Aerospace
its data acquisition algorithms, we also provided them with a ‘look-up’ chart listing the individual temperature errors over the complete range of environmental temperatures expected to be met in the application. This enabled RUAG to correct in real time for the effects of temperature and deliver more accurate results.” For mechanical pointing accuracy, the inclinometers were
used to measure the pointing vector of the TOM with respect to a reference frame, with accuracy to higher than 0.05° being essential. “The inclinometers were used to measure and characterise how the pointing vector of the mechanism varied in different thermal conditions,” continues Andrew Skulicz at RUAG Space. The performance of the potentiometers was also checked
under different thermal conditions to ensure they could return accurate telemetry back to the spacecraft, while motor margin tests were conducted to verify that the performance of the on-board stepper motors did not degrade. The inclinometers were used to verify the performance of the potentiometers over the full angular range of -14°/+34°, with the required accuracy being better than ±0.05°. The inclinometers were removed during vibration and shock testing however, as they would have been damaged. “Such tests were arduous for both the mechanism and
the inclinometers, given that it was necessary to detect if the motor looses steps with an accuracy of at least 0.01°,” says Andrew. “Additionally, tests were carried out at extreme positions (+34°) to further test the performance of the
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inclinometers over their full range. The inclinometers on the TOM not only successfully operated throughout a sequence of thermal vacuum cycles, but also sustained that operation for nearly three months while the mechanism was undergoing its life test.” According to Andrew, the fact that the pointing
performance of the mechanism did not change throughout the programme while the variation in motor margin at different temperatures was clearly visible showed that the inclinometers were sensitive and able to perform well under extreme temperature and thermal vacuum conditions. “I could also be confident the inclinometers performed all the way through the test programme as expected, because the inclinometers measure pointing accuracy, which is based on gearbox geometry and should remain constant. It’s a bit of a circular reference, but this substantiates the fact the inclinometers didn’t degrade during the test.” RUAG’s TOM programme represents the cutting edge
of the European scientific community, with the test results having been approved by ESA. “This is not easy to obtain and requires that we are able to substantiate that the results are valid. The team at Sherborne Sensors has been very co-operative, providing strong technical support and we worked together really well to ensure that this part of the programme ran smoothly,” Andrew concludes. ●
For more information, visit
www.sherbornesensors.com or
www.ruag.com/space
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