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how that environment is changing, and how those changes affect us." The goal of Mission to Planet Earth would be to obtain a comprehensive scientific understanding of the Earth as a system, describe how its various components function, how they interact, and how they may e expected to evolve on all time scales. The challenge would be to understand the consequences of changes to the system, and eventually to develop the capacity to predict changes that might occur--either naturally, or as a result of human activity.

The concept behind Mission to Planet Earth is to take advantage of the capabilities of our space program to develop an integrated approach to studying the earth--to establish and maintain a global observational system in space. What would such a system look like? It would include a suite of experiments and sensors in polar orbit, in low inclination orbit and in geosychronous orbit. It would also, most importantly, include a data managing and processing system that would integrate data from space, and data from in situ measurements, to enable scientists to monitor, to document, and over the years to understand and model the earth system. 

The experiments would measure global cloud cover, vegetation cover, ice cover, rainfall and moisture. Other experiments would measure ocean chlorophyll, ocean levels, motion of the tectonic plates, and atmospheric concentrations of ozone, methane, and carbon dioxide. It is clear that a program like this would continue to our understanding of global change, and in particular to our understanding of issues such as ozone depletion, the bulidup of greenhouse gases, and the extent of the effects of acid rain. 

Several different space-based elements would be required to gather this information. To meet the objects of a scientifically comprehensive global observing system, Mission to Planet Earth would include four sun-synchronous polar orbiting platforms; five geosynchronous satellites (the number required to cover the whole earth from geosynchronous orbit); experiments and satellites carried

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