Sept. 25, 2003: Here's a challenge for you: Using only what you can find lying around your house, put together an experiment to test a question in science that's never been answered.
Astronauts onboard the station are adaptable, natural experimenters, and they don't always need fancy equipment to do science. So researchers have dreamed up some clever ways to use what's already on hand aboard the station: maintenance tools, food supplies, hygiene items, cameras ... and, of course, weightlessness.
Above: Cosmonaut Nikolai M. Budarin, Expedition Six flight engineer, squeezes inside a Soyuz spacecraft. Space is tight. [more]
We begin with Miscible Fluids in Microgravity, an experiment concocted by University of Southern Mississippi chemistry professor John Pojman with colleagues Vitaly Volpert and Nick Bessonov of the Université Lyon I in France. They want to find out what happens when two miscible fluids are combined in microgravity.
"Miscible means mixable," explains Pojman. "When miscible fluids are combined, they merge. For instance, water and molasses are miscible. One diffuses completely into the other. Immiscible fluids are just the opposite; they remain separated like oil and water."
Sounds simple. But 100 years ago a Dutch physicist named Diederik Korteweg pointed out a complication: sometimes miscible fluids act like immiscible fluids.
Left: A 19th century photograph of Diederik Korteweg. [more]
Korteweg was fascinated by what happens during that curious time just after miscible fluids are combined and just before they dissolve. Do they really behave like immiscible fluids? Korteweg knew that immiscible fluids tend to break apart into little droplets--a side-effect of surface tension. He calculated that miscible fluids should break apart in the same way during the early moments of gentle mixing.
Miscible fluids, gently mixed, are widely used in the plastics industry and they're necessary for certain types of medical research--"especially protein crystal growth in microgravity," notes Pojman. How they merge, dissolving evenly or breaking apart into droplets, actually makes a difference.
Yet no one knows if Korteweg was right. "It's impossible to test his theory on Earth because gravity overwhelms surface tension," says Pojman. Fluid streams fall apart because of their own weight. "We need to do this experiment in space."
Right: Pojman has tried the experiment before using water and glycerine onboard NASA's KC-135 "Vomit Comet." Only a few seconds of good microgravity could be achieved--not enough to solve the puzzle. Image courtesy John Pojman.
Pojman has planned for some time to investigate the problem using a sophisticated experiment called Transient Interfacial Phenomena in Miscible Polymer Systems, but the equipment won't arrive on station until later this decade. Meanwhile, he's going to get a preview of the physics from Miscible Fluids in Microgravity.
The first thing they need for their experiment is some kind of container in which to do it. The container needn't be large, but it must be transparent so that cameras can record the outcome.
Unused urine collection syringes fit the bill perfectly. Cameras that the space station crew uses to document life in orbit fill the data-acquisition role. A video camera will film the entire 10-minute experiment, and a digital still camera will snap shots every 30 seconds.
While the body of one syringe serves as a container for the first fluid, the needle of another syringe will slowly inject a stream of the second fluid.
Air bubbles could spoil the experiment, Pojman says. To plug small holes in the syringes that could introduce air bubbles, Pojman considered a widely used sealant: chewing gum. "I like the idea of an experiment that uses chewing gum," Pojman jokes. Nevertheless, they ultimately chose to use Duxseal™, a plumber's leak-repair compound from the station's maintenance kit.
Water was an obvious choice for the first fluid, but what about the second one? Pojman says they considered several of the materials available on the station: shampoo, shaving cream, even ultrasound gel. (The space station is equipped with an ultrasound imager for use in medical experiments.)
In the end they settled on honey. The crew has cans of Russian honey on board to use for sweetening their tea. As anyone who has had honey in their tea before knows, honey dissolves in water quite nicely--i.e., water and honey are miscible.
One small Ziplock™ bag will serve as a reservoir for the water, and two larger bags will dispose of the leftover waste.
Voilà! A microgravity experiment, no custom-built equipment required.
Miscible Fluids in Microgravity will probably take place before the end of this year. Although it won't answer all the questions about Korteweg's ideas, it's an important prelude to experiments that will. Not bad for a few odds and ends … and a little ingenuity.
NASA's Office of Biological & Physical Research (OBPR) supports experiments in fundamental physics for the benefit of humans on Earth and in space.
Vitaly Volpert and Nick Bessonov of France have performed computer simulations that show a stream of a miscible fluids can break apart from the Korteweg stress and an elliptical drop will become spherical – just as seen with immiscible fluids. "The great unknown,” says John Pojman, "are the values of the parameter describing the intermolecular interactions.” Performing the Miscible Fluids in Microgravity experiment will help his team estimate this value and to test their model.
Miscible Fluids in Microgravity (MFMG) is a prelude to a more sophisticated space-experiment called Transient Interfacial Phenomena in Miscible Polymer Systems (TIPMPS) led by John Pojman, Vitaly Volpert and Hermann Wilke of Berlin, Germany. TIPMIPS is planned for later this decade. Meanwhile, Pojman is interested in gathering information to test their computer models--hence MFMG.
Diederik Korteweg -- biographical information about the Dutch scientist who first proposed the theory mentioned in this article
Videos: click here for a 5.3 MB QuickTime movie of Professor Pojman doing an earlier miscible fluids experiment aboard the KC-135 "Vomit Comet"; click here for a 1.8 MB movie close-up of the samples during that experiment. Videos courtesy John Pojman.
Press release -- about this research, from the University of Southern Mississippi