Primary Failure Mode
Consequence #1: Load Path Failure
Consequence #2: Main Escape Failure
Consequence #3: Main Performance Failure
As with all Recovery operations, the tangling of various lines (webbing, shroud lines, etc.) is a potential cause of failure. To date, the primary tangling-based failure mode that has been identified for Hermes' Recovery system is shown to the left. In this scenario, prior to main parachute deployment, the webbing from the fin can wraps itself around and tangles with the webbing connecting the drogue parachute to the mission package. Three potential consequences of this failure mode are depicted and described below.
Note: these images are not to scale. The lengths of lines and components will be very different for the flight vehicle (learn more about our webbing lengths here). Furthermore, during descent under drogue, the relative forces on each falling body may be similar enough that all parts (mission package, drogue, and fin can) are tumbling together in a more chaotic arrangement than what is featured here.
The first potential consequence is that the tangling of lines will be tight enough such that the load path from the drogue parachute travels down the fin can webbing. Notably this would occur if two conditions were satisfied:
- The fin can path length from the knot to the mission package is shorter than the tender descender path length.
- The knot is tight enough such that load from the drogue could be offloaded to the fin can webbing path rather than the tender descender webbing path.
This failure mode renders the tender descender useless since, after firing, the drag of the drogue will not pull the deployment bag off of the main parachute.