In 1976, renowned astrophysicist Carl Sagan brought a weird, reflective prop with him to the Tonight Show Staring Johnny Carson. The toy was a mockup of a solar sail—a revolutionary idea for space travel propulsion that eschews fuel. “[It] travels on the radiation and particles that come out of the Sun—the wind from the Sun,” Sagan explained to Carson, comparing the technology to how an ordinary sail boat moves through the ocean.