Confronting Obstacles in Final Frontier : Technology: Before long space travel becomes real, issues ranging from radiation to zero gravity must be conquered.

For two decades, robots have gone where humans could not: to nearby planets and to some of the outer reaches of the solar system. Each voyage has offered tantalizing information to whet the appetite of would-be space travelers.

Before humans can follow, however, scientists will have to overcome some significant health problems caused by long space flights. Just what hurdles lie ahead are examined in an exhibit at the National Air and Space Museum, “Where Next, Columbus?”

“We are leaving this planet on wings of desire to explore,” said Valerie Neal, the exhibit’s curator.

The exhibit begins with homage to Christopher Columbus and the challenges he faced 500 years ago in journeying to the uncharted New World. From there it jumps to the future, to a hypothetical spacecraft constructed for a voyage to Mars, and finally to Mars itself and a habitat there.

Based on the most current scientific information available, the exhibit confronts the physical challenges of space travel--radiation, inefficient transportation and high-speed collisions with meteoroids--problems that must be solved before humans can venture into space on long voyages.

Whether astronauts wing to relatively nearby Mars (a three-year round trip) or explore the farthest reaches of the solar system, some of the biggest problems they will face relate to health.

“What do you do to conquer weightlessness and the loss of bone structure during long space flights?” asked Martin Harwit, director of the museum. “What about solar radiation, which can be as bad as atomic bombing?”

As the exhibit describes, the first space travelers will have to be equipped with an array of devices: shields to buffer them from solar flares, artificial gravity to compensate for bone and muscle loss and a biosphere to grow enough food and produce sufficient oxygen to survive the trip.

The mission to Mars alone, for example, requires 22 tons of food, water and oxygen to sustain a crew of four, not to mention devising a way to deal with equal amounts of waste and other body products that will be produced during the voyage.

One answer to this problem, as the exhibit shows, is a closed ecosystem, a biosphere that can provide food and oxygen from plants. In this section of the exhibit, called “Green Thumb in Space,” visitors view a hydroponic garden growing lettuce, tomatoes, herbs and cucumbers in a mock habitat on the surface of Mars. Similar gardens have been designed by NASA for the space station Freedom.

Plants and tomato seeds have already flown in space as part of experiments to test their viability there. But as the exhibit notes, it is not known how long plants will survive.

Even more daunting is how to protect space travelers against dangerous solar radiation.

The Earth’s atmosphere normally shields against radiation exposure, particularly the unpredictable solar storms that spew damaging protons. These protons move so quickly that they reach the Earth’s surface within 30 minutes of a solar flare, placing anyone outside the atmosphere in the direct line of fire.

Although it has not yet happened, astronauts who leave their space vehicle--to walk in space or step on the Moon, for example--take the small chance they might be caught unprotected during a solar storm.

“Space suits are not built to protect against solar flares,” said Arnauld Nicogossian, chief medical officer for NASA. “If they are caught in a solar storm, the exposure would be lethal.”

Those who fly to Mars and beyond will also face the risk of chronic radiation exposure, unless scientists can come up with solutions.

The most damaging effects from chronic exposure during long-range space travel are to the thyroid, eyes, breasts, testes, ovaries and skin, Nicogossian said.

Acute exposure, like that from solar storms, is worst for the immune and digestive system as well as the ovaries, testes and bone marrow.

One option under study to reduce radiation risks is to have crew members sleep in specially sheltered areas of the ship or to shield the entire vehicle with more effective materials, like water, liquid hydrogen or plastics. It may even be possible in the future, the exhibit notes, to give medication to protect against radiation exposure, although as Nicogossian notes, none is yet available.

Researchers also must deal with weightlessness.

The exhibit shows how within hours of launch, the body adapts to zero gravity by moving blood and other body fluids from the legs to the head and chest. The heart then speeds up and the endocrine system tries to compensate for this shift in fluids, a change that usually stabilizes within days.

More troubling is the significant decline of bone and muscle that occurs with space flight. Without the force of gravity experienced on Earth, bones lose calcium and muscles, including the heart, lose some mass.

Walking or jogging on a treadmill or riding a stationary bike can help maintain cardiovascular fitness but won’t affect bone loss, the exhibit notes.