On April 12th, 2016 we learned about

Breakthrough Starshot’s plan to fly to Alpha Centauri with flimsy flying saucers

Science fiction has teased us with convenient interstellar travel for ages. We’ve often seen our intrepid heroes hop into their ships and make a journey to another solar system in less time than it takes to even get through airport security, much less make a cross-country flight. The premise is that they’ve moved away from relying on rocket propulsion, somehow getting their spacecraft to move faster than light, through dimensional pockets, or other zip around on a new form of sweet special-effect engineering. Reality is trying its best to catch up, although the new Breakthrough Starshot initiative announced Tuesday is actually aiming to use a really old concept in transportation to reach speeds and distances unheard of for more conventional spacecraft— sailing. Oh, and lasers. Turning the Earth into a bit of a Death Star is part of the plan too.

Using light as an engine

A sail works around the idea that the wind pushes on a sail with enough energy that the sail can then drag the ship along in that direction too. For hundreds of years, people have wondered about similarly-driven craft sailing through the stars, just without the water, or wind. By the twentieth century, these notions were getting picked apart a bit more, and the concept was that without the drag of the water or atmosphere, it might be feasible to push a big, reflective sail with light substituting for wind. In 2015, the Planetary Society oversaw the launch of Lightsail 1, and plans for a second iteration are well underway.  While these designs are otherwise very different from what’s been proposed by Breakthrough Starshot, they still demonstrate how light can propel a ship. The big advantage in these concepts is that the energy supply for the craft’s propulsion doesn’t have to come in the form of heavy, onboard fuel, but could be supplied by local stars, or better yet, lasers. Insanely gigantic lasers.

Just like many sailors have probably wished for a personal breeze to aim them directly at their destinations, the team at Breakthrough Starshot is planning on creating the 100 gigawatt laser to push their proposed spacecraft through space. The laser would need to be built in a dry, high-altitude location to avoid distortion by the atmosphere, and be powered by hundreds of square miles of solar panels for one huge blast a day. The immense amount of power wouldn’t actually be aiming to blow up any planets, but would instead be focusing all that energy on a single little spacecraft, theoretically propelling it to 20 percent of the speed of light, around 37,282 miles-per-hour. In an hour, such a ship would sail past Mars (not nine months). In a day, it would be sailing past Pluto, all so that it might reach our closest neighboring stars at Alpha Centauri in 20 years.

Keeping the craft lightweight

Even with the biggest laser, achieving that speed requires some tiny spacecraft. Light hits you all the time, but you’ve probably never felt a push for any photons. If you had less mass though, and less sources of friction all around you, and were more reflective, you might notice something. With these constraints in mind, the probes Breakthrough Starshot is proposing will need to weigh no more than a few grams to work, even with a push from that giant laser. They’d likely look like shiny disks a few feet across, with a small collection of sensors and electronics embedded inside, theoretically smaller than the circuitry in your cell phone (which gets most of its weight from infrastructure like the battery, not the processors.) Assuming these flying saucers were reflective enough, they could survive a direct hit from the laser without being vaporized instead. A successful design would be small and cheap enough to deploy a fleet hundreds of discs, catapulting one a day for a year towards the next solar system.

Postcards from the next solar system

The goal in all this is to look for, and hopefully at plants orbiting the two stars at Alpha Centauri. This may be complicated by the fact that two orbiting sources of gravity may make the formation of Earth-like exoplanets very difficult, and there are some concerns about if there would even be a planet there to photograph once our sailing discs arrived. To further complicate things, Breakthrough Starshot recognizes that while all the technologies necessary may be theoretically possible, they don’t exist in the state we’d need to actually launch this mission right now. To that end, Yuri Milner’s $100 million funding is really meant to kick start research and design to put these ideas in reach. If this sounds overly optimistic,  the LIGO facilities that detected gravitational waves were conceived in a similar fashion, designed around the assumption that as general technology progresses, what may seem out of reach now will be much more practical in the years to come.

Source: ​Inside a Billionaire’s New Interstellar Mission by Ross Andersen, The Atlantic

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