The Large European Acoustic Facility (affectionately known as LEAF) is part of the satellite testing facilities located at the European Space Agency’s Research and Technology Center, located in Noordwijk, the Netherlands. Very simply, it aims to simulate the noise levels reached during launch, in order to make sure the satellite will not fall apart during the launching process.

The noise levels, and the associated shakes and vibrations, which a satellite is exposed to during launch are amazingly high. Trying to simulate these conditions, in a controllable and safe manner, is more complex than you might think.

The room

LEAF consists of one large room, 11 metres by 9 metres (and 16.4 metres high), with a small control room next to it. All the walls are made of 50cm thick concrete, and the entire facility is mounted on springs to reduce vibrations affecting the rest of the building (and possibly causing it to collapse…). The room is kept at a constant temperature of 20degC, is a class 100, 000 clean room, and contains pressurised gaseous nitrogen. These last three precautions are mainly to avoid any contamination of the delicate satellite equipment.

There are several suspension points throughout the room, which allow the satellite to be ‘hung’ in various positions relative to the speakers. This allows the operators to reproduce the relative alignment of the satellite during launch. The suspension system includes 18 microphones, placed near to the satellite to monitor the noise levels in particular areas. As well as the microphones, up to 250 accelerometers and 50 strain gauges are used to record data from all parts of the spacecraft.

The speakers

Against one wall of the facility are four speaker horns, which create the low-frequency noise. These low frequencies are the most important during testing, since they are most likely to damage the satellite. The horns have cut-off frequencies of 25 Hz, 35 Hz, 80 Hz, and 160 Hz. Three high-frequency generators also add to the cacophony.

The speakers are, unsurprisingly, completely controllable. Operators in the control room can alter not only the volume, but also the spectral shape produced by the ‘noise generation system’.

The noise

Currently, LEAF can achieve noise levels between 125 dBL and 154.5 dBL, although in future is should be possible to reach levels of up to 158.5 dBL.

So how loud is 154.5 dBL? Well, according to the ESA information, it could be compared to several Boeing 747’s taking off 30 metres away from you. According to dragoon’s write-up, it is louder than the loudest rock music (150 dBL), but quieter than the loudest possible noise (194 dBL). Bear in mind that decibels are a logarithmic unit, and start to damage human hearing after 125 dBL..!

On a practical note, this means that despite all the precautionary insulation and the spring mounted room, when tests are occurring in LEAF the rest of the building tends to know about it!

Overall, a very useful test facility, which is contributing to European efforts in space. Particularly since, without LEAF, there would be satellites falling to pieces before they even reached orbit...

For more technical specifications, see http://www.estec.esa.nl/pr/facilities/documents/leaf.pdf

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