‘Photonic crystal’ sail could help laser beams push spacecraft faster

Researchers at Tuskegee University have developed a novel photonic crystal light sail designed to improve upon conventional metal-coated polymer solar sails used for spacecraft propulsion. Traditional solar sails rely on reflecting light to generate thrust, but metal coatings often absorb some light, converting it into heat that can degrade or melt the sail, especially under powerful laser illumination. The new design replaces the metal coating with a nanoscale photonic crystal structure composed of germanium pillars, air holes, and a polymer matrix. This structure creates a photonic band gap that selectively reflects laser light used for propulsion while allowing other wavelengths, such as sunlight, to pass through, reducing unwanted heating. Testing showed that a 1-square-meter sample of this photonic crystal sail achieved approximately 90% reflectivity at a 1.2 µm wavelength when illuminated by a 100 kW laser, demonstrating efficiency suitable for experimental propulsion. This efficient reflection could enable continuous thrust, potentially accelerating a spacecraft to hundreds of meters per second within an hour. While