This movie was compiled in 1978, in the wake of Star Wars: Episode IV - A New Hope (1977)'s success. This explains the scrolling foreword "homage" at the start of this movie.
The date was changed from 2004 (as it was in the original two-part Space: 1999 (1975) story "The Bringers of Wonder") to a more futuristic 2100.
The 1983 US video release (the only one as of 2020) has an irrelevant summary on the box. The summary describes the plot of the "Space: 1999" pilot episode "Breakaway", which is condensed to only a few minutes for this film version rather than the episode "The Bringers Of Wonder", which provides the bulk of the film. The film itself contains none of the plot developments described on the box, and almost nothing that happens in the film is described there.