Last month, we brought you a report that Sandra Bullock was in negotiations, though virtually “locked in” for the lead role in Gravity, written by Alfonso Cuarón and his son, Jonas Cuarón. Later on, Robert Downey Jr. who was originally set to star in the film opposite the female lead, had exited the project after wrestling with scheduling issues that he had hoped to resolve.

Now, THR reports that Sandra Bullock (Kiss & Tango, Most Wanted) has been confirmed to star in Gravity as the female astronaut who becomes trapped in space after debris wipes out her space station. In addition, George Clooney (The Descendants) has been now been cast as the second main lead in the film, opposite Bullock. Clooney will be replacing Robert Downey Jr., who left the project due to scheduling conflicts with the as yet Untitled Sherlock Holmes Sequel.

Production on Gravity will get underway in the Spring, after Clooney finishes shooting his fourth directorial feature film, The Ides of March.

Gravity is slated to hit theaters in 2011,