Huygens HASI servo accelerometer: A review and lessons learned

The servo accelerometer constituted a vital part of the Huygens Atmospheric Structure Instrument (HASI): flown aboard the Huygens probe, it operated successfully during the probeʹs entry, descent, and landing on Titan, on 14th January 2005. This paper reviews the Servo accelerometer, starting from its development/assembly in the mid-1990s, to monitoring its technical performance through its seven-year long in-flight (or cruise) journey, and finally its performance in measuring acceleration (or deceleration) upon encountering Titanʹs atmosphere. m of this article is to review the design, ground tests, in-flight tests and operational performance of the Huygens servo accelerometer. Techniques used for data analysis and lessons learned that may be useful for accelerometry payloads on future planetary missions are also addressed. in finding of this review is that the conventional approach of having multiple channels to cover a very broad measurement range: from 10−6g to the order of 10g (where g=Earthʹs surface gravity, 9.8 m/s2), with on-board software deciding which of the channels to telemeter depending on the magnitude of the measured acceleration, works well. However, improvements in understanding the potential effects of the sensor drifts and ageing on the measurements can be achieved in future missions by monitoring the ‘scale factor’—a measure of such sensors’ sensitivity, along with the already implemented monitoring of the sensorʹs offset during the in-flight phase.