Astronauts Conduct Water Experiment Aboard Columbia : Science: The effect of weightlessness on liquid drops is tested. The ‘first successful coalescence in space’ is achieved.

Astronauts bounced drops of water the size of Ping-Pong balls around an air chamber Sunday, a fourth of the way into NASA’s longest shuttle flight. They also caught a glimpse of Russia’s space station.

Columbia pilot Kenneth Bowersox saw the Mir space station when the orbits of the two spacecraft crossed off the east coast of Africa. Mir and its two cosmonauts passed 58 miles above Columbia and 80 miles to the side.

Payload Cmdr. Bonnie Dunbar spent hours squirting drops of water into an enclosed chamber. The luminous drops, filled with tiny air bubbles, quivered as sound waves emitted from four loudspeakers pushed the floating spheres back and forth.

The sound generated was 150 decibels--about as loud as a stereo playing full blast. Outside the acoustic enclosure, it sounded like a low hum to the five men and two women aboard Columbia.

Dunbar had trouble getting her first drop off the thin injector nozzle. She succeeded on the next try, drawing cheers from scientists at the payload control center at the National Aeronautics and Space Administration’s Marshall Space Flight Center in Huntsville, Ala.

Yale University physicist Glynn Holt and his team were even more excited when Dunbar combined two drops into a single, slowly-spinning sphere.

“That was the first successful coalescence in space,” Holt said.

Researchers want to see how liquid drops merge in weightlessness, especially when containing detergent and other materials that gravitate toward the surface. These materials, called surfactants, are used in cosmetics production and oil recovery, which could benefit from the space findings.

“You can do all the thinking you want, but until you actually do the experiments you don’t know how it’s going to behave in space,” Holt said.

The 13-day Spacelab flight, which began Thursday, isn’t due to end until July 8. That’s two days longer than the longest shuttle trip to date, a 1990 satellite-retrieval mission by Columbia.

The astronauts completed a foam-smoldering experiment Sunday. Unlike Friday’s test in still air, weak air currents were circulated in the sealed, flame-resistant chamber to simulate the environment of the shuttle and NASA’s planned space station Freedom.