Could a Tiny Spacecraft Sail on a Beam of Light Across the Galaxy?

The spacecraft would sail on photons emitted by a powerful laser beam. Maryna Stamatova/Shutterstock

We don't know much about the closest star system to our own.

So let's aim an absurdly powerful laser beam at it and see what happens.

In the most basic sense, that's what the Breakthrough Starshot project is about — a series of lasers jerry-rigged to produce a single, fantastically powerful beam that could not only cast a light on our nearest celestial neighbor, Alpha Centauri, but even take passengers.

Those "passengers" would be the tiniest spacecraft ever dispatched to explore the cosmos, microchip-sized bundles of sensors and communications equipment called StarChips. They would ride that beam of light, essentially using sails to capture the momentum of photons, to travel at unprecedented speed.

For now, although enticing, Starshot is still an idea in progress, despite the scientific pedigree behind it. Indeed, the plan was first floated by University of California cosmologist Philip Lubin in 2015 as means to spring humanity from the confines of its own solar system. It has since gained the endorsement of late astrophysicist Stephen Hawking, and more importantly, perhaps, the backing of Israeli-Russian billionaire Yuri Milner.

Milner explains how the tiny spacecraft would use sails to harness the light beam's power in the video below:

But could the Starshot deliver on its promise to make interstellar exploration a reality? Certainly, there are few bigger prizes than Alpha Centauri and all the secrets it keeps just out of humanity's grasp.

Alpha Centauri is actually three stars. Two of them — conveniently named Alpha Centauri A and Alpha Centauri B — are binaries, meaning they're locked in a gravitational tango with each other. The third, Proxima Centauri, may or may not be just passing through the star system. At 4.22 light-years away, it's considered the closest star to our own homebase that isn't our sun.

Aside from those three bright beacons, the star system offers scant details about itself. But those details are tantalizing. For example, back in August 2016, astronomers detected a planet that's a little bigger than Earth orbiting Proxima Centauri. Even more exciting, the world, which is likely rocky, happens to occupy the Goldilocks Zone, an orbital region that leaves it neither too hot, nor too cold. Just right, it would seem, for life.

Alpha Centauri
Alpha and Beta Centurai, with nearby Proxima Centauri shining faintly in the red circle. Wiki Commons

But prying more details from the exoplanet, dubbed Proxima b, is far beyond the means of Earthly telescopes — although computer models and simulations suggest the world is likely no Shangri-La.

To know for sure, we would need to send a probe there. And wait countless lifetimes for any kind of result. You see, that part about Proxima Centauri being 25 trillion miles away is a bit of a sticking point.

We obviously don't have the means to travel at the speed of light. On a traditional liquid fuel diet, a spacecraft would take impossibly long to get there, even if it could somehow weather the journey.

That's where Starshot comes in. The beam itself would produce a whopping 100 gigawatts of power — enough perhaps to fill the highly reflective sails of tiny spacecraft no heavier than a gram. Thousands of micro-ships would literally ride the light beam, sailing through space at a rate of about a fifth the speed of light. And maybe — yes, this is a big maybe — one of them will actually reach Alpha Centauri in about 20 years.

That's a great burden to bear on the slender shoulders of the wafer-like chips. But they've already proven able spacefarers. In fact, several of these "Sprites" are already traveling in Earth's low orbit, powered by the sun and packing radios, sensors and computers in a svelte four-gram form.

"This is a new frontier of tiny, gram-scale spacecraft," Avi Loeb, Harvard professor and chair of the advisory committee for the Breakthrough Starshot Initiative, told The Guardian. And, he adds, at around $10 per Sprite, they're cheap.

The unflappable performance of those Sprites may be the wind in the sails of the ultimate dream: laser beaming probes to Alpha Centauri.

But even if Starshot should fall short of that fabled star system, the technology behind it could exceed our wildest expectations when it comes to exploring our own celestial neighborhood. Since equipment would be propelled by a laser beam, it wouldn't need to carry any fuel, reducing weight dramatically.

"That's going to change our understanding of objects in our solar system, and the search for life," Pete Worden, a former research director of NASA's Ames Research Center, told Technology Review. "And commercially, it's going to be hugely valuable when looking for space resources."

The beam itself could also be used to clear a path through our increasingly cluttered space-scape. Dead satellite blocking the route? Give it a shove with the beam.

But for the Breakthrough Starshot project, the real prize has always been Alpha Centauri. Now, if we can only build that 100-gigawatt beam, the light sails and navigation system required by those intrepid space sailors, we may just be all set for our close encounter with the enigmatic star system.

For an illustration of how Starshot works, watch the video below: