Solar sails are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large surfaces. A number of spaceflight missions to test solar propulsion and navigation have been proposed since the 1980s. The two spacecraft to successfully use the technology for propulsion were IKAROS, launched in 2010, and LightSail-2, launched in 2019. A further demonstrator, Advanced Composite Solar Sail System (ACS3), was launched in 2024, and deployed successfully but is not being actively controlled due to a fault.