The idea of sending tiny spacecraft to another star system, not with rocket engines, but by riding a beam of light, may once have been science fiction, but new research published in Nature Communications is illuminating how the idea could become reality. 

Led by Matthew Campbell, Research Assistant Professor in Mechanical Engineering and Applied Mechanics (MEAM), Igor Bargatin, Associate Professor in MEAM, and Deep Jariwala, Peter and Susanne Armstrong Distinguished Scholar and Associate Professor in Electrical and Systems Engineering, along with collaborators at the California Institute of Technology (Caltech) and UCLA, the research team leveraged a surprisingly simple driving force to power these light sails. 

Just as wind fills the sails of a boat, photons (particles of light) carry momentum. If enough laser light is directed at a highly reflective, ultralight sail, those photons can push a spacecraft to extraordinary speeds, potentially reaching one-fifth the speed of light. At that pace, a mission to Alpha Centauri, the closest star system to our own, could take about 20 years, with data returning to Earth within a human lifetime. In contrast, this journey could take anywhere from 75,000 to 165,000 years using current spacecraft.

“The idea of laser photons has been around for a while,” says Campbell. “The question is: what material could actually survive the journey?”

Now, these researchers have demonstrated a new class of ultrathin “light sails” that brings that question closer to an answer. Their prototype combines exceptional reflectivity, mechanical strength and extremely low weight — three properties that have proven difficult to achieve simultaneously in previous designs.

The work represents an important step toward laser-driven spacecraft capable of traveling at relativistic speeds while also opening new possibilities for exploring our own solar system.

Chemical rockets have powered every human mission beyond Earth’s atmosphere, but they face fundamental limits. Carrying enough fuel to reach another star within a reasonable time frame would require impossibly large spacecraft.

Instead of carrying fuel, researchers have long envisioned leaving the energy source on Earth.

In concepts such as Breakthrough Starshot, a massive array of ground-based lasers would direct an intense beam toward a sail attached to a tiny spacecraft weighing about one gram, roughly half the weight of a Dorito chip. Rather than burning fuel, the spacecraft would accelerate as photons bounced off the sail, steadily building speed over several minutes.

“It’s the difference between a breeze and a gust of wind,” says Bargatin. “Photons from the sun are already being leveraged to push current solar sails, but a laser can deliver far more intensity.”

Solar sails have already flown in space, using sunlight to gradually change the trajectory of spacecraft. A laser-driven sail would use the same physics but dramatically amplify the force, accelerating tiny probes to speeds impossible with sunlight alone.

That increased power, however, creates an enormous engineering challenge.

A material that absorbs even a small fraction of the laser’s energy can rapidly overheat and fail. At the same time, the sail must be light enough to accelerate quickly while remaining strong enough to withstand tremendous forces without tearing or wrinkling.

“No one design has successfully balanced all of those requirements at once,” says Campbell. “Our work marks the first-ever fabricated sail that accomplished this and meets both optical and mechanical requirements to turn the idea of light sails into a reality.”

Several years ago, Bargatin’s group developed theoretical designs describing what an ideal light sail might look like. This latest work moves those ideas into the laboratory.

“The right material needs to solve multiple problems,” says Jariwala. “We had to find materials that were strong and had the right optical properties that we could actually manufacture using existing semiconductor fabrication techniques.”

The researchers built their sails from a three-layer nanolaminate structure consisting of a core of molybdenum disulfide (MoS₂), a material chosen for its ability to reflect infrared laser light, sandwiched between two ultrathin layers of alumina.

The outer alumina layers serve multiple purposes: They protect the delicate MoS₂ during fabrication while helping the sail radiate heat away before it can build to destructive levels.

“I applied my expertise in growing atomic-thin 2D materials to develop a comparatively thicker MoS2 layer,” says Pawan Kumar, co-first author and former postdoctoral researcher in Materials Science and Engineering. “This layer was subsequently encapsulated under a specially engineered alumina structure, allowing each requirement to be satisfied. The entire journey, from conducting the research to achieving the outcome, provided valuable insights into the advanced applications of ultra-thin layers in space science.”

The researchers fabricated the sails using scalable microfabrication processes similar to those used throughout the semiconductor industry.

But selecting the right materials solved only part of the problem.

A sheet only a few hundred nanometers thick behaves much like a piece of plastic wrap: lightweight but prone to wrinkling, tearing, sticking to itself and collapsing under stress.

To overcome that weakness, the team borrowed a design principle used throughout engineering.

Rather than remaining perfectly flat, the sail is patterned with microscopic hexagonal corrugations resembling a honeycomb. The architecture works much like corrugated cardboard or the vertical web of a steel I-beam, dramatically increasing stiffness without adding much weight.

“Corrugation has been used to make materials both lightweight and strong for a long time,” says Campbell. “We use that design principle to make doors light and to make airplanes fly, so it made sense to apply it to this material.”

The corrugated design allows the sail to resist wrinkles, recover from bending and better withstand damage from tiny particles encountered in space. 

The team’s prototype sails measured only about three millimeters across, but their performance demonstrated why the design is so promising.

The films weighed less than one gram per square meter, roughly one-hundredth the weight of ordinary printer paper. Laboratory measurements showed they reflected more than half of the incoming laser light while absorbing less than four percent, with experimental uncertainty suggesting the true absorption could be even lower. Together, these properties allow more laser energy to propel the sail instead of heating it.

“Our role was to verify that the sails performed the way they were designed to,” says Ramon Gao, a collaborating postdoctoral researcher at Caltech. “By precisely measuring how much laser light the prototypes reflected and transmitted, we could determine that they absorbed very little energy, a critical requirement because every photon absorbed results in heat, which could weaken or even melt the sail.”

Using those experimentally measured values, the researchers modeled how a larger version of the sail could perform during laser acceleration. Their analysis suggests the design could accelerate a one-gram spacecraft to one-fifth the speed of light in roughly seven minutes using a 100-gigawatt laser array, meeting one of the ambitious performance goals proposed by the Breakthrough Starshot initiative.

Perhaps most importantly, the team experimentally demonstrated a complete sail architecture rather than relying solely on computer simulations.

Interstellar travel remains a long-term goal, and significant challenges remain before laser-driven spacecraft become reality. Researchers must further reduce how much light the sail absorbs, scale the design from millimeters to meters and address the enormous infrastructure required to generate and control powerful laser arrays.

Even so, the researchers see nearer-term applications for the technology.

“Laser sails could dramatically shorten travel times throughout the solar system, enabling lightweight probes to rapidly investigate planets, asteroids and interstellar visitors to the solar system like Oumuamua,” says Bargatin. “The same ultrathin reflective films could also find uses in deep-space optical communications, large space-based reflectors and other aerospace technologies requiring strong lightweight materials.”

It’s clear that this technology isn’t just valuable for interstellar travel, but a fundamental materials science advance that could impact many different space technologies.

“This work expands the range of materials being explored for laser-driven light sails,” says Gao. “At Caltech, we’re continuing this work by studying how nanophotonic structures can help sails passively stabilize themselves while riding a laser beam, another key challenge on the path toward practical light sail propulsion.”

“Years ago, we were asking what these sails should look like,” says Bargatin. “Now we’re actually building them.”

Learn more about Matthew Campbell’s work here and the work being conducted in both Igor Bargatin’s lab and Deep Jariwala’s lab.

This work was primarily supported by the Breakthrough Initiatives, a division of the Breakthrough Prize Foundation. It was carried out in part at the Singh Center for Nanotechnology, which is supported by the NSF National Nanotechnology Coordinated Infrastructure Program under grant NNCI-2025608. It was also funded in part by a National Science Foundation CAREER Award under grant CBET-1845933, the National Institutes of Health under grant number K25-AI-166040-01, National Science Foundation Graduate Research Fellowship under grants DGE-1650605 and DGE-2034835 and a NASA Space Technology Graduate Research Opportunities fellowship under grant 80NSSC20K1191.