Refractive sail and its applications in solar sailing

Radiation pressure can be generated by interactions of electromagnetic (EM) waves with matter. Conventional in-space photonic propulsion systems like solar sails or solar photon thrusters operate by reflection of EM waves. This paper introduces a new type of solar sail which generates thrust by means of refraction of light through a thin film composed of micro-prisms. The main feature of the proposed refractive sail is its relatively large tangential radiation pressure, generated at near-normal radiation incidence. A method for computation of radiation pressure, by having the direction and power of input and output light beams, was introduced. Then a simple analytical approach for optimal design of the refractive film was presented, and ray tracing was utilized for computation of the radiation pressure to a good approximation. A refractive sail can be utilized in applications which a tangential force, especially at near-normal radiation incidence, is required. By utilizing this sail for orbit raising from low-Earth orbit (LEO), the minimum possible altitude for solar sailing can be reduced to about 500 km under the mean solar activity. Attitude control of solar sails along the sail's normal axis is another possible application of refractive films. Refractive films can also be utilized as solar collector (Fresnel lens) in space, which besides the convenience of their shape keeping, can be designed to be passively stable at the Sun-pointing attitude.