ESA GNC Conference Papers Repository

The Geostationary Operational Environmental Satellite-R Series (GOES-R), which launched in November 2016, is the first of the next generation geostationary weather satellites. GOES-R delivers dramatic improvements in Earth and solar weather observation capabilities relative to the previous generation of GOES satellites, providing 4 times the resolution, 5 times the observation rate, and 3 times the number of spectral bands for Earth observations. The solar-pointed instrument configuration is unique in that the arc-sec level precision pointing is provided by the spacecraft gimbal control, based upon instrument data. With both Earth-relative and Sun-relative pointing and pointing stability being maintained throughout reaction wheel desaturation events and station keeping activities, the GOES-R spacecraft provides continuous Earth and sun observation availability. The GN&C design requirements to achieve these expanded capabilities were extremely demanding. This paper reviews the pointing stability, pointing control, attitude knowledge, and orbit knowledge requirements necessary to realize the ambitious Image Navigation and Registration (INR) objectives of GOES-R. Because the GOES-R suite of instruments is sensitive to disturbances over a broad spectral range, a high fidelity simulation was created with modal content up to 600 Hz to predict the pointing stability of the vehicle. The flight instrument suite includes 6 seismic accelerometers sampled at 2 KHz, allowing in-flight verification of pointing stability and comparison back to simulation predictions. This paper compares the observed flight results with the simulation predictions for acceleration, shock response spectrum (SRS), and instrument line of sight responses for various operational scenarios and instrument observation modes. On-orbit results demonstrate excellent performance relative to the pointing and pointing stability requirements, with line of sight jitter of the isolated Earth Pointed Platform (EPP) of approximately 1 micro-rad. This paper also presents a comparison between low-frequency on-orbit pointing results and simulation predictions for both the EPP and Sun Pointed Platform (SPP). Results indicate excellent agreement between simulation predictions and observed on-orbit performance, and compliance with pointing performance requirements. Attitude knowledge and rate data are provided to the primary Earth-observing instrument with an accuracy defined by the Integrated Rate Error (IRE) requirements. The data are used to adjust instrument scanning. The accuracy requirements of the Integrated Rate Error (IRE) ranges from 1 to 18.5 micro-rad, depending upon the time window of interest. This paper discusses the on-orbit IRE results, showing compliance to these requirements with margin. During the spacecraft checkout period, IRE disturbances were observed and subsequently attributed to thermal control of the Inertial Measurement Unit (IMU) mounting interface. Adjustments of IMU thermal control and the resulting improvements in IRE are presented. The final piece of the INR performance is orbit knowledge. Extremely accurate orbital position is achieved by GPS navigation at GEO. On-orbit performance results are shown demonstrating compliance with the 50 to 75 m orbit position accuracy requirements of GOES-R, including during station keeping activities and momentum desaturation events. As we show in this paper, the on-orbit performance of the GN&C design provides the necessary capabilities to achieve the GOES-R mission objectives.