NOTICE ADVISORY TO NAVSTAR USERS (NANU) #057-90088
SUBJ: SPS ACCURACY LEVELS IMPLEMENTATION 25 MARCH 1990
1. CONDITION: THE DOD IS WORKING TO ESTABLISH A FULLY OPERATIONAL
GPS CONSTELLATION CONSISTING OF 21 SATELLITES. SELECTIVE
AVAILABILITY AND ANTI-SPOOF (SA/ASL ARE SYSTEM CAPABILITIES THAT
MAY BE IMPLEMENTED AT ANY TIME. IN KEEPING WITH NATIONAL POLICY,
THE CURRENT GPS CONSTELLATION BEGAN BROADCASTING NAVIGATION MESSAGES
AT ACCURACY LEVELS CONSISTENT WITH STANDARD POSITIONING SERVICE
SSPSL ON 25 MARCH 1990.
2. RECOMMENDATION: THE CONSTELLATION IS STILL IN BUILD UP PHASE AND
IS NOT EXPECTED TO BE DECLARED FULLY OPERATIONAL UNTIL 1993. ANY
GPS USERS OPERATING NOW DO SO AT THEIR OWN RISK.