Make no mistake:  When “Deep Sky” opens Tuesday at the Museum of Science Boston they’re not exaggerating with the revelation that to build and launch the James Webb Space Telescope took 14 countries, 20 years and more than 10,000 people.

Nathaniel Kahn’s “Deep Sky” documentary goes into deep space never previously seen.

“It’s the largest space telescope ever built, ever conceived,” Kahn, 61, said.  “As you know from the movie, it’s bigger than a rocket and that was the biggest challenge of many challenges: How do you build a telescope that’s bigger than the rocket that goes into space with it?

“That had never, ever been done before. It took a lot to figure out and that’s part of the reason it took so long to build. But that’s also part of the reason why it’s so powerful.

“Because the Hubble Space Telescope, its great predecessor, which changed our vision of the universe, is only about 2.4 meters across. That is one big solid piece of glass that could fit in a rocket.

“This,” he said of the James Webb, “is 6.5 meters across by 21 feet. The thing that is so remarkable about that mirror is we didn’t have a chance to get into it as much as one might have — but in a 40-minute movie you can’t do everything.

“But the mirror is so perfect optically that if you were to stretch the entire mirror out to the size of the United States — you expand it to that size and then you look at it — there would be no hill or valley. It’s that perfect.

“There are over 300 what’s called ‘single point failures’ on this telescope,” he added. “So there are more than 300 things that could have gone wrong. And if any single one of them went wrong during the launch and the deployment of the telescope, the entire mission could have been just space junk.

“So it really is a technical achievement. Like no other in the telescope business certainly. It was at the limit of what was possible for NASA and its partners to the European Space Agency and the Canadian Space Agency.”

Kahn is a two-time Oscar nominee for documentaries, notably “My Architect” about his father, Louis Kahn.

“I’ve loved astronomy since I was a kid,” he said. Documenting the James Webb telescope, “I immediately realized these beautiful images coming down from the telescope needed more time in the movie.

“For us to really luxuriate, understand and just revel in those completely revolutionary images returning to Earth. They’re completely changing our vision of the universe and our place within it. It’s a universe never seen before.”

“Deep Sky” (IMAX) opens at the Mugar Omni Theater at Museum of Science Boston Jan. 16