GPS OPERATIONAL ADVISORY 91018.OA1
SUBJ: GPS STATUS 18 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
007-91007 071800Z JAN 91  23     FCST  UNUSABLE 011/1315-012/1315
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
015-91016 162009Z JAN 91  9/23   ADV   USABLE   016/1912
016-91016 162306Z JAN 91  23     ADV   UNUSABLE 016/2042-016/2234
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 #015-91016: PRN9 WILL BE SET USABLE ON DAY 16 (16 JAN
91) BEGINNING AT 1912 UTC. THE EPHEMERIS CODE WILL BE SET USABLE.
USER RANGE ACCURACY (URA) FOR PRN9 WILL BE FIXED AT 16 METERS.
4. POINT OF CONTACT: MAJ FAUVER AT (719)550-6379.