Travelling at near-light speed, the journey takes around 28 months for the astronauts, although the effects of relativity mean that 15 years will have elapsed on Earth by the time they reach their destination.

During the flight, the 40-strong multinational crew must adjust to life in space, as well as dealing with various hazards they encounter, including a derelict 20th century spaceship armed with nuclear weapons, a deadly radioactive "dark star" whose radiation caused the mental breakdown of one of the crew, who threatens to destroy the spacecraft.

Almost ten minutes of footage was cut, the names of the cast and staff in the opening credits were anglicized, and the ship's destination was renamed "The Green Planet".

For the English version, AIP excised the last few seconds and substituted stock aerial footage of view of southern Manhattan and the Statue of Liberty.

According to one reviewer, Glenn Erickson, AIP's edits and script changes were intended to create a gimmicky "surprise" ending, revealing that the Ikarie and its crew have come from an alien world and that the "Green Planet" is in fact Earth.