of electronic flight components. The mass simulators tend to have a higher impedance than the flight components.

For a mass simulator to properly represent a flight component in the high frequency domain, the impedance at the interface must match with the flight configuration impedance. This includes the number of fasteners, interface bolt patterns, and the structural materials at the interface.

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See also:

Pyrotechnic Shock Joint Attenuation
Shock Propagation

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– Tom Irvine

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