Which combination lists the four principal Earth orbits used in national security space operations?

• A. LEO, MEO, Sun-Synch, and GEO.
• B. Polar, equatorial, inclined, and stationary.
• C. Prograde, retrograde, elliptical, and circular.
• D. LEO, MEO, GEO, and HEO.

Answer: (D)

The main idea is that mission planners categorize Earth orbits by altitude bands and how the satellite moves around the planet. The four primary Earth orbits used in national security space operations are low Earth orbit for close, high-detail coverage; medium Earth orbit for longer visibility and broader reach; geostationary orbit for a fixed position over the same ground point, ideal for continuous communications and weather data; and highly elliptical orbit for very long dwell times over a target area due to a distant apogee. This combination—LEO, MEO, GEO, and HEO—captures the common orbit classes used to support a wide range of surveillance, communications, and reconnaissance roles. Other options mix modes or descriptors that aren’t the standard four orbit families, such as a specific imaging mission mode or orbital shapes and orientations that don’t define the main set used in national security planning.