"Voyager's Return" is the sixth episode of the first series of Space: 1999, with a screenplay written by Johnny Byrne from an idea by Joe Gannon, and was first screened on 9 October 1975 in the UK, and 21 November 1975 in the United States. The final shooting script is dated 31 July 1974, with filming taking place from 7–21 August. The episode is based on the Moon encountering a spaceship from Earth, Voyager One, the dangerous power source of which could have fatal consequences. Plot A spaceship approaches Alpha signalling that "This is the voice of Voyager One, with greetings from the people of Planet Earth." This causes consternation in Main Mission, as Voyager One, launched in 1985, is fitted with a propulsion system (the "Queller drive", named after its inventor Ernst Queller) based on the emission of fast neutrons, which can be dangerous to anything too close. This is made clear when the two Eagles sent to investigate the incoming ship encounter violent vibrations from the drive. One manages to pull away, but the other disintegrates. While it is decided that Voyager must be destroyed, Prof. Bergman argues that there must be a better way to save the huge amount of data that the ship has gathered in its travels. Dr. Ernst Linden, an Alpha scientist working in the Experimental Laboratory overhears that Voyager is returning and approaches Koenig and explains that he is "Ernst Queller" the inventor of the drive, whose identity was changed by Space Command due to issues with a previous disaster. Linden is asked if there are any means of overriding Voyager's security codes to enable instructions to be given to shut down the drive. While he is attempting to do this, his assistant Jim Haines, whose parents were killed in an accident involving the Queller drive of another Voyager craft, learns that Linden is in fact Ernst Queller, the inventor of the drive. He assaults Linden, who, despite his injury, manages to shut down Voyager's engines with seconds to spare. As Alphans explore Voyager, an image of an alien appears - he introduces himself as Aarchon, the "Chief Justifier of the Worlds of Sidon". He explains that Sidon is seeking vengeance for the millions on two of their worlds who were killed when the Queller Drive poisoned them. Three Sidon warships then appear approaching Alpha, intending to destroy it, and Aarchon will not