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Following the deployment of the Goddard Space Flight Center's (GSFC) Upper Atmosphere Research Satellite (UARS) on Sept. 15, 1991, from the Space Shuttle Discovery, scientists have gained a better understanding of the energy input, chemistry and dynamics of the upper atmosphere and the coupling between the upper and lower atmosphere. UARS, the first satellite dedicated to studying stratospheric science, focuses on the processes that lead to ozone depletion, complementing and amplifying the measurements of total ozone made by the Total Ozone Mapping Spectrometer (TOMS) onboard NASA's Nimbus-7 and the Russian Meteor-3 satellites.
Ten UARS instruments have provided the most complete data on upper atmospheric energy inputs, winds, and chemical composition ever gathered. Together, these observations constitute a highly integrated investigation of the nature of the upper atmosphere. In its first two weeks of operation, UARS data confirmed the polar ozone-depletion theories by providing three-dimensional maps of ozone and chlorine monoxide near the South Pole during development of the 1991 ozone hole. UARS, developed and managed by GSFC, in Greenbelt, Md., provides information that nations around the world can use to guide decisions on environmental policies, according to scientists.
Moreover, UARS is collecting data on the chemistry, dynamics and radiative inputs to the upper atmosphere far beyond its designed lifetime. UARS was designed to last 18 months, but is still operational into its 28th month. UARS is the first spacecraft launched as part of Mission to Planet Earth (MTPE) -- the NASA element of the U.S. Global Change Research Program.
MTPE studies how the global environment is changing. Using the unique perspective available from space, NASA will observe, monitor and assess large-scale environmental processes, focusing on climate change. MTPE satellite data, complemented by aircraft and ground data, will allow us to better understand natural environmental changes and to distinguish natural changes from human-induced changes. MTPE data, which NASA will distribute to researchers worldwide, is essential to human making informed decisions about protecting their environment.
NASA officials see the need for a long-term, national program of space research into global atmospheric change because of concern over composition changes of the Earth's atmosphere, caused in part by human activity. UARS is providing NASA and a broad, international scientific community, with comprehensive data sets on the upper atmosphere's chemistry, energy and dynamics, including data crucial to expanding our understanding of changes taking place in the ozone layer. UARS is a complex spacecraft consisting of 10 scientific instruments, eight of which are still operating, mounted on a platform, which provide communications, altitude control and other spacecraft systems, such as propulsion and electrical power.
The UARS team that developed these systems is quite diverse. Instruments were developed by different contractors, universities and NASA centers and are managed by principal investigators who provide scientific analysis. In addition, 10 theoretical principal investigators head teams that focus on scientific analysis of the UARS data.
The overall spacecraft development required major integration to assure that the instruments and spacecraft systems work together as intended. During operations, a central data handling system manages the processing and transfer of scientific data from the spacecraft to investigator sites located throughout the United States, Canada, the United Kingdom and France.
Of the 10 UARS scientific instruments, nine are designed to conduct the first systematic, comprehensive and detailed satellite investigation of the stratosphere, mesosphere and lower thermosphere. The 10th instrument measures total solar energy output. Each instrument gathers data on a particular aspect of the upper atmosphere that affects the global environment: composition, temperature, winds and energy. Operating simultaneously, these 10 instruments constitute a single scientific investigation. A principal investigator (PI), a scientist who leads a team focused on effective instrument operation as well as data analysis, is responsible for each instrument. In addition, 10 theoretical PIs lead teams for analysis of the UARS science data.
The UARS instruments cover three specific areas in the upper atmosphere: chemistry/ temperature, winds and energy.
The stratospheric ozone concentration is determined by a balance between production processes, photolysis of oxygen molecules (O2) and subsequent recombination of oxygen atoms (O) with (O2), and the loss processes. The loss processes include reactions with naturally occurring species, such as nitrogen dioxide (NO2), and with species which have a natural source but are mostly produced in the stratosphere from man-made chemicals such as chlorine monoxide (CLO). The concentrations of the species that destroy ozone are influenced by reactions involving long lived reservoir species such as hydrogen chloride (HCL) and by reactions with stable "source gas" compounds such as nitrous oxide (N2O) and chlorofluorocarbons (CFCs), such as CF3CL and CF2CL2.
The distributions of ozone and the trace gases that affect ozone through chemical interactions are influenced by the winds. The winds transport gases between various atmospheric regions and affect their photochemical behavior.
The High Resolution Doppler Imager (HRDI) and the Wind Imaging Interferometer (WINDII) provide direct observations of wind velocity through measurements of the Doppler shifts. These instruments produce a three-dimensional global map of the upper-atmosphere wind field. HRDI focuses on an altitude of six to 37 miles (10 to 60 kilometers) and WINDII focuses on altitudes above 49 miles (80 kilometers).
The energy, which produces ozone in the stratosphere and the atmospheric circulation, comes from the sun. The balance between ozone production processes, loss processes, and transport by the winds, produces the ozone layer. High energy solar radiation is absorbed by oxygen molecules and ozone in the mesosphere and stratosphere. In addition, energetic particles from the sun, which enter the Earth's atmosphere, can lead to the production of species such as nitrogen dioxide (NO2), which influence the ozone distribution.
The UARS data system is the bridge between satellite and scientist. The data system captures, processes and distributes scientific data and enables the correlation and exchange of results among investigators. Scientific data from the instruments are continuously recorded onto one of two alternating tape recorders located on the satellite. The UARS data are then transmitted to Earth via a Tracking and Data Relay Satellite (TDRS), received by the ground terminal located at White Sands, N.M., and relayed to the NASA Communications Network for transmission to GSFC. The data are received for preprocessing at the Data Capture Facility (DCF) at Goddard. The DCF merges, edits and sorts the data, performs quality checks and removes redundant data. The output, called Level 0 data, is then transmitted to Goddard's UARS Central Data Handling Facility (CDHF). There, programs developed by the instrument investigators will process the data into a form suitable for scientific analysis.
The instrument and theoretical investigators gain access to this data using Remote Analysis Computers (RAC) at their home institutions. The RAC allows all UARS instrument and spacecraft performance data to be available to investigators (both instrument and theoretical) for any part of the satellite's observation period. The data system encourages frequent interactions between the different investigation groups and facilitates quick response to unusual events, such as the effects of solar flares, sudden stratospheric warmings and volcanic eruptions.
The UARS CDHF receives, processes, stores and provides access to UARS scientific and engineering data. The CDHF supports three different types of DCF transfers: production processing, quick-look and "near-real time." Once a day, the CDHF receives data from the DCF covering the previous 24-hours, or approximately 15 UARS orbits. Three times a day, the CDHF receives and processes quick-look data covering a single UARS orbit to support PI activities requiring a faster reaction time. "Near-real time" processing makes 10-15 minutes of real-time data available to the PIs within minutes for each of the 15 UARS-TDRS contacts per day.
The UARS mission represents the first major flight element of NASA's Mission to Planet Earth, a coordinated, long-term program that is studying the Earth as a global environmental system. It comprises satellites such as UARS, space shuttle/spacelab missions such as the Atmospheric Laboratory for Applications and Science (ATLAS-2), airborne and ground-based studies.
The UARS mission objectives are to reveal and further understand the mechanisms that control the structure and variability of the upper atmosphere, improve the predictability of ozone depletion and define the role of the upper atmosphere in the Earth's climate system.
The Atmospheric Chemistry and Dynamics Branch, located at the Goddard Center, manages the UARS for NASA's Office of Mission to Planet Earth, Washington, D.C. Spacecraft operations and control also are carried out from GSFC. At Goddard, the UARS project scientist is Dr. Mark Schoeberl.
The GE Astro Space, now Martin Marietta Astro Space, Valley Forge, Pa., designed and built the UARS structure for NASA.
January 1994