A RAIM system of a NAVSTAR GPS receiver has excluded a satellite. How many satellites are required to maintain a 3D position fix with RAIM capability?

To maintain a 3D position fix with RAIM (Receiver Autonomous Integrity Monitoring) capability, a minimum of five satellites is required when one satellite is excluded from use. In a standard GPS configuration, four satellites are generally needed for a 3D fix; however, when accounting for RAIM, which is used to assess the integrity of the satellite signals and ensure accurate positioning, an additional satellite is necessary.

RAIM works by using information from multiple satellites to detect anomalies or failures in one or more signals. If a satellite is excluded from the fix due to integrity checks, the system must still have enough satellites to continue providing accurate three-dimensional positioning. With one satellite excluded, five satellites are essential: four are used for the 3D position fix, and the fifth is used for RAIM to evaluate the integrity of the data being received. Thus, the correct answer reflects the requirement for five satellites in this scenario.