ATLAS 3 Public Affairs Status Report #13
6:00 p.m. CST, Nov. 9, 1994
MET 6/7:00
Spacelab Mission Operations Control
Marshall Space Flight Center
Huntsville, Ala.

ATLAS 3 atmospheric instruments have finished another two days of
observations to check the health of the atmosphere, and the four solar
instruments are in the midst of their third set of observations. 

With the mission less than a day past its mid-point, the Atmospheric Trace
Molecule Spectroscopy (ATMOS) instrument has already gathered more data
than it did during either ATLAS 1 or ATLAS 2.  One of the gases it focused
on in the last observing period was hydrogen chloride, which provides a
direct measurement of the amount of chlorine available in the atmosphere
for ozone chemistry. 

Payload Commander Ellen Ochoa explained this morning that ATMOS is unique
not only because it measures as many as 30 or 40 trace gases
simultaneously, but also because it can detect very small concentrations
of those gases -- down to a few parts per billion.  "Even though the
quantities are small," she observed, "these gases can play a large part in
ozone destruction." 

The ATMOS team has encouraged the crew to get as many photographs of the
atmosphere as possible, and this afternoon Commander Don McMonagle made
pictures as a sunrise illuminated Earth's thin protective blanket.  Ochoa
viewed the sunrise with high-magnification binoculars, and she commented
that she could see 13 or 14 atmospheric layers above the clouds. 

The Shuttle Solar Backscatter Ultraviolet (SSBUV) experiment completed a
series of Earth ozone measurements to calibrate those being made by NASA's
Total Ozone Mapping Spectrometer (TOMS) aboard the Russian Meteor-3
satellite. 

A six-orbit period of solar observations began at around 1 p.m., with the
Solar Constant (SOLCON) experiment and the Active Cavity Irradiance
Monitor (ACRIM) making very precise measurements of the total radiation
arriving at Earth from the sun.  The Solar Spectrum (SOLSPEC) instrument
and Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) are looking at
the sun's radiation as a function of wavelength. 

This morning, principal scientists for SUSIM, SOLSPEC and SSBUV announced
that preliminary data for their first set of ultraviolet solar
observations agree approximately to five percent of one another.  This is
the closest agreement ever achieved by three individual solar instruments
without post-flight calibration.  The correlation is especially
significant since each instrument uses different physics to achieve their
calibration.  The scientists expect to refine the agreement even further
during post-flight analysis. 

"It is important to obtain very accurate measurements of ultraviolet
radiation, because it sets up the chemistry in the atmosphere, triggers
catalytic cycles that make and destroy ozone, and drives heating in the
atmosphere," said SSBUV Principal Investigator Ernest Hilsenrath.  Changes
in this ultraviolet output are very subtle, but their impact is of the
same order as that of chemicals released into the atmosphere by industrial
activity.  To distinguish changes due to solar variations from those
caused by human activity, both must be closely tracked.  "Measurements
made by the ATLAS missions and the satellite instruments they calibrate
will provide a baseline for the future," said Hilsenrath.  "They will be a
legacy for environmental investigators in the next century, so they can
look back at our data and compare it with changes they may observe in the
atmosphere." 

While the Shuttle-based experiments concentrate on the sun, the Cryogenic
Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA)
experiment and the Middle Atmosphere High Resolution Spectrograph
Investigation (MAHRSI) are continuing atmospheric observations from aboard
Germany's free-flying CRISTA-SPAS satellite. 

CRISTA Principal Investigator Dr. Dirk Offermann, of the University of
Wuppertal in Germany, reported his instrument has made the first global
readings of atomic oxygen in far-infrared wavelengths as low as 62 miles
(100 kilometers).  "This is important because it will help us understand
how atomic oxygen functions as a cooling mechanism in the upper
atmosphere," explained Offermann.  Though far-infrared readings of atomic
oxygen at similar altitudes have been made during brief sounding rocket
flights, and by satellite instruments at higher altitudes, they have never
before been made so low in the atmosphere on a global scale.  Atomic
oxygen is produced in the upper stratosphere when solar ultraviolet light
strikes molecular oxygen (the form of oxygen people breathe), breaking it
down into single oxygen atoms. 

The MAHRSI team has processed preliminary data showing global
concentrations of hydroxyl.  Hydroxyl is very influential in the ozone
chemistry of the middle atmosphere. 

Solar observations will continue until around 9:30 p.m. CST.  An
orbit-long communications period with the CRISTA-SPAS satellite will
follow, and then atmospheric observations will resume.