JOHNSON SPACE CENTER, Texas — Last year John Lewis spent 91 days locked in an isolation tank, deprived of his wife, fresh food, sunlight and even a normal toilet. And he can't wait to go back.
"I don't feel that I've been here for that many days," said Lewis, a 31-year-old aerospace engineer who has spent a total of 121 days inside the cylindrical steel tank during two tests with three other volunteers. "You get this blurred vision of what was yesterday."
NASA is stepping up isolation-tank research as it drafts plans to embark on one of the most ambitious space flights ever undertaken, a 1,000-day odyssey to Mars. With Russia, Europe, Japan and Canada, the space agency will also launch the first elements of a new space station this year, extending manned presence in space well into the next century.
The goal of the isolation experiments is to perfect a life-support system to turn urine, sweat and old shower water into clean drinking water. The system should also make oxygen from the carbon dioxide humans exhale.
Recycling is vital because a crew en route to Mars will not be able to stop off for more supplies.
"All these tests are invaluable in determining where we need to do more research," said Donald Henninger, Johnson Space Center's chief scientist for life-support systems. "They're also the best way we'll convince the operational folks they're ready to go."
NASA's three-story, 20-foot-wide isolation tank simulates the confined environment of a spaceship. It was used to test space suits for Gemini flights in the early 1960s but now is a cramped home for four resembling a giant can.
The first floor has a living room, kitchen and toilet, known as the "hygiene waste-water cabinet" in NASA-speak. The facility features a tube that leads to the recycling system for urine and a thick plastic bag atop a seat for other waste, which is not recycled.
"The kind of people who sign up . . . are the kind of people that overcome hardships," said Laura Supra, 29, one of four volunteers in the three-month experiment. "If you're the kind of person who likes camping, you don't like going to the outhouse but you do it because it's camping."
Up a steep metal ladder, the second floor stores scientific equipment and the third holds four tiny bedrooms. NASA cameras keep an eye on the crew except in the bedroom and bathroom.
It looks like a dull place for an extended stay, but the volunteers say a full program of work kept them from getting bored.
"We were very busy. Time went by very quickly," said Vickie Kloeris, 41, another veteran of the 91 days, which ended in December. "It's a mindset. You get yourself prepared for the duration you know you're going to be there. It really doesn't matter if it was 90 days or 291 days."
In fact, the crew's hopes to catch up on reading or learning a foreign language quickly evaporated under their daily regimen. "I brought my Russian book with me," Supra said. "I think I cracked the book once."
The NASA program also demanded a lot of time on the treadmill and other exercise, which astronauts need to maintain their muscles in the weightlessness of space.
"I came out of here in better shape than I'll probably be in the rest of my life," said Lewis, a tall, thin man with glasses and a Vandyke beard. "I'm one of these guys who doesn't do a lot of running unless someone is chasing me."
Crew members say no romances developed between the two men and two women, although all said relations remained friendly. Three of the four volunteers are married, and Lewis' wife was in the last trimester of a pregnancy during his time inside.
"It's not like a bunch of fraternities and sororities heading off for six months at the shore," said psychologist Al Holland, who monitored the experiment, noting the professional dedication of the crew.
The volunteers did have some perks that astronauts lack. They could easily call friends and family and see them with a video linkup, and they could watch television. And--unlike a Mars mission--the isolation-tank crew knew they could leave any time.
The NASA isolation experiments are not the first of their kind but are the most sustained and ambitious. The space agency plans a series of ever-longer tests, leading to a 420-day isolation study in 2005.
Four Russians spent six months in a Siberian underground chamber in 1974, paving the way for a series of pioneering Russian space stations leading to the Mir station, in its 12th year in orbit. The United States did a 90-day test in 1972.
An Italian sociologist set the record in 1992 and 1993 by spending 366 days alone in a subterranean chamber, but the focus was largely on psychological research. At the height of the Cold War in the 1950s, others spent extended periods in bomb shelters as survival tests.
Russian engineers have already made important advances in designing the life-support system for Mir, which has worked, albeit with well-publicized recent difficulties, since 1986. The Russian system recycles sweat and urine for drinking water and oxygen but does not recycle carbon dioxide.
Those taking part in the NASA isolation experiment have seen that it is not easy to perfect a life-support system that always works--an absolute requirement when it comes to air and water. "We had some situations where we came close to leaving," said Lewis, who, like many of his colleagues, hopes to become an astronaut one day.