Brad Pitt says Ad Astra is 'the most challenging film' he's done, amid delays and tweaked ending

"Fly me to the moon" this was not.

With his long-awaited Ad Astra finally ready for liftoff, Brad Pitt is opening up about the travails he and director James Gray faced trying to bring the latter's mysterious spacefaring adventure to the big screen.

"This has been the most challenging film I have ever worked on," the star told a press conference at the Venice Film Festival, per Variety, where the sci-fi epic is set to premiere Thursday.

Among the issues plaguing Ad Astra were various post-production delays thanks to Disney's merger with 20th Century Fox, the studio that originally backed the film, which nearly landed it in a black hole without a release date.

Then there were the marketing challenges. A heady exploration on the nature of masculinity and human existence, the flick finds Pitt playing astronaut Roy McBride, who embarks on a voyage across the solar system to discover the source of a dangerous power surge that threatens humanity. He also hopes to locate his astronaut father, played by Tommy Lee Jones, who went missing on a mission to Neptune 10 years earlier and may not want to be found. What Roy uncovers could well end up altering humankind's relationship to the cosmos.

Such adult themes are more in line with sci-fi classics like 2001: A Space Oddyssey and Interstellar than, say, Star Wars or Marvel blockbusters, posing a test for the marketeers at Disney.

"The story ... is so delicate, and any clip of a frame too early or music cue or voice-over could easily tip the thing over or be too much or be too obvious," said Pitt. "It was a constant effort just to try to maintain this balance and try to keep this story unfolding in a very subtle and delicate way."

All of which is to say Ad Astra isn't your usual $80 million space epic — though the movie does have its share of eye-popping action sequences by design. As Gray revealed to The Los Angeles Times, those include a lunar rover chase on the moon, a scene where McBride has to break into a rocket as it's about to blast off from Mars and then subsequently hurtling through open space.

"You can’t make an Ingmar Bergman movie. You have to embrace what an audience will need as red meat, as a sugarcoating of the pill," Gray told the paper. "And so you ask yourself, is it worth it to express yourself on this scale, but include red meat and some sugarcoated pill for the audience, or to say, ‘No, no, I have no interest in communicating anything but precisely what it is I’m after,’ in which case, good, you’ve got no movie. And I would rather have a movie."

Source: 20th Century Fox

The production faced technical hurdles as well given Ad Astra's vast scale, such as Gray's team simulating Pitt in zero gravity utilizing horizontal and vertical versions of the same sets, among other effects-driven considerations (Pitt said he exchanged "discomfort stories" with his Gravity pal and sometime costar George Clooney). But in the end, the film still retains the intimacy of Gray's previous features like Two Lovers, We Own the Night, and The Immigrant.

"James and I were both on the same investigation. I certainly grew up in an era of, you know, men show strength. You don’t show weakness. We are capable in all situations,” Pitt told the Times. “And there is a strength in that, but also what comes with that is an inability to take a personal inventory on oneself. And so we were asking the question, what’s the real value of living? Why do this? Why go on? And that is human connection."

Shooting on Ad Astra, which also costars Liv Tyler, Ruth Negga, and Donald Sutherland, wrapped in late 2017, and the film was originally scheduled to hit theaters in January 2019. But it was then pushed back to May, with industry observers predicting a bow at the Cannes Film Festival, where Gray premiered The Immigrant back in 2013.

With Disney assuming ownership of Ad Astra following its purchase of Fox, Gray was briefly worried his passion project might be shelved, especially since the studio didn't announce its official release date of Sept. 20 until late July. But such fears were unfounded.

"I won’t lie to you, it’s strange that you make this adult-oriented science fiction epic and it’s the Disney corporation that’s releasing it," Gray said. "But having said that, they’ve been fantastic. They love the film, they’ve been really embracing of it."

To ensure Ad Astra didn't stray too far off the mark of audience expectations, the helmer revealed he went back and shot a new scene earlier this year that tweaked his original ending, noting that "if this was a compromise that I had to make, then I was willing to do it to get the film out there."

And Pitt, whose production company Plan B produced the movie, was fully on board.

"I don’t see it as a change, I see it as evolved," Pitt said. "From the beginning when we started with the script, the basic structure was there, the architecture of ‘we’re going to go to the moon, then we’re going to go to Mars and then we’re going to go to Neptune.’ But so much of it has constantly been in flux, I don’t see that as change. I see that as a natural part of its growth."

When it comes to taking audiences on an exciting cinematic journey, we can't wait to see the results.