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This was a ground test of the Hermes Pathfinder rocket. It occurred on Field A at 3:45 PM on November 10, 2017. It was the first use of the Pyrotechnic Piston to separate the rocket. The piston contained 1g of 4F black powder. The tender descender contained .2g of black powder. The shear pins used were not document documented but were likely 2x 6-32 nylon pins and 1x 4-40 nylon pin. The rocket successfully separated, and the tender descender released the main parachute appropriately. After de-integration it was found that the Avionics Bulkhead was seriously deformed. This prevented the planned flight on November 11, 2017 from occurring.

Failure Investigation

Black Powder Sizing Investigation

Upon further reflection, we identified the likely cause of failure. The 1 gram of black powder used in the test was sized for a worst case scenario in which the rocket would not separate until full piston extension. This meant that when the piston was not fully extended, it applied a much greater load (due to a smaller volume causing an increased pressure) to the booster section, which in turn applied an equal and opposite reaction force onto the piston rod and thus the Avionics Bulkhead by Newton's 3rd Law.

FEA Investigation

Solidworks FEA confirmed that the deformation is consistent with a 2-bolt load application.

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