Listen for gasps in the "Gravity" audience when 50-year-old leading lady Sandra Bullock first slips out of her space suit and shows off her flawless figure in a tiny crop top and itty bitty shorts. And then know her body isn't the only miracle -- her being in the movie at all was a long-shot at best.

Originally written for Angelina Jolie, the lead female role was reportedly offered to a bevy of much younger stars. In mid-2010, Marion Cotillard, 38, screen tested. A couple of months later Scarlett Johansson, 28, and Blake Lively, 26, were being linked to the movie. When director Alfonso Cuarón got the green light from Warner Bros., he offered the part to Natalie Portman, 32, without a screen test. But she passed.

Which is when Oscar winner Bullock entered the picture. And even she admits she was a weird choice for a movie about an astronaut floating helplessly in space, but for a totally different reason.

MORE: How Sandra Bullock trained for weightlessness.

“I don’t like to fly. I’ve never been a good flyer," Bullock told FOX411. “I have a lot of friends that have permanent nail marks in their arms… The moaning that comes from me when there is turbulence. It’s awkward for everyone around.”

Luckily for Bullock, filming "Gravity" didn’t require any actual soaring. Instead Bullock, like her co-star George Clooney, was harnessed with around a dozen carbon-thin wires across her body to train, and tied into a rig inside a tailor-made cube adorned by over four thousand LED light bulbs. The bulbs could simulate whatever brightness, speed and color were required to capture the light of Earth below and sun in the distance as her astronaut character spun and slammed into stuff

“The toughest aspect (of filming) was gravity. We had to have the actors floating around the way they would react in space and there is no resistance in space and we needed to invent a new set of tools to achieve that,” Cuarón explained. “The journey of inventing those tools is what took a while.”

Four-and-a-half years to be exact.

And while the process wasn’t always a walk (or rather or whirl) in the park, it did teach Bullock a few extra life lessons.

“It was frustrating, scary, exhilarating, humbling… But mostly, it just pissed you off. It took away all your control, and your crutches and forced you to (surrender),” she added. “But I have gotten to that point in my life where I know I am absolutely out of control, and if anything should happen other than what I do, than that is all I have got. And even if I am not always controllable.”

“Gravity” opens in theaters Friday