SUBJ: GPS STATUS 15 JAN 91
1. SATELLITES, PLANES AND CLOCKS (CS=CESIUM RB=RUBIDIUM):
A. BLOCK I : PRNS  3,  6,  9, 11, 12, 13
   PLANE   : SLOT C4, A3, A2, C3, A1, C1
   CLOCK   :      RB, RB, RB, CS, CS, CS
B. BLOCK II: PRNS  2, 14, 15, 16, 17, 18, 19, 20, 21, 23
   PLANE   : SLOT B3, E1, D2, E3, D3, F3, A4, B2, E2, E4
   CLOCK   :      CS, CS, CS, CS, CS, CS, CS, CS, CS, CS
2. CURRENT ADVISORIES (ADV) AND FORECASTS (FCST):
INFORMATION IS REPEATED FOR SEVEN DAYS AFTER EVENT CONCLUDES
NANU      MSG DATE/TIME   PRN    TYPE  SUMMARY
266-90345 111315Z DEC 90  9      ADV   UNUSABLE 345/1305-UFN
276-90365 311942Z DEC 90  16     FCST  UNUSABLE 007/1200-010/1200
001-91002 021713Z JAN 91  3      FCST  UNUSABLE 009/1300-009/1700
007-91007 071800Z JAN 91  23     FCST  UNUSABLE 011/1315-012/1315
009-91009 092005Z JAN 91  16     ADV   USABLE   009/1639
010-91009 092007Z JAN 91  3      ADV   USABLE   009/1855
011-91010 102241Z JAN 91  9      FCST  USABLE   012/0800-012/1000
012-91011 112240Z JAN 91  23     ADV   USABLE   011/1850
013-91014 142231Z JAN 91  13     ADV   UNUSABLE 014/2100-014/2145
014-91014 150041Z JAN 91  9      FCST  USABLE   015/2359
3. REMARKS:
A. REF NANU #057-90088: IMPLEMENTATION OF STANDARD POSITIONING
SERVICE: THE CURRENT GPS CONSTELLATION BEGAN BROADCASTING
NAVIGATION MESSAGES AT ACCURACY LEVELS CONSISTENT WITH STANDARD
POSITIONING SERVICE ON 25 MAR 90. GPS IS NOT EXPECTED TO BE
DECLARED FULLY OPERATIONAL UNTIL 1993. ANY GPS USERS ARE OPERATING
AT THEIR OWN RISK.
B. REF NANU #265-90345: PRN23 WAS LAUNCHED ON DAY 330 (26 NOV 90).
THE SATELLITE WAS USABLE FOR NAVIGATION BEGINNING DAY 344
(10 DEC 90) AT APPROXIMATELY 2345 UTC.
C.  REF NANU #266-90345: PRN9 WAS SET UNUSABLE ON DAY 345
(11 DEC 90) AT APPROXIMATELY 1305 UTC.
D. REF NANU #276-90365: PRN16 WILL BE USING A CESIUM FREQUENCY
STANDARD FOLLOWING THE UPCOMING SCHEDULED MAINTENANCE.
E. REF NANU #011-91010: PRN9 WILL BE SET HEALTHY ON DAY 012 (12 JAN
91) BEGINNING 0800 UTC FOR TWO HOURS. DUE TO THE CONDITION OF THE
SATELLITE, USERS MAY EXPERIENCE NAVIGATION/POSITION ERRORS OF UP TO
250 METERS USING PRN9. USERS SHOULD AVOID USING PRN9 WHERE BETTER
ACCURACY IS REQUIRED.
F. REF NANU #014-91014: PRN9 WILL BE SET HEALTHY IN ALL GPS
SATELLITE ALMANACS NO LATER THAN 15 JAN 91 AT 2359 UTC. ALTHOUGH
THE ALMANACS WILL SHOW A USABLE STATUS, PRN9 WILL ACTUALLY BE
UNUSABLE UNTIL THE EPHEMERIS CODE IS ALSO SET TO USABLE. IF USING
PRN9, THE USER RANGE ACCURACY MAY REACH UP TO 128 METERS.
4. POINT OF CONTACT: MAJ FAUVER AT (719)550-6379.