Director Ib Melchior was given just 9 days to shoot the film, on a budget of $200,000.
$54,000 - or just over a quarter of the film's budget - was spent turning the footage into the so-called Cinemagic process.
The 40-foot alien monster was actually a marionette about 15 inches high. It was essentially a combination of a rat, bat, spider, and crab.
Master Marionette artist, Bob Baker, was called in to manipulate the Batratspidercrab creature. Mr. Baker's talents were also called into play for Steven Spielberg's Close Encounters of the Third Kind (1977).
The "Cinemagic" process, used for all scenes on the surface of Mars, was the result of an attempt by producer Norman Maurer to turn live-action footage directly into hand-drawn animation - or to simulate that. This would enable hand-drawn backgrounds to look as real (or as unreal) as the live action footage. It didn't have that effect here, of course. See The Three Stooges in Orbit (1962) for Maurer's second (and failed) attempt at the same process.
Sidney W. Pink wrote the screenplay at home on his kitchen table, recruiting his children in to act as critics. His initial draft was called "The Planet Mars" and included all sorts of strange creatures and an entire Martian city. Naturally, budgetary restraints precluded all that.
The much-touted Cinemagic process which was used for the scenes set on Mars was actually the result of a film-developing mistake. The budget was slashed mid-production so the producers considered turning the film into black and white to keep costs down. However, one reel became accidentally double-exposed which produced a shimmering, vaguely psychedelic glare that director Ib Melchior latched onto, thinking it would suit his purposes for the Mars scenes. (It also helped to camouflage the cheap Martian monsters and scenery.)
The alien monster is the same one featured on the cover of the album "Walk Among Us" (1982) by The Misfits.
The cameras that Ryan and Gettell used on the surface of Mars were Hasselblad model 500 or 1000.
Coincidentally, NASA used modified model 500s in all of the Apollo missions to the moon.
At one point, during the shooting of the film, the title was "Invasion Mars". (see Ib Melchior: Man of Imagination by Robert Skotak)
The "acceleration couches" featured in the spacecraft were aviation ejection seats, designed and manufactured by the Weber Aircraft Corporation.
There is a practical reason why the helmets have no faceplates. This way the actors' breath doesn't fog the glass.
At one point Tom says "Well at least we know there's animal life up here". Note that "up here" suggests looking up from Earth at Mars high in the sky. "Up here" is irrelevant on the planet surface.
At 47:17 the DAYS IN FLIGHT is blank.
When our heroes first venture onto the surface they leave the ramp and entrance to their ship wide open. Very inviting to any locals.