When the space shuttle Columbia touched down at Kennedy Space Center two weeks ago, much attention was focused on Air Force Col. Eileen Collins, the first woman to command a shuttle mission, and on her crew's successful launch of an X-ray observatory. But among more than a dozen scientific experiments, the shuttle crew also carried out two medical tests to see if certain drugs might protect future space voyagers from the bone and muscle degeneration caused by weightlessness.

These tests are part of NASA's long-term medical mission: How do you monitor people who are hundreds, thousands and potentially millions of miles away from the nearest hospital -- much less treat them if something goes wrong?

"We all long for the day when we'll have something like Dr. McCoy's tricorder, but we're a long way from that kind of quick, thorough assessment of physiological function in space flight," said John B. Charles, a mission scientist for NASA who tracked the health of American astronauts on the Russian space station Mir. "Nobody wants these expensively trained crew members laid up because of something that could have been anticipated or fixed."

In more than three decades of research on space flight and its effects on the human body, the National Aeronautics and Space Administration has yet to match the wizardry of the "Star Trek" writers who "invented" the tricorder for that television show, but the space agency's scientists have made numerous contributions to medicine. For example, "the coronary care unit as we know it today wouldn't even exist if it weren't for NASA," said physician Jeffrey Borer, chief of the division of cardiovascular pathophysiology at New York Hospital-Cornell Medical Center. From lab tests that require smaller blood samples to microminiaturized systems for monitoring patients, dozens of medical advances have their roots in the space program.

"NASA is the ultimate human-engineering interface," said Russell W. Jennings, a pediatric surgeon at the University of California San Francisco who uses a NASA-designed sensor system to monitor fetuses that have undergone surgery. "Their success requires humans and machines to work effectively together in unique ways."

"The work we do has to be multidisciplinary," said Joan Vernikos, the director of NASA's Life Sciences Division. "Overcoming the obstacles of space flight requires input from almost every field of science." NASA therefore brings together scientists who might otherwise never cross paths.

Among the results of this collaboration: A blind space scientist has pointed the way to a new form of mammography. And a probe designed to test Martian soil is being turned into a robotic brain surgeon.

While the goal is to make it possible for humans to survive in the most remote and stressful of environments, "you can't send an entire hospital into space," said Robert W. Mah, a research scientist at NASA's Ames Research Center in California. "So you have to provide the medical crew with the smartest possible tools." The latest of NASA's smart tools include these:

REMOTE SENSORS To simplify the monitoring of space crews, NASA is developing an array of Band-Aid-sized sensors that can collect data on everything from an astronaut's brain waves to blood gases and transmit the information to Mission Control.

The sensors are already in use in the pediatric surgery department of the University of California, San Francisco, where doctors place them on fetuses during intrauterine surgery. "It's an incredible advance," Jennings said. "All the mother has to do is be near a receiver that picks up signals from the sensor and we can tell what's going on with the fetus. We can even send Mom home and get the information via a phone line."

SMART PROBE In 1989, Mah was charged with developing a robotic probe to penetrate the surface of Mars and analyze everything from its texture to its chemical composition. Although this device has yet to reach Mars, the Smart Probe is being retooled to tell the difference between healthy and damaged tissue.

"The scenario I envisioned was a head injury during a mission to Mars," said Mah. "Hemorrhaging in the skull would be pretty hard to treat, because it's easy to cause more damage. Using the Smart Probe will be safer than manual procedures, because you can do it more delicately without severing arteries." Currently being tested with animals, the Smart Probe may become not just a diagnostic tool but one that can also deliver medication and cauterize blood vessels.

BONE ANALYZER Space is hell on bones. Without gravity's pull, the genes that control bone growth switch off, and the body begins to drain calcium out of the bones and into the bloodstream. After long missions, astronauts could arrive back on Earth with bones as brittle as dry twigs.

"The nature of the problem is really biomechanical," explained NASA physician Sara B. Arnaud, who is researching bone metabolism in a gravity-free environment. "In space, the skeleton isn't bearing any weight. There's no need for a whole lot of calcium in the weight-bearing bones, so it simply leaves those bones."

Millie Hughes-Fulford, a professor in the department of medicine at the University of California, San Francisco, has flown in the space shuttle and discovered that bone-forming genes are switched back on by the pressure of gravity when the astronauts come back to Earth. "The question is how much pressure you need for . . . normal bone growth," says Hughes-Fulford. "If we can simulate gravity while in space, perhaps we can prevent bone loss. But we still don't know if it will take one hour, two hours or more to get normal gene expression."

The answer to that question has implications for those whose calcium deficit is a result of their advancing years. "No one's really looked at the problem of just how much weight-bearing exercise you need to make bone grow," Hughes-Fulford explained. "Is it 10 minutes? Is it 20 minutes? And how much pressure do you need? That's a real important question for post-menopausal women like me: Do I need to get on that treadmill for 50 minutes or will 15 minutes do it?"

To understand what happens to the skeleton in a gravity-free environment, NASA scientists are also developing more sensitive techniques for analyzing the strength of bones. "Most existing techniques can only assess a bone's density, not how likely it is to break," said Arnaud. "But density of bone isn't the whole story when it comes to bone strength. If the mineral density is low, you still need to know the fracture risk -- if the bone's mechanical properties are intact despite low mineral density."

The Ames researchers are working on a simple, noninvasive device to measure those properties. Called the Mechanical Response Tissue Analyzer, or MRTA, it is a probe placed on the skin to apply a short vibration to the bone and measure how it responds.

"The MRTA won't replace bone density [analysis] as a diagnostic instrument for osteoporosis," Arnaud said. "But it can measure the strength of a bone and tell you whether it is functionally competent or incompetent, which will be very important when monitoring astronauts on long-term missions. In those situations you really want to know who is most likely to break a bone so you can keep them away from high-risk tasks."

DIGITAL BIOPSIES David Dershaw owes a lot to the Hubble Space Telescope. As director of the Breast Imaging Section at Memorial-Sloan Kettering Hospital Center in New York, Dershaw is one of hundreds of physicians who are using technology derived from the Hubble to obtain clearer, more accurate images of the breast during needle biopsy procedures. "It's truly wonderful," Dershaw said. "It's faster, it's less expensive, it requires less exposure to X-rays, it's more accurate, and there's no scarring that might interfere with later mammograms."

Astronomers try to find small objects, such as stars, in the complicated environment of the universe. Likewise, gynecologists try to find cancer cells in breast tissue. In space, the Hubble captures light and converts it to an electrical signal, which a computer analyzes and turns into a visual image. In a medical setting, similar technology converts X-ray images of the breast into detailed digital pictures.

An important advance in breast imaging lies in the mathematical formula that analyzes these digital signals -- a formula based on one created for NASA's Search for Extraterrestrial Intelligence program, or SETI.

"A blind scientist at the SETI institute developed this algorithm because we need to detect faint signals against a very dense noise background," explained NASA's Vernikos. "He realized that if we applied the algorithm to the signal coming out of a digital mammogram, we could sharpen the image and make it easier to detect abnormalities in the breast."

"This technology allows us to very precisely position a needle in the breast to remove tissue to be biopsied, which otherwise would have to be done surgically," Dershaw said. "It's easier on the patient, and prevents unnecessary surgery."

Digital breast imaging is being used only for biopsies, but Dershaw expects to see digital mammograms in the near future. "When this is available for mammograms, the original mammogram can be stored electronically and duplicated without any loss of the quality of the information," Dershaw said. "That means we can convey this information electronically over telephone lines, which will allow instantaneous real-time consultations."

ROTATING BIOREACTOR When most researchers try to grow cancer cells, they end up with a thin layer of slime in a Petrie dish. When Jeanne L. Becker grows them, she ends up with mini-tumors: three-dimensional clusters of cells that look and act much as cancer does in the human body. To create them, Becker employs the rotating bioreactor, a device that allows scientists to simulate gravity-free conditions.

Like other NASA inventions, the bioreactor was the product of hard work and pure luck.

Researchers had been trying for years to find a way to suspend cell cultures so they could grow in three dimensions. In 1986, along came a NASA lab technician with a drill, a syringe and some time on his hands. "One of our electrical technicians was playing around during his lunch hour and placed a syringe in an electric drill," recalled astronaut and physician David A. Wolf. While watching the drill spin the syringe just like a drill bit, he said, "I noticed that the material in the syringe was being kept perfectly suspended. And I thought, `We have to build a tissue culture vessel that spins.' "

Wolf and his colleagues put a few cells in a test version of the bioreactor and waited to see what would happen as the rotating action allowed the cells to float rather than sink to the bottom of the device or stick to its sides. A few days later, Wolf said, "one of the lab techs came in and said, `We've got a big problem with our culture, it's clumping up.' When I looked in the microscope I saw that the `clumping' wasn't a problem, it was three-dimensional tissue formation. The tissue was organized and healthy. It was incredible."

When Wolf and colleagues Ray P. Schwarz and Tinh Trinh presented their findings to the scientific community, "they didn't believe us," said Wolf with a laugh. "They thought we were showing photographs of human tissue grown in the body." For their efforts, Wolf, Schwarz and Trinh were named NASA's Inventors of the Year in 1992, and the bioreactor soon found its way onto the space shuttle and into dozens of labs around the United States.

"The ability to grow cells in three dimensions has opened up a whole new world for cancer research," said Becker, an associate professor at the University of South Florida School of Medicine who uses the bioreactor to study ovarian cancer. "Let's say you have a type of tumor cell that is sensitive to drug X when you grow it in a Petrie dish. If you take that exact same cell and allow it to grow in three-dimensional configuration, the way it grows in the body, it will be resistant to drug X," she said. "And that's just the kind of thing you see when you're treating actual cancer patients. My goal is to use this as a means of determining how cells become resistant and to overcome that resistance with more effective treatments."

Several groups are using the bioreactor to grow spare "body parts" -- pieces of tissue that can replace damaged cartilage. Eventually, they hope to grow heart tissue and even entire organs. "It's phenomenal stuff," Becker said, "although for that you really need to work in space. On Earth, cultures just can't grow that big; gravity eventually pulls them down to the bottom of the reactor."

Cancer cells grown in the bioreactor have already yielded more information than most researchers could have achieved in years of working in Petrie dishes, said Becker, who believes that treatment advances are not far behind. "We're not talking 50 years from now," she said confidently. "We're talking things that could be done in the next decade."

When the Body Goes Haywire

When freed from the constraints of gravity, the body goes haywire. The brain can't tell which way is up, leading to a nasty form of motion sickness. Sleep becomes disordered. Muscles atrophy. The heart weakens. Immune cells fail to respond to threats. Bones become thinner and more brittle. Blood and other fluids rush toward the head.

These changes are fairly benign in space, but pose a problem when astronauts return to Earth. Balance is off, muscles are weak, and the heart has to "relearn" how to beat effectively against the force of gravity. Returning astronauts have reported problems ranging from the merely annoying to the downright scary.

Of the nine days he spent on the space shuttle, "the return to Earth was the only time in my whole mission that I did not feel good," said Lawrence DeLucas, director of the Center for Macromolecular Crystallography at the University of Alabama, Birmingham. "My heart was real confused; it would race, and then it would slow down. I actually thought I was going to have a heart attack. And it took about a week for my balance system to get to normal. Just turning my head sideways made everything spin."

"Humans evolved in the presence of gravity," explained Marian L. Lewis, a NASA scientist who teaches gravitational biology at the University of Alabama at Huntsville. "Every system in the body is designed to compensate for its influence. When you remove that influence, as in space flight, the body has to adapt. And not all of those adaptations are beneficial."

Understanding the effects of zero gravity and how to prevent them remains one of NASA's unsolved mysteries. How can the United States dispatch a crew to Mars if they are going to arrive so debilitated that they can't do any work? More immediately, how can crews spend extended periods working on the Earth-orbiting international space station that is now being assembled if each visit leaves them too weak to stand when they return?

"We need to understand how to counteract the changes caused by lack of gravity if we are to continue to explore the solar system," said DeLucas. "We need to find out what it takes to allow a person to stay in space for a long period of time without suffering from these detrimental effects."

There's a very down-to-earth benefit to this inquiry. That's because the effects of space flight closely resemble several common health problems, including osteoporosis, heart disease and neurological disorders such as Parkinson's disease. "It's a tremendously exciting research opportunity," said astronaut and physician James A. Pawelczyk. "With two weeks of space flight, we can mimic what might happen in 30 or 40 years of aging."