A team of researchers at the California Institute of Technology devised a means of measuring the thin membranes of a lightsail, helping prove out a futuristic travel concept first imagined by Johannes Kepler over 400 years ago.
The team’s research, published this month in Nature Photonics, describes a miniature lightsail in a laboratory setting. The researchers measured radiation pressure on the sail from a laser beam, revealing how the material reacted to the laser beam. Ultimately, these findings will help develop space-ready lightsails—one of the most promising vehicles for interstellar travel, as they rely on an essentially limitless energy source: light.
“There are numerous challenges involved in developing a membrane that could ultimately be used as lightsail. It needs to withstand heat, hold its shape under pressure, and ride stably along the axis of a laser beam,” said Harry Atwater, a physicist at Caltech and corresponding author of the paper, in a Caltech release.
“We wanted to know if we could determine the force being exerted on a membrane just by measuring its movements,” Atwater added. “It turns out we can.”
In the study, the team interrogated a miniature lightsail—just 40 microns by 40 microns in area—made of silicon nitride. The team beamed an argon laser at visible wavelengths at the tethered sail to see how it wobbled and reacted to the warmth generated by the laser. The team measured the sail’s movements on a picometer scale—down to trillionths of a meter (3.4 feet).
“We not only avoided the unwanted heating effects but also used what we learned about the device’s behavior to create a new way to measure light’s force,” said co-author Lior Michaeli, a physicist at Caltech, in the release.
The team reported measurements of side-to-side motions and rotation in the lightsail, an important capability for when such a device is propelling a vehicle through space. Space may be a vacuum, but it has plenty of stuff floating around in it, from micrometeoroids to gusts of solar wind. These external phenomena can impact a lightsail’s performance and potentially jeopardize a mission.
“Our research marks an important step toward realizing laser-driven lightsails by making the first direct experimental measurements of radiation pressure on ultrathin membranes designed for propulsion,” Michaeli said in an email to Gizmodo. “While previous studies largely focused on theoretical models, our work provides real-world data on how these sails respond to long-range laser forces under varying illumination conditions, including power, incident angle, and spot size.”
Lightsails could be the future of spaceflight. Last year, Gizmodo awarded the Planetary Society’s LightSail 2 in the Gizmodo Science Fair for the experiment’s test of the feasibility of photons as a means of satellite propulsion. The 344-square-foot (32-square-meter) sail propelled a small spacecraft on what was ultimately a 5-million-mile (8-million-kilometer) journey encompassing 18,000 orbits.
In 2016, the group Breakthrough Initiatives proposed a fleet of lightsail-powered spacecraft that could be accelerated to 20% the speed of light—very, very fast. At such speeds, spacecraft could reach Alpha Centauri, the nearest star to Earth besides the Sun, in just a couple decades. Accordingly, the advent of lightsail-propelled spacecraft could make light-years of distance a less insurmountable hurdle for space travel.
Though the recent experiment was in a laboratory, it provides some small—but important—steps towards a functional light sail that could power long trips out into space.
“I believe lightsail technology has the potential to revolutionize space exploration,” Michaeli said. “While interstellar missions may still be decades away, we aim to demonstrate this new propulsion technology on smaller-scale missions within our solar system in less than a decade.”
This article has been updated to include comments from Lior Michaeli.
