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The Upper Atmosphere Research Satellite (UARS) is the first
major flight element of NASA's Mission to Planet Earth, a multi-year
global research program that will use ground-based, airborne and
space-based instruments to study the Earth as a complete
environmental system. Mission to Planet Earth is NASA's
contribution to the U.S. Global Change Research Program, a
multi-agency effort to better understand, analyze and predict the
effect of human activity on the Earth's environment.
UARS is designed to help scientists learn more about the
fragile mixture of gases protecting Earth from the harsh environment
of space. UARS will provide scientists with their first complete
data set on the upper atmosphere's chemistry, winds and energy
inputs.
One of UARS' focuses will be an area in which humanity's
technological advancement is changing the Earth on a global scale --
depletion of ozone in the stratosphere, or upper atmosphere. The
stratosphere ranges from approximately 9 to 30 miles above the
Earth's surface. Ozone, a molecule made up of three oxygen atoms,
blocks ultraviolet light that can cause skin cancer and damage food
crops.
Although there are some natural causes of stratospheric
ozone depletion, such as volcanic eruptions, the "ozone hole" that
forms over Antarctica in the Southern Hemisphere's spring season and
the 5 percent depletion observed over northern mid-latitudes in the
last decade are a direct consequence of human activity. These
long-term ozone trends are caused by chlorine compounds released
into the atmosphere as byproducts of industry, including
refrigeration and the making of plastic foam.
To study ozone depletion more completely and to better
understand other aspects of Earth's fragile atmosphere, scientists
need the global perspective available from an orbiting satellite,
one that makes simultaneous measurements of all the factors of ozone
depletion with state-of-the-art instruments. To that end, the UARS
science program has been designed as a single experiment with nine
component instruments that will study the upper atmosphere's
chemical, dynamic and energy systems. In addition to the UARS
instrument science teams, 10 other teams will use the data to
improve theoretical models of the upper atmosphere and consequently,
scientists' ability to predict the effects of change in the
atmosphere.
An extensive program of correlative investigations using
ground-based, aircraft and balloon-carried instruments is also
planned. As a whole, the UARS program is designed to give
scientists the data they need to address the challenge of Mission to
Planet Earth -- to understand and predict the effect of human
activity on the environment.
UARS's nine complementary scientific instruments each
provide measurements critical to a more complete understanding of
the upper atmosphere, concentrating their observations in chemistry,
dynamics and energy input.
UARS carries a 10th instrument, the Active Cavity Radiometer
II (ACRIM II), that is not technically part of the UARS mission.
ACRIM II will take advantage of a flight opportunity aboard UARS to
study the Sun's energy output, an important variable in the study of
the Earth's climate.
Chemistry Studies
Four of UARS' instruments will measure the concentrations
and distribution of gases important to ozone depletion, climate
change and other atmospheric phenomena.
Cryogenic Limb Array Etalon Spectrometer
Like all spectrometers, the Cryogenic Limb Array Etalon
Spectrometer (CLAES) will search for the tell-tale spectra that
indicate the presence of certain chemicals. In particular, CLAES
will determine concentrations and distributions by altitude of
nitrogen and chlorine compounds, ozone, water vapor and methane, all
of which take part in the chemistry of ozone depletion. Principal
Investigator for CLAES is Dr. Aidan E. Roche, Lockheed Palo Alto
Research Laboratory, Palo Alto, Calif. Dr. John Gille of the
National Center for Atmospheric Research, Boulder, Colo., is a
collaborative investigator.
Improved Stratospheric and Mesospheric Sounder
The Improved Stratospheric and Mesospheric Sounder (ISAMS)
will study atmospheric water vapor, carbon dioxide, nitrous oxide,
nitric acid, ozone, methane and carbon monoxide. Like CLAES, ISAMS
detects infrared radiation from the atmosphere and uses it to derive
information on atmospheric temperature and composition. Principal
Investigator for ISAMS is Dr. Fred W. Taylor, University of Oxford,
Department of Atmospheric Physics, Oxford, United Kingdom. Dr. James
M. Russell III of NASA's Langley Research Center, Hampton, Va., is a
collaborative investigator.
Microwave Limb Sounder
The Microwave Limb Sounder (MLS) will provide, for the first
time, a global data set on chlorine monoxide, the key intermediate
compound in the ozone destruction cycle. MLS data also will be used
to generate three-dimensional maps of ozone distribution and to
detect water vapor in the microwave spectral range. Principal
Investigator for MLS is Dr. Joseph W. Waters, NASA's Jet Propulsion
Laboratory, Pasadena, Calif.
Halogen Occultation Experiment
The Halogen Occultation Experiment (HALOE) will observe the
vertical distribution of hydrofluoric acid, hydrochloric acid,
methane, carbon dioxide, ozone, water vapor and members of the
nitrogen family. Each day, HALOE will observe 28 solar
occultations, that is, it will look through Earth's atmosphere
toward the sun to measure the energy absorption of the Sun's rays by
these gases. Principal Investigator for HALOE is Dr. James M.
Russell III, NASA's Langley Research Center, Hampton, Va.
Dynamics
Two instruments, the High Resolution Doppler Imager and the
Wind Imaging Interferometer, will provide scientists with the first
directly measured, global picture of the horizontal winds that
disperse chemicals and aerosols through the upper atmosphere.
High Resolution Doppler Imager
By measuring the Doppler shifts of atmospheric chemicals,
the High Resolution Doppler Imager (HRDI) will measure atmospheric
winds between 6.2 and 28 miles and above 34 miles. These data are
important to understanding the essential role of atmospheric motion
on the distribution of chemicals in the upper atmosphere. Principal
Investigator for HRDI is Dr. Paul B. Hays, University of Michigan,
Space Physics Research Laboratory, Ann Arbor.
Wind Imaging Interferometer
The Wind Imaging Interferometer (WINDII) also will use the
Doppler shift measurement technique to develop altitude profiles of
horizontal winds in the upper atmosphere. WINDII's measurements
will tell scientists about the winds at and above 49 miles.
Principal Investigator for WINDII is Dr. Gordon G. Shepherd, York
University, Ontario, Canada. The investigation is provided by a
partnership between Canada and France, with the latter making
important contributions to the data analysis software.
Energy Inputs
Three instruments, the Solar Ultraviolet Spectral Irradiance
Monitor, the Solar Stellar Irradiance Comparison Experiment, and the
Partial Environment Monitor, will measure solar energy that reaches
the Earth and study its effect on the atmosphere.
Solar Ultraviolet Spectral Irradiance Monitor
Ultraviolet light from the Sun is the driver of the ozone
cycle, dissociating chlorine compounds into reactive chlorine atoms
that in turn break up ozone molecules . The Solar Ultraviolet
Spectral Irradiance Monitor (SUSIM) will measure solar ultraviolet
energy, the most important spectral range in ozone chemistry.
Principal Investigator for SUSIM is Dr. Guenter E. Brueckner, Naval
Research Laboratory, Washington, D.C.
Solar Stellar Irradiance Comparison Experiment
Like SUSIM, the Solar Stellar Irradiance Comparison
Experiment (SOLSTICE) will conduct in-depth ultraviolet studies of
the Sun. SUSIM will compare the Sun's ultraviolet energy to the UV
radiation of bright blue stars, providing a standard against which
the solar energy level can be measured in future long-term
monitoring of the Sun. Principal Investigator for SOLSTICE is Dr.
Gary J. Rottman, University of Colorado, Boulder.
Particle Environment Monitor
The Particle Environment Monitor (PEM) will help to answer
questions about the effect of energetic particles from the Sun on
the upper atmosphere, detecting and measuring the particles as they
enter the atmosphere. PEM uses four primary instrument subunits to
take detailed particle measurements in different energy ranges.
Principal Investigator for PEM is Dr. J. David Winningham, Southwest
Research Institute, San Antonio, Texas.
Solar Constant
Active Cavity Radiometer Irradiance Monitor
The Active Cavity Radiometer Irradiance Monitor (ACRIM II)
will provide accurate monitoring of total solar activity for
long-term climate studies. ACRIM II is an instrument of
opportunity, added to the UARS spacecraft after the engineering team
determined that the spacecraft could fly a 10th instrument. Though
not a part of the UARS program, ACRIM II data is important to other
studies within Mission to Planet Earth. Principal Investigator for
ACRIM II is Dr. Richard D. Willson, NASA's Jet Propulsion
Laboratory, Pasadena, Calif.
Propulsion
The UARS observatory consists of a standard design
Multi-mission Modular Spacecraft (MMS), coupled to a module that
includes the 10 instruments. The MMS Hydrazine Propulsion Module
will power orbit adjustment maneuvers for the initial boost to orbit
and maintain the required altitude. The system consists of four
5-pound thrusters and 12 small 0.2-pound attitude control thrusters.
The MMS was built by Fairchild, Inc., Germantown, Md.
Modular Attitude Control System
For UARS to make the minute changes in its orientation
toward the Earth needed for the long-duration measurements of the
atmosphere, the spacecraft must know at all times where it is
pointed. To do this, UARS uses a system known as the Modular
Attitude Control System (MACS). The MACS subsystem is a three-axis
system made up of many flight- proven NASA components contained
within the MMS. The system contains sensors that tell UARS where
it's pointed and actuators that can point the spacecraft as
required. The MACS module originally flew aboard the Solar Maximum
Mission (SMM). It was returned to Earth as part of the 1984 SMM
repair mission and refurbished for flight aboard UARS.
Communications and Data Handling
The Communications and Data Handling (CADH) system uses
software based on proven modular technology that flew on the Solar
Maximum Mission and Landsat 4 and 5. The modular programming allows
sections of the software to be rewritten or repaired without
requiring end-to-end verification of an entire new program. The
CADH system consists of the CADH module, a high-gain antenna and two
omni-directional low-gain antennas.
The CADH also has a Tracking and Data Relay Satellite System
(TDRSS) transponder for communications between UARS and TDRSS. UARS
uses a NASA standard spacecraft computer which provides for some
autonomous operation of the spacecraft. It will perform such tasks
as command processing, attitude determination computations and power
management.
Payload Operation and Control Center
Instructions to UARS during its space voyage begin with the
controllers at computer terminals located in the UARS Payload
Operations Control Center (POCC) at the Goddard Space Flight Center,
Greenbelt, Md. The POCC is the focal point for all UARS pre-mission
preparations and on- orbit operations. For the UARS mission, the
POCC is part of the Multi-satellite Operations Control Center
(MSOCC) at Goddard that provides mission scheduling, tracking,
telemetry data acquisition, command and processing required for down
linked data.
UARS Ground Data System
A dedicated Central Data Handling Facility (CDHF), located
at the Goddard Space Flight Center, will process the UARS scientific
data. The CDHF is linked to 20 Remote Analysis Computers at the
instrument and theoretical principal investigator's home
institutions via an electronic communications system. This will
make all UARS data available to all investigators. The CDHF also is
designed to encourage frequent interactions between the different
investigation groups and facilitate quick response to unusual
events, such as solar flares and volcanic eruptions.
UARS scientific data will be continuously recorded on two
alternating onboard tape recorders at the rate of 32 kilobits per
second. Upon acquiring contact with the Tracking and Data Relay
Satellite, the UARS data will be transmitted via the NASA
Communications Network to the Data Capture Facility (DCF), located
at Goddard. The DCF will perform telemetry preprocessing, which
includes time- ordering, merging, editing and sorting of the data
stream. The output will be transferred to the UARS CDHF.
Thermal Subsystems
Thermal control of UARS during launch and orbital operation
will be largely through passive means -- paint, blankets, coatings
and temperature sensors augmented by electrical heaters. The CLAES
and ISAMS instruments have special cooling requirements met by
subsystems within the instruments.
UARS was built and integrated by General Electric
Astro-Space Division, Valley Forge, Penn., and East Windsor, N.J.
The UARS project is managed by the Goddard Space Flight Center,
Greenbelt, Md., for NASA's Office of Space Science and Applications.