For a detailed introduction to spaceflight, I recommend the NASA/JPL Basics of Space Flight.
- Ground track
- The satellite track in orbit, traced on the surface of the Earth is termed the satellite
- Satellite footprint or coverage
- The coverage circle or footprint is the area on the Earth from where the satellite is
- Prograde and Retrograde orbits
- The rotation sense of the satellite in the orbit is referenced with respect to the
rotation of the Earth. Satellites with inclination angles up to 90 degrees are termed
prograde, and those with larger inclination angles retrograde. Launchers make use of the
rotational speed of the Earth when launching into prograde orbits, and for retrograde
missions more fuel must be carried to counter this initial velocity.
- Equatorial orbit
- An orbit with a low inclination, or angle between the orbital plane and equatorial
plane. This type of orbit is ideal for frequent coverage of the equatorial regions, but
for Low Earth Orbit equatorial orbits the satellite coverage circle is limited, and higher
latitudes can not be covered.
- Polar orbit
- A polar orbit is inclined at about 90 degrees to the equatorial plane, covering both
poles. The orbit is inertially fixed in space, and the Earth rotates underneath. For a Low
Earth Orbit, the entire globe is covered. Consequently this orbit is ideal for
communications and mapping missions.
- Sun-synchronous orbit
- A Sun-synchronous or helio-synchronous orbit is a special form of Low Earth polar Orbit,
where the angle between the orbital plane and Sun remains constant. This is achieved by
careful choice of orbital height, eccentricity and inclination. This type of orbit is
favoured by many weather and Earth Observation satellites, as it provides constant
- Geosynchronous orbit
- A geo-synchronous orbit has an orbital period that is an integer multiple or
sub-multiple of the Earth's rotation rate, resulting in a repeating ground track.
- Geostationary orbit (GEO)
- If a satellite is placed in a circular prograde equatorial orbit, and the height is
chosen such that the orbital period is equal to that of the Earth, then the satellite will
appear fixed above the Earth's surface. The required orbital height is about 36786km,
which gives a footprint covering almost 1/3 of the Earth's surface. In practice a
Geostationary orbit has small non-zero inclination and eccentricity, causing the satellite
to trace out a small figure of eight in the sky.