ATLAS 3 Public Affairs Status Report #12
6:00 a.m. CST, Nov. 9, 1994
MET 5/19:00
Spacelab Mission Operations Control
Marshall Space Flight Center
Huntsville, Ala.

Halfway through the eleven-day ATLAS 3 mission, the atmospheric
instruments continue to amass detailed information on the chemical
constituents of the middle atmosphere.  These instruments are working well
and are providing high-quality data to the science teams. 

The solar instruments are in standby, as science teams evaluate data from
the first two solar observation periods and prepare for the third. 

The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment measured
the chemical and physical composition of the middle atmosphere.  Since
ATMOS first flew on Spacelab 3 in 1985, scientists have retrieved height
profiles of over 30 trace gases from ATMOS data, including several
chlorofluorocarbons, nitrogen-oxygen compounds, ozone, carbon monoxide,
carbon dioxide, water and methane.  The instrument measures these gases
selectively and can simultaneously observe about ten to fifteen trace
gases in one observation. 

The ATMOS instrument viewed the stratosphere at orbital sunrise and
sunset, gathering information in the infrared portion of the
electromagnetic spectrum.  Since trace gas molecules absorb solar
radiation at different wavelengths, ATMOS determines which wavelengths are
being absorbed, giving scientists a more detailed picture of the molecular
makeup of the atmosphere.  ATMOS data from ATLAS 3 will be compared to
information gathered during other missions to examine worldwide, seasonal
and long-term atmospheric changes.  According to Principal Investigator
Mike Gunson, ATMOS has already far exceeded its minimum success
requirements for the mission, performing "well beyond expectations" on its
"most productive, and certainly most scientifically interesting, flight
ever on any Shuttle mission."  ATMOS has now filled about 80 percent of
its onboard recorder, having completed a total of 166 sunrise and sunset
observations. 

The Shuttle Solar Backscatter Ultraviolet (SSBUV) experiment continued to
perform coincident measurements for NASA's Total Ozone Mapping
Spectrometer (TOMS) and with ozone measuring instruments flying on the
NOAA 9 satellite as called for by the National Plan for Stratospheric
Monitoring.  The SSBUV instrument makes its ozone measurements by
comparing the amount of solar radiation reaching the top of the Earth's
atmosphere to the amount being scattered back from the atmosphere.  This
information gives scientists a measure of the amount of ozone present in a
given area. 

At around 3:45 CST this morning, the SSBUV team participated in what
Principal Investigator Ernest Hilsenrath called "a spontaneous experiment
collaboration" with the Middle Atmosphere High Resolution Spectrograph
Investigation (MAHRSI) instrument to test the possibility of using
MAHRSI's limb-scanning ability to measure ultraviolet radiation and ozone
in the lower stratosphere.  Taking advantage of a planned CRISTA-SPAS
maneuver in which MAHRSI scanned the ultraviolet portion of the
electromagnetic spectrum at heights between 55 and 15 km, the SSBUV team
cooperated with the MAHRSI team to demonstrate the feasibility of this
ozone limb-scanning technique in preparation for a solar limb- scanning
instrument currently under development for possible use on future space
missions. 

SSBUV measures ozone in the upper stratosphere by looking straight down at
the Earth using ultraviolet backscatter observations.  MAHRSI, on the
other hand, measures hydroxyl and nitric oxide in the stratosphere and
mesosphere, using limb-scanning, or edge on viewing above the Earth's
horizon.  This experiment successfully demonstrated the feasibility of
using limb-scanning of the ultraviolet spectrum to obtain ozone
measurements in the lower stratosphere.  According to MAHRSI Principal
Investigator Robert Conway, "there was a question about whether our
instrument had enough sensitivity to perform this experiment successfully,
but, sure enough, we did.  The data look excellent."  Analysis of this
experiment's results will continue throughout the next shift. 

During the second half of the next 12 hour shift, the four solar science
instruments for ATLAS 3 will begin their third period of solar
observations.  The Active Cavity Radiometer Irradiance Monitor, from the
Jet Propulsion Laboratory, and Belgium's SOLCON experiment will measure
the total solar energy received by the Earth.  The SOLSPEC experiment will
concentrate on the sun's radiant output in ultraviolet, visible and
infrared wavelengths while the U.S. Naval Research Laboratory's Solar
Ultraviolet Spectral Irradiance Monitor examines solar output in the
ultraviolet wavelengths.  SSBUV will also observe the sun during one or
two of the solar orbits, and the second Experiment of the Sun for
Complementing the Atlas Payload and for Education (ESCAPE-II) will be in
operation for all solar orbits.