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Director Alfonso Cuaron is offering up the most coveted female role in Hollywood... so why can't he find an actress to fill it?

Warner Bros.' Gravity tells the story of a "lone survivor of a space mission to repair the Hubble telescope desperately trying to return to Earth and reunite with her daughter." The sci-fi thriller, which also stars Robert Downey Jr. (who's locked in for a limited amount of time), is set to be shot and released in 3-D.

Let's break it down! Angelina Jolie was the first actress to be cast but subsequently dropped out not once but twice because, reportedly, she wanted her role "enlarged." This seems odd because the pic's focus is already on the actress' character, much like the way Tom Hanks carried Cast Away in 2000.

Next up for the role? Natalie Portman, who was offered the lead after her performance in Black Swan began receiving so much positive buzz. But now Deadline reports that Portman has passed. Hmm, perhaps because she has too many other film projects on her plate and wants to take a break? The actress' reps cite scheduling conflicts, natch.

Warner Bros.' latest prey is Sandra Bullock. According to insiders, the company is making a big push for her to play the main character due to her recent Oscar win and box office draw. But does she have the acting chops for such a weighty dramatic role? Watch Bullock in The Blind Side and decide for yourself!

So who should star in this project? A project that "numerous actresses have wanted to make because it is ambitious and original," claims Deadline. But if an A-list actress doesn't lock in soon, Gravity will get stuck in development hell!