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NASA studying Sunita's tests

NASA plans to spend next few months analysing results of experiments conducted by Sunita Williams during her space stay.

world Updated: Jul 04, 2007 17:01 IST
Arun Kumar

US space agency NASA scientists plan to spend next 12 to 18 months analysing the results of experiments conducted by Indian American astronaut Sunita Williams during her record 195 day stay in space.

The study of a group of experiments she dubbed "lava lamp" will help engineers design more efficient fluid management systems, such as fuel tanks, cooling systems and water recycling systems, for future space missions, NASA said.

"I call it the 'lava lamp' experiment because some of the fluid is pink, and we hang out watching it with video and pictures," Williams wrote in her mission log at the International Space Station. "If only we had a black light."

While these Capillary Flow Experiments (CFE) are mesmerising, they actually have nothing to do with lava or lamps. They are a suite of three experiments designed to investigate how fluid flows in microgravity.

On Earth, fluid management systems rely on gravity. In a car, for instance, a pipe runs from the bottom of the fuel tank to the engine. Gravity positions the fuel at the bottom of the tank, and the fuel pump forces it through the pipe and up to the engine.

But in space, where gravity is virtually absent, fluids aren't so predictable. Propellants float around inside tanks, and water drops bounce about recycling systems. This makes designing fluid management systems for spacecraft a difficult endeavour.

"It's been a challenge since the 1950s," said project scientist Bob Green of NASA's Glenn Research Centre. "Once you're in orbit, there's always an uncertainty about where the fluid is in the tank. As the tank drains and less fluid is left inside, it sometimes becomes a bigger problem."

To compensate, engineers have developed devices called vanes and screens. Vanes are grooves designed to guide fluid through a tank, and screens filter out bubbles. Both devices use capillary forces to position the fluid, or create "capillary flow".

This scientific term describes the way the surface of a fluid responds when it comes in contact with a solid. Capillary flow occurs when the adhesive forces between the solid and the fluid are different than the cohesive forces within the fluid.

"A classic example of capillary flow is when you stick a tiny tube in a beaker of water," Green said. "The water will rise into the tube due to capillary action." The same effect causes porous materials, like paper towels and soil, to absorb water.

On Earth, the force of gravity typically overwhelms the capillary force, reducing the fluid to rise to millimetres. But in space, where the force of gravity is nearly zero, capillaries such as vanes and screens carry fluids much higher. Scientists still have a lot to learn about the phenomenon in order to use it to its full potential.

In fact, spacecraft have always flown with extra fuel, because some of it remains in the tank unaffected by the capillary devices.

The pink fluid that reminded Williams of a lava lamp is actually silicone oil floating inside a Plexiglas container. The experiments are comprised of six such containers, each simulating shapes and conditions commonly found in fluid management systems for space.

During her long stay aboard the station, Sunita Williams worked with the Capillary Flow Experiments more than twice as many times as any other astronaut, earning herself a regal title from the team.

"Suni has operated the experiments nine times," said NASA Glenn project engineer Chuck Bunnell. "That's why we call her the Queen of CFE."

During operations, the team of scientists and engineers watched the astronauts conduct the experiments on a live video feed from NASA Glenn's Telescience Support Centre. As they watched the fluid flow, they made changes to the procedures in real time by sending feedback to payload communications.

"The operations are the fun part," said Bunnell. "They're the culmination, like when you finally reach the peak of the mountain you've been climbing."