Folded Lightweight Actuated Position System (FLAPS) for CubeSat Deployables

Abstract

Precision actuation of mechanical structures on small spacecraft is challenging. Currently the solutions include single-use actuators based mainly on pyrotechnics and springs, and multiple-use actuators that typically consume more size, weight, and power than available on CubeSats. Multiple-use actuators may also be complex with several moving parts and a higher probability of failure. The Folded Lightweight Actuated Positioning System (FLAPS) demonstrates the use of shape memory alloy (SMA) strips along with a feedback control loop as a repeatable use actuator for small satellites. SMAs are metal alloys that remember a stored shape when transitioning to the austenitic phase at a certain temperature, and are easily deformable in the martensitic phase. The transition temperature is well-defined and typically ranges from 0°C to 90°C. The SMA used in this work was nitinol and had a transition temperature of 80°C. To program the shape, the SMA was trained by high-temperature annealing, being placed in a mold in an oven at 500°C for approximately 30 minutes. The FLAPS mechanism consists of a pair of SMA strips that actuate in opposition and are mounted to a hinge assembly; one side of the hinge is attached to the satellite bus model and the other side of the hinge is attached to a solar panel model. We use a magnetic encoder to provide feedback to the developed controller board and algorithms, actuating the SMA hinge. Current is applied to the SMA strip and Joule heating actuates the SMA, consuming at most 1 W of power. The current FLAPS prototype has shown to be small, lightweight (35 g), repeatable and precise (error within 2°). The range of actuation of the hinge is yet to be increased, being currently only 18°. The FLAPS team will validate the actuator system and collect angle responses in a microgravity environment on a parabolic flight in the summer of 2019.