uninova's software diagnosed errors on esa's satellite gyroscope
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Fuzzy Logic diagnostic software developed in UNINOVA has detected a failure on one of the gyroscopes of ESA's ENVISAT satellite
Image source: ESA/Denman
Successor of the ERS-2 satellite, ENVISAT is the new component of the European Remote Sensing (ERS) program, a long-term program of environmental remote sensing of the Earth. The ERS initiative aims to collect highly reliable data on the entire planet to be used in scientific studies of critical environmental problems. ENVISAT uses four two-axis dry tuned gyroscopes in its Inertial Measurement Unit. This unit is part of the Attitude and Orbit Control System and has redundancy built in (there are more sensitive axis and gyroscopes than necessary) to provide for coherency checking of outputs and specially to supply backup gyros in case of failure. The attitude of the satellite (its orientation) needs to be very accurate (solar array pointed to the sun, environmental sensors pointed to the earth, sensitive parts protected from solar wind, etc). A severe failure in the Inertial Measurement Unit is then critical because in the worst case it could mean the end of the satellite's life.
A consortium between the CA3 group of UNINOVA and GTD (a Spanish company) built a fuzzy expert system to detect failures in the gyroscopes and in the attitude level of the ENVISAT satellite, as well as to monitor the data quality of the gyroscopes telemetry. The fault detection process includes three modules: a fuzzy attitude alarm level model; a fuzzy gyroscope fault detection model and a fuzzy data quality model. This work was part of the ESA project “Fuzzy Logic for Mission Control Processes”.
The results of the fuzzy expert system are proving very successful since it became operational (2002) and the ENVISAT Flight Control Team has been using the tool during launching operational tests, platform commissioning and routine operations for:
- Routine gyroscope health & performance verification via automatic analysis of relevant telemetry covering a default 7-day cycle
- Back-up gyroscopes health and performance verification during yearly maintenance operations
The main achievements through the operational use of the fuzzy expert system are:
- Early detection of a slight noise increase affecting gyroscope #1 measurements, despite the fact that noise levels are still well within the specifications
- Implemented Fuzzy Logic model demonstrated reliable in performing correct early anomaly detection.
- Independent capability of assessing hardware status of back-up gyroscopes, in quasi real-time verified (already proved with an out-of-limit parameter incident).
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