You've heard of moonshots. Now introducing "star shots."
Yuri Milner, the Russian billionaire and Internet entrepreneur, is unveiling a plan to develop spacecraft that could travel to stars outside the solar system at a press event atop One World Trade Center in New York City on Tuesday. Stephen Hawking, the English theoretical physicist and Cambridge University professor, as well as other scientists are accompanying him.
The proposal? Build tiny interstellar devices—robotic probes called "nanocrafts"—capable of traversing the interstellar medium at speeds as fast as a fifth the speed of light, the fastest known speed in the universe. These wafer-like computer chips, weighing grams (on the scale of paperclips), would receive thrusting power from an experimental method involving laser beam propulsion.
Get Data Sheet, Fortune’s technology newsletter.
“The human story is one of great leaps,” said Milner, who donated $100 million of his estimated $3 billion net worth to the project, in a statement. "Fifty-five years ago today, Yuri Gagarin became the first human in space. Today, we are preparing for the next great leap—to the stars.”
Milner, who is named after Gagarin, the Russian cosmonaut, has donated more than $200 million to philanthropic science projects over the past several years, including the Fundamental Physics Prize (later the Breakthrough Prizes), which is an Oscars-styled awards ceremony for members of the scientific community; a 10-year-long search for extraterrestrial life, which he introduced last year; and the most recent announcement.
Trained as a theoretical physicist, Milner quit working on his Ph.D. to pursue business opportunities. He led Russia's biggest web portal, Mail.ru, before making a series of prescient investments in Russian dot-coms and other popular Internet companies such as Facebook (fb), Twitter (twtr), Spotify, Groupon (grpn), Xiaomi, and Alibaba (baba), among others. (His winning streak-prone investment firm, DST Global, recently raised a $1.7 billion fund.)
Mark Zuckerberg, co-founder of Facebook, will join the "breakthrough starshot" project's board alongside Milner and Hawking.
"Earth is a wonderful place, but it might not last forever," Hawking said in a statement. “Sooner or later, we must look to the stars. Breakthrough Starshot is a very exciting first step on that journey.”
For more on billionaires' extraterrestrial ambitions, watch:
The multimillion-dollar science project aims to create proof-of-concept prototypes to demonstrate that star-trekking is possible. Ultimately, the project aspires to send a flyby mission to Alpha Centauri, the nearest star system to Earth (other than the sun's own, of course) at 25 trillion miles away. If everything goes according to plan, the probes could reach their destination a mere 20 years after their launch date. Compare that to the 30,000 years it would take present-day spacecraft to make the same trip.
While the futuristic "starchips" would cost about the price of an iPhone each to manufacture, the ground-based "light beamer"—kilometers in size—would require significant investment. Think on the scale of CERN's Large Hadron Collider, the European particle accelerator that took billions of dollars, unprecedented international cooperation, and a decade to build.
“We take inspiration from Vostok, Voyager, Apollo, and the other great missions,” said Pete Worden, former director of NASA AMES Research Center who has been tapped to lead the starshot project, in a statement. “It’s time to open the era of interstellar flight, but we need to keep our feet on the ground to achieve this.”