Modern global navigation services use orbiting satellites to meet many demands.
Positioning information must be available all the time, regardless of time of day, weather conditions, or other factors.
Services must be available anywhere in the world, so satellites need to be visible anywhere on Earth and their orbits must be carefully tracked.
Precise positions need to be determined to identify tiny land features, locate individual structures, and allow vehicles, ships, and aircraft to avoid hazards.
Equipment used on Earth must be small and portable, requiring satellites to operate precise time and data systems in the harsh environment of space.
Positions must be determined quickly, without requiring users to receive extensive training or perform multiple steps.