Proton survivability measurements for candidate solar sail materials

Once thought to be difficult or impossible, solar sailing has come out of science fiction and into the realm of possibility. A solar sail is a thin membrane material that uses the momentum carried by photons, to propel spacecraft. These photons originate from the Sun, or can be beamed onto the sail with a laser. Any spacecraft using this method would need to deploy a thin sail that could be as large as many kilometers in extent. A perfectly reflective solar sail (R = 1) at a distance of 1 AU from the Sun experiences a light pressure of 9.1 muN/m. Radiation from a variety of sources exists in the space environment with protons and electrons primarily dominating the distribution. Practical sails must be resistant to the effects of long duration proton exposure. For this reason, sail irradiation research was initiated using 1 MeV protons because it represents the approximate upper limit for these particles in the Earth´s radiation belts. Tested solar sail materials include aluminized Mylar, CP1, and aluminized CP2. These materials were chosen on the basis of application, availability, and manufacturability. Sail samples were exposed to a 1 MeV proton fluence of about 10¹³ mm^-2 using a tandem pelletron accelerator at Alabama A&M University. The Mylar samples showed no observable damage as a result of the irradiation. However, a small amount of darkening was observed on the CP1 and CP2 samples. The CP1 and CP2 samples are much thicker than any of the tested Mylar. It is likely that the darkening was caused by the deposition of large amounts of energy into the CP1 and CP2, causing dislocation damage and sooty carbon formation in the polymer