ATLAS 3 Public Affairs Status Report #4
6:00 a.m. CST, Nov. 5, 1994
Spacelab Mission Operations Control
Marshall Space Flight Center
Huntsville, Ala.

Solar instruments aboard the third Atmospheric Laboratory for Applications
and Science (ATLAS 3) completed their first eight orbits of observations
last night, and the mission's second session of atmospheric observations
is currently in progress.  Scientists need both types of data to view the
"big picture" of factors which influence this planet's atmospheric
life-support system, especially its protective ozone layer. 

The period of solar observations concluded around midnight CST, and the
crew pointed the Shuttle toward the Cryogenic Infrared Spectrometers and
Telescopes for the Atmosphere-Shuttle Pallet Satellite (CRISTA-SPAS) to
receive a sample of science data to be relayed to the ground.  Science
teams for the four solar instruments at Spacelab Mission Operations
Control in Huntsville report their observations went very smoothly, and
the quality of the data collected looks good. 

At around 6:45 p.m. CST, Commander Don McMonagle, aided by Mission
Specialist Ellen Ochoa, maneuvered the Orbiter Atlantis to perform a
special calibration of the Solar Ultraviolet Spectral Irradiance Monitor
(SUSIM).  This planned procedure allowed the SUSIM device to scan across
the sun, pointing at the sun's center and at four off-center points to
verify the alignment of the instrument on the center of the sun.  Changes
in ultraviolet radiation output bring about changes in Earth's atmospheric
conditions, such as the amount of ozone in the middle atmosphere.  A
better record of the sun's ultraviolet output will help scientists
distinguish between atmospheric changes caused by variations in
ultraviolet radiation and those brought about by human activity. 

The Active Cavity Radiometer Irradiance Monitor (ACRIM), from NASA's Jet
Propulsion Laboratory, and Belgium's Solar Constant experiment (SOLCON)
each made extremely precise, independent measurements of the total solar
irradiance, or total energy from the sun received by the planet Earth. 
Computer models suggest that even small variations in this total solar
irradiance could have significant impacts on climate.  Therefore, these
instruments measure this quantity to a long-term accuracy of plus or minus
0.1 percent or better.  SOLCON commands were sent from their remote
control facility in Brussels. 

France's Solar Spectrum (SOLSPEC) experiment concentrates on measuring
solar radiation as a function of wavelength in the ultraviolet, visible
and infrared.  The device is monitored by scientists at the Spacelab
Mission Operations Control center in Huntsville, Ala., but most
calibrations and observations for this instrument are controlled through
the onboard equipment computer.  Some commands are sent from the remote
center in Brussels. 

The Shuttle Solar Backscatter Ultraviolet (SSBUV) instrument, from NASA's
Goddard Space Flight Center, completed a cooling period and then made its
first observations of the mission during the last two orbits of the solar
observation period.  Scientists will compare those measurements with
readings of ultraviolet radiation scattered back from the Earth's
atmosphere, to be obtained by SSBUV in the atmospheric observation periods
of the ATLAS 3 mission.  Ozone absorbs different wavelengths of
ultraviolet light at different altitudes, so comparisons of the incoming
ultraviolet radiation with backscattered radiation give scientists a
highly accurate picture of the total amount of ozone in the atmosphere, as
well as its distribution by altitude. 

Atmospheric observations resumed at around 1 a.m. CST, with remote-sensing
operations by the Jet Propulsion Laboratory's Atmospheric Trace Molecule
Spectroscopy (ATMOS).  The instrument is observing orbital sunrises around
the South Pole to study the Antarctic ozone hole and compare ozone amounts
inside and outside the edge of the swirling mass of cold air known as the
"polar vortex."  This vortex acts as a container for chemical reactions
that cause ozone depletion. 

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere
(CRISTA) and the Middle Atmosphere High Resolution Spectrograph
Investigation (MAHRSI), two new atmospheric instruments aboard the
retrievable CRISTA-SPAS satellite, continue to make observations of the
middle atmosphere's chemistry.  CRISTA measures a variety of gases in the
middle atmosphere, and MAHRSI detects the amounts of nitric oxide and
hydroxyl in the middle atmosphere and lower thermosphere.  With its fast
scanning technique, CRISTA recorded several hundred thousand spectra of
trace gases in Earth's atmosphere.  Currently, all systems aboard the
CRISTA-SPAS satellite are working nominally. 

The ground control team for the Millimeter-Wave Atmospheric Sounder (MAS)
instrument is currently working with ATLAS 3 payload controllers to
determine the nature of a problem which is preventing the reception of
scientific data from the instrument.  It is suspected that the problem is
internal, possibly a malfunction in the instrument's microprocessor. 
Until the source of the problem is determined, its potential impact on
MAS's science remains uncertain. 

Atmospheric observations will continue throughout the next twelve hours.