At what altitude are Navy Navigational Satellite System (NNSS) satellites placed in a circular polar orbit?

The Navy Navigational Satellite System (NNSS) satellites are placed in a circular polar orbit at altitudes ranging from 500 to 700 nautical miles (NM). This altitude range is optimal for providing global coverage and maintaining a stable orbital path that allows the satellites to consistently provide navigation data to users on the surface.

In a polar orbit, satellites pass over the Earth's poles and can view the entire surface of the Earth over time as the planet rotates beneath them. The altitude of 500 to 700 NM is particularly effective for ensuring that the satellites can transmit their signals with minimal interference, allowing for accurate positioning and timing information essential for navigation purposes.

Other altitude choices, such as 400 NM or 800-1000 NM, do not reflect the operational specifications set for NNSS satellites. Altitudes below 500 NM may lead to a shorter satellite lifespan due to increased atmospheric drag, while altitudes above 700 NM could complicate signal strength and the latency of data transmission. Thus, the range of 500 to 700 NM is precisely chosen to balance satellite maintenance, data accuracy, and coverage efficiency.