What is the inclination of the NAVSTAR GPS orbital planes?

• A. 28.5 degrees
• B. 33 degrees
• C. 55 degrees
• D. 90 degrees

Answer: (C)

Inclination is the tilt of the satellite’s orbital plane relative to the Earth’s equator. For NAVSTAR GPS, the six orbital planes are tilted about 55 degrees from the equator. This tilt makes the satellites’ ground tracks swing between roughly 55 degrees north and 55 degrees south, so from anywhere on Earth there are typically several satellites high enough in the sky to enable a reliable position fix with good geometry. A smaller tilt would limit visibility at higher latitudes, reducing accuracy for users near the poles, while a polar (90-degree) orbit would change the constellation’s geometry and generally require more satellites to maintain the same global performance. The 55-degree choice thus provides broad global coverage with efficient satellite use.