The vulnerability of GNSS became obvious more than ever in the Ukraine conflict. Massive electronic warfare renders GNSS useless. Unfortunately, there is not the “one” GNSS-denied navigation method which alone can substitute GNSS in all aspects such as worldwide operability and excellent position accuracy.
All onboard autonomous GNSS-denied navigation means have in common that they correlate sensor data with environmental features. The availability and performance largely depend on the existence of environmental features and capability to sense these environmental features. For example, a camera of Vision-based Navigation (VBN) system may not “see” environmental features (although physically present) in foggy conditions.
Therefore, complementary GNSS-denied navigation means need to be combined to cover the wide range of environmental conditions. The approach of Airbus Defence and Space combines VBN, Terrain-Referenced Navigation (TRN) and Star Navigation (StarNav). The environmental conditions are divided by the availability of landmarks, visibility conditions (e.g. obstruction by clouds) and altitude. VBN is operational if visibility to landmarks is given. StarNav is complementary to VBN as no landmarks are required but visibility to the stars is mandatory. Last but not least TRN completes the GNSS-denied navigation system for operation in low-visibility conditions.
In the era of systems of system Collaborative Navigation becomes part of the solution for GNSS-denied navigation, although it does not directly contribute to it. What marks collaborative navigation is its high relative accuracy which may be achieved by data link ranging between collaborating platforms. The relative accuracy is essential that accurate absolute navigation information can spread within the formation.