[Source: NASA's Science Mission Directorate, Earth Sciences, http://science.nasa.gov/earth-science/decadal-surveys/
NASA relies on the science community to identify and prioritize leading-edge scientific questions and the observations required to answer them. One principal means by which NASA’s Science Mission Directorate engages the science community in ... this task is through the National Research Council (NRC). The NRC conducts studies that provide a science community consensus on key questions posed by NASA and other U.S. Government agencies. The broadest of these studies in NASA’s areas of research are decadal surveys. As the name implies, NASA and its partners ask the NRC once each decade to look out ten or more years into the future and prioritize research areas, observations, and notional missions to make those observations.
Information regarding all missions is available at the following home page: