Onboard Autonomous Integrity Monitoring using Intersatellite Links

摘要

The integrity of the broadcast ephemeris and clockrnparameters plays an important role in the frame of thernGNSS 2 design. In order to monitor integrityrnmeasurements have to be taken, statistically evaluated andrncompared to some decision thresholds. One importantrnaspect, driving false alarm rate and misdetection (besidesrnmeasurement accuracy) is the observation geometry. Arnway to enhance geometry is using ranging measurementsrnbetween spacecrafts (intersatellite links).rnAlthough these intersatellite links could be also processedrnon ground, they have a great potential for autonomousrnonboard processing. A conceptual design for an onboardrnorbit estimator has been proposed and implemented. Thernintegrity processing algorithms have been embedded in arnmedium complex simulation environment. To evaluaternperformance of the design and algorithms, several typesrnof non-integrity cases like unintended orbit manoeuvresrnor excessive clock drift have been simulated.rnAlthough integrity is processed autonomously fromrnground, the onboard processors of each satellite are farrnfrom being independent. Induced by the intersatelliternlinks, there is a coupling between the onboard processorsrnof the satellites, additionally driven by the false alarmrnrate. In fact, as a major issue in a complete autonomousrnscenario it has been found that there is a threshold for thernallowed simultaneous alarms, which - if exceeded ? canrncause the complete constellation to be "locked" atrnunhealthy.rnThis paper describes the integrity algorithms, presentsrnresults of a simulation scenario consisting of a completernconstellation of autonomous monitored spacecrafts andrnpoints out problems and solutions.