The concept of lightsails, envisioned by Johannes Kepler over four centuries ago, is moving closer to reality. Researchers at the California Institute of Technology (Caltech) have developed a method for measuring the thin membranes of a lightsail, paving the way for this futuristic propulsion technology.
This groundbreaking research, published in Nature Photonics, details the study of a miniature lightsail in a controlled laboratory environment. By measuring the radiation pressure exerted by a laser beam on the sail, the team gained valuable insights into the material’s interaction with light. These findings are crucial for developing space-ready lightsails, which hold immense promise for interstellar travel due to their reliance on an abundant and inexhaustible energy source: light.
“Developing a membrane suitable for a lightsail presents numerous challenges,” explains Harry Atwater, a physicist at Caltech and the study’s corresponding author. “It must withstand extreme temperatures, maintain its shape under pressure, and remain stable along the laser beam’s axis. Our goal was to determine if we could measure the force exerted on the membrane solely by observing its movements. And we discovered that we could.”
The Caltech team experimented with a miniature lightsail, measuring a mere 40 microns by 40 microns, constructed from silicon nitride. An argon laser, emitting visible wavelengths, was directed at the tethered sail to observe its oscillations and reactions to the laser-generated heat. The team meticulously measured the sail’s movements on a picometer scale—equivalent to trillionths of a meter.
“We successfully mitigated unwanted heating effects and leveraged our understanding of the device’s behavior to develop a novel method for measuring the force of light,” adds co-author Lior Michaeli, a physicist at Caltech.
The team documented both lateral motions and rotation of the lightsail, a critical capability for space-based propulsion. While space is a vacuum, it’s not empty. Micrometeoroids and solar wind gusts can affect a lightsail’s performance and potentially endanger a mission. Understanding and controlling these movements is essential for successful lightsail navigation.
Lightsails represent a potential revolution in spaceflight. Last year, the Planetary Society’s LightSail 2 successfully demonstrated the feasibility of photon propulsion, completing a 5-million-mile journey and 18,000 orbits using a 344-square-foot sail.
In 2016, Breakthrough Initiatives proposed a fleet of lightsail spacecraft capable of reaching 20% the speed of light. At these speeds, reaching Alpha Centauri, the closest star system to our own, could be achieved within a few decades. Lightsail propulsion could dramatically reduce the time required for interstellar travel, making what once seemed impossible, a tangible possibility.
Although this recent Caltech experiment was conducted in a laboratory setting, it represents a significant advancement towards the development of a functional lightsail capable of powering extended voyages into the cosmos. These findings offer a crucial stepping stone towards realizing the dream of interstellar exploration.
