NASA has successfully extended into orbit an 80 m² (860 square foot) sail that is designed to catch emissions from the Sun and convert them into propulsion for space exploration.

The Advanced Composite Solar Sail System (ACS3) was launched on April 23 from New Zealand aboard Rocket Lab’s Electron hardware and - after months of careful checking - was successfully unfurled at 1333 EDT (1033 PDT) on Thursday, August 29. Such is the compact nature of the spacecraft that the whole thing fit inside a 23x23x34 centimeter (9x9x13 inch) CubeSat before being deployed.

"The sail will appear as a square about half the size of a tennis court," NASA Ames reported.

"Now, with the sail fully extended, the Solar Sail System may be visible to some keen skywatchers on Earth who look up at the right time. Stay tuned to NASA.gov and @NASAAmes on social media for updates on how to catch the spacecraft passing over your area."

The sail is orbiting much higher than the International Space Station's orbit. This is to avoid the drag of the Earth, since while the ISS regularly uses thrusters to move upwards and away from atmospheric drag, ACS3 produces a tiny amount of thrust, so must be further out. Once testing is complete NASA hopes to use this demonstrator to change altitudes without the need for propellant.

Solar sails were first discussed in the 17th century, by astronomer Johannes Kepler in a letter to Galileo which suggested that some force emanating from the Sun was causing comets to stream tails of debris away as they circled the star. "Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void," he is quoted as saying.

NASA proposed a 2015 solar sail mission, dubbed Sunjammer after the 1964 short story by science fiction legend Arthur C Clarke describing an off-planet sailing race. Sadly the NASA mission was canceled for budgetary reasons a year before launch.

In principle the idea of solar sailing is pleasingly simple, and the sails have proved somewhat steerable as they can be rotated or reefed to maneuver. And while the thrust is tiny, it accumulates in the frictionless fields of space and a solar-powered spacecraft has already reached another planet.

In May 2010 the Japanese space agency JAXA launched IKAROS, a probe using a 14x14 meter (46×46 ft) sail that was intended to prove the efficacy of the technology. Under constant acceleration the spacecraft was able to fly by Venus before the end of the year, earning it the world record as the first interplanetary sailing craft in 2012.

For NASA, once the current demonstration flight is carried out, the next step is to build the HIPERSail [PDF] system, which will be around six times the size of the ACS3 and will be used to prove the technology's worth for interplanetary missions. Just don't expect any crewed missions using sails - unless they crack cryogenics as well. ®

https://www.theregister.com//2024/09/04/nasa_acs3_solar_sail/