What did they think of the experiment? "Well, it was an experiment - and an experience for my wife, too, to spend three, four months with the children on her own. My children are quite proud of their father, I think, and of course they're glad I'll be home for Christmas."

"When I saw the advertisement for volunteers, I knew I had to try for it. Simulating a long space mission was a challenge all right. Standing up for the first time a few days ago symbolized landing. It was quite something after three months lying down to rediscover the vertical, the sense of weight."

Showering in bed

For both Frank and Gilbert the experience has been an enriching one. "You're part of something important," said Gilbert, "and 90 days lying down gives you a chance to discover things about yourself, too."

During the three months of the bedrest mission, no visitors - neither family, friends or curious journalists - were allowed to visit the volunteers. "We were not isolated though, we all had a telephone, an Internet connection and of course the TV," said Frank. Gilbert adds "We had excellent communications with the outside world. Also there were two of us in each room and we often met together. After all we were a group of 14. We discussed things with each other - and with the MEDES psychologists."

So what were the toughest moments? "The first few weeks," said Frank. "I suffered from dizziness, vertigo, muscle aches and back pains but the medical support staff were superb."

"It's adaptation," said Gilbert. "That first month, when your whole organism is adapting to a new environment was hard, like seasickness if you like, but you're determined to see it through."

Now, all the volunteers have to re-adapt. "Dizziness, vertigo and muscle pains again," said Frank, "but the medical team here is really excellent, and we know we can count on their support over the next few months."

Three months in bed

Both men hope to be back at work in January, although it will be three to six months before their bodies have completely readjusted to normal, vertical living. Over the next two years MEDES will keep a careful eye on them all.

A second volunteer team is due to start another 90-day bed mission next Spring. Have Frank and Gilbert any advice for the newcomers?

"You have to know what you're letting yourself in for," said Frank. Not surprisingly, Gilbert was in full agreement. "You have to be motivated," he said, "you have to want to do it."

Would they do it again? "Of course", said Frank, "absolutely" agreed Gilbert.