Voile Solaire

Solar sails have been studied in the literature for decades as a novel propulsion system for planetary and interstellar missions. Solar sail propulsion could enable missions never considered possible (McInnes, 1999, Leipold, 1996), such as non-Keplerian orbits around the earth or sun, or exciting commercial applications, such as polar communication satellites. NASA’s drive to reduce mission costs and accept the risk of incorporating innovative, high payoff technologies into its missions while simultaneously undertaking ever more difficult missions has sparked a greatly renewed interest in solar sails. Solar sails are now included in National Oceanic and Atmospheric Administration (NOAA), National Aeronautics and Space Administration (NASA), Department of Defense (DOD), Deutsche Forschungsanstalt fur Luft-und Raumfahrt (DLR), and European Space Agency (ESA) technology development programs and technology roadmaps (Garner, 1999). A solar sail is a large, flat, lightweight reflective surface deployed in space-essentially a large space mirror-that can propel spacecraft without the use of propellant. Propulsion results from momentum transfer of solar photons reflected off of the sail (photons have no rest mass, but they do have momentum). The concept of solar sailing is not new. Tsiolkovsky (Wright, 1992) proposed in 1924 that large spacecraft could be propelled through space using photon pressure, and in the same year Fridrikh Tsander (Wright, 1992) proposed the lightweight solar sail design that is discussed today-a metallized plastic film. The technical challenge in solar sails is to fabricate sails using ultra-thin films, deploy these structures in space, and control the saillspacecraft. For reasonable trip times the sail must be very lightweight-from 20 g/m2 for missions that could be launched in the near-term to 0.1 g/m2 for far-term interstellar missions. Modern sail designs make use of thin films of Mylar or KaptonB coated with about 500 angstroms of aluminum with trusses and booms for support structure. The thinnest commercially-available KaptonB films are 7.6 pm in thickness and have an areal density (defined as the total material mass divided by the material area) of 11 g/m2. A propulsion trade study (Gershman, 1998) identified the benefits and sail performance required to provide significant advantages over other propulsion technologies. The study concluded that sails with areal densities (defined as the total sail mass divided by the sail area) of about 10 g/m2 are appropriate for some “mid-term missions” such as a Mercury Orbiter (Leipold, 1996) or small spacecraft positioned between the sun and the earth. More “far-term” missions such as an Asteroid Rendezvous/Sample Return require sails with an areal density of 5-6 g/ m2 and films with a thickness of approximately 1-2 pm. More advanced missions require sails with areal densities of under 3 g/m2 for positioning spacecraft in non-Keplerian orbits or 1 g/m2 for fast trip times to 200 AU.