SUBJ: GPS STATUS 19 SEP 91
1. SATELLITES, PLANES AND CLOCKS (CS=CESIUM RB=RUBIDIUM):
A. BLOCK I : PRNS  3,  6, 11, 12, 13
   PLANE   : SLOT C4, A3, C3, A1, C1
   CLOCK   :      RB, RB, CS, CS, CS
B. BLOCK II: PRNS  2, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24
   PLANE   : SLOT B3, E1, D2, E3, D3, F3, A4, B2, E2, E4, D1
   CLOCK   :      CS, 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.
A. FORECASTS:
NANU      MSG DATE/TIME   PRN    TYPE  SUMMARY
121-91182 011354Z JUL 91  BLKII  FCST  SA ON    182/0400- UFN
161-91253 101554Z SEP 91  PRN21  FCST  OUTAGE 260/0015 => 8 HRS
163-91259 161444Z SEP 91  PRN19  FCST  OUTAGE 267/0500 => 12 HRS
B. ADVISORIES:
NANU      MSG DATE/TIME   PRN    TYPE  SUMMARY
162-91258 151000Z SEP 91  PRN20  ADV   UNUSABLE 258/0430-UFN
164-91253 171448Z SEP 91  ALL    ADV   URA CHG IMPLMNT 253/1500
165-91262 191338Z SEP 91  PRN13  ADV   UNUSABLE 262/0155-262/0159
                  SEP 91  PRN3   ADV   UNUSABLE 262/0534-262/0559
                  SEP 91  PRN6   ADV   UNUSABLE 262/0800-262/0813
3. REMARKS:
A. USERS OF GPS ARE CAUTIONED THAT THE SYSTEM IS NOT YET FULLY
OPERATIONAL. SIGNAL AVAILABILITY AND ACCURACY ARE SUBJECT TO
CHANGE DUE TO AN INCOMPLETE CONSTELLATION AND OPERATIONAL TEST
ACTIVITIES.
B. REF NANU 121 - SELECTIVE AVAILABILITY WAS REACTIVATED AT STANDARD
POSITIONING SERVICE ACCURACY LEVELS ON DAY 182 (01 JUL 91) AT 0400
UTC. VARIATIONS MAY BE SEEN IN THE EFFECT OF SA DURING TESTING, BUT
THE EFFECT SHOULD NOT EXCEED STANDARD POSITIONING SERVICE LEVELS.
THE POINT OF CONTACT IS MAJ ROB WORLEY (719)554-5770 OR DSN
692-5770.
C.REF NANU 164 - THE METHOD USED TO COMPUTE USER RANGE ACCURACIES
(URA) WAS CHANGED ON DAY 253 (10 SEP 91) AT 1500 UTC. PER A RECENT
CHANGE TO INTERFACE CONTROL DOCUMENT (ICD)-200, THE NEW METHOD
REFLECTS MORE ACCURATE STATISTICAL INDICATIONS OF THE CONTRIBUTION
OF THE APPARENT CLOCK AND EPHEMERIS PREDICTION ACCURACIES TO THE
RANGING ACCURACIES OBTAINABLE WITH A SPECIFIC SV BASED ON HISTORICAL
DATA. THIS CHANGE HAS NO EFFECT ON THE POSITIONING ACCURACY OF THE
NAVSTAR CONSTELLATION.
4. POINTS OF CONTACT:
A. CIVILIAN: US COAST GUARD AT COMMERCIAL (703)866-3806 VOICE OR
(703)866-3890 COMPUTER BBS.
B. MILITARY: 2SCS/DOCI CAPT DODD AT (719)550-6379 OR DSN 560-6379.