In an interview with Starlog magazine in the late 1970s, Douglas Trumbull revealed that the plot of the movie in the original version of the script was quite a bit different from what was actually filmed. In this version, the Space Freighters were on permanent duty carrying biological domes. When they're finally told to blow the domes and return to earth, it is because the freighters are going to be scrapped. The Freeman Lowell character in this version was an older, more curmudgeonly man who simply doesn't want to return to earth and forced into retirement, so he steals the Valley Forge, "Shoots the rapids" through Saturn's Rings to make it look like his ship is destroyed, and heads off into deep space. As in the filmed version, he reprograms the robots for some companionship, and the subplot involving the plants dying due to a lack of light were involved, but his main interest in the plants was simply as a means of extending his limited food supplies on the ship. In the second half of the film, he receives a signal which he realizes is from an alien ship passing through the solar system, and decides to approach it - humanity's first contact with aliens - around the same time, his superiors on earth have realized what he did, and are trying to re-capture the ship. The last act of the movie was to have been a race against time, with Lowell trying to contact the aliens, and the recovery force trying to re-take the ship. Finally, in desperation, Lowell detaches one of the domes with one of the robots aboard only seconds before he's killed by the forces that have boarded the Valley Forge. The dome drifts off into deep space, where it's spotted by the as-yet-unseen aliens, who board it and find the robot. The robot, unsure what to do, pulls out a snapshot of itself, the other two robots, and Freeman Lowell taken earlier in the film, a "Family Portrait" after a fashion, and shows it to the aliens, who look at it and the robot confusedly, and there the film ends.
The decommissioned Essex-class aircraft carrier "Valley Forge," a veteran of World War II, Korea, and Vietnam, served as the interior of the space freighter "Valley Forge." The flight control area and hangar deck of the carrier were modified and painted to represent the space freighter in the film. The carrier was scrapped after filming was complete.
The "Saturn sequence" was originally intended to be featured in Stanley Kubrick's 2001: A Space Odyssey (1968), but the technology needed for the visual effects team to do such a sequence was not ready for use.
The model of the "Valley Forge" space freighter was 26 feet in length and was constructed of steel, wood, plastic, and over 650 army tank model kits. This model no longer exists, as it was disassembled and destroyed several years after filming. At least one original "dome" from the model has survived in good condition, and was offered on an Internet auction site in 2003 - it sold for $11,000, and currently rests in a science fiction museum in Seattle, Washington, USA.
After the success of Easy Rider (1969), Universal Studios hit upon the idea to let young filmmakers make "semi-independent" films for low budgets in hopes of generating similar profits. The idea was to make five movies for low budgets (one million dollars or less), not interfere in the filmmaking process, and give the directors final cut. The movies were: this movie, The Hired Hand (1971), The Last Movie (1971), Taking Off (1971) and American Graffiti (1973)
The dome jettisoning sequences were based on Trumbull's viewing of actual footage of Apollo Saturn V rocket stage separations. The miniatures of the dome couplings were 10 inches in diameter, and were filled with mica and compressed air to get the separation effect Trumbull wanted.
This movie follows the same basic outline of another environmental movie, "Ark" from 1970. The earth's environment has been devastated. One lone scientist is trying to preserve samples of plant and wildlife under a dome. He comes under attack and the dome is destroyed.
Footage of the three ships drifting through space and the jettisoning of the domes appears in the story "Different Ones" from Rod Serling's Night Gallery TV series. In an usual twist, the TV episode aired December 29th 1971, months before the movie's release date of March 10th, 1972.
Each of the four characters wears a unique "signal flag" patch on his jumpsuit. Not only do the signal flags stand for the initial letter of their respective last names, but they all have other meanings in the naval code, which are somewhat significant to the characters. For example, Lowell's flag "L" means "You should stop your vessel immediately". "B" means "I am carrying dangerous goods or explosives".
Although only three "space freighters" are visible ("Valley Forge", "Berkshire", and "Sequoia"), several other freighters are mentioned in radio communications. They are "Yellowstone", "Acadia", "Blue Ridge", "Glacier" and "Mojave" (each freighter is asked to report the final jettisons of their domes). Each freighter's name refers to an American National Park or Preserve.
Some of the actual corporate logos visible throughout the movie include (but are not limited to) Dow Chemical, Coca-Cola, AMF, American Airlines, Rockwell International, and Ditch Witch. Most of the logos can be seen on the storage modules in the main cargo deck. The Ditch Witch can be seen digging the hole to bury Keenan.