The NASA NPOESS Preparatory Project (NPP) is designed to collect radiometric data to make comprehensive measurements of atmospheric temperature and humidity, and cloud and aerosol properties. NPP will provide NASA with continuation of global change parameters after the Earth Observing System Terra and Aqua missions. In addition, NPP will provide a pre-operational risk reduction demonstration and validation of three critical instruments for the National Polar-Orbiting Operational Environmental Satellite System (NPOESS). NPP is a joint mission with NASA, NOAA, and the Department of Defense. NPP will launch in 2006 and operate in a sun synchronous descending node orbit, with a 10:30 AM equator crossing time. This paper discusses the NPP mission and the design of the satellite. The key Earth System Science observations that are to be taken are highlighted, along with the key Environmental Data Records (EDRs) that NPP will provide. The Key EDRs for which NPP will provide data are vertical moisture profile, vertical temperature profile, imagery, sea surface temperature, and soil moisture. The mission concept, including the satellite and ground system architecture, combines elements provided by NASA, the DoD, and NOAA. One of the driving requirements is providing complete EDRs within 180 minutes of observation, with a goal of within 90 minutes or less. For the NPOESS spacecraft the goal is 15 minutes from time of observation.