This film centers on a flight to the moon in a Gemini spacecraft modified for a lunar landing. In fact, there were several proposals in the mid 1960s to use modified Gemini craft for lunar orbital and even lunar landings, in lieu of, or complementing, the Apollo flights. They were rejected for various technical, budgetary, and political reasons.

Portions of this movie were filmed at the TRW (now part of Northrop Grumman Aerospace Systems) Space Park campus in Redondo Beach, California. In 1965, TRW delivered the descent engines for the Apollo moon landing missions.

Released eighteen months before the first manned mission to the moon.

The moon landing was simulated in the Mojave Desert.

N.A.S.A. co-operated fully with the film, lending the producers its facilities, including Cape Canaveral as a location.

Re-edited by the studio, which didn't care for Robert Altman's nascent indulgences, like overlapping dialogue. New footage was shot by Executive Producer William Conrad, to make the film more dramatic.

This marked Robert Altman's return to feature films after working in television for ten years.

Executive Producer William Conrad supplied the television announcer's voice.

In later years, Director Robert Altman liked to claim that the movie never played in theaters in Los Angeles (all those drugs he did over the years must have affected his memory), but it did.

Robert Altman finished shooting on Friday only to receive a call on the Sunday night telling him that he would not be allowed through the gates of Warner Brothers again. Jack L. Warner had looked at some of the footage and insisted on Altman's immediate firing because "that fool has actors talking at the same time".

In the scene where Chiz (Robert Duvall) first instructs Lee Stegler (James Caan) on the Gemini trainer, in the background there is an Apollo spacecraft, apparently under assembly, marked "CM-104". CM-104 would eventually be flown as "Gumdrop" on Apollo 9.

This movie was based on the book, "The Pilgrim Project", by Hank Searles.

Robert Duvall joined Director Robert Altman in his breakout film M.A.S.H. (1970). Two years after that, Duvall rejoined James Caan in Francis Ford Coppola's The Godfather (1972). Incidentally, Coppola was the screenwriter for Patton (1970), the movie that beat out M.A.S.H. (1970) for the Academy Award for Best Picture.

James Caan and Robert Duvall appeared in numerous television and movie productions, most notably this movie, The Rain People (1969), The Godfather (1972), and The Godfather: Part II (1974).

Mike Farrell plays a bit part as a Houston engineer. He played Captain B.J. Hunnicutt on the television series M*A*S*H (1972), which was based on Director Robert Altman's breakout film, M.A.S.H. (1970).