Interstellar mission powered by lasers

Australian researchers have just designed a propulsion system for an interstellar mission to shoot a spacecraft off to one of our closest stellar neighbours – using 100 million lasers.

The research team at the Australian National University (ANU) are answering the call of the Breakthrough Starshot project for an ultra-light spacecraft that uses “light sail” technology. The ambitious mission aims to send this interstellar traveller zooming across tens of trillions of kilometres of space to reach Alpha Centauri, the second-closest star to the Sun – within just 20 years.

For reference, the spacecraft currently furthest away from Earth is Voyager 1, which is only around 22 billion kilometres away, just outside our solar system – and it was launched in 1977. Even with the conventional spacecraft technology we have today, it would take more than 100 lifetimes to reach the nearest stellar systems.

But ANU astrophysicist Chathura Bandutunga, lead author of the new study, says their laser propulsion system could be the answer to this cosmic conundrum.

“To cover the vast distances between Alpha Centauri and our own solar system, we must think outside the box and forge a new way for interstellar space travel,” Bandutunga explains.

The paper, published in the Journal of the Optical Society of America B, outlines the design concept: a giant array of millions of lasers down on Earth, acting together as one to illuminate the “sail” of a spacecraft and send it speeding off on its interstellar mission.

Robert Ward, the physicist who founded the ANU node of the project, says the lasers’ coordination is key.

“The Breakthrough Starshot program estimates the total required optical power to be about 100 GW – about 100 times the capacity of the world’s largest battery today,” Ward explains. 

“To achieve this, we estimate the number of lasers required to be approximately 100 million.”

One of the main challenges the researchers faced was how to measure how much each laser “drifted”.

“We use a random digital signal to scramble the measurements from each laser and unscramble each one separately in digital signal processing,” says co-author Paul Sibley.

“This allows us to pick out only the measurements we need from a vast jumble of information. We can then break the problem into small arrays and link them together in sections.”

The design concept requires not only an enormous number of lasers on the ground, but also one in space – a “guide laser” will be placed on a satellite in orbit around the Earth and will act as a conductor for the ground-based show. By measuring subtle changes in the atmosphere and beaming back the information, it will correct the path of the lasers down on Earth so they won’t be distorted by the planet’s atmosphere.

“Once on its way, the sail will fly through the vacuum of space for 20 years before reaching its destination,” Bandutunga speculates. “During its flyby of Alpha Centauri, it will record images and scientific measurements which it will broadcast back to Earth.”

But this paper just outlines a design – next, the team have to start building.

“The next step is to start testing some of the basic building blocks in a controlled laboratory setting,” Bandutunga says. “This includes the concepts for combining small arrays to make larger arrays and the atmospheric correction algorithms.”