Suspended in Orbit

Dudley A. Saville in 2004. Courtesy of Joy Saville

By Patrick H. Shea

In the summer of 1996, from the viewing area of Kennedy Space Center, Dudley Saville (1933–2006) watched wide-eyed as the space shuttle Columbia blasted off with one of his own experiments on board. Saville, then a professor of chemical engineering at Princeton University, had been passionate about flight since his days in the U.S. Air Force, but on this day he was more excited about scientific inquiry than the romance of space. The shuttle’s Life and Microgravity Spacelab (LMS) carried an experiment on the electrohydrodynamic properties of suspensions that Saville had been waiting to send into orbit since 1990. If given the opportunity, Saville would almost certainly have accompanied his experiment in space, but he had to settle for the next best option: carrying out the experiment via computer from NASA’s Marshall Space Flight Center in Huntsville, Alabama. Saville’s project was one of dozens planned for the spacelab, on topics ranging from the human heart’s performance in space to the growth of protein crystals in a gravity-free environment.

Microgravity first attracted scientific interest in the 1950s as the possibility for space flight began to look like a reality. (Scientists refer to microgravity rather than weightlessness because objects in orbit are not in a perfect state of freefall. Slight decelerations from atmospheric drag and disturbances from items outside the spacecraft’s center of gravity alter an orbiting object’s freefall by a force equivalent to one millionth the force of Earth’s gravity, a micro-G.) The effects of gravity on Earth are such an accepted part of our lives that we may rarely think about it, but such simple, everyday actions as boiling a pot of water, mixing oil and vinegar for salad dressing, or mopping up a spill are profoundly affected by gravity. Convection, surface tension, buoyancy, sedimentation, and hydrostatic pressure are all gravity induced, and all mask the true nature of fluid processes.

Gravity can also play a detrimental role in certain manufacturing industries, such as those that manufacture crystals, value-added chemicals, metals, ceramics, and countless other products. Transforming sand into silicon crystals, separating ordinary biological materials into modern pharmaceuticals, and producing high-strength, temperature-resistant alloys from ordinary metals are all processes that are affected by gravity. These industries must operate mixers almost constantly to keep ingredients blended, and molten items like glass must be continuously spun to retain their shape in a 1 G environment (i.e., on the surface of the earth). Manufactured crystals are often not as perfectly ordered as they could be because of the effects of gravity, not an insignificant problem as even impurities at the parts-per-billion level can render a crystal useless. In contrast, a microgravity environment allows researchers to isolate and control gravity-related phenomena and permits processing techniques that are not possible in ground-based laboratories.

Improving the production of certain materials, with or without gravity, requires a keen understanding of fundamental fluid processes. By 1976, when Saville joined the Universities Space Research Association, his impressive academic credentials and expertise in fluid mechanics gave him a unique insight into the effects of gravity on fluids. Saville had graduated from the University of Nebraska with a degree in chemical engineering in 1954. He returned to graduate school after a brief stint at Union Carbide and three years of flying fighter jets, eventually receiving a Ph.D. from the University of Michigan in 1966. He then worked in industry for two years before joining the faculty of Princeton University as an assistant professor in 1968. Within three years Saville had tenure, largely on the strength of several seminal papers on the exact conditions required for an electrically controlled jet of fluid to maintain stability.

Although Saville was enthusiastic about space flight, he was at first skeptical that an orbital microgravity environment could provide a suitable place to conduct fluid physics research. Power and weight restrictions had severely limited the capability of space experiments during the Apollo program, and although Skylab, a short-lived space station in Earth’s orbit from 1973 to 1979, expanded these opportunities, it was nevertheless inadequate for NASA’s lofty goals. At the same time NASA was already developing its new space-shuttle program, which would open a new era of microgravity research by allowing heavier payloads, repeated missions, and longer flights. The shuttle program would effectively make more complex experiments possible, especially those related to biotechnology and materials processing. Saville soon came to share this view after beginning to serve on various NASA committees on space science. As he explained to Microgravity News in 1996: “I began to realize that in some sense, science has been trapped in a 1 G environment forever, so there are a lot of things we don’t know because we haven’t had the opportunity to do laboratory science in microgravity.”

In 1990 NASA accepted Saville’s proposal to investigate the dielectric and electrohydrodynamic properties of suspensions in microgravity, and the project was later given a place on board the space shuttle as part of the spacelab mission. Saville’s experiment was slated for the spacelab’s Bubble, Drop and Particle Unit, which was developed by the European Space Agency to study fluid mechanics on the second International Microgravity Laboratory, which flew aboard the Columbia in 1994. Since the behavior of fluids is at the heart of many phenomena related to materials science and biotechnology, Saville’s proposed experiment was a perfect match for the spacelab program goals. His experiment was designed to study the stability of cylindrical columns of liquid under the influence of an electric field, focusing on the series of shape changes that occur in a liquid bridge. Several kinds of oil, including castor and silicone, would be suspended in the form of a column that bridged two electrically charged plates. As the plates were moved farther apart, an electric field was applied to the plates, thereby stabilizing the column so that it would not break into droplets. Saville and his team would be looking for two transition points: first, when the shape changed from a cylinder to a vase-like amphora, and, second, when the bridge broke, creating suspended droplets. Although he had conducted similar experiments on Earth, the effects of gravity required that the two liquids be studied with a host liquid of the same density, thereby complicating the experiment. In microgravity the liquid bridge could be suspended in a low-density gas. He named his experiment “A Liquid Electrohydrodynamics Experiment” and gave it the acronym ALEX after his son by the same name.