Kate Upton Floats In Zero Gravity For 'Sports Illustrated' Swimsuit Issue (PICTURES)

Kate Upton has become the first model to pose in underwear in zero gravity.

The 21-year-old American model took a trip in the Zero Gravity Corporation's exhilarating plane to model a bikini for the 2014 Swimsuit issue of Sports Illustrated.

"The ZERO-G experience was really exhilarating for everyone involved," MJ Day, editor of the Sports Illustrated swimsuit issue, said in a statement.

"We have been almost everywhere in the past 50 years with SI Swimsuit, but we have never done anything like this. It was certainly the most out-of-the-box shoot. Once again, Kate surprised us all with how she handled modelling in weightlessness."

The Zero G plane lets passengers experience 30 seconds of weightlessness at a time, through a series of parabolic flights high above the Earth's surface.

The experience is similar - though obviously shorter in duration - to a space flight.

Upton and the team had to endure 13 of the flights in a row in order to get the pictures.

Take a look at the making-of clip, above.