 Let's get this straight. A bunch of scientists, including Stephen Hawking, want to send a tiny spacecraft to the next closest star. Using a giant laser. Russian billionaire Yuri Milner has already invested $100 million into the project, called Starshot, to see if this type of technology can actually work. So let's break this idea down a bit. It's known as laser propulsion and works exactly how it sounds. A laser beam is used to propel a vehicle very rapidly through space. It's kind of like using a hose to push a ball forward. The laser's light carries momentum just like the water from the hose, though it's nowhere near as powerful. But if you have a big enough laser and a small enough spacecraft, you can potentially transmit enough force to the probe so that it moves very, very fast. That's what Hawking and Milner want to do. The idea is to create a tiny wafer-sized spacecraft connected to a reflective sail that stretches a few meters wide but is only a few atoms thick. It's kind of like the Planetary Society's solar sail concept, which uses the sun's light to move through space. The wafer is also meant to hold a number of miniaturized instruments, including a power supply, cameras, and a communication system. Once the spacecraft is positioned in orbit, then it's time to turn on the laser, or actually, lasers. First, that involves building an array of laser amplifiers on Earth that take up about one square kilometer. One laser is fed into these amplifiers, which break the light apart into thousands of beams. The directions of those beams can be adjusted to form one giant beam of light that travels up out of Earth's atmosphere and hits the spacecraft's sail. The lasers will be turned on for about three to five minutes, sending the probe through space at one-fifth the speed of light. At that pace, the spacecraft should get to Alpha Centauri in a mere 20 years. That may seem like a long time, but you have to remember that Alpha Centauri is four light years away. That's 25 trillion miles. For comparison, NASA's Voyager 1 spacecraft has been traveling to Alpha Centauri at 40,000 miles per hour since 1977, and it's only.005 percent of the way there. Starshot sounds really cool, but there's still a lot of work to be done before this idea can become a reality. The array of lasers needed for propulsion has never been built before, and scientists still need to figure out how to miniaturize all the instruments on board the spacecraft. That includes miniaturizing a communications system that can span four light years of space. The sail also poses an engineering challenge. It needs to be made extra robust so that it can withstand the intense accelerations through space, and it must be as reflective as possible. If it absorbs too much laser light, the sail can melt. Additionally, the path between Earth and Alpha Centauri isn't exactly empty. The chances of hitting something big like an asteroid are small, but lots of interstellar dust still stands in the way. And with the spacecraft moving at one-fifth the speed of light, hitting just a tiny speck of dust will pack a big punch. Engineers will have to build a redundancy system for the sail so that it can withstand a few high-speed dust collisions along the way. And of course, there's always money to consider. The $100 million from Yuri Milner will help jumpstart some of the research and development needed to prove this technology actually works. But a project like this is comparable to CERN or the Apollo program. It's going to need billions of dollars to succeed. That means it could be many years before we see this spacecraft even start its journey to Alpha Centauri. Interested in a much slower form of space transportation? Check out our video on the ExoMars mission. Or if planets are more your jam, we break down if there is a mysterious Planet 9 at the edge of our solar system.