UARS Monthly Status  December 1991

Jessie Katz
Office of Public Affairs
Goddard Space Flight Center
Greenbelt, MD 20771

December 24, 1991


UPPER ATMOSPHERE RESEARCH SATELLITE (UARS) MONTHLY STATUS REPORT
                          December 1991



At the UARS Science Team meeting this month, all investigators
reported that instrument performance continues to be very good.
By the end of 1991, UARS will have been in orbit 108 days.

There have been several instances of irregularities with the
onboard computers resulting in the loss of some data.  The
computers have since returned to normal operation.  The High
Resolution Doppler Imager (HRDI) instrument computer has stopped
three times.  The first time, on December 4, has been traced to a
software error in revised code loaded earlier that day.  The
subsequent stoppages on December 9 and 15 are also related to
software errors.  Instrument operations have resumed using the
"old" code.

The Solar/Stellar Irradiance Comparison Experiment (SOLSTICE)
instrument experienced anomalies on December 9 and 13.  Both
incidents were caused by incorrect computer instructions to the
instrument.

Several minor adjustments were made to enhance the spacecraft
systems' operating efficiency.  On December 8, the rate at which
the solar array adjusts itself to obtain the maximum energy from
the Sun's rays was changed to keep the array at the best angle to
the Sun.

Revised alignment and calibration parameters were uplinked to the
Solar Stellar Pointing Platform.  It is now well within the
pointing limits of .05 degrees in both the vertical and
horizontal axis.                                 

Another routine yaw maneuver, switching the observatory from
forward to backward flight, was executed December 4.  The purpose
of the maneuver, executed approximately every 36 days, is to keep
the solar array on the Sun side of the spacecraft and to keep the
instruments in the correct orientation angle with respect to the
Sun.  The next yaw-around maneuver, which will change the
observatory from backward to forward flight, is scheduled for
January 14, 1992, according to project officials.

During this reporting period, the Mass Storage System (MSS) in
the Central Data Handling Facility (CDHF) was upgraded with the
addition of two more optical disk drives.  This and future
additions will occur as the need for data handling capability
increases.

Early results from the Microwave Limb Sounder (MLS), one of the
10 scientific instruments aboard the observatory, have confirmed
the link between the presence of chlorine monoxide and the
depletion of ozone in Earth's upper atmosphere.  The data showed
that extremely high amounts of chlorine monoxide occur only where
ozone is severely depleted.  Those data are expected to improve
scientific understanding of the ozone depletion process.

The MLS also is seeing the effects of the large eruption of Mount
Pinatubo in the Philippines on June 15, 1991.  The volcano
injected huge amounts of sulfur dioxide into the stratosphere,
the remnants of which appear to the MLS as a band of high sulfur
dioxide concentrations over the tropics.  

In another result, the High Resolution Doppler Imager (HRDI)
aboard UARS has discovered large, violent windstorms in the
mesosphere 43 to 60 miles (69.2 to 96.5 kilometers) above Earth's
surface.  HRDI looks at the mesosphere to measure wind speeds in
various directions.  The biggest windstorm HRDI detected
stretches from western Australia across southern Africa and
halfway across the Atlantic Ocean.

The UARS is managed and operated by Goddard for NASA's Office of
Space Science and Applications.