The Navigation Layer will establish a GPS-independent navigation capability for the National Defense Space Architecture (NDSA) using optical communication terminals (OCT), and optical space to ground links. The Navigation Layer requires advanced in-flight software known as the Speed, Time, and Range (STAR) Orbit and Clock Determination Application (OCDA), and the Constellation, Speed, Time, and Range (COSTAR) OCDA that combines inputs from multiple sources to ensure a robust and resilient position, navigation, and timing (PNT) solution. The OCT range and timing measurements are the key to operating the NDSA as a GPS-independent navigation system of systems.
With GPS independent operation, the Navigation Layer will offer two vital PNT services to the warfighter: situational awareness monitoring, and alternative PNT services.
Situational awareness monitoring will provide information about the availability, and possible corruption of, GPS signals in both the terrestrial and space domains.
Alternative PNT services will provide the warfighter a GPS-independent source of positioning, and time transfer signals transmitted to emerging navigation receivers in development by the Joint Services and Combatant Commands.
Accordingly, SDA is exploring technical areas enabling GPS-independent positioning, navigation, and timing including:
- Systems and algorithms enabling highly precise and accurate range measurements with free-space optical communication terminals,
- Optical and radio frequency (RF)-based precise sub-nanosecond time transfer space-to-space and space-to-ground modems,
- Capabilities required to enhance the STAR and COSTAR navigation and timing performance, including those embedded within communication services,
- Mass-producible, space-capable low-size, weight, power & cost (SWaP-C) atomic clocks, inertial navigation systems, star trackers, and other space navigation sensors, and
- Space-based situational awareness systems that act as monitors for global navigation satellite system (GNSS) signal-in-space integrity, and can measure potential terrestrial interference.