Atmospheric drag limits most solar sails to altitudes>1000 km. A two-sail variant, the Solar-Photon Thruster (SPT) , could be used in Low-Earth Orbit (LEO). An SPT has a fixed-orientation collector sail that focuses light against a smaller, adjustable thruster sail. Maintaining the collector surface parallel to the Earth minimizes SPT drag in LEO. To minimize solar-radiation back pressure towards Earth, the upper collector surface is non-reflective. The reflective lower collector surface directs light reflected and reradiated from the Earth against the thruster. Thruster orientation is adjusted in LEO to increase the orbital energy by the net radiation-pressure. Experiments reveal that holograms are tolerant to solar-wind radiation. SPTs with white-light holographic thrusters are useful in LEO because small thruster rotations produce greatly altered reflectivity. It may be possible to holographically combine SPT collector and thruster.
