text: Chapter 1
  and may also include satellite payload signals such as the SATCOM signal enabling
  communication between points on the ground, or the PNT signal enabling navigation.
  1-57. Military activities are conducted in the space domain to achieve national security objectives. Space
  operations are generally supported in some way by satellites in orbit around the Earth. The space domain is
  interrelated with the other domains and properly integrating these complex functions with the other military
  activities is critical for successful operations.
  ORBITAL CHARACTERISTICS
  1-58. The unique operating parameters of sensors on space-based assets are a function of orbital
  characteristics, not the sensors. A space-based asset may have frequent revisit rates or long dwell times, but
  never both. Different orbits are conducive to different missions and support different operations. Inclination
  is the degrees an orbital plane is angled relative to the equatorial plane—an orbit with zero inclination orbits
  over the equator. Higher inclinations provide more northern/southern ground coverage. Satellite orbits are
  grouped into general categories defined by their altitude above the Earth and the shape of the orbit. The four
  primary orbit types are briefly discussed and illustrated in figure 1-2.
  * Low Earth orbit (LEO)—up to 1,600 kilometers (km) (1,000 miles) above the surface of the Earth.
  Satellites in this orbit are close to the Earth and move quickly relative to the ground.
  * Medium Earth orbit (known as MEO)—any orbital asset above LEO and below geosynchronous
  Earth orbit (GEO). This orbit is most frequently associated with GPS, which operates at
  approximately 19,300 km (12,000 miles) above Earth’s surface. Satellites in this orbit can provide
  SATCOM with less signal delay, higher capacities, and may support resilient operations.
  * GEO—an orbit approximately 37,000 km (22,300 miles) above the Earth where a satellite circles
  the Earth once every 24 hours, keeping pace with the Earth’s rotation. A geosynchronous orbit
  with inclination other than zero will trace a figure 8 over to the surface of the Earth, centered on
  the equator. A geosynchronous orbit with inclination equal to zero is called a geostationary orbit.
  This orbit hovers over one point on the surface of the Earth, directly over the equator.
  * Highly elliptical orbit. These orbits are oval-shaped with the Earth offset to one end. A satellite’s
  altitude typically ranges from 1,000 km (600 miles) above the Earth at perigee (point closest to
  Earth), to about 40,000 km (25,000 miles) at apogee (point farthest from Earth) where it has a
  long dwell time over a large area. The highly elliptical orbit is inclined from the equatorial plane
  so a satellite may dwell for long periods over latitudes where GEO do not have coverage.
  Figure 1-2: Illustration of basic satellite orbits