A space destined camera unit is tested on a Kistler dynamometer regarding micro-vibrations and jitter.

Micro-vibration and jitter testing

Satellite jitter, or blurring of the images originating from micro-vibrations, is a severe deviation source that affects the geometric accuracy of high-resolution imagery. Recent years have seen major advances in terrestrial observation – accompanied by a dramatic increase in the need to measure the earth's surface and atmosphere with ever greater precision.

The quality of these images would have been unimaginable only a few years ago. Critical steps in achieving this progress include the reduction of micro-vibrations on board satellites. Every satellite requires numerous drives, position controls, reaction wheels, actuators and cryo-coolers: the list could go on. These devices comprise mechanical components that cause vibrations when they operate. Micro-vibrations consist of extremely small accelerations of very low intensity. Measuring them is a challenging task. High-frequency jitter can be measured with piezoelectric force sensors, charge amplifiers and low-noise accelerometers and dynamometers.

Recent innovative designs using ceramic top plate dynamometers allow higher sensitivities, higher frequency ranges and the possibility of water cooling optimized for reaction wheel jitter and cryo-cooler micro-vibration applications.


Measurement of minimal dynamic force changes

    

Measurement of high frequencies up to 500 Hz

    

High force measurement and moment calculation accuracy

    

Prevention of mass loading effects when using accelerometers

    

Important technologies for the application

High-resolution dynamometers

Piezoelectric force sensors and dynamometers combined with high sensitivity charge amplifiers are ideally suited thanks to their very high resolutions (up to 100 000). This makes it possible to measure dynamic force changes down to 0.01 N (0.002 lbf) and moments down to 0.08 10-3 Nm (0.7 mlbf-in), even if the object to be measured weighs more than 10 kg (22 lb).

High-frequency response dynamometers

Optimized micro-vibration dynamometers featuring high rigidity offer very high natural frequencies of over 1500 Hz, enabling measurements of up to 500 Hz.

Low-crosstalk dynamometers

The resulting forces and moments are calculated from the 3 signals provided by each of the 4 triaxial force sensors that constitute the dynamometers. The lower the crosstalk, the higher the force measurement and moment calculation accuracy.

Lightweight, low-noise accelerometer solutions

Lightweight acceleration sensors generating the lowest possible noise are generally preferred in cases where micro-vibration levels are still sufficiently high. These key properties prevent mass loading effects while still allowing detection of micro-vibration levels.

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