Sunday, April 25, 2004
New Physics Discovered on the Space Station
RedNova News:Understanding how fluids behave, singly or in mixtures, is important to the space program, especially now that NASA plans to send people back to the Moon and on to Mars.

"We're going to have to manufacture things in space," explains Pojman, "and that means dealing with fluids." As an example, he offers plastics--a key component of habitats, radiation shields, rovers, etc. Plastics are usually formed by combining dissimilar fluids or fluids and powders, then heating the mixture. "If you've ever used BondoTM to repair your car, you've done this yourself: you mix a resin together with peroxide to create a sticky plastic substance," adds Pojman.

Mixing is also necessary for certain types of medical space-research--"especially protein crystal growth in microgravity," notes Pojman. When two fluids are put together, do "Korteweg currents" flow? Do the fluids dissolve evenly? Do they break apart into droplets? These details actually make a difference.

Pojman himself couldn't go to the ISS to investigate such questions, so he devised an experiment that astronauts could do for him: the Miscible Fluids in Microgravity Experiment or MFMG for short. "MFMG is a very simple experiment," he says. "It involves two syringes, a drinking straw, honey and water. All of these things were already onboard the ISS."

One syringe is filled with honey or a honey-water solution, the other with pure water. The tips of the syringes are connected via a short tube (the straw). When all is ready, an astronaut gently squirts a blob of honey into the water, or vice versa, and films what happens. ISS science officer Mike Foale did the experiment last week, and transmitted the video to Earth.

"We've already learned something new," says Pojman.

There's a number in fluid physics theory called "the square gradient parameter" or k. It's proportional to the strength of intermolecular forces between two different fluids, like honey and water.

"How two fluids behave when mixed in low-gravity is going to depend on k," says Pojman. "We've never been able to measure k on Earth for a pair of miscible (mixable) fluids. It's value could be anything! But just from watching the video of MFMG we've got an upper limit on k--it must be less than 10-8 Newtons."

He reached this conclusion in the following way: If k were much greater than 10-8 Newtons, honey blobs injected into water would quickly assume a spherical shape. But they didn't. The blobs, squeezed into elongated shapes as they passed through the nozzle of the syringe, remained elongated.

"The fact that we could do this using only odds and ends onboard the space station is encouraging," says Pojman. A similar procedure could be used to set limits on, or actually measure, k for many different pairs of fluids.

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