We used to imagine space was so vast that we could launch satellites without worrying about littering it with mechanical debris.

We used to think we could dump waste in the oceans and atmosphere without repercussions, too.

The Minnesota-made Imax documentary “Space Junk 3D” is an eye-opening look at the growing problem of dangerous trash threatening commercial, military and civil satellites that routinely orbit Earth.

As English actor Tom Wilkinson narrates reprovingly, “After half-a-century of space exploration, we’re now suddenly faced with what has long been a staple of science fiction, an orbiting junkyard of cast-off space debris.” With true British finesse, his voiceover remains dryly factual while his tone makes explicit what a bloody nuisance all this clutter has become.

We’ve left literally tons of flotsam in our wake. There are more than 20,000 objects bigger than a softball (some the size of a school bus) whose trajectories can be tracked by ground-based radars. They are chunks of solid fuel waste, fragments of booster rockets, broken solar panels and the like. There are countless small, undetectable metal shards, bolts and even chips of paint that can threaten spacecraft. The refuse is traveling at 17,000 miles per hour, at which speed a paper clip becomes an armor-piercing shell.

Produced and directed by Melissa Butts (“Mars 3D,” “3D Sun”), the new film illustrates how the problem is escalating. Our on-screen guide, Donald Kessler, retired senior scientist for NASA’s Orbital Debris Program, warned about the vicious circle of collisions decades ago. He expected collisions in the orbiting junkyard to create more rubble, meaning more collisions, and so on.

It was not a widely shared hypothesis. Then in 2009 a defunct Soviet military satellite T-boned the Iridium 33 phone communications satellite, producing a massive cloud of wreckage. The “Kessler Syndrome” gained a lot of new believers.

The 38-minute documentary explores remediation schemes, from laser-zapping junk-hunter satellites and vast space nets to orbiting recycling centers fed by scavenger shuttles.

It’s not all about terrestrial trash troubles, though. The film dramatizes colossal natural astronomical collisions, as well. It visits the mile-wide, bowl-shaped pit of Arizona’s Meteor Crater impact site and uses computer animation to represent the impending collision between the star fields of our Milky Way galaxy and its nearest neighbor, the Andromeda system. The computer visualizations are not uniformly impressive — an early image of multiple rocket launches is downright wonky — but the film delivers its message loud and clear. What goes up eventually needs to come down.