Solar sails is a propulsion method using radiation pressure exerted by sunlight. The main drive for such propulsion method is the growing need and interest in interstellar travel, for which current popular propulsion methods are not sufficient, limiting interstellar travel quite a lot. The paper I used brought Voyager-1 as an example – and its 35 years of travel at 17 km/s.
Solar sails remove the need for onboard propellant and also heavy engines – thus reducing mass and enabling the use of solar radiation pressure for propulsion. The main challenges from the materials aspect is constant excessive heating and excessive radiation, which sets clear limitations on the types of materials that can be used.
Currently, the popular solution used is a few microns thick polymer film which is aluminised with 50-100 nanometer aluminium layer. The paper emphasises the relevance of increasing backside thermal emissivity of the sails as the key parameter for success. High temperature sail materials can bring the spacecraft up to 0.2AU distance from the sun, with near-unity backside emissivity it could be even 0.06AU, allowing for very close maneuvers to the Sun that can propel far and long-lasting missions.
The authors of the paper list various future developments of interest – nanophotonic structures, ultralight and ultrathin films and the utilisation of novel materials for dielectric sails. The possible candidates for optical materials include TiN, TiC, HfO2, TiO2, SiC and W.
Source:
Artur R. Davoyan, Jeremy N. Munday, Nelson Tabiryan, Grover A. Swartzlander, and Les Johnson, "Photonic materials for interstellar solar sailing," Optica 8, 722-734 (2021)