... it's the contestants:

According to London’s Evening Standard, the British TV network Channel 4 is launching a new reality TV show that claims to be the biggest hoax in TV history. The show, called Space Cadets, aims to fool 9 contestants into believing they have been blasted into space. According to the report, the series has been under wraps since its inception 18-months ago.

Well, I guess if they paid me enough I'd probably pretend to believe anything. I'm actually a little afraid to find out just how many of these bubble-heads never noticed the lack of gravity...