Final answer:
If OBS fails, accurate positioning and navigation operations are not possible with the DGNS.
Step-by-step explanation:
If OBS fails, the main operations and functions that are not possible with the DGNS (Dynamic Global Navigation Satellite System) are accurate positioning and navigation. OBS (On-Board Software) plays a crucial role in processing and analyzing satellite data, calculating the receiver's position on Earth, and providing accurate positioning information. Without OBS, the DGNS cannot perform these operations effectively.
For example, in a car navigation system that relies on the DGNS, if OBS fails, the system may not be able to determine the vehicle's location accurately, leading to incorrect directions and guidance.