This week, a bevy of scientists including famed theoretical physicist Stephen Hawking announced a new way to explore space called Starshot — and how it works is something that sounds straight out of science fiction.
The project involves developing a way to send a tiny spacecraft to the next closest star, Alpha Centauri, which sits 4 light years away from our Solar System. As for how that spacecraft is going to get there, that’s where things get even wilder: the light from a giant laser beam is meant to propel the spacecraft forward at one-fifth the speed of light.
t’s a concept known as photonic propulsion. Rather than use typical means of space propulsion — producing thrust through intense chemical reactions — the photons within a laser beam carry momentum; when they’re shined on a reflective surface, the energized photons can push an object forward. How fast that object moves forward depends on how big it is and the power of the light shining on it. “If you shine a flashlight at a ball, it just kind of sits there,” said Lubin, a physicist at UC Santa Barbara, who is working on the Starshot initiative. “But if you have a big enough flashlight and a small [enough] thing, you can impart significant force and accelerate it.” Photonic propulsion could work with any sized object, but it all depends on how fast you want that object to go. “You can propel any mass object, but the more mass it is, the lower the speed is going to be,” said Lubin.
With those restrictions in mind, the idea is to create a tiny, wafer-sized spacecraft connected to a reflective sail; that sail will stretch a few meters wide, but will only be a few atoms thick. The wafer is meant to hold a number of miniaturized instruments, including a power supply, cameras, and a communications system. Once the spacecraft is positioned in space, an array of laser amplifiers on Earth will shine thousands of beams on the object. The directions of those beams can be adjusted to form one giant laser light that travels up out of Earth’s atmosphere and hits the spacecraft’s sail. That will then send the probe speeding through the universe toward Alpha Centauri at one-fifth the speed of light. That means the probe could reach the star in 20 years.
That’s the best case scenario, but there’s a still a long way to go before all this can happen. And some physicists have a few concerns about Starshot. “What’s not so clear is whether the sail material can survive that sort of acceleration, and so that’s a question that I have,” said Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. “How are they going to accelerate this sail vehicle without them falling apart?”
There’s also the question of the spacecraft’s communications system and how it will span four light years of space. And then you have to worry about debris. A lot of interstellar dust lies between here and Alpha Centauri; while that debris may be small, hitting dust at one-fifth the speed of light has the potential to damage the spacecraft’s sail. The probe is going to have some kind of redundancy system to make sure it survives the trip. But though there’s a lot of work to be done on this project, McDowell doesn’t see these engineering challenges as insurmountable. “When physicists are skeptical of what you’re saying, that’s their way of showing they’re interested,” he said. “If we’re not trying to pick your idea apart, it’s because we’ve decided it’s already hopeless.”