How many orbital planes does the NAVSTAR GPS constellation use?

• A. 4
• B. 6
• C. 8
• D. 12

Answer: (B)

The idea being tested is how a satellite navigation system structures its constellation to ensure global coverage. NAVSTAR GPS uses six orbital planes. These planes are equally spaced around the Earth, each inclined about 55 degrees to the equator. With roughly four satellites in each plane, the system totals about 24 satellites. This arrangement guarantees that from any location, enough satellites are visible at once to compute a precise position and time, even as satellites move along their orbits. Five or fewer planes would leave gaps in coverage or poorer geometry for many locations, while more planes would add complexity without needing more satellites to meet navigation needs.