Discovery in a Drop of Water
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The experiments now being conducted aboard the Microgravity Sciences Laboratory (MSL-1) are descended from engineers' questions about how best to refuel rockets in orbit and to build larger space stations. Those concerns led to broader questions about how materials behave, and to the dazzling range of experiments in combustion, proteins, alloys, and other areas.
Among the options studied in the 1960s for going to the Moon was the idea that a rocket could be refueled in orbit much as jet fighters are refueled by flying tankers. The question that arose, as early as the 1950s, was, If there is no "down," how do you get the fuel and oxidizer to flow "downhill" into the tanks? Other engineers worried about how welded metals would behave in weightlessness.
Soon, rudimentary materials experiments were flying aboard the last Apollo missions, and a major line of experiments was developed for the Skylab space station. It was a new concept, and in many cases the experiments were adaptations of ground-based processes.
"I don't recall anyone on any of the Skylab crews reacting with skepticism towards these experiments" in this untried field, said Dr. Owen Garriott, who spent 58 days aboard Skylab as science pilot of the second Skylab crew. Garriott would later fly as a mission specialist on the Spacelab 1 mission, in late 1983, the direct ancestor of the MSL-1 mission now in progress. He now works with a medical technology firm.
Skylab carried a Materials Processing Facility in its docking adapter and 10 other experiment apparatus throughout the station. The Materials Processing Facility allowed the crews to install new samples and equipment for the first containerless processing tests, space welding experiments, metals melting, and other research.
|The Skylab space station, launched in May 1973 and manned three times through early 1974, carried the first multi-purpose microgravity Materials Processing Facility (right) mounted in the docking adapter in the station's nose.||
One of the big surprises that came from the mission was the result of the crew playing with their food.
"Everybody did droplets," Garriott said. "You very quickly learned that if you were careful, with your drink you could make very large liquid drops. If it ever got out of control, you had to mop up this big mess."
The drops would oscillate and float seemingly with lives of their own. Garriott said the astronauts would maneuver the drops by blowing air through a straw to change air pressure on one side or another, but that also caused the drop to oscillate even more. Garriott found that he could pull a string of dental floss through a drop, surface tension (the attraction between molecules which lets the drop form in the first place) exerted just enough force to hold the drop in place
Today, the technique is used - with a fireproof silicon carbide thread - in the MSL-1 glovebox to position fuel droplets for the fiber-supported droplet combustion experiments.
Another experiment surprised scientists when two drops of fruit drink, strawberry and grape, were squirted toward each other. When they collided (see picture at the top of this story) they oscillated through a number of bizarre shapes. Even stranger, the two flavors did not mix right away.
"The science community, if anything, may have been stimulated by the sight of the droplets to do later experiments in space," Garriott said.
|Astronaut Owen Garriott (left, at the controls of the Apollo Telescope Mount in the docking adapter) was part of the second Skylab crew. He and other crewmen, like Joe Kerwin (right) conducted planned experiments in the materials facility (above) and impromptu experiments with droplets that led to research in fluid dynamics.||
Skylab was left unmanned after February 1974 and reentered the atmosphere in 1979. The only one manned flight planned before the start of Space Shuttle operations was the Apollo-Soyuz Test Project, in 1975, which help set some of the groundwork for today's International Space Station. While the Apollo-Soyuz mission carried some materials experiments, NASA felt that the more needed to be done to keep microgravity materials research going.
The result was the Space Processing Applications Rocket (SPAR) program which put automated materials hardware atop suborbital rockets. While things that orbit or coast to other planets get most of the attention, rockets that soar briefly to the edge of space and then fall back to Earth provide an inexpensive means of testing new instruments that lead to new satellites.
A rocket is weightless from the time it leaves Earth's atmosphere until it reenters. With the Black Brant V rockets selected for the SPAR program, this was about 5 or 6 minutes.
Ten SPAR flights were made during 1975-79; nine succeeded (this is average for suborbital rockets). A few firsts were made in materials experiments, said Roger Chassay, the former SPAR manager at NASA-Marshall, but those did not have the most important lessons.
"We learned how to work with principal investigators [PIs] (the lead scientist on a project)," he said. "They needed to be able to do one aspect of an experiment, look at the results, and then fly it again to look at a different aspect.
|A NASA Marshall engineer adjusts the first SPAR payload before its launch in 1975. SPAR, like many other sounding rocket payloads, are 19 inches wide to match standard electronics racks in laboratories.|
"We learned that they needed a considerable amount of time to analyze their results, from 6 to 24 months," he said. "Even the most aggressive PIs were not ready in a few months." This is because analytical chemical work takes dozens or hundreds of measurements, sometimes in several different laboratories. Even when a sample looks obviously different, scientists want to quantify exactly how and why it looks different, and then to design the next experiment to take advantage of that.
The results from SPAR led to "no exciting breakthroughs," Chassay said, "but a lot of advances that led to the foundation for a good, solid Spacelab program. It was a good learning process."
Among the firsts were acoustic levitator experiments where sound waves are used to position molten droplets of glass and metal, and experiments with beryllium alloys. They also learned that mixing certain immiscible metals - fluids that prefer to separate, like oil and water - is not as easy in weightlessness as scientists had expected.
Materials experiments were a small part of the Spacelab 1 mission which was designed as an all-purpose demonstration. The first Spacelab mission dedicated to microgravity sciences was Spacelab 3 in 1985. And even since the second Space Shuttle mission in November 1982, experimenters started taking advantage of the orbiter middeck and, later, small, automated facilities in the payload bay. Several Spacelab missions have been flown since 1988, many (USML-1 and 2; IML-1 and 2; SL-J; SL-D1 and D2; LMS) dedicated to microgravity sciences.
"The experiments had become a good deal more sophisticated by the time we flew Spacelab 1," Garriott said. "In the intervening 10 years [since Skylab] the degree of sophistication had taken a big step. "In particular, he cited the large, complex Fluid Physics Module developed by English researchers and flown as part of the European Space Agency's share of Spacelab 1.
Working on Spacelab, though, was more demanding than it was on Skylab, he said.
|Astronaut Owen Garriott emerges from the transfer tunnel into the Spacelab 1 module. During the mission, the payload crew conducted advanced materials experiments with facilities like the Fluid Physics Module, shown at right as European astronaut Ulf Merbold makes adjustments.||
"They didn't know how much work we could get done on Skylab," he said, plus the crews were up for as long as 83 days compared to 16 days for the longest Spacelab missions. So the crews worked 8-hour shifts rather than the 10- to 12-hour shifts on Spacelab where the short duration demands a maximum effort in flight and on the ground.
He hopes that the crews of the International Space Station will have schedules that allow them to experiment on their own and possibly develop new avenues of research for future scientists.
Related reading: Tutorial on the behavior of fluids in low gravity
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