Private Pilot Private Exam

What is the minimum number of GPS satellites that are observable by a user anywhere on Earth?

1. 2

2. 3

3. 4

4. 5

The correct answer is: 5

To determine the minimum number of GPS satellites that are observable by a user anywhere on Earth, it is essential to understand how GPS technology works. The Global Positioning System (GPS) relies on a constellation of satellites that transmit signals to receivers on the ground. For a GPS receiver to accurately calculate its position in three-dimensional space (latitude, longitude, and altitude), it requires signals from at least four satellites. With three satellites, the receiver can determine its position in two dimensions (latitude and longitude), but cannot accurately calculate altitude. The fourth satellite is critical for triangulating the exact altitude and to account for timing discrepancies. Each satellite is positioned such that there is generally always a minimum of four satellites in the sky visible to a user, regardless of their location on Earth. Therefore, the answer reflects the necessity of having four satellites to achieve accurate and reliable positioning data.