ATLAS 3 Public Affairs Status Report #2
6:00 a.m. CST, Nov. 4, 1994
MET 0/19:00
Spacelab Mission Operations Control
Marshall Space Flight Center
Huntsville, Ala.

Instruments aboard the third Atmospheric Laboratory for Applications and
Science (ATLAS-3) Spacelab mission have been powered up, and two of them
took readings of a variety of gases in the middle atmosphere throughout
the past twelve hours.  Information from the ATLAS experiments, along with
that gathered by free-flying satellites, will give scientists increased
insight into the complex chemistry of the middle atmosphere which affects
global ozone levels. 

The mission's atmospheric studies continued as the Millimeter-Wave
Atmospheric Sounder (MAS), made its first set of measurements and employed
its improved scan mode to continuously observe Earth's far horizon and
look for traces of water vapor, ozone and chlorine monoxide at different
altitudes.  The instrument, mounted on the Spacelab pallet, uses a
dish-shaped antenna to study the chemistry of ozone, and also to measure
temperature and pressure, in Earth's middle atmosphere.  Using its new
chlorine monoxide receiver, that is twice as sensitive as the one that
flew on the ATLAS 1 and 2 missions, MAS can take better measurements of
chlorine monoxide, an important compound involved in ozone depletion, over
both hemispheres. 

Also, the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument
continued to operate nominally, making its observations of orbital
sunrises and sunsets and measuring the concentrations of more than 30
gases in the middle atmosphere.  The device uses a technique called limb
sounding, which involves viewing the infrared portion of sunlight as it
shines through the Earth's horizon, or 'limb.' Because trace gases absorb
at very specific infrared wavelengths, the science team can determine what
gases are present, in what concentrations, and at what altitudes.  A more
thorough knowledge of which gases are present, and of how their
concentrations change over time, can help scientists determine the
extent of man-made and natural changes.

Mission Specialist Ellen Ochoa activated the Shuttle Solar Backscatter
Ultraviolet (SSBUV) experiment, which will be used to verify the accuracy
of atmospheric ozone and solar ultraviolet irradiance data obtained by
instruments on free-flying National Oceanic and Atmospheric Administration
and NASA satellites.  Its door was opened to expose the instrument to the
space environment, and a period of "outgassing" followed, during which the
device cooled until 5:30 a.m. CST.  SSBUV will take its first atmospheric
readings after the first period of solar observations. 

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere
(CRISTA) experiment began its checkout and pre-deploy activities in
preparation for its release aboard the ASTRO-SPAS retrievable satellite at
6:50 a.m. CST.  This instrument will gather the first global information
about medium and small scale disturbances in trace gases of the middle
atmosphere.  These measurements will be taken in three dimensions
simultaneously and will provide information about disturbances caused by
winds, waves, turbulence and other processes.  A pressure increase
observed earlier in CRISTA's liquid helium container has since leveled off
and should not affect the scheduled deployment of the satellite.  Also
aboard the ASTRO-SPAS carrier, the Middle Atmosphere High Resolution
Spectrograph Investigation (MAHRSI) will measure amounts of hydroxyl and
nitric oxide in the middle atmosphere and lower thermosphere, from 24 to
72 miles (40 to about 120 km) high. 

The solar instruments have been activated and calibrated for the first
period of solar observations.  SOLSPEC and SUSIM are operating nominally. 
ACRIM successfully completed its shutter test and is undergoing further
testing.  During the next twelve hours, solar observations will begin
after the deployment of ASTRO-SPAS as ATLAS 3 starts its second day in
orbit.  All Spacelab systems are working well at this time.