Watch The Day After Tomorrow: Into Infinity (1975) Official Trailer

The spaceship Altares, with a photon drive capable of accelerating it to the speed of light, leaves an Earth-orbiting space station. The Altares crew, two families of scientific specialists, journeys at light speed with time-dilation to Alpha Centauri, where they launch several satellites to transmit information on the Centauri star system back to Earth and guide future manned vessels in exploring.