Mars or bust: science helps those with the right stuff keep their stuff right

Science News,  Nov 26, 2005  by Katie Greene

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The Apollo moon missions were a 21st-century idea that was slipped into the 20th century, said former astronaut Eugene Cernan in his 1999 book The Last Man on the Moon (St. Martin's Press). In the 1970s, soon after Cernan and his Apollo 17 crew completed the last moon mission of the 20th century, NASA developed the ferrylike space shuttle that has since dominated the U.S. space fleet. The shuttle was not intended to fly further than the distance required to orbit Earth, so there was no need to consider the health risks of years-long journeys into outer space.

Recently, however, plans to travel beyond Earth orbit have received new life. In January 2004, President Bush announced an initiative to return people to the moon, build a base there, and eventually travel to worlds beyond, namely Mars. As a first step, NASA's current official goal is to get back to the moon no later than 2020.

Sending people to Mars, however, would produce a unique set of complications for engineers and mission planners, most of which arise because the planet is so far away. William H. Paloski, a scientist at the Johnson Space Center in Houston, explains that the most probable mission would spend 6 months traveling outward; 18 months on the planet building a habitat, researching, and waiting for Mars and Earth to realign; and then 6 months homeward bound.

By comparison, a moon mission would be only 2 weeks long. In terms of duration, the difference between a moon and Mars mission is comparable to that between taking a family vacation in a spaceship and moving into one.

Early this year, in a document called a Bioastronautics Roadmap, NASA described the health risks of long-duration space travel. At the top of the list of risks is cosmic radiation. To protect astronauts from atomic nuclei that zip around the universe with high energy, some engineers propose deploying a giant magnetic field to surround the ship and deflect the radiation.

Biomedical researchers are already making progress on other items on NASA'S risk list. Microgravity atrophies muscles and depletes bone mass. A noisy spaceship and unnatural lighting disrupt sleep-wake cycles. And because there will be only limited medical expertise and equipment on board, an accident or illness, if serious, could abort a mission. Solutions to these problems would help make a Mars mission a go.

TETHERED TO TREADMILLS To the NASA physicians watching videos of astronauts on the moon, it was obvious that the few days of weightlessness on their lunar voyage had diminished the men's strength. By the time they stepped out on the lunar surface, "these individuals looked very spastic moving around on the moon" says Kenneth M. Baldwin, a member of the National Space Biomedical Research Institute (NSBRI), a consortium that coordinates a range of research in areas from psychology to medical technology. He notes that the physicians were surprised that the astronauts didn't injure themselves while performing tasks.

Baldwin, a physiology professor at the University of California, Irvine, studies muscle loss in space. The first muscles to atrophy in microgravity, Baldwin says, are in the calves, thighs, and back. "These are all the muscles that define posture and the ability to oppose gravity," he explains, "They're all compromised" by space conditions.

Currently, astronauts at the International Space Station exercise for at least 2.5 hours per day 6 days a week, either on a rowing machine or a treadmill. Most astronauts prefer the treadmill, Baldwin says. It's equipped with bungee cords to simulate 60 percent of Earth's gravity and to keep the user from floating away.

According to Baldwin, when these astronauts come back to Earth after 60 to 100 days in space, even though they've exercised, they've lost 25 to 30 percent of the muscle mass in their calves, thighs, and backs. "This implies that no matter what they've been doing in space, it hasn't prevented atrophy," Baldwin says.

He says that a better muscle-conditioning regimen could keep astronauts strong. Toward this end, he and his colleagues are exploring the genes and proteins responsible for muscle growth and, conversely, muscle loss in mice.

Rodents serve as good models for muscle loss in people, Baldwin says. When researchers suspend mice in slings that keep their hind legs off the ground, the unused leg muscles atrophy.

Baldwin's team has found that just a few days of muscle idleness reduce the activity of genes that regulate protein synthesis and the amounts of certain proteins in those muscles. Mice with atrophied muscles produce smaller-than-normal amounts of a protein called insulin receptor substrate 1 (IRS 1), which normally turns on several genes responsible for the production of other proteins in muscles.

Baldwin says that he intends to measure amounts of IRS 1 by monitoring blood chemistry in astronauts during tests of various exercise regimens. The results could tell researchers whether a specific workout is beneficial even before muscle atrophy becomes physiologically evident.