This reminded me of a sci-fi short story that I read a while back. (I would put a spoiler warning here, but I can't remember the author or title; it was probably by Robert A. Heinlein, Harry Harrison, or Arthur C. Clarke.) Basically, astronauts were put inside a "biodome" that would simulate the surface of Mars, then they'd have to practice various experiments. Anyway, the simulations kept going wrong, so eventually they stuck two astronauts in there and said "If you leave, you're fired. Don't call us unless it's a life-threatening emergency, otherwise we'll turn off the radio." All went well, until an astronaut got bored and threw a rock at a robot that was scuttling around (an animatronic alien), and discovered that it was bleeding. In other words, they really were on Mars, and their boss had lied to them by telling them that it was a simulation. (They'd been in some kind of coma/stasis for the duration of the trip, but they'd assumed it was just for a couple of hours, like general anaesthetic during surgery.) At this point, they went a bit crazy, since they couldn't really cope with the isolation of being so far from Earth. One of them was able to sedate his friend, then himself, so that the auto-pilot would bring them back home. Their boss said that future missions would go better, now that everyone else knew it was possible.
A few years ago, I wrote about the "Space Cadets" series on Channel 4. This was a hoax, where the volunteers thought that they were going into orbit but they were actually sitting inside an aircraft hanger in Suffolk. Putting these ideas together, I wonder whether any reality TV show could get away with the reverse approach? "Surprise - you think you're in Russia, but you're actually on Mars! You've just been Punk'd (TM)."
Edit: The story I was thinking of is "Simulated Trainer" by Harry Harrison, reprinted in "Galactic Dreams".