Posted Nov 04

How MR. X strived for scientific accuracy in ‘Ad Astra’ nuke explosion

by Jane Bracher
How MR. X strived for scientific accuracy in ‘Ad Astra’ nuke explosion by Jane Bracher

Towards the end of Ad Astra, director James Gray’s contribution to space odyssey films, a pivotal sequence takes place in the outer reaches of space – just outside of Neptune, to be specific. It involves a nuclear explosion as astronaut Roy McBride, played by Brad Pitt, escapes the blast and uses its power to propel his spacecraft on a course back to Earth.

The audience is aware this explosion is coming well before it occurs, as Roy takes the explosive with him to Neptune with the express intention of detonating it. But sitting in a cinema, it’s easy to visualise beforehand – even expect – that this explosion would look like the ones often seen on Earth with a fiery blast and smoke. None of that materialises in this sequence. Instead, a blinding flash of white light fills the environment, engulfing Roy’s spacecraft.

The visual effects in that sequence quietly but defiantly stray from the conventions of sci-fi films – and that was all by design.

“James Gray did instruct to make the film as scientifically accurate as possible, that was quite important to him,” said Olaf Wendt, VFX Supervisor from MR. X who led work on Ad Astra.

“James didn't want it to feel like the average science fiction picture, he wanted it to feel a bit different and have its own sort of visual logic,” he added.

That credo is what guided MR. X’s VFX work of around 100 final shots for this film. That included two key bookend sequences: the 80,000-foot antenna shots at the beginning and the nuclear explosion at the end.

Balancing scientific accuracy with imagination

Obtaining references, Wendt said, was crucial to the early process of creating the film’s VFX.

Understandably, real-life references for nuclear explosions in space or an 80,000-foot antenna jutting out above the Earth’s atmosphere are hard to come by. But Wendt said MR. X utilised whatever they could find and built upon that while ensuring every detail – whether imagined or scientifically accurate – served the story well.

“With the nuclear explosions, we looked at high-altitude tests that the US did in the '50s. And there's some footage there. It shows these actually quite beautiful explosion clouds, some of them are a bit like flowers, up high in the atmosphere. They're very scratchy films with very little resolution and some of it, it's not very colourful but it gives you a starting off point and then you build from that,” Wendt explained.

Vital to determining what that explosion would look like was understanding the science behind a nuclear explosion and how it would work in space, where the conditions are vastly different compared to Earth. Most notably, there’s no oxygen in space.

“That's kind of an interesting challenge because a lot of the time you look at any sci-fi film and there are starships exploding in space and a lot of the time they actually look like Earth-bound explosions,” noted Wendt, who has 10 years of experience as a VFX Supervisor.

He added: “When you're on Earth and you set up a bomb, yes, you get these nice pyroclastic clouds and usually that's dust or pulverized matter mixed in with gas, with the atmosphere to give that kind of effect. In space you don't have the gas, it all happens in a vacuum.”

But the team also had help from NASA scientists who, according to Wendt, were pulled in to consult for the project, particularly for the 80,000-foot antenna at the beginning of the film.

While there were more references for that looking at structures in space such as the International Space Station, MR. X still needed guidance on the kind of “advances in material science that would make possible to build such a tall structure, for example, in the way that it's depicted in the film”.

The level of scientific accuracy for the film’s VFX work also extends to the most minute details, such as the faint starfield background visible in many of the space shots. Wendt said those were “derived from an astronomically accurate dataset that includes the positions, brightness and color of about nine million stars as seen from our solar system”.

Around 167 people worked on Ad Astra across MR. X’s studios in Toronto, Montreal, and Bangalore.

“This show for us, it wasn't a huge shot count but every shot in it was big,” Wendt noted. “Every shot required the works really.” – 
