Onboard science processing on a microsatellite with limited resources

The National Aeronautics and Space Administration (NASA) Cyclone Global Navigation Satellite System (CYGNSS) mission aims to understand the coupling between ocean surface properties, moist atmospheric thermodynamics, radiation, and convective dynamics in the inner core of tropical cyclones (TCs). The mission is comprised of eight microsatellites (μSats) in low-earth orbit (LEO) at an inclination of 35 degrees. The mission faces unique challenges in hardware and software design to satisfy mission restrictions: the small size of the μSats implies a low power budget for telemetry downlink bandwidth, science data processing, and Attitude Determination and Control (ADC) processing. Additionally, the LEO path of each μSat implies shorter ground passes that limit the downlink time. To accommodate these constraints, creative and efficient hardware and software designs are required. This paper discusses how downlink and power limitations will be accommodated by the design of the CYGNSS Spacecraft hardware and software. Each μSat contains a Delay Doppler Mapping Instrument (DDMI) which receives direct signals from Global Positioning System (GPS) satellites as well as GPS signals scattered by the ocean surface. The direct signals pinpoint the location of the μSat, while the scattered signals respond to ocean surface roughness from which wind speed is derived. The science data derived from these direct and scattered GPS signals, Delay Doppler Maps (DDMs), will be used to provide information about and improve forecasts of the intensity of TCs.