Traveling through space on starlight may sound like science fiction, but the theory dates back to the time of Johannes Kepler, who observed comets' tails "blowing" in the winds of the Sun. The first technical review of solar sails, however, was not published until 1958 in the journal Jet Propulsion. In it, physicist Richard Garwin demonstrated that a massive sail built of lightweight, reflective materials could harness solar winds to travel through space.

Solar sails rely on the fact that sunlight applies a slight force to any surface it strikes. In the frictionless void of space, solar pressure is a constant source of free energy capable of propelling a spacecraft. On these winds, Sunjammer will become the first NASA solar sail to leave Earth's orbit and journey to deep space.

The Sunjammer spacecraft includes three main components: the sail, the vehicle "bus", and the steering vanes. When unfurled, the sail covers 13,000 square feet (1,200 m²), about a third the size of a football field. In the center of the sail, the bus houses electronics, the Cosmic Archive, communications antennas, and other devices that serve as the sail's "brain." Finally, on each of the sail's four corners are steering vanes that behave like rudders on a boat and help steer the craft to its destination.

At launch, the sail will fit into a package that weighs only 70 pounds (31 kg) and is roughly the size of a dishwasher. The entire spacecraft is easily stored as a secondary payload on rockets bound for orbit.

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