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New Sensor Finds Leaks in Spacecraft
Roland Piquepaille writes "With financial support from NASA, Iowa State University (ISU) engineers have developed a sensor to quickly find leaks in a spacecraft. This sensor locates an air leak by listening to the noise generated by the air rushing out of the leak and includes an array of 64 elements that detects vibrations as they radiate along the spacecraft. Because astronauts cannot hear the noise caused by escaping air, NASA needed to design a system to help them. As one ISU researcher said, 'NASA wants to be able to find these leaks. Fixing them is easy. But the question is, "Where is the leak?"' Now that this sensor has successfully been tested on the ground, NASA is evaluating a proposal to build a prototype of the leak detection system for future missions.
The summary states that the detection system detects the sound made by air escaping. This is not true. The sound of the air escaping is OUTSIDE the spaceship (as said in the article) and therefore cannot be detected within the craft. The detection system is simply the array of vibration sensors.
This type of survey has been used in the oil industry since the 1980's...
"noise log" leak detection
But I have to admit this is 3D against 2D.
"The likes of Facebook and WhatsApp are free to those whose privacy is of zero value."
think of small leaks..
They can be viciously hard to dedect, hat lose tons of air over a larger timeframe (and air isnt really replaceable up there).
I work with vaccum chambers, where the same problem can happen (just inverted). And even having a rather good access to all parts, it can be terrible hard to find a leak without disassembling parts of the chamber. (Thats the reason you use helium and a mass spectrometer for leaktesting. Just hose down the thing and check where helium seeps through...)
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
The telephone company (way back when there was just ONE big one, ATT), used to have like lots of copper wires running from pole to pole (way back when there were wires, and poles, and above-ground stringing).
In the wetter climates the wires were covered in a lead casing (back when lead wasn't so despised). The lead "tubes" were pressurized to keep the moisture out. If the lead sheathing got a leak, a guy (back when telephone company people in the field were guys) would walk down the street holding up an ultrasonic microphone.
A little box on his belt would map the ultrasonic frequencies down to the audible range and feed it to his headphones (back when headphones were big clunky black bakelite things).
Well in this case the simple solution might not be the best, ;)
because you will hardly see smoke moving towards the leak,
and when you see you should run
Think of the ISS it's constructed from cylindrical elements, and you have a quadratic shaped interior, so the space gap is filled with computers (some Laptops == fan) possible cooled instrument racks which emmit heat (convection) and on the inner layer an insulation.
If your presure- and ultrasoundsensors detect such a leak you have to generate
smoke, this smoke will going to follow the airflow which is driven by presure diferences,
but you also have temperaturdifferences or forced convection nearly everywere,
even the astronauts moving will disturb the free flow extremly, and you have no
gravition which helps you to settle the turbulences fast.
The leak might be so tiny, so the volume flowing through it will not interfere with the inside
atmosphere in deep.
As one of the principal developers of this technique, I can clarify a few points:
1. 99% of the leak noise escapes into the vacuum on the downstream side of the leak. Thus conventional industrial leak detection devices are much less effective for leaks into vacuum than for leaks into air.
2. The real challenge is the extraction of the leak noise from other noise sources. We do this by recording cross-correlations of noise measured at different locations. Electronic (preamp) noise does not correlate and is rejected. Thus we can get far higher sensitivity than a single sensor.
3. This device uses a piezo sensor with an array of multiplexed electrodes to sense the direction of sound propagation under the sensor. A 3D time-x-y Fourier transform maps the measured correlations from the time/space domain to the frequency/wavevector domain. The wavevector points precisely away from the leak, allowing us to find the leak through triangulation from two or more sensor arrays.
4. For all you Linux fans, this sensor was developed entirely using open-source software. We used Linux with gEDA schematic capture and pcb.sourceforge.net for board layout. Lab measurements are done using the soon-to-be-published open-source Dataguzzler software on Linux x64.
(Contact me for more information about Dataguzzler)
5. One paper on this sensor, published in the journal Ultrasonics, vol 45 (2006) pp 121-126,
can be found at http://thermal.cnde.iastate.edu/~sdh4/home/leakarray.pdf
Stephen D. Holland
Assistant Professor, Iowa State University
The sound being picked up is not carried by air - it is the vibrations caused by the escaping air transmitted through the spacecraft itself.