Flight Performance Analysis of the CYGNSS MicroSatellites from On-Orbit Telemetry

The Cyclone Global Navigation Satellite System constellation of eight micro-satellites in low-Earth orbit was designed to provide continuous, gap-free coverage for hurricane forecasting and monitoring throughout the life-cycle of a tropical storm. To provide the capability, the spacecraft Attitude Determination and Control System must accurately and reliably slew and hold its attitude - and by extension, its payload data collection antennae - to prescribed knowledge and pointing requirements. The CYGNSS constellation launched in December 2016 and has been collecting and serving data since the start of the tropical storm period in 2017. This paper presents the flight performance of the ADCS system in key ADCS modes and compares its on-orbit performance to its design and simulation predicted responses. Flight telemetry analysis uncovered an anomaly in one of the ADCS modes that interfered with the spacecraft's observatory mode and induced a sustained, once-per-orbit pitch oscillation in all eight spacecraft. This anomaly was conjectured to trace to a spurious magnetic dipole induced on the spacecraft due to some electrical effects in the main power circuitry. This root-cause analysis is summarised in this paper as is the retuning that was undertaken on the estimation and control system parameters to improve disturbance prediction and rejection within the existing ADCS architecture. Data is presented from spacecraft simulations as well as flight, before and after the redesign, that shows the efficacy of the redesigned ADCS system to reject the spurious, anomalous disturbance and recover the required performance.