Sometimes, non-standard ICD numbers (like a hypothetical 153) refer to Control Segment documents (how the Air Force controls the satellites) rather than the User Segment (how users receive signals).
The U.S. Department of Defense is currently transitioning from SAASM to M-Code (Military Code) on the GPS III satellites. M-Code offers improved anti-jam capabilities, greater power, and better security. icd-gps-153 protocol
Will ICD-GPS-153 become obsolete?
No. The current MGUE (Military GPS User Equipment) Increment 1 and Increment 2 receivers continue to support the ICD-GPS-153 message set for backward compatibility. However, new message types are being added to the ICD to support: Payloads per MessageType:
The industry is also seeing a push toward ICD-GPS-872 (for Next Generation DAGR) and ICD-GPS-060 (for High Anti-Jam waveforms), but the original -153 remains the most widely implemented legacy standard. For the foreseeable future, any "plug-and-play" military GPS receiver will support ICD-GPS-153. icd-gps-153 protocol