Wolfgang Seboldt, Bernd Dachwald
Solar Sailcraft of the First Generation - Technology Development
54th International Astronautical Congress, 2003, Bremen, Germany
Based on the experience gained with the ground deployment demonstration of a 20m x 20m solar sail, performed in December 1999 at DLR, the future development of solar sails has been investigated recently by DLR on behalf of ESA within the PROPULSION 2000 – PHASE II study. The paper highlights some of the findings and gives recommendations for near-term actions. Solar sails are large and light-weight, generally deployable or inflatable, space structures that reflect solar radiation and thereby utilize the freely available solar radiation pressure (SRP) for propellant-free space propulsion. They have a characteristic length of several tens to hundreds of meters and specific masses of several grams to tens of grams per square-meter. Typically, the reflecting material consists of aluminum coated thin plastic films with a thickness of a few micrometers. The considered system design displays a three axes stabilized square sail with diagonal deployable or inflatable booms for tensioning the thin film. In order to derive the necessary technology development, the paper identifies minimum performance requirements for near-term solar sailcraft missions, using results from recent hardware developments and mission analyses, including trajectory simulation and optimization. A characteristic acceleration of 0.1 to 0.2mm/s2 seems to represent a ‘lower bound’ for useful acceleration levels within typical planetary missions. The DLR/ESA ground demonstration cannot achieve this required characteristic acceleration. Thus, to improve the performance, it seems necessary to go to larger and thinner sails, and to modify the design of the deployment module. A technology development roadmap on sub-system-level is outlined, represented by different sails with increasing performance. In-orbit deployment demonstration missions are proposed for low Earth orbit with an altitude of about 350km, so that automatic de-orbiting takes place after the mission due to atmospheric friction. Other missions are proposed for deep space (C3 ≥ 0km2/s2), requiring a launcher that injects the sailcraft into an Earth escape trajectory.