Lightsails are becoming an even more powerful tool for space exploration

In theory, a laser-powered lightsail — in development by a company called Breakthrough Starshot — will be able to reach Alpha Centauri in 20 years.

However, the $100 million mission relies on new advances in laser technologies that will eventually allow it to power a lightweight spacecraft at 20 percent the speed of light.

Now, a new study from researchers at the University of California suggests current lightsail technologies could be used to power tiny spacecraft across our solar system and beyond, massively boosting our capabilities for space exploration in the short-term.

Flight by light

One of the great obstacles the Starshot mission faces is that it requires a ground-based laser array measuring 0.4 square miles with an output of 100 gigawatts. It would be the most powerful laser created in history and it would rely on the creation of laser technology that is not currently available to the scientific community.

The new University of California study reveals that a more simple laser array measuring only about 32.8 feet in width with an output of somewhere between 100 kilowatts and 10 megawatts could still greatly boost humanity's capabilities for exploring the cosmos, by reaching much higher speeds than traditional rockets.

In an interview with Space.com, study senior author Artur Davoyan, a materials scientist at the University of California, Los Angeles, said "such lasers can be built already today with a relatively small investment. We do not need to wait until a 100-gigawatt laser becomes available."

"Our work is the first step to fast and low-cost interplanetary and deep space missions," they continued. "We see that a new model for space exploration can emerge, where individual users, which typically do not have access to space, could now spend just a few thousand dollars and launch a real deep space mission." 

Dramatically cutting the travel time to Mars

For its mission, Breakthrough Starshot would send an extremely lightweight spacecraft on its way to Alpha Centauri. It would weigh roughly one gram so that it could reach speeds high enough to reach the star within our lifetime. This means it would only be able to carry a small camera and communication equipment.

By contrast, the new study calculated how far similar spacecraft could get within a reasonable timescale around our solar system. They found, for example, that a 0.9-gram spacecraft with only a 4-inch sail could reach speeds of about 112,000 mph, allowing it to reach Mars in only 20 days. As a point of reference, NASA's Perseverance rover took 200 days to reach the red planet. Lightsail spacecraft with heavier payloads would take a little longer, though they'd still be able to reach higher speeds than traditional rockets and ion thruster spacecraft.

Lightsail missions are powered by the propulsive power of photons or light, and one such mission, called LightSail 2, is already orbiting Earth, powered purely by sunlight. It was the first-ever mission to prove that light sails could power a spacecraft. In a recent interview with IE, Planetary Society president Bill Nye said the mission had completely "exceeded" his expectations. Now, the new study provides yet another indication that light sails will play a key role in the future of space exploration.

The study was published in ACS Publications.

Abstract:
Space exploration is of paramount importance to advancing fundamental science and the global economy. However, today’s space missions are limited by existing propulsion technologies. Here, we examine the use of laser-driven light sailing for agile Earth orbital maneuvering and for fast-transit exploration of the solar system and interstellar medium. We show that laser propulsion becomes practical at laser powers ≥100 kW and laser array sizes ∼1 m, which are feasible in the near term. Our analysis indicates that lightweight (1–100 g) wafer-scale (∼10 cm) spacecraft may be propelled by lasers to orbits that are beyond the reach of current systems. We discuss material requirements and photonic designs and introduce new figures of merit. We show that lightsails made of silicon nitride and boron nitride are particularly well suited for the discussed applications. Our architecture may pave the way to ubiquitous Earth orbital networks and fast-transit low-cost missions across the solar system.