In Noomi Rapace’s screen test for the lead role in “Prometheus,” the actress had to portray a young scientist trying to persuade a giant corporation to invest billions of dollars to take her on a journey to another planet in hopes of unraveling the origins and meaning of human life. The company has little more than her passion and intensity as its guide in determining whether to fund the venture.

The situation was strikingly similar to what director Ridley Scott was asking 20th Century Fox to do with Rapace: take a flier on an unknown. The 32-year-old Swedish actress had achieved fame beyond her national borders thanks to her portrayal of the punk, damaged cyber-sleuth Lisbeth Salander in the three original “The Girl With the Dragon Tattoo” films. Still, her English was shaky and her first studio film, “Sherlock Holmes: A Game of Shadows,” was not set to hit theaters for another year, so she was still largely unfamiliar to mainstream American audiences. Casting her as the lead character Elizabeth Shaw alongside Michael Fassbender and Charlize Theron in a big-budget potential summer blockbuster wasn’t a slam-dunk.

Except to Scott, who was smitten with the actress from the first time he met her and worked closely with her on mastering the test. “Ridley worked with me as if it was a real scene,” Rapace said. “He kept saying to me, ‘You don’t have to prove anything, this is not a test for me. You’re my girl. We’re just doing this together so they can see that you can act in English.”‘

The duo’s collaboration quickly convinced the studio she was the right choice.

“The film itself is about a lot of big, compelling ideas, so you can be a little risky in terms of the casting and take some chances,” said Emma Watts, Fox’s president of production. “The character of Shaw is an interesting mix. She’s a powerful character and she has a real inner strength, but she also has a vulnerability. I think it’s a hard role to fill, but Ridley was confident in Noomi from the get-go and he has a pretty good track record with casting.”

Indeed. More than 30 years ago, as Scott was preparing to make “Alien,” he cast the then-unknown Sigourney Weaver as Ellen Ripley, launching her to stardom. Now after a long break from sci-fi, he is returning to the genre to explore what he sees as some still-unanswered questions.

Although an R rating is likely to keep box office for “Prometheus” below that of summer PG-13 tentpoles such as “The Avengers,” anticipation for the film — which Fox says cost $130 million after tax credits — was high, and 3-D will add to its earnings.

“Prometheus” — the name of the Earthlings’ spaceship — is not a traditional prequel to the “Alien” series. According to Scott, the two share the same DNA, meaning that in the new film, similarly bad things happen on another planet — as they did in Scott’s 1979 original. But Rapace is not a mere replacement or reincarnation of Weaver’s Ripley. Rather, she is a God-fearing scientist who hopes her studies lead her to uncover the meaning of life — mysteries Scott wanted to address in his return to the world that altered his nascent career.

“What stuck in my mind was in none of the four ‘Alien’ movies, no one ever asked the question, the big question of who’s the big guy,” said Scott, who directed only the first of the four “Alien” films (James Cameron, David Fincher and Jean-Pierre Jeunet stepped in for the later editions). “When the franchise finally ended, I thought you can’t go again because the alien himself is too familiar now, it’s no longer frightening. You have to reinvent the wheel and I kept thinking about the big guy.”

To do that, he needed to find his Elizabeth Shaw — someone who could endure challenges such as fighting off a batch of tentacled monsters and enduring a horrific self-mutilation. One night on TV, he caught Rapace’s performance in “Dragon Tattoo.” “I was taken and curious,” Scott said. “Who was this punk and which alleyway did (the director) get her?” He watched the film two more times before meeting with Rapace; when they finally came face-to-face, he was surprised. “Into my office walked this beautiful young woman, and I found myself dealing with a real actress,” he recalled. “She’s special, indestructible.”

Rapace said that to make the character of Shaw believable, she felt the need to reconnect to her spiritual upbringing in Iceland, to a time when her belief system felt more certain. “I felt I had to face myself and find her in me,” Rapace said. “There’s a line in the movie, ‘That’s what I choose to believe,’ and I think that’s a key sentence in her life. She lost her dad when she was 9, her mother when she was a baby, and she’s been on her own. It’s like you have a choice: to either be destructive or to say everything happens for a reason and I just have to find the reason. She is driven by passion and an almost naive obsession to find out who made us.”

Rapace, who is intent on grounding all her performances in reality, was worried that the movie — shot primarily on soundstages at London’s Pinewood Studios — would be a green-screen spectacle with nothing to help anchor her. She was pleasantly surprised to find Scott and his crew had created soundstages that relied more on physical sets than blank spaces with effects to be added later.

“They built those amazing, huge sets,” Rapace said. “There were real creatures to react to. It was pitch-black. We used our flashlights. It felt like we were on a planet. I was deeply connected to the real world because I really felt like we were on this journey together.”

For Rapace, “Prometheus” seems likely to open new acting avenues. Her next few roles, though, don’t involve any spaceships or aliens. She’s in Philadelphia working on a crime thriller, “Dead Man Down,” with Colin Farrell and directed by her “Dragon Tattoo” helmer Niels Arden Oplev. She’s also in Brian De Palma’s coming revenge tale “Passion.”

“I pre-judged Hollywood. I thought it was a little more hollow and a little bit more superficial,” she said. “I didn’t know there were so many artists: directors, producers and actors living there with the same passion as I have. When I first came to Hollywood I met amazing people and I realized that I was wrong.”