The Orion Crew-Service Module (CM/SM) umbilical retention and release mechanism supports, protects, and disconnects all of the cross-module commodities between the spacecraft's crew and service modules. These commodities include explosive transfer lines, wiring for power and data, and flexible hoses for ground purge and life support systems. Initial development testing of the mechanism's separation interface resulted in binding failures due to connector misalignments. Separation of the umbilical lines between the Crew Module (CM) and the Service Module (SM) happens as part of the vehicle separation activities prior to reentry. If the umbilical fails to separate successfully, the crew and spacecraft will likely be lost.
The umbilical lines have to be routed around the heat shield and attach above it on the sidewall of the CM. As a result, the disconnected hardware needs to be rotated out of the way. Because the commodity connectors require linear separation, and the deployment of the umbilical is a rotational motion, the mechanism must accommodate both types of motion. The separation must operate under abort conditions, which are on the order of milliseconds.
The Apollo umbilical separation used a pyrotechnic-activated guillotine. The commodity lines were cut with blades to release the connection. To use a guillotine for the Orion application, an expensive development program would need to happen. It is estimated that the mass of such a guillotine cutter would be more than using separation plates/connectors.
Some of the main driving requirements of the umbilical separation mechanism are to separate the commodity connections within a defined amount of time to ensure compliance with abort and nominal vehicle separation timelines, fully separate the SM side of the umbilical within a defined amount of time under nominal conditions, initiate the separation only upon receipt of the separation command from the CM, prevent re-contact of the SM umbilical hardware and the CM for all separation scenarios, and meet functional and performance requirements after being exposed to acceptance and qualification testing environments.
The baseline plate separation process consists of two stages. When the CM/SM separation command is received, the center separation bolt fires and releases the first stage of separation (Stage 1). This allows the separation springs in the corners of the SM plate to push the plates apart, which separates all of the connections that go across the interface. The SM plate assembly rides on the guide pin/linear bearing setup, and is stopped by a hard stop located on top of the guide pins. A short time after the center bolt fires, the two outside bolts are fired (Stage 2). This releases the umbilical boom assembly and terminates the structural connection of the umbilical to the CM. The boom is then pushed away by the actuator assemblies, and locked out in a position that will not interfere with the departing CM.