Actors and director Tom Harper tell EW about filming the thriller thousands of feet in the air.

When the threat of death looms somewhere between a wicker balloon basket and several thousand feet of air separating your body from the ground below, it’s important to keep your survivalist instincts intact. Like, you know, making sure you still look pretty.

“It takes quite a while to get the basket up and down, so, we’d be sitting there doing our own makeup checks and chewing the fat,” Oscar-winner Eddie Redmayne tells EW of comfortably settling into shooting Tom Harper’s upcoming thriller The Aeronautswhich sees the Oscar-winning actor reunite with his Theory of Everything costar Felicity Jones — impossibly high in the sky “for real, in a gas air balloon,” as Jones puts it.

“Suddenly you’re just 1,000 feet in the air. And, because it’s totally silent, there’s no moment for the fear to kick in,” remembers Redmayne.

“It’s so ostensibly, sort of, safe,” Harper continues. “Until it’s not,” Redmayne quips.

The Aeronauts
Credit: Robert Viglasky/Amazon Studios

The duo learned exactly that on day one of filming the 1800s-set film, as they launched their maiden voyage in character as real-life scientist James Glaisher and his maverick pilot, a fictional woman with a daredevil spirit named Amelia Wren, who (in a dramatized story adapted from several historical flights) attempt to travel higher into the sky than any human before them while studying the planet’s weather patterns from their 90-foot air balloon. Shortly after lifting off for the inaugural take, their balloon collided with a patch of trees, sending the pair hurtling toward the ground for a crash-landing. Undeterred (and ultimately uninjured, though Jones wasn’t so sure at first), they literally moved onward and upward, continuing to make a movie “in a basket for three months.”

But, the pair had each other, which gave the taxing shoot a placidity smoother than the natural chaos unfolding in the environments around their characters.

“We could push each other and challenge each,” Redmayne observes, drawing upon the chemistry they honed on Theory for shared comfort and assurance. “We had complete trust.” And they absolutely needed it.

“We went up about 8,000 feet,” Harper remembers, with his crew — including an experienced pilot and cameraman — shooting the high-altitude sequences from a nearby helicopter before production shifted back to earth, where they filmed the rest of the movie in front of a giant screen inside a massive studio.

The Aeronauts
Credit: Amazon Studios

“We did one sequence in a cold box for a few days, putting our hands in ice-cold water before scenes. For endurance, it was nothing like I’ve ever done before,” Jones admits, referencing key scenes that see intense weather patterns threatening Wren’s mission with Glaisher, including one which forces the fearless airwoman to climb the side of the vessel to break open a frozen valve. Still, while the film is a surprisingly kinetic thriller with dizzying visuals and feel-it-in-your-gut stretches of action, Jones sees the most power in its “combination of having fantastic action sequences, telling a story on a huge scale, and having intimate scenes and a moving story about two people within such a huge fantastical context.”

At its core, The Aeronauts is about the endurance of the spirit as much as it is about science and the strength of the human body. Wren, though an accomplished pilot, is often told that “women don’t belong in balloons,” and flexes her might while manning the craft.

The Aeronauts
Credit: Robert Viglasky/Amazon Studios

“I kept thinking it was going one way, and it kept punching me in another direction,” Redmayne says of Harper and co-writer Jack Thorne’s script, which took inspiration from scores of actual pilots and scientists — both men and women — when devising the film’s brainy heroine. “They took expectations and kept knocking them around right to the end. The climax of the movie, when I read it, felt so visually outside of anything I’d ever imagined.”

In hindsight, their joint venture in dangling precariously above the earth might seem a bit insane, especially if you’re afraid of heights (both Jones and Redmayne maintain that they’re not), but, as all great artists do, going to great lengths for the craft is what it’s all about.

“You can’t get anything more suspenseful than literally [being] suspended 37,000 feet up in the air where you could die at any moment…. I should’ve asked you if you were scared of heights before we did the film,” Harper admits with a laugh. Without missing a beat — a confident glint in her eye recalling Wren’s own grit and determination — Jones teases: “It was too late by the time we were up there.”

The Aeronauts
Credit: Amazon Studios

The Aeronauts is in a limited number of theaters Friday, ahead of its Dec. 20 streaming bow on Amazon Prime Video. Watch EW’s interview with Jones and Redmayne above.

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