G.S Wong, F.A. Kronberg, H.D. Meriwether, L.S. Wong, C.L. Grassi
           Center for EUV Astrophysics, 2150 Kittredge St.,
      University of California, Berkeley, California 94720, USA


   The EUVE Science Operations Center (ESOC) is a satellite payload operations
center for the Extreme Ultraviolet Explorer project, located on the Berkeley
campus of the University of California.  The ESOC has the primary responsibili-
ty for commanding the EUVE telescopes and monitoring their telemetry.  The ESOC
is one of a very few university based satellite operations facilities operating
with NASA.  This article describes the history, operation, and advantages of
the ESOC as an on-campus operations center.


   Bringing the EUVE Science Operation Center to the UC Berkeley campus accom-
plished four main objectives.  First, it enabled a core group of astronomers
and instrument engineers to work closely on the interpretations of data.  Also,
the EUVE Science Operations Center (ESOC) receives telemetry around the clock,
reducing the time between observation and delivery.  Third, the scientist-
trained staff of the ESOC provides specialized monitoring of the health and
safety of the EUV instruments.  The full-time staff of six plus twelve part-
time undergraduate assistants continuously monitor and adjust the instruments
to ensure the optimum observation parameters.  Last, the ESOC's location on a
university campus provides selected undergraduates the experience of working
on a NASA project, exposing them to NASA protocols and spacecraft operations.
   The ESOC became active during the early integration and test phases of the
EUVE project.  The ESOC tested the functionality of the scientific instruments
while they were exposed to simulated space environments at NASA's Goddard Space
Flight Center (GSFC) in Greenbelt, Maryland; the instruments were checked for
electromagnetic compatibility and ability to withstand vibration and thermal
vacuum.  These tests certified that the payload was ready for launch and that
the ESOC was capable of operating and monitoring it remotely from UC Berkeley.
   The ESOC was an integral part of launch preparation and countdown, monitor-
ing the instruments on the launch pad at Kennedy Space Center until five mi-
nutes prior to booster ignition.  During the countdown sequence, the ESOC was
responsible for confirming the payload's mechanical and functional readiness
for launch.


   With the EUVE now in orbit, the ESOC is the primary interface between UCB
and GSFC.  The ESOC creates and sends to GSFC instrument commands, pointing
instructions, and administrative messages.  The ESOC receives from  GSFC te-
lemetry, orbital ephemeris, attitude, and scheduling information.
   Three types of data flow from the EUVE satellite to NASA ground control and
the ESOC:

 (1) science data (the output of the EUVE telescopes);
 (2) engineering data (health and safety information about the satellite's
	mechanical and electrical components); and
 (3) navigation data (satellite orbital position and attitude).

   The science, engineering, and navigation data are stored on tape recorders
aboard the satellite.  Every ninety minutes, EUVE comes into contact with
NASA's space communications link -- the Tracking and Data Relay Satellite
System (TDRSS) -- a system of three geosynchronous satellites that receive
data from other spacecraft and relay it to ground stations at White Sands,
New Mexico.  For twenty to thirty minutes, there exists a bidirectional com-
munications link between the EUVE satellite and NASA/UCB ground control.  This
is called a real-time "pass" or "event".
   NASA satellite controllers and the ESOC payload controllers receive and
analyze both stored and real-time data during the pass.  In Berkeley the ESOC
payload controllers observe the data transmission from NASA/GSFC; analyze the
engineering health and safety information; and contact UCB scientists and
engineers with reports.  A suite of software developed at Berkeley's Center
for EUV Astrophysics (CEA) is used for this activity.  One part of the soft-
ware, called "Soctools", displays over 700 engineering monitor values on Sun
workstations in the ESOC.
   During the pass, commands from NASA ground control and the ESOC are uploaded
to the satellite.  These commands change parameters to point and operate the
telescopes, as well as operate the satellite.  ESOC controllers upload commands
for routine procedures and in response to emergencies.  These commands open and
close the seven detector chamber doors; power the detectors and the telescope
heaters; shut down the payload instruments and telescopes during emergencies;
and restore the payload to its normal operating state afterwards.  Using long-
term plans submitted by the ESOC, NASA ground controllers issue commands to
point the spacecraft at specific EUV sources.  All ESOC commands are checked
by NASA's Command Management System before they are uplinked to the satellite
(see fig. 1).
   This activity of supporting science investigation using NASA satellites,
but at science operations centers away from NASA installations, has been called
"teleoperations".  The scientist can receive the requested data without ever
traveling to a NASA facility.  The data can be analyzed for the scientist in
Berkeley or sent directly to the scientist's workplace.


   ESOC payload controllers must understand the instrument thoroughly so that
they can diagnose and respond quickly to threats to the satellite or its data.
To ensure a capable understanding, controllers must pass a three-part certifi-
cation.  The first part involves a one-hour written examination, which tests
the examinee's knowledge of the functions, causes of failure and problem reso-
lutions of the various subsystems in the EUVE payload.
   The second part of the certification is a rather challenging four-hour simu-
lation.  The test setup follows actual operations as closely as possible, in
the equipment, programs, and personnel.  A telephone line between the control-
ler and the examiner simulates the voice link between ESOC and NASA.  The ex-
aminer also manipulates the EUVE payload simulator, also known as the Kiwi --
the nonflight instrument.  The examinee must create all the necessary commands
on a terminal, verify them, and electronically send them to a site representing
the Command Management System at Goddard for uploading to the EUVE simulator
(fig. 1).
   The examinee is given a list of passes scheduled to occur within a four-hour
period.  The list includes the times that passes begin and end and when the 
payload enters day, dusk, night, dawn, and the South Atlantic Anomaly.  When
passes begin, the examiner simulates payload anomalies using the Kiwi.  At the
same time, the examiner may cut off the real-time telemetry connection to the
examinee's terminal to simulate ground system problems (fig. 2).  Amidst these
activities, the examinee may also be interrupted by other personnel entering
the ESOC, and the examinee is graded on ability to take command of the situa-
tion in the ESOC.
   The third part is a one-hour oral examination in which EUVE scientists ask
questions concerning all aspects of the operation of the EUVE payload.  A sig-
nificant portion of this oral examination explores the controller's judgement
in cases where no procedure exists for a given problem.
   To be certified, the payload controller must pass all three examinations as
determined by EUVE duty scientists and the ESOC manager.


   To keep all concerned parties informed of the payload's status, the ESOC
produces several distinct reports, each varying in content, frequency, and
   The primary record for EUVE operations is the logbook.  This documentation
started during the integration and calibration phase, three years prior to
launch.  The logbook consists of handwritten notes chronicling all spacecraft
and ground system activities in a prescribed format.  The logbook, as a primary
source, has proven invaluable in numerous investigations.
   The daily summary is a CEA internal document detailing the activities and
status of the payload during the previous day.  Included in the summary is
the current target, operating parameters, significant events affecting EUVE,
NASA/UCB interface issues and upcoming activities.  The daily summary is kept
to a few succinct paragraphs and distributed daily at 14:00 GMT via e-mail.
   A weekly summary is issued primarily to NASA for inclusion in the EUVE re-
port for NASA Headquarters.  This report is divided into two parts.  Part one
concerns the previous week's observations.  Part two deals with the instrument:
lost observation time, changes in spacecraft constraints, anomalous events,
and upcoming engineering fixes and tests.  The weekly report is also distribu-
ted via e-mail on the Internet.
   The observation log is a vehicle for informing guest observers what happened
during their observation.  It details all information that might affect their
data, such as instrument parameter changes, exact start and stop times of the
observation, startracker information, South Atlantic Anomaly ingress/egress and
times EUVE was in Earth's shadow.  This electronic log is packaged and sent only
to the guest observer along with the observer's data.
   The data discrepancy log (DDL) reports anomalies and unexplained occurrences
noticed in the hardware or software.  DDLs are analyzed within 24 hours of
creation by the appropriate CEA scientist, engineer, or programmer.
   Finally, controllers at the end of their shift prepare shift change forms
detailing changes or upcoming events for the oncoming controller.  These forms
facilitate smooth and continuous 24-hour coverage.


Figure 1:  Commanding Path Flow Chart.
Figure 2:  Telemetry Path Flow Chart.

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Last modified 10/14/98