What kind of pull will “Gravity” have on moviegoers when it hits theaters Oct. 4?

The looming question for Warner Bros. is how to sell a unique 3D saga set entirely in space that predominantly relies on the performance of one star — Sandra Bullock — with virtually no supporting cast.

Moreover, director Alfonso Cuaron, despite being a highly respected auteur, hasn’t made a film since 2006’s “Children of Men.” That critically acclaimed sci-fi thriller cost around $80 million, and grossed less than $70 million worldwide.

“Gravity” isn’t a recognizable property (it’s based on an original script by Alfonso and his son, Jonas), and its harrowing premise — the terror of being stranded in outer space — doesn’t have an obvious marketing hook.

That said, Warner Bros.’ marketing maven Sue Kroll has had plenty of experience taking non-slam dunk movies such as “Argo,” “The Departed” and “Million Dollar Baby” from the starting gate to box office success — and even the Oscar finish line.

She has been campaigning carefully for “Gravity” since the spring, starting by unveiling a minute of footage in April during the film’s CinemaCon presentation in Las Vegas for exhibitors and press.

Three months later, in late July, Warners continued “Gravity’s” promotional trek, with a key stop at Comic-Con, where fanboys were shown about six minutes of footage, and Cuaron, Bullock and producer David Heyman tubthumped the pic. The movie then embarked on the Big Three late-summer festival circuit, opening Venice (Aug. 28), where it generated a burst of strong reviews, en route to Telluride and Toronto (premiering there Sept. 8).

Kroll notes that being promoted at a fan fest like Comic-Con and at three prestigious film festivals is quite an unusual distinction. “That’s a very rare combination for any film,” she says.

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Warners’ key selling point is that audience members will feel as if they’re in outer space with Bullock and George Clooney after space debris destroys their shuttle.

“ ‘Gravity’ is a unique movie that’s very visceral,” Kroll says. “As a viewer, you’re put right in the middle of the experience. I get a bit of a stomach ache from watching it.”

Warners has used only one tagline so far — “Don’t let go” — on its stark poster art, and has released several straightahead trailers (“Detached,” “Drifting” and “I’ve Got You”). One trailer began thusly: “Explorer, this is Houston.” “Go ahead, Houston.” “Mission abort.”

The studio is targeting a broad audience with spots that will run on football games, morning shows, TV season premieres and shows that include ABC’s “Modern Family,” NBC’s “The Voice” and AMC’s “Breaking Bad,” concurrent with an awards-season campaign, just as it did last year when it launched “Argo” at Toronto.

Kroll also believes that Bullock is a huge asset. Four years ago, the studio released “The Blind Side,” which grossed more than $300 million worldwide and won her the actress Oscar.

“Women and men really like her,” Kroll notes. “You really care about what happens to her character. You really want her to win.”

“Avatar” director James Cameron, who says he’s a huge fan of “Gravity,” which his pal Cuaron showed him weeks ago, says he hopes Warner Bros. “is going to sell it as the human story it is.”

Kroll, recently named president of worldwide marketing and international distribution at Warners, played a major role in the campaign for “Argo” — leading to the movie’s top Oscar and better than $230 million in worldwide ticket sales. But that film’s story was gossamer compared with “Gravity’s.”

The studio is also opening the Cuaron movie day-and-date in several major overseas markets including Australia, Germany, Italy, South Korea and Spain.

So sometime in early October the studio will begin to get a global answer to the question: Will audiences be drawn to “Gravity,” or will it land with a thud?