Astronauts may one day be able to pinpoint potentially life-threatening air leaks aboard a spacecraft just seconds after they occur, using sensors that detect ultrasonic vibrations in its walls.
Today, astronauts aboard the International Space Station use microphones to listen for the hiss of air escaping into space. "The trouble with that is the sound goes out into the vacuum with the air," says Stephen Holland, a researcher at the Center for Nondestructive Evaluation at Iowa State University in Ames, US. "That means conventional leak detectors are not very effective."
Indeed, it took about a week for astronauts to locate and patch a 1-millimetre-wide breach on the ISS in January 2004. The station's air pressure had dropped so much that some onboard instruments were in danger of failing and ground controllers were preparing to confine the crew in the Russian living quarters in order to seal off other modules and pinpoint the leak. If the problem had not been fixed, the astronauts may eventually have had to escape to Earth on a Soyuz lifeboat docked with the station.
"With that size of leak, you've got a few weeks before you've got to start thinking of bringing the astronauts home," Holland told New Scientist. But he says air pressure could drop to dangerous levels in just hours with a hole just 5 mm across. "Then the ability to find a leak becomes critical," he says.
Holland described research led by colleague Dale Chimenti on a sensor that can detect the direction of an air leak in just 30 seconds. It consists of a 2.5-centimetre-wide array of 64 piezoelectric sensors. These small sensors convert mechanical motion into an electric voltage that can then be amplified and analysed.
"As the air leaks out, it's going to make the spacecraft's skin vibrate just a little bit – but it is indeed detectable," says Holland. Studying how the vibration affects each individual sensor differently will help researchers locate the direction of the sound.
He envisions building future spacecraft with several of these sensor arrays attached to the inside of the hull so that data from each of them can be triangulated to help pinpoint the source of the noise.
Retrofitting the technology to the ISS would be more difficult, Holland says, because instruments cover most of the spacecraft's walls. But he says astronauts could use hand-held sensors and remove equipment blocking the walls in case of a serious leak at the space station.
Holland says the technology could probably be put into production within five years but that it should be tested in space beforehand. He adds that a key issue to test is how much background noise exists on the ISS at the ultrasonic frequencies the sensors detect. Such noise could potentially drown out the signal of an air leak.
The research is one of 17 projects NASA is sponsoring at the Center for Nondestructive Evaluation. The projects have received $7 million in funding for the period from 2002 to 2005.
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