Into Infinity (1975)

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, journey 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. The Day after Tomorrow (also known as Into Infinity in the United Kingdom) is a 1975 British science-fiction television special produced by Gerry Anderson between the two seasons of Space: 1999. It stars Brian Blessed, Nick Tate, Joanna Dunham, Katherine Levy and Martin Lev. It aired in the United States on NBC as part of the network's Special Treat childrens series in December 1975, and in the UK on BBC1 in December 1976.

Unfortunately the movie Into Infinity is not yet available on HBO Max.