FOR astronauts on the longest space shuttle mission to date, the watchword is "stability."
Their orbiter, Columbia, is packed with microgravity experiments to study phenomena that depend on weightlessness. There has been concern that the jiggle and thump of on-orbit fitness routines could disturb these subtle processes.
Now that Columbia is more than halfway through its 12-day, 20-hour and 28-minute mission, the seven astronauts on board have shown that exercise and microgravity research can coexist. A stabilizing platform uses motor-driven masses to cancel almost all of the gravity-like accelerations the astronauts produce as they pump the pedals of an exercise machine.
"We've gone over the hump," says information officer Jim Sahli at the Marshall Space Flight Center in Huntsville, Ala., control center for the scientific aspects of the mission. He adds that "things are going pretty steady" with the experiments and that the data that have come back "look pretty good."
Launched from the Kennedy Space Center in Florida at 12:12 p.m. June 25, Columbia reached the "hump" or midpoint of its mission at 10:30 p.m. July 1st. At press time, the mission continued to go smoothly, according to the Johnson Space Center in Houston, which controls the overall flight. A spokesman confirmed that experimenters "are getting the results they're looking for." These results come mainly from 31 experiments, carried out in the Spacelab laboratory supplied by the European Space Agency. Mounte d in Columbia's payload bay, Spacelab provides an environment where astronauts can work in shirt-sleeve comfort. These experiments investigate such processes as combustion, crystal growth, and fluid flow.
Combustion is tested by starting fires with different materials in a sealed container. Without gravity and the buoyance-driven convection it induces, various aspects of the process can be studied. Crystals of electronic materials can be grown free of gravity-induced disruptions to better understand the crystal-growth process. Subtle aspects of the flow of fluids that are usually masked by gravity-driven flow patterns stand out. Gravity-like accelerations have to be minimized for such delicate research. A ccelerations due to Earth's gravity are virtually eliminated because Columbia is falling freely around the planet as it travels its orbital path.
The main concern is with accelerations due to thruster firings and astronaut movements. Because these can't be entirely eliminated, Columbia is said to provide a "microgravity" rather than a "gravity-free" environment.
Thruster firings can be held down by letting the spacecraft drift in a self-stabilizing nose-up vertical attitude. Astronauts can move with care. But they also must exercise regularly to maintain physiological fitness. Their treadmills, pedal machines, and other equipment are bolted to a shuttle bulkhead for stability. This means that the forces an astronaut exerts while exercising are transmitted to the spacecraft.
The Isolated/Stabilized Exercise Platform the astronauts now are testing buffers such disturbance. It is designed so that an astronaut may exert 100 pounds of force, but only about one pound is transmitted to the spacecraft.
Buddy Nelson, spokesman for Lockheed Missiles & Space Company, says the platform on Columbia "has lived up to its promise." Lockheed is developing the platform for the National Aeronautics and Space Administration. If the concept continues to prove to be effective, it could solve what would otherwise be a serious problem for NASA's planned space station, which will be devoted largely to microgravity research.
This is the first of a series of long-playing shuttle missions. Columbia can carry enough supplies for missions of up to 16 days. The newest orbiter, Endeavor, can be equipped for 28-day flights. With such long missions, NASA expects to make extensive studies of human adaptation to weightlessness in preparation for the 90-day duty tours that will operate Space Station Freedom.