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#Lightsail launches to test revolutionary solar technology in Earth orbit A small spacecraft designed to test solar sail technology in Earth orbit has taken flight in a successful launch. The Planetary Society's revolutionary Lightsail vehicle took off on an Atlas v rocket today, and it will later unfurl its giant sail in orbit and test how effective the sun is at pushing it. If it works, the technology could signal a breakthrough in space propulsion and will allow vehicles to explore distant destinations, such as the moon and Mars, at very low cost. Lightsail was designed by a Californian non-government organisation called The Planetary Society. The launch took place on United Launch Alliance's 206ft (63 metres) Atlas v rocket at 4: 05pm BST (11: 05am ET) from Launch Complex 41 at Cape canaveral in Florida. At its core is a tiny raftmade up of three ubesats which are essentially tiny spacecraft that can be launched relatively cheaply. In total, the core of the vehicle weighs 22lbs (10kg) and is just 11.8-inches (30cm) high and 3. 9-inches (10cm) wide-about the size of a loaf of bread. At the bottom of the four spacecraft on each of its four sides, though, a huge solar sail has been olded upthis sail, measuring 345 square ft (32 square metres) in total in size, is made of an extremely reflective material called Mylar. It is just 4. 5 microns thick-about a quarter of the thickness of a bin bag. When it is unfurled, photons from the sun will strike the sail and push it forwards, similar to how a sail On earth catches the wind. The push is extremely minimal-less than holding a sheet of paper in your hand -but it is theorised that, over time, this push could build up enough to reach high speeds. This is because the force from the sun is constant, and there is no air resistance or friction holding the spacecraft back, so it will always accelerate. f youe out in space where there nothing to stop you, and you have a big enough object, a sail, and a low enough mass spacecraft, it gets pushed, chief executive of The Planetary Society Bill Nye said in a webcast after the launch. On this particular flight, though, Lightsail will be in too low an orbit to escape the clutches of Earth. It will ultimately fall back and burn up in the atmosphere. But this flight will be a key test to not only prove that the physics of solar sailing works as theorised but also that it can successfully unfurl the sail in space. Cameras on board should capture the moment this happens. Previous attempts to test solar sail technology, such as Nasa Nanosail-D2 in 2010, were less successful in this latter part-the sail didn't unfurl properly, which hindered its propulsion. If all goes to plan on this current launch, a second Lightsail spacecraft will then be sent into space on the first launch of Spacex powerful Falcon Heavy rocket next year. This spacecraft will be placed into a much higher orbit 447 miles (720km) up far enough away from Earth that it should be able to escape the gravitational pull of our planet. Another spacecraft called Prox-1 will take images. This will allow this second spacecraft to use the push from the sun to travel into the solar system. Aside from journeys deep into the cosmos, another uses for solar sail technology involves not actually moving at all but staying stationary. A spacecraft using a solar sail could be placed in an orbit between Earth and the sun, where it could remain in place without falling into the sun thanks to the push it receives, known as tation keepingsuch a spacecraft could be used to either observe the sun in detail, or to look at Earth and track asteroids near the planet. The idea for a spacecraft to be equipped with a solar sail to use the solar wind for propulsion was described by the late astrophysicist Carl Sagan four decades ago. ecause it has a constant acceleration, it can get you around the inner part of the solar system a lot faster...than the usual sorts of rocket propulsion, he said in a 1976 broadcast of the Tonight show with Jonny Carson. It was theorised that solar sails could accelerate spacecraft far beyond the speeds of traditional fuels, to make interplanetary-and interstellar travel more feasible. As the technology is still relatively new, it not clear what speeds will be achieved. The Planetary Society has said also not what the second spacecraft destination will be, but in future the technology could be used for missions to the moon and other planets in the solar system. ith solar sailing, in principle you can go vast distances, and do it in relatively small amounts of time, said Neil degrasse Tyson, a board member for The Planetary Society. Doug Stetson, Lightsail Programme Manager, added: olar sailing can take us to the moon, to other planets, and even to interstellar space. e

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