After launching into orbit aboard SpaceX's Falcon Heavy rocket last month, The Planetary Society's LightSail 2 satellite has now entered the most critical phase of its mission. The spacecraft has successfully unfurled its solar sail and begun surfing through space on the power of the Sun, a milestone moment for a technology with interstellar potential.

The idea of the Sun propelling things through space dates back as far as the 17th century, when Johannes Kepler observed comet tails being blown about by what he believed to be a solar breeze. Centuries of science since have confirmed that the German astronomer was onto something, but rather than wind, sunlight actually exerts tiny amounts of pressure in the form of photons that can be harnessed for propulsion.

One noteworthy example of this was NASA's Mariner 10 spacecraft, which ran out of fuel en route to Mercury in 1974 but was able to use its solar arrays to harness these tiny forces and control its orientation.And in 2010, the Japan Aerospace Exploration Agency (JAXA) launched IKAROS toward Venus, which would become the first spacecraft to demonstrate solar sailing technology in interplanetary space.

The Planetary Society's plans for the LightSail 2 don't involve such distant destinations, but the organization hopes to reinvigorate interest around the technology by making Lightsail 2 the first spacecraft to use sunlight alone to alter its Earth orbit. Mission control today confirmed that the bread-loaf-sized spacecraft successfully deployed its solar sail, which is around the size of a boxing ring, and completed its first orbit in solar sailing mode.

The thrust provided by the Sun's photons is roughly equal to the weight of a paperclip, so LightSail 2 won't be going anywhere in a hurry. But tiny adjustments to the orientation of its sail over the coming month will change its path ever so slightly, and hopefully just enough to swing to higher and higher altitudes as a way of demonstrating controlled flight.

And some will be watching on with a very keen interest in how the spacecraft fares. This method of propulsion is the same the Breakthrough Starshot hopes to use to eventually reach the nearest star system, Alpha Centauri. It says this technology could help it arrive within around 20 years from launch rather than the 30,000 or so it would take with today's fastest spacecraft (though there is a bit more to the mission than that).

The plan is to have LightSail 2 orbit the Earth for a year, before reigning it in again to burn up in the atmosphere.

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