Engineering of the global precipitation measurement system

Global Precipitation Measurement (GPM) is an international effort to improve climate, weather, and hydrological prediction through more accurate and more frequent precipitation measurements. GPM will be conducted through an international partnership led by the National Aeronautics and Space Administration (NASA) of the United States and the National Space Development Agency (NASDA) of Japan, with other organization and countries providing additional data streams and scientific analysis. Measurements are made with a constellation of Earth observing satellites and a global ground validation program. NASA provided two spacecraft to the constellation, the Core and the Constellation spacecraft. For instrumentation, NASA provides a conical-scanning, polarization-sensitive, multi-frequency microwave radiometer termed the GPM Microwave Imager (GMI) for both the Core and Constellation satellite. NASA also provide the mission operations for the two spacecraft, two ground validation "Supersites", and the Precipitation Processing System (PPS) needed to assimilate all of the various data streams and produce the products. NASDA provide the Dual-frequency Precipitation Radar (DPR) for the Core spacecraft, the launch of the Core spacecraft, and a data stream from the GCOM-B1 spacecraft. This paper presents the engineering of the NASA portion of GPM from scientific objectives to viable system design. GPM\´s six elements, (1) the flight instruments, (2) the Core spacecraft, (3) the Constellation spacecraft, (4) the mission operations system, (5) the ground validation system, and (6) the PPS, must operate together and within the political environment of partnership in order to achieve the science objectives. Decisions on topics such as autonomy, Internet Protocol, Virtual Direct Broadcast, and orbits affect multiple elements across the mission. Advances in system engineering tools and techniques enable a more cost-effective development effort. As GPM approaches its Preliminary Design Review (PDR) and the start of implementation, we take a look at the current system design, how we arrived here, and where we plan to go.