Delivering hurricane science: Data processing review of the CYGNSS mission

This paper reviews the telemetry downlink and data processing implementation currently in use for the eight spacecraft of the National Aeronautics and Space Administration (NASA) Cyclone Global Navigation Satellite System (CYGNSS) mission (launched December 2016). The NASA 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 in Low-Earth Orbit (LEO) at an inclination of 35 degrees. The CYGNSS mission faces unique constraints with respect to telemetry downlink: there are eight satellites to juggle with limited staff (implying unstaffed passes are a necessity), cost constraints limit passes to ~7 minutes once every two days (implying the downlink must be 100% utilized), and the onboard processor runs at 25 MHz (implying hardware must be utilized to off-load the software). In summary, a microsatellite must downlink the equivalent of 2500 digital photos every two days, using the horsepower of a 2001 Palm Pilot, in less time than it takes to cook a batch of cookies. The ground data processing must then package and deliver the science data cookies to the eager scientists as soon as possible so that it may be used to accurately update forecasting models. The CYGNSS Flight Software (FSW) telemetry downlink implementation is reviewed, including the observed on-orbit advantages, and the lessons learned that could have led to a better implementation. The implementation has now been shown to work well, and was able to avoid the complexity and resource requirements of integrating a third-party Application Programming Interface (API), such as CFDP, into the FSW. In addition to the flight segment implementation, the ground segment data processing of CYGNSS will also be assessed. The ground data processing must be robust: it must handle asynchronous data streams from each microsatellite ground pass, it must handle delivery of science and engineering data to their own unique end-user system, identify any data loss, support ingest of any re-downlinked data, and perform parallel data processing for all eight spacecraft. These implementations are reviewed, noting observed advantages and lessons learned.