WASHINGTON -- You're an astronaut on the way to Mars in the year 2034.
Your mission is to fulfill the national goal laid out three decades earlier by President George W. Bush when he called for the United States to return to the moon and then venture on to the Red Planet.
"Mankind is drawn to the heavens," Bush had said back then. "We choose to explore space because doing so improves our lives and lifts our national spirit."
So now you're living with five other astronauts in the small cabin of a spacecraft that left Earth orbit three months ago. Your home planet is just a tiny pinpoint of light in space, millions of miles behind you, and Mars is still three months ahead.
Outside your craft, space crackles with radiation. High-energy particles stream through the spacecraft hull and zap your body, leaving an unseen, potentially damaging wake. A sudden burst of harmful radiation from the sun could force you into a reinforced safe room, a place you call the "storm shelter."
Your crewmates are beginning to get on your nerves. You see the same people, every day, all day. You eat together, work together, depend on each other for survival. You've heard the same stories, over and over. There are no more secrets. You're alone only in the unconsciousness of sleep, and that's sometimes hard to find because the whirring, buzzing, clanking din of machinery never stops inside your home among the stars.
You feel isolated and alone, and yearn for home, ache for a loving contact with family. You know them now only as video images occasionally beamed from Earth. Your 3-year-old will be 6 by the time you get back. Conversation with your children is difficult because the words take so many frustrating minutes to make the long radio journey. Sometimes the homesickness is almost unbearable.
Weightlessness is doing its best to destroy your body - weakening bones and reducing muscle mass. Even the food tastes different. You exercise hard on special machines two hours a day just to maintain muscle tone and keep your heart strong. But still your bones grow more brittle.
You live with stress because there's always danger. Millions of things could go wrong with your complex spacecraft, and any one of them could kill you. Just beyond the window there is a vacuum and deep, deep cold. In an instant you could become a lifeless bit of space debris, ever drifting, never to return.
And Mission Control is always on your back. Every day they send long lists of chores to maintain the craft and to get ready for the Mars landing. They just don't understand what you're going through and you're not sure anymore that they even care. Your crewmates grouse constantly, and you join the chorus of discontent.
The scenario above is an illustration of just some of the complex human problems the National Aeronautics and Space Administration must overcome before the agency is ready to send people on three-year trips to Mars, the most hazardous voyage ever undertaken.
Guy Fogleman, head of NASA bioastronautics research, said the four toughest problems that must be solved are space radiation, bone loss from weightlessness, the psychology of long-term spaceflight, and developing technologies for remote medical diagnosis and treatment.
"There is a wide range of things we have to look at and they all have to be managed if we minimize the risk," Fogleman said this week after Bush pronounced his vision of NASA's future.
Radiation, particularly from cosmic rays, pose a high health risk in deep space, so much so that NASA has established a radiation laboratory that uses high energy beams to study the effects of heavy ion particles on biological specimens.
Walter Shimmerling, a NASA radiation expert, said high energy particles from supernovae that exploded in our galaxy permeate interplanetary space.
"They are considered to be much more destructive biologically than common X-rays or gamma rays," Shimmerling said. "The particle acts like a very tiny bullet going through a living cell."
It can damage DNA and cause a cell to die or turn cancerous.
Scientists also worry about solar flares that can spray nearby space with extremely energetic and destructive particles. To guard against these infrequent events, solar-observing satellites will be posted to automatically give warning, allowing Mars-bound astronauts to move to a safe room that is shielded against the radiation.
NASA has been studying the phenomena of bone loss in astronauts since early in the space age, but no real solution has been found. People in space tend to lose about 1 percent of their bone mass a month while in orbit. All countermeasures, so far, have failed to correct this problem.
Muscles can be kept toned with exercise, but even this is not a solution. If muscles are stronger than bone, said one expert, then a flexed muscle can actually pull away a sliver of brittle bone.
The psychological effects of spaceflight are still a puzzle.
Studies of people confined in tight quarters, such as in Antarctica, show that even the most dedicated and determined people tire of their companions, become withdrawn, and feel lonely and isolated. Often crewmen redirect their anger toward headquarters, or, during space missions, toward Mission Control. In some long term flights in the past, mild-mannered astronauts turned mean and ugly, railing at Mission Control, scolding engineers and complaining about work assignments. And that was after only a few weeks.
Dr. Jeffrey P. Sutton, head of the National Space Biomedical Research Institute, said solving the potential psychological issues of a Mars flight is critical to mission success.
At this point, NASA is not sure what would make up an ideal Mars crew. Should it include both men and women? Should parents with young children be included? What skill mixes are needed? Should there be a doctor on board? What is the ideal number?
All of these and other questions are still unanswered.
On the Net:
Human spaceflight: http://www.nasa.gov/vision/space/features/index.html