How many satellites need to be received to determine complete position and time?

To determine a complete position and time using satellite signals, a minimum of four satellites is required. This is because each satellite provides a piece of data regarding the user’s position in three-dimensional space: latitude, longitude, and altitude.

The first three satellites can pinpoint the user's location in terms of three-dimensional coordinates (X, Y, and Z), but to accurately determine the time component and correct for any discrepancies in the receiver's clock (as satellite clocks are extremely precise), a fourth satellite is essential. The additional satellite allows for an accurate time calculation, ensuring that the location fix is precise.

This method relies on triangulation principles and time-delay measurements. The signals sent by the satellites include the time at which the signal was transmitted, enabling the receiver to calculate the distance from each satellite based on how long it took for the signals to arrive. Thus, without the fourth satellite, the system cannot resolve these variables accurately, resulting in less precise positioning information.