NOTICE ADVISORY TO NAVSTAR USERS (NANU) 2025077 NANU TYPE: GENERAL
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This is an amendment to NANU 2025075.

OPERATIONAL NOTICE:
Testing will be starting no earlier than JDAY 339 (05DEC25) using PRN 34 with the third Navigation Technology Satellite (NTS-3) and is planned to continue through June 2027.  GPS users should not attempt to track or use the signals transmitted by NTS-3 since they will not be IS/ICD compliant. 

TECHNICAL INFORMATION:
To mitigate the risk of backward-compatibility issues with GPS user equipment, the NTS-3 PRN34 L1 C/A-code transmissions will include modified Legacy Navigation (LNAV) data comprising alternating 1's and 0's in the message content portion of words 3-10 of subframes 1-5 with proper (32,26) Hamming Code parity bits throughout. The most significant bit (MSB) of the six-bit space vehicle (SV) health indication in subframe 1 will be set to 1, indicating "some or all LNAV data are bad".
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POC: CIVILIAN and MILITARY -- AFRL.RV.NTS3@us.af.mil