The future of solar sailing

A useful technology

One of the biggest advantages of solar sail-powered spacecraft is that while they are near the Sun, they enjoy unlimited thrust. This allows them to reach complex orbits that require constant acceleration to maintain.

An example of this is an orbit that would allow a spacecraft to continually circle the poles of a planetary body. A “pole sitter” spacecraft could offer insight into polar processes happening on Earth, the Moon, and other planets.

Another use for the technology could be parking a spacecraft between Earth and the Sun, creating an artificial orbit from which to watch for solar storms. Solar storms are ejections of high-energy particles from the Sun. These particles can disrupt power grids, cause communication blackouts, and harm astronauts in space. A solar sail parked between Earth and the Sun could sound the alarm on incoming solar storms, allowing protective measures to be taken.

Solar sailing could also propel spacecraft to distant destinations more quickly than conventional propulsion. Proposed far-flung targets range from the outer planets to the Oort cloud to our Sun’s gravitational lens region, where the Sun’s gravity magnifies distant objects in a way that might allow us to image an exoplanet in high resolution.

The ultimate destination for a solar sail would be Proxima Centauri, our stellar neighbor. The organization Breakthrough Starshot has proposed using lasers to accelerate tiny Proxima-bound spacecraft up to 20% the speed of light, cutting the travel time to just 20 years.

NASA solar sails

LightSail 2’s immediate solar sail successor was NASA’s Near-Earth Asteroid Scout. NEA Scout launched aboard the agency’s Artemis I Moon mission in November 2022 along with nine other CubeSats. Unfortunately, NEA Scout didn’t phone home as planned, and all efforts to communicate with the spacecraft failed.

The CubeSat was equipped with a solar sail roughly 2 1/2 times larger than that of LightSail 2. It would have used the sail to leave the vicinity of the Moon and perform a slow flyby of asteroid 2020 GE, which measures just 18 meters (60 feet) across. Had NEA Scout succeeded, 2020 GE would have become the smallest asteroid ever visited by a spacecraft.

The loss of NEA Scout came on the heels of news that NASA was no longer pursuing another solar sail mission named Solar Cruiser. Solar Cruiser would have deployed an ambitiously large solar sail with an area of 1,650 square meters (17,800 square feet), big enough to cover six tennis courts. The spacecraft would have parked itself in a straight line between Earth and the Sun, a location that future missions could use to watch for solar storms. Only a solar sail can reach and maintain such a unique orbit, given the perpetual thrust required.

That leaves NASA with just one upcoming solar sail mission: ACS3, the Advanced Composite Solar Sail System. ACS3 is scheduled to launch into Earth orbit as early as mid-2023 for a test of next-generation solar sail technologies.

The spacecraft will use carbon fiber booms to deploy a sail with an area of about 80 square meters (860 square feet) — about 2 1/2 times larger than LightSail 2. NASA says the carbon fiber booms are 75% lighter than metal booms and less susceptible to buckling due to extreme temperature shifts in space.

W. Keats Wilkie, the mission’s principal investigator at NASA’s Langley Research Center, said ACS3 is essentially a scaled-down version of a much larger solar sail spacecraft that would measure roughly 500 square meters (5,400 square feet). He said that as the technology matures, scientists will come to see solar sail spacecraft as attractive options for their missions.

“Once we start flying these, we’ll get people who say, ‘Hey, this isn’t just science fiction anymore,’” he said.