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NOUS41 KWBC 131622 AMD
PNSNMC
NATIONAL TECHNICAL INFORMATION MESSAGE /NTEM/ 97-4
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
1130 AM EST FRI JAN 13 1997
TO: FAMILY OF SERVICES /FOS/ SUBSCRIBERS...NOAA WEATHER
WIRE SERVICE /NWWS/ SUBSCRIBERS...OTHER NATIONAL
WEATHER SERVICE /NWS/ CUSTOMERS...NWS EMPLOYEES
FROM: ROBERT S. WINOKUR
ASSISTANT ADMINISTRATOR FOR NATIONAL ENVIRONMENTAL
SATELLITE...DATA...AND INFORMATION SERVICES /NESDIS/
RON S. GIRD
NWS OFFICE OF METEOROLOGY SATELLITE PROGRAM MANAGER
SUBJECT: GOES-8 SATELLITE STATUS
AT 8:45 P.M. ON JANUARY 10 THE GOES-8 SATELLITE WAS RETURNED TO
SERVICE. THE SATELLITE IS NOW OPERATING IN WHAT WE CALL THE "L"
MODE WITH THE BACKUP /SMALLER REACTION WHEEL/ REPLACING THE
SECOND LARGER MOMENTUM WHEEL FOR SPACECRAFT STABILIZATION. THE
SPACECRAFT STOPPED PROVIDING IMAGES AT 8:30 A.M. EST JANUARY 9.
DURING THE OUTAGE 182 IMAGES AND 73 SOUNDINGS WERE MISSED.
WE COMPLETED A RECOVERY SCHEDULE /ABBREVIATED FULL DISKS...
EXTENDED STAR WINDOWS/ THAT EXTENDED FOR 36 HOURS TO ALLOW THE
IMAGE NAVIGATION AND REGISTRATION /INR/ SYSTEM TO SETTLE BACK
INTO ACCEPTABLE PERFORMANCE. USERS DID EXPERIENCE LARGER THAN
NORMAL INR ERRORS DURING THAT TIME. THE "L" MODE HAS NEVER BEEN
USED OPERATIONALLY ON GOES AND DOES REQUIRE THE WHEELS TO RUN AT
A FASTER SPEED THAN NORMAL BUT STILL WITHIN SPECIFICATION.
WHILE GOES-8 HAS BEEN TESTED USING THE REACTION WHEEL SYSTEM...WE
HAVE NOT PREVIOUSLY PERFORMED IMAGING AND SOUNDING OPERATIONS IN
THIS MODE. INR PERFORMANCE...WHILE ACCEPTABLE...IS NOT FULLY
CHARACTERIZED. IT IS LIKELY THAT THE CORRECTIONS THAT WE
ROUTINELY MAKE FOR THE "BATWING" ANOMALY...THE MAGNETOMETER "BOOM
SNAP" AND EARTH SENSOR SINGLE CHORD OPERATION WILL REQUIRE
RECALIBRATION. USERS...THEREFORE...SHOULD EXPECT LARGER THAN
NORMAL ERRORS AT MIDNIGHT AND FROM 1830Z TO 1900Z UNTIL THESE
SYSTEMS ARE CORRECTED. WITH 3 DAYS OF DATA THE PERFORMANCE OF
THE CONTROL SYSTEM APPEARS NOMINAL...ALTHOUGH THERE HAVE BEEN
SOME MECHANICAL INTERACTIONS BETWEEN THE MOMENTUM WHEEL AND THE
EARTH SENSOR WHICH WILL REQUIRE FURTHER INVESTIGATION. THESE
INTERACTIONS...WHICH WERE CHARACTERIZED DURING THE GOES-8 POST
LAUNCH TESTING...DO NOT APPEAR TO IMPACT IMAGING BUT MAY REQUIRE
SOME WHEEL SPEED ADJUSTMENTS.
THE ANOMALY APPEARS TO HAVE BEEN CAUSED BY A FAILURE WITHIN THE
WHEEL DRIVE ELECTRONICS FOR MOMENTUM WHEEL 1. THIS CAUSED THE
LOSS OF MOMENTUM WHEEL SPEED DATA TO THE ATTITUDE AND ORBIT
CONTROL ELECTRONICS /AOCE/ COMPUTER. THE LOSS LEAVES GOES-8 WITH
NO MOMENTUM WHEEL REDUNDANCY. THE AOCE AND THE REST OF THE
SPACECRAFT REMAIN NOMINAL. NOAA...NASA AND SPACE SYSTEMS/LORAL
ENGINEERS ARE LOOKING AT A POSSIBLE ALTERNATIVE MODES OF
OPERATION TO REGAIN SOME LEVEL OF REDUNDANCY.
DURING THE GOES-8 OUTAGE...A GOES-9 /WEST/ AND METEOSAT COMPOSITE
IMAGE WAS AVAILABLE TO NWS-RAMSDIS SITES...STARTING FRIDAY
AFTERNOON. THIS "BACK-UP" CAPABILITY WAS THE RESULT OF EXCELLENT
COOPERATION BETWEEN THE NWS AND NESDIS.
END
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