Brian Dunbar
Headquarters, Washington, DC          Feb. 2, 1995
(Phone:  202/358-1547)

Ernie Shannon
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-8955)


RELEASE: 95-114

SUCCESSFUL U.S.-RUSSIAN OZONE-MONITORING MISSION 
APPEARS OVER

     More than three years after it began, the mission of 
NASA's Total Ozone Mapping Spectrometer (TOMS) aboard the 
Russian Meteor-3 spacecraft appears to be over. 

     Recent attempts to revive the instrument, which failed 
in December, have been unsuccessful.  Though monitoring of 
the device will continue through April, the instrument team 
has said it is unlikely that further efforts will succeed.

     Launched from Plesetsk in the then-Soviet Union on 
Aug. 15, 1991, the TOMS instrument has already exceeded its 
design life of two years, providing important data and 
global maps of total ozone levels.  TOMS data is used 
primarily to determine long-term ozone trends, detect 
sulfur dioxide clouds from volcanic eruptions and detect 
atmospheric aerosols and dust storms.

     "Even though it appears we will lose the instrument, I 
am quite pleased with TOMS and the Russian spacecraft's 
performance during the past 3 years," said Dr. Jay Herman, 
TOMS/Meteor-3 principal investigator, of NASA's Goddard 
Space Flight Center, Greenbelt, MD.  "The instrument has 
produced a large quantity of critical atmospheric data 
longer than its designed 2-year lifetime."

     The TOMS/Meteor-3 instrument is NASA's second.  The 
first, which operated from 1978 through 1993, provided part 
of the scientific underpinning for international treaties 
banning the manufacture and use of ozone-depleting 
chemicals.

     No useful data have been received since Dec. 27, 1994, 
when spacecraft telemetry indicated a lack of steady 
electrical current to the instrument's chopper motor.  The 
chopper divides, or Rchops,S incoming solar energy for 
measurements of ultraviolet radiation.

    The chopper reduces the amount of noise in the observed 
radiance data and improves the accuracy of the ozone 
determination.  Recently, ground controllers in Russia 
successfully "warmed" the Meteor-3 spacecraft in hopes of 
recovering the instrument, but without results.

     "We appreciate our Russian colleagues' efforts to help 
us try an innovative approach to spacecraft operations," 
Herman said.  "This kind of cooperative spirit has marked 
all phases of the mission, from planning and operations to 
data analysis.  The result has been a very smooth mission."

     U.S. and Russian engineers will continue to monitor 
the instrument.  A power cycling technique will be tried 
again in April, when the spacecraft's orbit will lead it to 
warm naturally.  Members of the instrument team, however, 
believe the chance of reviving TOMS is very small.

     NASA plans to fly two more TOMS within 13 months.  The 
first is scheduled for launch aboard a Pegasus launch 
vehicle in May, the second aboard the Japanese Advanced 
Earth Observing Satellite in February 1996.  The fifth TOMS 
instrument will fly aboard a Russian Meteor-3M satellite in 
2000.

     Even without an operational TOMS in orbit, ozone 
studies will continue.  A network of ground stations and 
satellites, including NASAUs Upper Atmosphere Research 
Satellite and Earth Radiation Budget Satellite and NOAA 
weather satellites, are still obtaining local, regional and 
some global ozone measurements.

     "We will still be able to provide ozone data to 
scientists," Jack Kaye of NASA Headquarters, the TOMS 
program scientist, "but not with the high quality and 
spatial coverage of TOMS.  This instrument is unique in its 
ability to provide highly accurate daily maps of ozone over 
the entire sunlit Earth.  The loss of TOMS will 
particularly affect our ability to study details of ozone 
dynamics at high latitudes in the winter and early spring, 
when substantial ozone depletion can occur."

     TOMS data are one of the most visible elements of 
NASA's Mission to Planet Earth, the Agency's long term, 
coordinated research effort to study the Earth's global 
environment.  It is comprised of ground-based, airborne and 
space-based investigations into how the Earth's large 
environmental systems - air, water, land and life - interact 
and change, and how human activities contribute to those 
changes.  Mission to Planet Earth data will be made 
available to scientists worldwide so that humans ultimately 
will be able to make informed decisions about how their 
activities will affect the environment.

     The TOMS instrument is managed by the Goddard Space 
Flight Center for NASA's Office of Mission to Planet Earth, 
Washington, DC.


- end -