The Cosmos 1 spacecraft will take off within about 7 hours, at approx. 19:46 p.m. GMT. The Cosmos 1 is the first spacecraft that utilizes a solar sail to move. The small Cosmos 1 satellite will likely only remain in orbit for a few weeks because the pressurized gas that keeps it together will start leaking, and the craft's orbit will decay until it burns up in the atmosphere.
Solar sails work by capturing the minuscule momentum of light particles emitted by the sun. Over time, the spacecraft can maintain a mild but constant acceleration--unlike the more powerful but briefer burst produced by chemical rockets. Some proponents have even speculated that orbiting lasers could be trained on the sail for propulsion when the spacecraft is far away from the sun.
More details here and a few pictures that explain how the craft works can be found over here. A countdown clock and the official site can be found here