Just as ocean winds drive sailboats across the ocean on Earth, solar radiation could one day send spacecraft between the stars. At least that’s what the French startup Gamma hopes for.
The space company was founded in 2020 by Louis de Gouan Matignon, Thibaut Alzire and Andrew Nutter with the goal of developing a low-cost solar sail that would use light as a means of propelling spacecraft. Gamma has raised $2 million in funding from the French Public Investment Bank (BPI), the French Space Agency (CNES) and business angels to demonstrate its technology in space in October. This mission will launch the CubeSat on a SpaceX Falcon 9 rocket, after which the 789-square-foot solar sail will be deployed at an altitude of 342 miles.
“We can test a lot of things on Earth, but implementation testing in these dimensions can only be done in the gravity of space,” Nutter told gaming-updates. (Measurements show that the sail should be about 10 meters wide.)
The shadow sail is not a new invention at all. They were first proven by astronomer Johannes Kepler, who reviewed them in a letter to fellow astronomer Galileo Galilei in 1608. But the first successful deployment of a solar sail did not come until 2010: the IKAROS “space yacht” mission of the Japan Aerospace Exploration Agency (JAXA). In the same year, NASA launched NanoSail-D, and in 2019 the Space Advocacy Group Planetary Society launched LightSail 2.
Now, in addition to Gamma, several organizations are developing new solar sailing missions. Illinois-based Nanoavionics is developing an 800-square-foot solar cell spacecraft under NASA’s Advanced Composite Solar Cell System (ACS3). The $100 million-funded Breakthrough Starshot mission plans to send hundreds of small, solar-powered spacecraft to the Alpha Centauri galaxy, 4.7 light-years away.
Gamma differs from previous and current missions in two ways. “Firstly, the Gamma team is aiming to move and move much faster, launching the first of many solar sails in record time,” Neuter says. “Secondly, we pulled out the sails by carefully rotating the satellite and using the resulting centrifugal force to open the petals of our sails. As a result, we save on structural weight and can end up using much larger surfaces.”
Ahead of its first launch, the company is already planning a second mission — a mission that will be deployed at high altitude and “demonstrate that we can steer the sails and provide a reliable low end compared to conventional propulsion technologies.” The alternative,” Nutter said.
Shadow sails work in much the same way as regular sails, except that they use photons to propel themselves rather than the air molecules that make up the wind. Although photons have no mass, when they travel through space, their momentum can be transferred to a reflective surface—a solar sail made of Mylar or polyamide—that can propel a spacecraft. The power is small, but in the vacuum of space it can add up quickly. It is possible that a solar sail could accelerate the spacecraft to 20% the speed of light, although this would take some time.
This would allow the spacecraft to eliminate (or at least reduce) the amount of propellant, freeing up mass on board for other uses. The use of a solar sail could also increase the duration of a spacecraft’s mission, as the craft could theoretically operate indefinitely. This will be important for long-duration deep space missions, which explains why there is so much interest in further developing the technology.