NASA Will Pay You to Eat Astronaut Food for 4 Months
forbes.com
forbes.com
I'm guessing the graduate student exception to professional experience is because that's where they're most likely to find reasonable candidates for this, because they might be able to take a semester off and possibly even get academic credit for doing something like this. Most other people couldn't just leave their jobs for a four month gig with NASA, however cool it might be.
Anyhow, it sounds like one of their goals is to have people who could be trained as NASA mission specialists. So if you want to be an astronaut someday, this might be your chance.
Here's a photo of the space food package and advertising pitch: http://db.tt/bUDfgi48