Shape Memory Alloy Cryogenic Transfer Coupling for Space Depot Docking Operations

The technical objective of the proposed effort is to establish the feasibility of using shape memory alloy (SMA) actuators for selected components of the automatic cryogenic coupling transfer system. This coupling will be built for space rendezvous and docking operations between a host spacecraft (e.g., fuel depot) and the client spacecraft (e.g., satellites, shuttles, stages), primarily for fluid resupply. As part of this work, a locking mechanism will be developed to provide a necessary holding force between a host orbital depot and the client spacecraft transfer fluid lines to allow for cryogen transfer. The locking motion will be obtained automatically through spring loading, while the unlocking function will be obtained using a novel SMA actuator design. SMA based coupling can integrate sensing, control, and actuation functions in a single entity, which significantly reduces design complexities and the overall weight and volume of the system. Performance parameters and sub-zero temperature alloys development will be explored. In the proposed effort, we will demonstrate the feasibility of SMA-based actuation system by designing and fabricating a prototype sub-component of a locking mechanism for automatic cryogenic coupling transfer system. The prototype will incorporate a semi-automatic locking/unlocking device, where the locking function can be accomplished automatically during docking (without a user/program input), and the unlocking function can be executed by an external command once undocking was initiated. Near-equiatomic NiTi shape memory alloys (SMAs) will be used as the sensing and actuating elements, but since the coupler needs to operate at cryogenic temperatures, effort will be directed towards developing and characterizing new sub-zero (< 0 °C) ternary NiTiFe SMA for this purpose.