THE space shuttle Columbia swept through a clear Florida sky yesterday morning and landed at Kennedy Space Center, bringing NASA's longest shuttle flight to an end.
The shuttle was scheduled to land in California but was diverted because of bad weather. The seven astronauts aboard have opened a new phase in American space exploration - the systematic study of physical, chemical, and biological processes under weightless conditions.
Scientists who watched with fascination as the crew in space carried out their experiments now have to complete the mission. "We'll do the hard work - learning what our observations have to teach us," Vanderbilt University physicist Taylor Wang said as he puzzled over the gravity-free behavior of liquid drops.
There have been many microgravity experiments in the past. But the on-orbit research concluded this week inaugurated what the National Aeronautics and Space Administration (NASA) calls its Microgravity Laboratory. This is a special configuration of the European-built Spacelab carried in the orbiter's payload bay.
NASA considers this laboratory and the microgravity research it represents a key part of what it calls "a science-and-technology program that will open NASA's next great era of exploration." The aim is to uncover fundamental properties of materials, natural processes, and various phenomena that are masked by gravitational influences on Earth.
Orbiting spacecraft remove these gravitational influences because they are falling freely around Earth. They do "feel" minute gravity-like accelerations from thruster firings and movements of astronauts. Hence they provide what scientists call a "microgravity" environment.
Six years ago, Bonnie Dunbar - payload commander on Columbia's mission - chaired a NASA task force that developed a long-term microgravity research program using the shuttle and, ultimately, the space station. Space is a new world for experimental scientists. Their early experiments under the new plan will be as much a learning experience in how to do effective research on orbit as they are investigations of nature.
"We're doing a totally new kind of science and building a base line for the future," says Joseph Henson, project manager for the Drop Physics Module equipment.
This equipment allows astronauts to carry out experiments for Dr. Wang and others as they study how liquid drops behave. They can use sound waves to put drops through rock and roll tests to see how they jiggle and twist.
This has implications for nuclear physics, among other things. Physicists' mental model of a nucleus undergoing fission resembles a drop elongating and dividing into two smaller drops.
Other fluid experiments were carried out in a glovebox. Astronaut Carl Meade used the box to carry out experiments in fluid flow for Robert Naumann, a fluid dynamicist at the University of Alabama at Huntsville. Dr. Naumann noted that these were simple tests. Until now, theory predicted how the fluids should behave without the force of gravity. "Until we try out theories in actual experiments, we can't know whether they are right or wrong," he observed.
Columbia's crew has carried out a variety of other experiments. They included burning various materials and growing crystals of proteins and semiconductors. Astronauts even stirred up miniature dust storms, using compressed air to scatter tiny quartz grains inside small chambers. This should help scientists understand how fine dust particles cluster. That, in turn, could help them understand how the atmosphere rids itself of dust.
The response of the human body to weightlessness is another important part of the new microgravity research program. Humans have been going into space for more than three decades. Some have spent many months in orbit. But the physiological effects still are not well understood. "There are a lot of changes that do occur, and we're still trying to understand them," says Astronaut Dunbar, who is herself a biomedical engineer.
The next shuttle mission is scheduled to orbit in the spring of 1995.