Design of a Passive Sun-Pointing Mechanism for CubeSat Solar Panels

CubeSats operating under nadir-pointing or mission-priority attitude conditions often experience unfavorable solar incidence on their solar panels, limiting available onboard power. This study proposes a thermally driven passive sun-pointing mechanism for CubeSat solar panels and evaluates its prototype-level feasibility. The mechanism uses a photothermal panel, heat pipe, heat cartridge, shape memory alloy (SMA) spring, and universal joint to convert external thermal input into panel tilting motion without direct electrical actuation. A prototype was evaluated through SMA spring actuation tests, single-module pointing experiments, four-direction pointing tests, orbital thermal analysis, and expected annual energy-generation analysis. The experiments showed thermally induced contraction and recovery tendency of the two-way SMA spring and demonstrated that selective thermal input can generate directional tilting and return motion in a four-direction prototype. Orbital thermal analysis indicated that heat can be transferred to the actuation region while maintaining directional thermal separation. The energy-generation analysis suggested that limited-angle pointing can improve annual energy generation compared with a fixed flat panel. These results support the prototype-level feasibility of the proposed mechanism, although further multi-axis measurement, long-term cycling, and thermal-vacuum validation are required.