A good read about sending probes to our nearest star. Click on the link for the full article, have only copy and pasted part of it
http://www.scientificamerican.com/article/100-million-plan-will-send-probes-to-the-nearest-star1/$100-Million Plan Will Send Probes to the Nearest StarFunded by Russian entrepreneur Yuri Milner and with the blessing of Stephen Hawking, Breakthrough Starshot aims to send probes to Alpha Centauri in a generationFor Yuri Milner, the Russian Internet entrepreneur and billionaire philanthropist who funds the world’s richest science prizes and searches for extraterrestrial intelligence, the sky is not the limit—and neither is the solar system. Flanked by physicist Stephen Hawking and other high-profile supporters today in New York, Milner announced his most ambitious investment yet: $100 million toward a research program to send robotic probes to nearby stars within a generation.
“The human story is one of great leaps,” Milner said in a statement released shortly before the announcement. “55 years ago today, Yuri Gagarin became the first human in space. Today, we are preparing for the next great leap—to the stars.”
“Breakthrough Starshot,” the program Milner is backing, intends to squeeze all the key components of a robotic probe—cameras, sensors, maneuvering thrusters and communications equipment—into tiny gram-scale “nanocraft.” These would be small enough to boost to enormous speeds using other technology the program plans to help develop, including a ground-based kilometer-scale laser array capable of beaming 100-gigawatt laser pulses through the atmosphere for a few minutes at a time, and atoms-thin, meter-wide “light sails” to ride those beams to other stars. Each pinging photon of light would impart a slight momentum to the sail and its cargo; in the microgravity vacuum of space, the torrent of photons unleashed by a gigawatt-class laser would rapidly push a nanocraft to relativistic speeds.
"Without new methods of propulsion we simply cannot get very far," Hawking said at the announcement. "Light is the most pragmatic technology available."
Deployed by the thousands from a mothership launched into Earth orbit, each nanocraft would unfurl a sail and catch a laser pulse to accelerate to 20 percent the speed of light—some 60,000 kilometers per second. Using a sophisticated adaptive-optics system of deformable mirrors to keep each pulse coherent and sharp against the blurring effects of the atmosphere, the laser array would boost perhaps one orbiting nanocraft per day. Each laser pulse would contain as much power as that produced by a space shuttle rocketing into orbit.
