Membrane Deployment Technology Development at DLR for Solar Sails and Large-Scale Photovoltaics

Following the highly successful flight of the first interplanetary solar sail, JAXA's IKAROS, with missions to come such as NASA's NEAscout nanospacecraft solar sail and JAXA's Solar Power Sail (a solar-electric propelled mission to a Jupiter Trojan asteroid), and on the back-ground of the ever increasing power demand of GEO satellites now including all-electric spacecraft, there is renewed interest in large lightweight structures in space. Among these, deployable membrane or `gossamer' structures can provide very large functional areas for innovative space applications which can be stowed into limited volumes of launch vehicle fairings as well as secondary payload launch slots, depending on the scale of the mission. Large area structures such as solar sails or high-power photovoltaic generators require a technology that allows their controlled and thereby safe deployment. Before using such technology for a dedicated science or commercial mission, it is necessary to demonstrate its reliability, i.e., TRL 6 or higher. A reliable technology that enables controlled deployment was developed in the Gossamer-1 solar sail project of the German Aerospace Center. It included the verification of its functionality with various laboratory tests to qualify the hardware for a first demonstration in low Earth orbit. We provide an overview of the Gossamer-1 hardware development and qualification campaign. The design is based on a crossed boom configuration with triangular sail segments. Using engineering models, all aspects of the deployment were tested under ambient environment. Several components were also subjected to environmental qualification testing. An innovative stowing and deployment strategy for a controlled deployment and the required mechanisms has been worked out. The tests conducted provide allow a mechanical characterization of this process, in particular the measurement of the deployment forces. The stowing and deployment strategy was verified by tests with an engineering qualification model of one (out of four) Gossamer-1 deployment units. According to a test-as-you-fly approach the tests included vibration testing, venting, thermal-vacuum testing and ambient deployment testing. In these tests the deployment strategy proved to be suitable as a controlled deployment for gossamer spacecraft. Deployments on system level were demonstrated to be robust and controllable. The Gossamer-1 solar sail membranes were also equipped with small thin-film photovoltaic arrays intended to supply the core spacecraft. In our follow-on project GoSolAr, the focus is now entirely on deployment systems for huge thin-film photovoltaic arrays. Based on the Gossamer-1 experience, deployment technology and qualification strategies, new technologies for the integration of thin-film photovoltaics are being developed and qualified for a first in-orbit technology demonstration within five years. Main objective is the further development of a deployment technology for a 25 m
²
gossamer solar power generator and a flexible photovoltaic membrane. GoSolAr enables a wider range of deployment concepts beyond solar sail optimized methods. It uses the S2TEP bus system developed at the Institute of Space Systems as part of the DLR satellite roadmap.