Sailing through space. Literally sailing on the solar wind, the photons emitted by the Sun. The idea was first introduced to the public by Carl Sagan, the founder of an organization called the Planetary Society, on a 1976 talk show where he spoke of a spacecraft pushed through space by nothing but the pressure of sunlight. And ever since that interview the idea has lived somewhere between a whimsical someday-maybe concept and some sort of science fantasy, until now.
Bill Nye (yes, The Science Guy) who saw Sagan's interview and was inspired by the idea is currently leading the Planetary Society in turning this concept which they call LightSail into a reality. Nye and has team have created a proof of concept version of their LightSail project, a CubeSat with a 32-square-meter mylar sail packed inside it.
CubeSat is a new miniature format for satellites that usually have volume of exactly one liter, 10 centimeters per side, and a mass of no more than 1.33 kilograms, that hitch a ride on the launch of a larger satellite. The LightSail flight unit takes up three CubeSats. The entire system is about the size of a loaf of bread.
So how does a solar sail work? According to the Planetary Society's website: "Light is made of packets of energy called photons. While photons have no mass, a photon traveling as a packet of light has energy and momentum. Solar sail spacecraft capture light momentum with large, lightweight mirrored surfaces-sails. As light reflects off a sail, most of its momentum is transferred, pushing on the sail. The resulting acceleration is small, but continuous."
The LightSail CubeSats scheduled to launch this month are only a proof of concept. They will only be launched high enough to deploy the sail and perform a system check before falling back into the atmosphere and burning up. "We won't fly high enough above the Earth's atmosphere for solar sailing," the LightSail team said, "but we'll test our sail deployment sequence and snap some pretty pictures." That's what the other two CubeSats are for: one to control the sail, and the other to monitor the entire procedure through a camera.
If all goes well with this proof of concept-sized device, a full-sized solar sailing demo capable of actual space flight will be launched atop a SpaceX Falcon Heavy rocket in 2016, inside Prox-1, a small satellite developed by the Georgia Institute of Technology (Georgia Tech). Prox-1 will be released into orbit at an altitude of 720 kilometers (450 miles), where it will eject LightSail into space and later will rendezvous with it. "When LightSail unfurls its solar sails," the team says, "Prox-1 will be nearby to capture images of the big moment."
A remarkable aspect of this project that Nye stresses is that LightSail is not a government program. As the Planetary Society says, it is "a citizen-funded project", and without having to lug all of the fuel necessary for a standard space mission into orbit, the price tag is a mere 4.5 million dollars.