An experimental NASA solar sail can be seen in the night sky as it orbits the Earth.
NASA's Advanced Composite Solar Sail System (ACS3) launched in April 2024 atop a Rocket Lab Electron rocket. The mission is designed to test solar sail technology to help NASA develop larger spacecraft in the future using this next-generation propulsion system. Solar sails work similarly to nautical sails, but instead of being pushed by wind, they are impacted by the pressure of sunlight as photons bounce off of the reflective material they're made from.
On Aug. 29, the ACS3 spacecraft deployed its 860-square-foot (80-square-meter) solar sail while operating at an altitude about 600 miles (1,000 kilometers) above Earth, which is nearly twice as high as the International Space Station. As the ACS3 spacecraft orbits Earth, it's large surface area means it reflects enough sunlight to be seen from the ground. Under some conditions, the solar sail demonstrator could even appear as bright as Sirius, the brightest star in the night sky. If you want to see it for yourself, you're in luck: NASA has an app that lets you track sighting opportunities from your location.
