Design and validation of an articulated solar panel for CubeSats

CubeSats are recently adopted for increasingly advanced mission profiles, e.g. as base for tests of solar sails or formation flight. This also leads to higher power demands on-board of the satellite. Currently most CubeSats are equipped with solar cells on their surface. Some satellites also employ additional deployable solar panels with a fixed end angle to meet the increasing power demands. Further improvements are attempted in the current work by including actuators which allow the movement of the deployable solar panel in one degree of freedom. The proposed design is based on a small stepper motor which is incorporated with a planetary gear-head. The selected material for most of the components iss aluminum to minimize the mass of the system. After the completion of the design, the system was validated by vibrational and thermal computational analyses. A prototype of the final design was manufactured for tests and validation of the computational simulations. Vibrational tests were performed at the Space Dynamics Lab of Utah State University for the vibrational loads during a simulated launch. A comparison of the frequency of the first vibration mode showed a reasonable agreement between simulations and validation test. INTRODUCTION CubeSats have become a low-cost and fast alternative to bigger satellites in the recent years. Many components were successfully miniaturized. The stabilization types changed from simple spin stabilization and passive stabilization using permanent magnets to fully three-axis stabilized spacecrafts. Some recent missions also validated propulsion systems for CubeSats. Despite this tremendous progress, two problems remain unsolved due to the small surface area of CubeSats with fixed body panels: energy generation and heat dissipation. One possible solution is to enlarge the available surface area by the usage of deployable structures. The developed design is based on a generic CubeSat mission and an orbit with an altitude of 400 kilometers and an inclination of 40 degrees during the year 2011. The satellite is assumed to be three-axis stabilized. In order to validate the survivability of the mechanism for launch vibration analyses and tests have to be performed. Damages of the mechanism and the satellite panels are usually prevented by locking them in a stored position and releasing them after reaching the final orbital position. In general, mechanisms on board of CubeSats are limited to small dimensions and masses by the CubeSat launch containers. Further details can be found in the CubeSat specification. Working in an environment with no possibility of later corrections or modifications requires a high functional reliability and repeatability. The two major impacts on the satellite are the compatibility of the thermal heat expansion ratios and the large occurring temperature changes. These result in thermally induced stresses which might cause cracks in components or delamination of glued components like solar cells. This can be prevented by the use of materials with a similar coefficients of thermal expansion. Beside the constraints discussed earlier, solar cells degrade during their lifetime. Therefore it is common practice to design solar panels with a higher energy output at the beginning of the mission to meet the requirements at the end of the mission. Another critical issue is the electric connection of the solar panel to the satellite bus. The most common solutions in this field are cables and slip ring devices. This report focuses on the use of deployed or articulated solar panels to generate the required energy during the whole mission. Hence, it presents the results of an evaluation for the design of the subsystems of a deployable or articulated solar panel for CubeSats. Afterwards, the environmental challenges during launch and orbiting phase are briefly introduced. This leads to the problem statement which states the requirements of the proposed articulated solar panel. Thereafter, the conceptual proposed design and a more detailed specification are presented. The paper closes with an computational and experimental validation of the proposed design and final conclusions.