Collins, a Fairbanks landlord, and his space club built the base in a rural Fairbanks neighborhood to simulate plant production in space.

The goal of the privately funded experiment is to help determine the minimum amount of growing space needed if humans were ever to colonize the moon, Mars or other planets.

While living inside the 1,056-square-foot greenhouse, the 46-year-old space enthusiast subsisted almost entirely on potatoes harvested from raised beds. He ate the lumpy vegetables for breakfast, lunch and dinner and learned that he needs to eat about 3.5 pounds a day, enough for about 1,400 calories.

"I figure 94 percent of my calories are from potatoes," Collins said last week, speaking to a reporter though murky Visqueen that covers the southern half of the Quonset-style greenhouse.

Ultimately, Collins and his nonprofit space club, the International Space Exploration and Colonization Co., hope to build an airtight underground biosphere called Nauvik, an Eskimo word for "nurturing place," also in Fairbanks.

That project would cost up to $1 million, according to Collins' estimates. The greenhouse off Goldhill Road is a training run for that project and so far has cost $30,000.

Most of the funding has come from income from Collins' rental properties, though some individuals and businesses have made small donations and helped with labor.

ISECCo has about 20 active members, most of them in Fairbanks, Collins said.

Though Mars Base Zero is not airtight, Collins said he decided to remain in the greenhouse so he would not be tempted to cheat on his self-sufficient diet.

Collins imported only electricity and water, plus a bit of salt that a friend passed through a hole in the door when Collins felt ill. Nothing left the base, including human waste, which he is sterilizing and composting.

When not tending crops, Collins spent his time in a 200-square-foot apartment inside the greenhouse, tinkering with a persnickety oil-fired furnace, documenting his work, researching on the Internet or communicating by phone and e-mail.

And did he ever grow weary of potatoes? Not really, he said.

When he began to get sick of them, he just ate less, and found that by the next day, his appetite returned. He tried all ways of cooking the tubers; his favorite was homemade potato chips crisped in a microwave oven.

Collins had no oil to cook with, only some parsley. He took daily vitamins and harvested a small amount of lettuce, tomatoes, Swiss chard, turnips, cauliflower, carrots and onions for variety.

Still, he figures potatoes are the key to making a space colony work.

Compared to grains and other foods, potatoes provide one of the highest calorie outputs per square foot of soil and do well in cold climates.

Fairbanks is cold, but space is colder, he noted. A nice sunny day on Mars can be around freezing, Collins said, while cold nights drop to between 100 and 150 below zero.

Collins said he felt fine most of the month. He had stomach problems and felt shaky for a few days but figured it was due to a lack of salt. When salt didn't help, he guessed it may have been due to a poison called solanine in potato skins. He began peeling the potatoes and soon felt better.

And contrary to what you'd expect from a high-carbohydrate diet, Collins actually lost weight eating potatoes, dropping from 196 pounds to 187.

While Collins' experiment may sound quirky, Meriam Karlsson, a University of Alaska Fairbanks professor of horticulture who specializes in greenhouse production, said NASA also used to conduct greenhouse studies in connection with space colonization.

However, the space agency hasn't done much with greenhouse production recently due to budget constraints and a change in the agency's focus, she said.

Collins said that's partly why his club was drawn to the biosphere idea.

They wanted to do something that might contribute new knowledge. Karlsson said it is remarkable that the project is privately financed and operated. "I don't know anyone else who is willing to do this," she said. "He's pretty unique in that aspect."

Collins grew up at a remote homestead at Lake Minchumina, so he is accustomed to solitude, he said. His interest in space began with a childhood love of science fiction. His sisters are twins Miki and Julie Collins, writers and trappers who still lead a subsistence lifestyle at the family's homestead.

Still, Collins said, he found isolation more difficult now that he has his own family. He met his wife, Frankie, at a garage sale for the space club, and they married in 2001. They have a 2-year-old boy, Richie, and are expecting a second child in December.

Frankie Collins said it has been difficult living apart from her husband but said she supports his passion for space. She said she may try living in Mars Base Zero next year, assuming the club can continue to afford the project.

And what will Collins do first when he gets out today?

"Kiss my wife," he said