A team of researchers from the California Institute of Technology has developed a way to measure the thin membranes of a light sail, helping to validate a futuristic travel concept first envisioned by Johannes Kepler more than 400 years ago.
The team’s study, published this month in the journal Nature Photonics, describes a miniature light sail in the laboratory. The researchers measured the radiation pressure on the sail from a laser beam, revealing how the material reacts to the laser beam. Ultimately, these results will help develop space-ready light sails, one of the most promising vehicles for interstellar travel because they rely on a virtually limitless source of energy: light.
“Developing a membrane that can ultimately be used as a light sail involves numerous challenges. It must withstand high temperatures, maintain its shape under pressure, and move steadily along the axis of the laser beam,” said Harry Atwater, a physicist at Caltech and author of the paper, in a Caltech press release.
“We wanted to know if we could determine the force acting on the membrane simply by measuring its movement,” Atwater added. “It turns out we can.”
In the study, the team investigated a miniature light sail made of silicon nitride, measuring just 40 by 40 microns. The team directed a visible-wavelength argon laser at the tethered sail to see how it oscillated and reacted to the heat generated by the laser. The team measured the sail’s movements with a picometer to within trillionths of a meter (3.4 feet).
“Not only did we avoid unwanted heating effects, but we also used what we learned about the device’s behavior to create a new way to measure light intensity,” said study co-author Lior Michaeli, a physicist at the California Institute of Technology (Caltech).
The team reported measuring the side-to-side motion and rotation of the light sail, which is an important capability when such a device propels a vehicle in space. Space may be a vacuum, but there is a lot floating around in it, from micrometeoroids to gusts of solar wind. These external phenomena can affect the operation of the light sail and potentially jeopardize the mission.
In 2016, the Breakthrough Initiatives group proposed creating a fleet of spacecraft with light sails that could be accelerated to 20% of the speed of light – very, very fast. At such speeds, the spacecraft could reach Alpha Centauri, the closest star to Earth other than the Sun, in just a couple of decades. Accordingly, the advent of light-sailed spacecraft could make light-years away less of an insurmountable obstacle to space travel.
Although the recent experiment was conducted in a laboratory, it takes small but important steps toward a functional light sail that could enable long-distance space travel.
