Novelty Detection: A New Telemetry Monitoring Paradigm


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Being able to quickly identify anomalous behaviour allows to reduce downtimes and keep our spacecraft healthy. The current approach built in our Mission Control System is to use out-of-limits checks. However, many behaviours are anomalous even if they are within limits. Novelty detection is a new monitoring paradigm that allows to detect unusual behaviours in telemetry parameters. Unusual behaviour is usually a signature of anomaly in their way to develop. The novelty detection monitoring approach requires very little engineering knowledge as it learns from given examples of nominal behaviour. It also features very seldom false alarms and is complementary to the out-of-limit paradigm.
The Novelty Detector has been validated with Venus Express, XMM and Cryosat2 anomaly cases. The Novelty Detector managed to detect the anomaly way before the out of limits checks did. In some cases, these anomalies were not even detected by the out of limits. Flight Control Engineers check the Novelty Detection results daily as part of their monitoring tasks.

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Novelty Detection: A New Telemetry Monitoring Paradigm

  1. 1. Novelty Detection for Anomaly Identification Introducing innovative technologies Novelty in support of mission operationsThe Case Study – Being able to quicklyidentify anomalous behaviour allows toreduce downtimes and keep ourspacecrafts healthy. The current approach OOLbuilt in our Mission Control System is touse out-of-limits checks. However, many Novelty Detection find the Anomaly 2 months before de Out-Of-Limitsbehaviours are anomalous even if they The most widely extended approach for Novelty Detector characteristics are theare within limits. automatically detecting anomalous behaviour following: in Space Operations is the use of Out-Of-  Systematic: it scans every parameter inThe Solution – Novelty Detection allows to Limits (OOL). The OOL approach consists of search for novel behaviour.detect new behaviours in all parameters. It defining an upper and lower threshold so that  Realistic: it takes into account thatautomates the process of having when a measurement goes above the upper parameters can behave nominally in limit or bellow the lower one, an alarm is several different ways.engineers looking every day to 20,000 triggered for engineers. Then engineers will  Robust: it does not make any assumptionparameters and noticing new behaviour. inspect the parameter that is out of limits and on what kind of behaviour or how manyThe Novelty Detection needs very little determine if it is an anomaly or not and different behaviours a parameter will have.configuration and can run unattended. decide which action to take.  Versatile: it works with any kind of parameter.Current Status – Novelty Detection is While Out-Of-Limits are useful and they  No prior knowledge required: the only successfully trigger alarms when parameter inputs required are a time period thatgoing to be integrated in the XEWS readings go out the defined thresholds, they makes sense (e.g. orbital period) andsystem (XMM News) to automatically suffer from the following limitations: examples of nominal periods.detect potential anomalies for the XMM-  Some behaviours are anomalous even if they are within the defined limits. The aim with the Novelty Detector was toNewton mission. XEWS will report the  OOL are not defined for every parameter. automatically identify anomalies. However,Novelty Detection findings automatically to Engineers only define OOL for a subset of we did not reach that far yet. At this stage weflight control engineers. parameter for which they want to receive can only detect new behaviour. In this sense alarms if they exceed the limits. Therefore, we can state: “What is happening today inOperational Assessment – Novelty OOL is not systematic in the sense that it parameter P never happened before”. InDetection has been validated with Venus does not cover every parameter. most of the cases this signals an anomaly,  Quite often engineers receive OOL alarms but could also mean a new nominalExpress and XMM cases. In particular, it that are completely expected. A typical behaviour.managed to detect an XMM anomaly 2 example is the OOL defined for themonths before the out-of-limits checks Automatic Control Gain (AGC) during a The Novelty Detector has been validated pass. At Acquisition of Signal (AOS) and both with Venus Express and XMM anomalytriggered. Loss of Signal (LOS) the AGC goes cases. For both missions, the Novelty outside limits. However, it is expected to Detector managed to detect the anomaly wayProject Team – Developed for the ESA happen and in every pass these two OOL before the out of limits checks did. In someAdvanced Mission Concepts and alarms will be raised. cases, these anomalies were not evenTechnologies Office by Black Hat S.L.,  It requires effort to adapt OOL to useful detected by the out of limits.Spain, and Solenix GmbH, Switzerland. values as the mission goes through different phases or simply ages. The Novelty Detector is in the process ofESA/ESOC, Darmstadt, Germany being integrated with the XEWS systemAdvanced Mission Concepts and Technologies Office The Novelty Detector project has been (XMM News) to automatically detect potentialContact: Alessandro Donati developed to cope with the current OOL anomalies for the XMM-Newton mission.E-mail: limitations. Its main goal is to automatically XEWS will report the Novelty DetectionTel: +49 6151 90 2574 detect anomalies and report them to findings automatically to flight control engineers for further investigation. The engineers.