Journey to the Far Side of the Sun (1969)

A planet is discovered in the same orbit as Earth's but is located on the exact opposite side of the sun, making it not visible from Earth. The European Space Exploration Council decide to send American astronaut Glenn Ross and British scientist John Kane via spaceship to explore the other planet. After a disastrous crash-landing Ross awakes to learn that Kane lies near death and that they apparently have returned to Earth, as evidenced by the presence of the Council director and his staff. Released to the custody of his wife, he soon learns things are not as they seem.