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Photographing Physics: Critical Research in Space

October 3, 2005

NASA — On a quiet March afternoon in Cleveland, Ohio, Bill Meyer browsed the second floor of Kohl’s Department Store. He was just about to buy a pair of shoes at 70 percent off when his cell phone rang.

Sighing, he lifted the phone to his ear and said, “Hello?”

“Is this William Meyer?” the voice on the other end inquired.

“Yes, it is,” he replied.

“This is CapCom at the Johnson Space Center,” the voice said. “Can you get to a land line? You have a phone call from the International Space Station.”

The normally mild-mannered scientist rushed to the customer-service counter. Astronaut Leroy Chiao had a question about an important space station experiment, and he could only take the call from a land line.

Store employees were more than happy to help. “They were so excited that they were jumping up and down,” said Meyer, who works at NASA’s Glenn Research Center. “I wouldn’t be surprised if their heads knocked out some of the ceiling tiles.”

Just before he called, Chiao had been photographing the Binary Colloidal Alloy Test-3 (BCAT-3). This book-sized container holds ten sample cells filled with colloids, or tiny particles suspended in fluid. A hundred times smaller than a fine human hair, colloids are everywhere. Milk, paint, makeup and smoke are just a few examples.

On Earth, the BCAT-3 colloids aren’t very surprising — they just sink to the bottom of the container. But in the absence of gravity, they behave like slow atoms, allowing scientists to model all sorts of atomic behavior.

According to the BCAT-3 scientists, studying colloids in space could lead to revolutionary advances in technology, such as computers that operate on light, new pharmaceuticals, clean power sources and unique propellants for rocket engines.

BCAT-3 focuses on two frontiers of science: critical points and crystallization.

Critical Point Research

In a pot of boiling water, bubbles of vapor begin to form at the bottom of the pot and grow until they escape into the atmosphere. The water exists simultaneously in two states — liquid and gas. If you could increase the temperature and pressure much higher than the average stove and pot allow, the water would reach its critical point, where the liquid and vapor cannot be distinguished.

Just above that is the supercritical region, where the liquid and gas are no longer distinct states, but rather form a homogeneous supercritical fluid. Like gases, supercritical fluids flow easily, but they also can transport dissolved materials and thermal energy, like liquids do.

Supercritical carbon dioxide is used to extract molecules from plants for pharmaceuticals. Supercritical water is used to remove toxic waste from contaminated soil. And some scientists believe supercritical fluids could be used to extract magnesium from rocks on Mars to make rocket fuel.

Six of the BCAT-3 experiment samples were created by David Weitz and Peter Lu at Harvard University to study atomic behavior near the critical point.

Crystallization Research

Scientists also study colloids because they are the right size to manipulate light. Over time, they form crystals that can split up light and send it in different directions.

By enhancing our ability to control light, scientists hope to improve fiber-optic communication systems and build computers that operate on light instead of electricity. Because cosmic rays degrade electronic circuits in space, these technologies are essential to fulfilling the Vision for Space Exploration with journeys to the moon, Mars and beyond.

The optical properties of a crystal vary depending on its size and shape. So scientists Peter Pusey and Andrew Schofield at the University of Edinburgh are studying BCAT-3 samples to see how changing the size and proportion of colloids affects the crystals. Meanwhile, University of Pennsylvania researchers Arjun Yodh and Jian Zhang are trying to determine how crystals form on the surface of a container in microgravity.

Catching Colloids in Action

Since the BCAT-3 scientists can’t join their experiments on the International Space Station, they depend on the station crew to photograph the samples and collect data for them.

Because colloids behave differently in space than they do on Earth, the researchers are seeing some surprising results — so surprising that NASA has agreed to keep the project on the space station for another year. In October, Expedition 12 Commander William McArthur will pick up the project where Chiao left it.

If only Meyer can get McArthur to call him while he’s shopping. The employees at Kohl’s were so happy to hear from Chiao that when Meyer checked out they gave him a scratch-off coupon — another 10 percent off that pair of shoes.

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