1. When vibration, shock, and resonance combine
Sebastian Junger’s The Perfect Storm returns because launch is another place where several ordinary loads add up to an extraordinary one. Random vibration, a pyrotechnic shock, and a structural resonance that happens to match a cell mode can combine to produce local stresses that no single load predicts.
This entry defines the vibration and shock test matrix for the rack and cell assembly.
2. Environmental bounds
The test must reproduce the launch environment. A reasonable starting set of bounds for a small-satellite-class launch is:
- Random vibration: 6.0 gRMS per axis for 120 seconds, with a profile shaped to the expected launch vehicle.
- Sinusoidal vibration: 20 mm displacement below 60 Hz, 3 g above 60 Hz, swept at two octaves per minute.
- Shock: 1000 g peak, 0.5 ms duration, at the mounting interface, in each axis.
- Number of axes: three orthogonal axes, with two runs per axis if the first run is used as workmanship screening.
These bounds are conservative. They can be tailored once the actual launch vehicle and dispenser are selected.
3. The test matrix
| Case | Load type | Axis | Level | Duration |
|---|---|---|---|---|
| Workmanship random | Random vibration | X, Y, Z | Acceptance level | 60 s per axis |
| Qualification random | Random vibration | X, Y, Z | Qualification level | 120 s per axis |
| Sinusoidal sweep | Sine vibration | X, Y, Z | See bounds | Two sweeps per axis |
| Shock | Pyrotechnic/mechanical | X, Y, Z | 1000 g, 0.5 ms | Three shocks per axis |
| Combined functional | All of the above | All | As above | With cells powered and monitored |
The qualification level is typically 3 dB above the acceptance level or has longer duration, depending on the program’s qualification philosophy.
4. What is measured
For each case the test records:
- Visual inspection for cracks, loosening, or deformation.
- Torque audit of fasteners after vibration.
- Electrical continuity of all connectors and cables.
- Thermal interface resistance before and after the campaign.
- Whether each cell still seats and latches correctly.
- Functional test of any powered electronics.
5. What this changes
- The vibration and shock test has a concrete matrix.
- The matrix links back to the attachment interface work in earlier entries.
- The next entry will define pass and fail criteria.