Enhanced Telemetry Monitoring with Novelty Detection

T he most widely extended approach for automatically detecting anomalous behavior in space operations is the use of out-of-limits (OOL) alarms. The OOL approach consists of defining an upper and lower threshold so that when a measurement goes above the upper limit or below the lower one, an alarm is triggered. Then engineers will inspect the parameter that is out of limits and determine whether it is an anomaly or not and decide which action to take (for example, run a procedure). This is the original out-of-limits concept. The current OOL concept has evolved to cope with more situations such as distinguishing between soft and hard limits ; for example, a soft OOL triggers a warning to pay attention , a hard OOL triggers an error that demands attention. Soft limits are contained within hard limits. In addition OOL thresholds (soft and hard) can be configured so that different thresholds are applicable in different situations (for example, depending on the working mode of a given instrument). n Typically, automatic telemetry monitoring in space operations is performed by out-of-limits (OOL) alarms. This approach consists of defining an upper and lower threshold so that when a measurement goes above the upper limit or below the lower one, an alarm is triggered. We discuss the limitations of the out-of-limits approach and propose a new monitoring paradigm based on novelty detection. The proposed monitoring approach can detect novel behaviors, which are often signatures of anomalies, very early — allowing engineers in some cases to react before the anomaly develops. A prototype implementing this monitoring approach has been implemented and applied to several ESA missions. The operational assessment from the XMM-Newton operations team is presented.