Advanced Triple Junction Research Articles

High-Current ESD Test of Advanced Triple Junction Solar Array Coupon

Testing was conducted on an advanced triple junction (ATJ) coupon that was part of a risk reduction effort in the development of a high-powered solar array design by Space Systems/Loral, LLC (SSL). The ATJ coupon was a small, four-cell, two-string configuration that has served as the basic test coupon design used in previous SSL environmental aging campaigns. The coupon has many attributes of the flight design; e.g., substrate structure with graphite face sheets, integrated by-pass diodes, cell interconnects, room-temperature vulcanizing grout, and wire routing. The objective of this test was to evaluate the performance of the coupon after it is subjected to secondary arc testing at two string voltages (100 and 150 V) and four array currents (1.650, 2.000, 2.475, and 3.300 A). An external test circuit, unique to SSL solar array design, was built that simulates the effect of missing cells and strings in a full solar panel with special primary arc (PA) flashover circuitry. A total of 73 PAs were obtained that included seven temporary sustained arcs (TSAs) events. The durations of the TSAs ranged from $50~\mu \text{s}$ to 2.75 ms. All TSAs occurred at a string voltage of 150 V. Post-test large area pulsed solar simulator, Dark $I$ – $V$ , and by-pass diode tests showed that no degradation occurred due to the TSA events. In addition, the post-test insulation resistance measured was $>50~\text{G}\Omega $ between cells and substrate. These test results point toward a robust design for application to a high-current, high-power mission.

Arc Mitigation via Solar Panel Grouting and Curing Under Simulated LEO-Like Plasma Environment

Electrostatic discharge is a common phenomenon in satellite solar arrays because of surface charging by low-density space plasma, which may sometimes permanently damage the solar array. Experiments were carried out in two types of solar cell arrays [Si and advanced triple junction (ATJ)] to arrive at arc generation statistics. The experiment was carried out for both grouted and nongrouted panels, and the effect of plasma density variation was also studied. It was observed that arc rate decreases drastically in the first 1.0 h of exposing the coupon to plasma and then it gets saturated. This value remains stable if the panel remains in vacuum and does not get exposed to atmosphere again. In the case of a grouted coupon, initial number of arcs was found to be much less compared with those on ungrouted coupon. In the case of grouted coupon, the arc rate after long curing does not change even after exposing to the atmosphere again, whereas for nongrouted coupon, the arc rate goes to a higher value of the same order as the initial value after exposure to atmosphere. Results show that the gases trapped inside the panel come out during arcing and thus reduce arc initiation. For the grouted coupon, the probability to reabsorb gases is low. The number of arcs is found to increase with increase in plasma density, probably because of panel charging at a faster time scale, and is always found to be higher in the case of ATJ solar cell than Si solar cell.

An innovative deployable solar panel system for Cubesats

One of the main Cubesat bus limitations is the available on-board power. The maximum power obtained using body mounted solar panels and advanced triple junction solar cells on a triple unit Cubesat is typically less than 10W. The Cubesat performance and the mission scenario opened to these small satellite systems could be greatly enhanced by an increase of the available power. This paper describes the design and realization of a modular deployable solar panel system for Cubesats, consisting of a modular hinge and spring system that can be potentially used on-board single (1U), double(2U), triple (3U) and six units (6U) Cubesats. The size of each solar panels is the size of a lateral Cubesat surface. The system developed is the basis for a SADA (Solar Array Drive Assembly), in which a maneuvering capability is added to the deployed solar array in order to follow the apparent motion of the sun. The system design trade-off is discussed, comparing different deployment concepts and architectures, leading to the final selection for the modular design. A prototype of the system has been realized for a 3U Cubesat, consisting of two deployable solar panel systems, made of three solar panels each, for a total of six deployed solar panels. The deployment system is based on a plastic fiber wire and thermal cutters, guaranteeing a suitable level of reliability. A test-bed for the solar panel deployment testing has been developed, supporting the solar array during deployment reproducing the dynamical situation in orbit. The results of the deployment system testing are discussed, including the design and realization of the test-bed, the mechanical stress given to the solar cells by the deployment accelerations and the overall system performance. The maximum power delivered by the system is about 50.4W BOL, greatly enhancing the present Cubesat solar array performance.