Combination of superelasticity and shape memory actuation in a bistable shutter for Venus exploration

Kurzfassung

Optical instruments on planetary missions require shielding mechanisms able to withstand corrosive, high-temperature atmospheres while remaining compact, reliable, and energy-efficient. The Venus Emissivity Mapper (VEM), aboard NASA's VERITAS and ESA's EnVision orbiters, is a spectrometer currently relying on a one-shot spring-loaded shutter that cannot reclose after firing, risking premature optics exposure and reducing mission control. This thesis presents the design, optimization, and validation of a bidirectional, passively locking shutter actuated by shape memory alloys (SMAs). A structured ruled-chain design methodology was employed to systematically explore the design space, leading to the evaluation of three candidate concepts through a weighted decision matrix. The selected architecture combines a bistable mechanism with antagonistic SMA actuation, enabling bidirectional motion without countinuous power consumption. Nonlinear finite element analyses were performed to compare Grade 5 titanium, a zirconium-based amorphous alloy, and superelastic nickel-titanium (NiTi) as candidate materials for the bistable flexures. The results demonstrate that the large recoverable strains provided by superelastic NiTi enable snap-through forces compatible with SMA actuation while remaining within its 8% recoverable strain limit, achieving displacements and safety factors unattainable with the alternative materials. PLA prototypes were subsequently used to validate the numerical model, with the refined simulations reproducing the force-displacement response within 5% deviation. The resulting actuator satisfies the dimensional constraints of the VEM instrument while providing compact, bidirectional, and passively locking operation. Furthermore, this work demonstrates the feasibility of integrating superelastic bistable flexures with shape memory actuation into a unified actuator architecture, an approach that, to the best of our knowledge, has never been reported in the existing literature and offers a promising direction for future spaceborne smart-material mechanisms.