UARS: THE MANDATE

We have probed the outer edges of our solar system with automated spacecraft, and Earth-orbiting astronomical observatories have opened new windows on the universe. Yet the earth's upper atmosphere - beginning only 10-15 km above the surface - remains a frontier largely unexplored from space. NASA's Upper Atmosphere Research Satellite (UARS) will carry out the first systematic, comprehensive study of the stratosphere and furnish important new data on the mesosphere and thermosphere.

A Global Research Program

The processes of importance in the upper atmosphere - energy balance, dynamics, and chemistry - are global in scale. Their study therefore requires the global coverage that can only be achieved by remote sensing from space. In this approach, spacecraft sensors measure the energy radiated by the atmosphere, or the energy absorbed or scattered from sunlight passing through the atmosphere. Analysis of the results furnishes detailed information on chemical constituents, temperature, winds, and the effects of energy inputs from sunlight and the solar wind. These finding will help to reveal the mechanisms that control the structure and variability ofthe upper atmosphere, to improve the predictability of ozone depletion, and to define the role of the upper atmosphere in the Earth's climate systems.

The UARS program builds upon decades of research with rockets, balloons, aircraft, and such satellites as the Television Infrared Observation Satellite (TIROS) and Orbiting Geophysical Observatory (OGO) series, the Solar Mesosphere Explorer (SME), and the Nimbus series. The UARS mission objectives are to provide an increased understanding of:

In addition to nine experimental groups, the UARS program includes ten theoretical groups with specific responsibilities for data analysis and interpretation. One important product of these studies will be computer models that simulate processes in the upper atmosphere. These simulations will test our understanding of these processes and provide predictions of changes in atmospheric structure and behavior important to future policy formulation.

Study of Global Change

The national mandate for UARS dates to 1976, when the U.S. Congress, responding to the identification of new causes of ozone depletion, directed NASA to expands its research program related to the upper atmosphere. A vigorous research initiative was soon Established involving rockets, aircraft, and balloons, together with laboratory and theoretical studies. These investigations have confirmed that man-made chemicals are indeed depleting stratospheric ozone, heightening concern over the effects of this depletion of life on Earth. In recognition of this concern, NASA has made the timely flight of UARS a key near-term component of a systematic, long-range plan for the study of global change from space.

The Mission

UARS was deployed by the Space Shuttle in Sept. 1991. UARS operates 585 km above the Earth' in an orbit inclined 57 degrees to the Equator. This orbit will permit the UARS sensors to "see" up to 80 degrees in latitude - thus providing essentially global coverage ofthe stratosphere and mesosphere - and to make measurements over the full range of local times at all geographic locations every 36 days.

The nine UARS sensors will provide the most complete data on energy inputs, winds, and chemical composition ever gathered. Taken together, the data sets will yield the first simultaneous, comprehensive, global coverage of three closely coupled atmospheric properties. These observations thus constitute a highly integrated investigation into the nature of the upper atmosphere. Additional correlative data, as well as theoretical studies linked to specific sensor objectives, will complement the UARS observations to provide a systematic, unified research approach.

An International Legacy

An important aspect of the UARS program is its coordination with additional national and international programs of study and data acquisition. Other nations are contributing to the UARS instruments, and scientists from many nations will ultimately participate in the analysis and utilization of UARS data

Upon completion of the UARS mission, we will have gained a dramatically expanded and detailed picture of the energetics, dynamics, and chemistry of the upper atmosphere. This information will then be available to governments around the world, enabling them to address more effectively the role of human activities in altering upper-atmosphere properties.

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