SUBJ: GPS STATUS 31 DEC 90
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, RB, 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
272-90359 251300Z DEC 90  3      ADV   UNUSABLE 359/1100-359/1115
273-90360 260100Z DEC 90  11     ADV   UNUSABLE 360/2125-360/2130
274-90360 260900Z DEC 90  13     ADV   UNUSABLE 360/0245-360/0430
275-90360 262243Z DEC 90  3      ADV   UNUSABLE 360/2131-360/2145
276-90365 311942Z DEC 90  16     FCST  UNUSABLE 007/1200-010/1200
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. ALMANAC DATA FOR PRN9 IS NOT
AVAILABLE.
D. REF NANU #276-90365: PRN16 WILL BE USING A CESIUM FREQUENCY
STANDARD FOLLOWING THE UPCOMING SCHEDULED MAINTENANCE.
4. POINT OF CONTACT: MAJ FAUVER AT (719)550-6379.