The first test flight of the experimental LightSail spacecraft blasts off today at approximately 11:05AM ET, with the live stream (above) starting at 10:45AM ET. The project is led by nonprofit The Planetary Society, with Bill Nye at the helm. It aims to test a new form of space travel known as solar sailing, in which a large reflective sheet is used to harness the solar radiation pressure produced by the Sun. In an interview on The Tonight Show in 1976, Carl Sagan described it as working "exactly as a sailboat does."
Today's flight won't launch the LightSail prototype into orbit, but is instead testing the deployment of the craft's sail: a piece of material 32 square meters in size and thinner than a strand of hair. If the concept proves successful, then solar sailing could be used for powering cubesats: miniature research satellites no bigger than a shoe box. Such tiny spacecraft are relatively cheap to launch, but their size also means they have no space for fuel needed for traditional propulsion methods: the small but steady push of a solar sail could be a perfect fit.
Interestingly, today's launch on an Atlas V rocket from Cape Canaveral won't just be carrying the SolarSail prototype — also onboard is the US Air Force's mysterious X37-B space plane. The real purpose of this uncrewed, reusable craft is still a bit of a mystery (most bets are on it being some sort of a spy plane), but we know that at least part of the reason for today's launch is for it to test another new type of propulsion system.