Ultra-thin lightsail created for faster space travel

A lightsail might be the key to going farther and faster in space. So far, Voyager 1, which has been NASA’s deep space traveler since 1977, has yet to achieve this. Despite covering over 15 billion miles, Voyager hasn’t even reached 1% of the distance to Alpha Centauri, the nearest star beyond our Sun.

It’s clear that, in order for spacecraft to truly reach the stars, they will need a serious speed boost. One promising solution is the lightsail – a super-thin, reflective sheet that gets pushed by light, much like a sailboat moves with the wind.

Unlike traditional propulsion methods, lightsails don’t rely on fuel. With the right design, they could cut space travel time from thousands of years to just a few decades.

A leap forward in lightsail design

Scientists from Brown University and Delft University of Technology (TU Delft) have worked together to develop a new type of lightsail that’s lighter, thinner, and more reflective than anything that’s come before.

The new design, described in Nature Communications, uses a material that is just 200 nanometers thick – thousands of times thinner than a human hair – and measures 60 millimeters by 60 millimeters.

Despite its size, this membrane is covered with billions of tiny holes that are carefully patterned to cut weight and reflect more light.

Miguel Bessa is an associate professor in Brown’s School of Engineering. Bessa co-led the research with Richard Norte, an associate professor at TU Delft.

“This work was a joint effort between theorists at Brown University and experimentalists at TU Delft, making it possible to design, fabricate and test a highly reflective lightsail with the largest aspect ratio recorded to date,” explained Bessa.

“The experimental breakthrough of Richard’s team proves their fabrication process is scalable to the dimensions needed for interstellar travel and can be done in a cost-effective manner.”

“Simultaneously, my team is very enthusiastic to see the essential role of our latest optimization method, guided by machine learning, in solving such an interesting and difficult engineering problem.”

Turning a lightsail concept into reality

The research brings scientists closer to achieving goals like those of the Starshot Breakthrough Initiative, which is a project founded by Yuri Milner and physicist Stephen Hawking.

The initiative imagines using powerful ground-based lasers to push hundreds of meter-wide sails, each carrying a microchip-sized spacecraft. The new design, the researchers say, could be scaled up to those sizes without breaking the bank.

To make the sail, the team chose silicon nitride. It’s light, strong, and a good match for this type of engineering. They focused on two key goals: make it as reflective as possible and keep the weight down.

A more reflective sail gets a bigger push from light, while a lighter sail needs less push to get moving. Together, these factors mean faster speeds.

The team used artificial intelligence to figure out how to place billions of holes in the material. The holes are smaller than the wavelength of light and play a key role in tuning how the sail reflects light.

Bessa’s team, including Ph.D. student Shunyu Yin, used their own machine learning tools to find the best design.

A record-breaking lightsail

Once the design was set, it was time to build it. That’s where the TU Delft team came in.

“We have developed a new, gas-based etch that allows us to delicately remove the material under the sails, leaving only the sail,” said Norte.

“If the sails break, it’s most likely during manufacturing. Once the sails are suspended, they are actually quite robust. These techniques have been uniquely developed at TU Delft.”

With traditional techniques, making a lightsail like this could take up to 15 years and be extremely costly. But with the new method, fabrication took about a day – and came in at a fraction of the price.

The result is a record-breaking lightsail with a centimeter-wide surface and nanoscale thickness.

Breakthrough in nanoscale engineering

The team believes this work could lead to more than just faster space missions. Their approach opens new doors for nanoscale engineering, using machine learning to solve tricky design problems.

“The new machine learning and optimization techniques we used here are very general,” Bessa said. “We could use them to create lots of different things for different purposes. This is really just the beginning. We might be on the verge of solving engineering problems that have remained unsolvable up to now.”

While reaching the stars may still be a long way off, this lightsail design shows that we’re getting closer – one thin sheet at a time.

The full study was published in the journal Nature Communications.

Image Credit: Norte lab, TU Delft/Bessa lab, Brown University

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