After spending 39 days in a greenhouse surviving on almost nothing but potatoes as part of a space colonization experiment, Ray Collins rushed to Wendy's on Tuesday afternoon with a craving for some fast food.

His order?

"Actually I had a baked potato," said Collins, who belongs to a Fairbanks-based nonprofit group called International Space Exploration and Colonization Co.

After a pause, he added, "And a hamburger."

Collins' stay in a 1,056-square-foot greenhouse off Goldhill Road is the latest experiment run by ISECCo., which formed in 1988 with the objective to help develop the technology necessary to colonize space.

His experiment-the second time Collins has holed up in a greenhouse with nothing but plants to keep him company-was designed to determine the minimum area a human would need to maintain a support system for life in space.

Collins, 46, calls the Quonset hut structure that was his home for more than a month Mars Base Zero.  The research from his experiment will be added to a similar test he subjected himself to in 1988, when he spent a shorter stint in a greenhouse.

The experiments are part of the group's efforts to develop a "closed ecological life support system" that could provide all the food, air and water needed to sustain human life in space.

When he entered Mars Base Zero, Collins' goal was to survive in the greenhouse for at least a month, maybe even two.

Tuesday, he made his exit after 39 days because he ran out of food.

"I ate my last potato plant this morning," he said.

With the exception of some onions, carrots, beets and other produce to spice things up, potatoes were all Collins ate during his tenure in the greenhouse.

"I was eating three to four pounds of potatoes every day," said Collins, who had a stove in the greenhouse for cooking.

Collins suspects his prodigious spud consumption was one of the factors that led to symptomos of stomach pain and shakiness midway through his stay.

The symptoms went away after he started peeling the skin off the potatoes and consuming salt sneaked into the greenhouse by a friend.  Collins said he figures the health problems were due to either a low sodium intake that was cured by a salt or a toxin that had developed on the potato skins.

A green toxin called solanine can show up on potato skins when they are exposed to light, said Roxie Dinstel, an agent with the University of Alaska Fairbanks Cooperative Extension Service.

"It would take a lot of it for it to kill you, but it is a problem," she said.  "That's why potatoes should always be stored in the darkest place possible."

Potatoes sold in the grocery stores are commonly stored in brown bags to limit light exposure, she said.

Collins said he had mixed feelings about running out of spuds Tuesday.  On one hand, he had hoped to make the two month mark.  However, Collins said he was also happy to return home to his family.

He has a 2-year-old son and his wife is pregnant, with the baby due in December.

Although his space club, which has about 20 members, learns something new from every experiment, Collins said, the group is still far from determining what it would take for humans to colonize space.

The next experiment is tentatively scheduled for next summer.  Collins said he wouldn't mind acting as the guinea pig again, though others have also expressed interest.

"Actually my wife is really keen on trying it," he said.