Aiaa 2002-1200 the Effect of Geometric Scale on the Configuration of a Solar Sail

Various configurations and geometric scales of solar sails are compared with alternate advanced propulsion technologies. The study illuminates certain critical parameters such as the specific stiffness of the structure, a minimum area density, a minimum ‘smoothing stress’, and a need for long duration missions (e.g. > 100 days). As the thrust requirement increases, the geometric scale of the sail increases, and the optimal configuration varies from a simple plate, to a stiffened radial rib topology. As the scale increases further, a rotating oblate ellipsoid that is inflated is the preferred configuration. As a first step toward substantiating some of the parameters chosen in this study some initial experiments were performed to determine some properties of membrane materials. These include surface reflectivity measurements using interferometers as a function of membrane stress. One consequence of using a solar sail propulsion technique is that to minimize the support mass, the payload and bus components are naturally driven toward a distributed layout. A limiting feature of sail’s propulsion capability is its inherently high compliance. There is strong coupling between the structural shape and the thrust performance and this leads to potentially large uncertainties in navigational parameters such as position † Associate Professor of Aerospace Engineering Copyright © 2002 by Peter D. Washabaugh.Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. INTRODUCTION Solar sails are a potential means to efficiently obtain large changes in velocity with the notable feature of using no propellant. ,2 Sails are typically portrayed as being reinforced membrane structures. For example Figure 1 is a solar sail configuration which consists of a membrane that is reinforced with radial ribs. It is necessary to keep the membrane in tension to provide a smooth surface. The radial ribs are under compression. The compressive load is used to place the overall membrane in tension. The ribs and membrane together are self-equilibrating. FIGURE 1: A schematic of a solar sail consisting of a membrane and four radial ribs. Thrust is obtained by the reflection of light off a large area. The properties of the reflecting surface are critical to the solar sail performance. A diffusive surface (i.e. surface roughness on the order of the wavelength of the reflected light) would impact efficiency in that rather than reflecting light in a single direction, light would be