The period marks a turning point where satellite-based navigation is integrated into a three-dimensional positioning framework, with the Global Positioning System concept and performance expectations shaping receiver design, timing synchronization, and robust operation under changing constellation conditions. Interferometric techniques begin to build precise geodetic networks, while early three-satellite configurations demonstrate reliable navigation even during partial-constellation periods. Intersections with high-resolution terrain mapping through interferometric radar extend navigation toward terrain awareness and geospatial context.