why GPS uses 24 satellites

The GPS (Global Positioning System) uses a constellation of at least 24 satellites to provide global positioning, navigation, and timing services. This number of satellites was chosen based on several technical and operational considerations. Here are some reasons why the GPS constellation consists of 24 satellites:

1. Global Coverage: To achieve global coverage and accurate positioning anywhere on Earth's surface, a sufficient number of satellites is needed. With 24 satellites, the GPS system ensures that there are multiple satellites in view from any point on the planet at any given time.

2. Redundancy and Reliability: Having multiple satellites in orbit provides redundancy. If one or more satellites experience technical issues or failures, the system can continue to function accurately using the remaining operational satellites.

3. Three-Dimensional Positioning: To determine a receiver's three-dimensional position (latitude, longitude, and altitude), at least four satellites are required. Three satellites are needed to calculate a two-dimensional position (latitude and longitude) without altitude information.

4. Optimal Geometry: A constellation of 24 satellites allows for optimal geometric distribution, ensuring that there are satellites at different angles above the horizon for accurate trilateration calculations by GPS receivers on the ground.

5. Availability and Accessibility: More satellites in the constellation mean that GPS signals are more likely to be available and accessible, even in challenging environments such as urban canyons, mountainous terrain, and densely forested areas.

6. Signal Diversity: Having multiple satellites transmitting signals across different frequency bands allows for signal diversity, reducing the risk of interference and improving signal reliability.

7. Time Synchronization: To provide accurate timing services, multiple satellites are necessary to ensure that a receiver can receive signals from multiple sources and calculate precise time information.

8. Global Navigation: The GPS system was designed to support various applications, including aviation, maritime navigation, land-based navigation, and timing synchronization for telecommunications and financial systems. A larger constellation of satellites supports these diverse needs.

9. Operational Flexibility: With 24 satellites, the GPS system can accommodate maintenance, replacement, and upgrades without significantly impacting the overall system's performance.

The choice of 24 satellites in the GPS constellation is a balance between providing global coverage, redundancy, accuracy, and operational feasibility. Each satellite is positioned in one of six orbital planes, and the system as a whole provides accurate and reliable positioning, navigation, and timing services that are used for a wide range of applications worldwide.