Theory of Radiation Pressure on a Diffractive Solar Sail

Solar sails propelled by radiation pressure enable space missions that cannot be achieved using chemical rockets alone. Significant in-space propulsion for missions such as a solar polar orbiter may be achieved with a sail that deviates sunlight at a large average angular direction. The momentum transfer efficiency of sunlight diffracted from a sun-facing diffractive sail comprised of periodic sawtooth prism elements is examined here. The spectrally averaged efficiency is found to approach that of a monolithic prism when the grating period is much longer than the peak of the solar spectrum. This idealized diffraction analysis predicts a greater transverse radiation pressure force compared to an idealized reflective sail. With modern optical design and fabrication techniques, diffractive solar sails may one day replace reflective sails.