There now exist global environmental phenomena which can only be scientifically understood by the development of a multidisciplinary approach to the study of our planet as a system consisting of the oceans, land masses, atmosphere, and biosphere. These phenomena are associated with continual global changes in the Earth's environment such as increases in the carbon dioxide content, fluctuations in the ozone layer, and increases in the acid content of precipitation. The future negative ramifications of these phenomena on our planet have been well documented. The solution to the long term problems arising from these changes requires both a multidisciplinary as well as a multinational approach. Part of the approach is in situ and laboratory measurements and experiments with concomitant satellite-based global remote sensing. An Earth Observing System (Eos) is planned to address many of the remote sensing requirements from low Earth orbiting satellites (Reference 1). A new initiative called Mission to Planet Earth, together with Eos, will eventually lead to a comprehensive scientific understanding of the entire Earth System (Reference 2). The overall Mission to Planet Earth envisions a space global observational system that includes experiments and free-flying platforms in polar, low inclination, and geostationary orbits, designed to operate for decades, serviced either by astronauts or robotic systems.