Abstract
The small satellite market has rapidly grown over the last couple of decades. Developments in deployable structures have enabled advanced satellite capabilities that were previously unattainable. Coilable thin-shell booms, known for their lightweight and efficiency, have been a key focus of research.
A deployment solution was required to position sensors with a clear field of view beyond the spacecraft. The Expandable Hexapod design, featuring nine Bistable Composite Slit Tube (BCST) booms, forms a six-DOF mobile platform with a high deployed-to-stowed ratio and sensor-pointing capability. However, BCST booms face the risk of “blossoming” failure, and rotary motors add excessive mass and complexity. BCSTs with a [±45/0/±45] layup were successfully manufactured but showed visible defects like thickness variations, matrix voids, and inconsistent fibre/matrix ratios.
A novel, patent-pending piezoelectric linear shear motor deployer was invented for lightweight, reliable, and low-power deployment, marking the first use of piezoelectric elements for rollable booms. The “pinch and push” mechanism prevents the “blossoming” failure mode, enables precise continuous deployment, and minimises magnetic interference. The primary limitation is boom slippage, determined by the holding force, which depends on the contact material's coefficient of static friction (µs) and the applied normal force (FN). This thesis examines the holding force and its key parameters.
Experiments measuring the µs between CFRP and alumina yielded values of 0.21 (inclined plane) and 0.25 (sliding plane). The prototype design limited the composite through-thickness deformation due to FN which was estimated as 6.69 N using a Michelson interferometer, which also characterised the composite’s viscoelastic response. Holding force experiments confirmed proportionality between FN and holding force. The µs, FN, and holding force experiments predicted the linear shear motor deployer’s holding force to range from 5.62 N to 9.68 N.
The Ultra-Thin Composite Boom Linear Motor Deployer offers a promising alternative to current deployers, with potential performance gains through optimising contact areas, actuator legs, and µs. This work lays the foundation for lightweight, reliable, low-power deployment mechanisms in future space applications.