The Breakthrough Starshot project aims to send a tiny spacecraft to Alpha Centauri, the closest star to Earth, in far less than a human lifetime, only twenty years. Instead of chemical propulsion using hydrocarbon or noble gas propellant, the project aims to use a series of lasers to push on a large sail.

Sails have flown in space before, but they accelerated on solar pressure alone. That’s not fast enough to get to another star in twenty years. Current designs for sails cannot handle the thermal and acceleration loads of being pushed by a laser, so a team in the University of Pennsylvania Department of Mechanical Engineering and Applied Mechanics and the Department of Materials Science and Engineering at UCLA have done some work on what properties the sail needs to have.

The team published two papers in the journal Nano Letters.

One of the key insights the authors present in their first paper is the structure of the sail. It cannot be rigid, as the pressure of the lasers would rip it. Instead, it needs to be curved to withstand the thousand gee force of the lasers. The authors note that other pressurized containers, such as rocket fuel tanks, also need to be cylindrical to withstand the forces on them.

The other paper the team prepared on the dynamics of the proposed laser sail covers how the sail could dissipate all the heat generated by the lasers. As the authors say: …if the sails absorb even a tiny fraction of the incident laser light, they’ll heat up to very high temperatures.

The key is a pattern woven into the material, a combination of holes and swatches in a grid. The holes and swatches combine to match the light and thermal emission, allowing the sail to be pushed by even more powerful lasers than previously planned or permit a shorter laser burst that can be more accurately controlled.

More Information

University of Pennsylvania press release

“Relativistic Light Sails Need to Billow,” Matthew F. Campbell et al., 2021 December 23, Nano Letters

“Multiscale Photonic Emissivity Engineering for Relativistic Lightsail Thermal Regulation,” John Brewer et al., 2022 January 11, Nano Letters