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University of Nebraska–Lincoln

Remote Sensing Glossary

Reference Information for Virtual Nebraska

Terms, Definitions and Concepts


KSC (Kennedy Space Center)

See NASA Centers.

Keplerian elements (aka satellite orbital elements)

The set of six independent constants which define an orbit--named for Johannes Kepler [1571-1630]. The constants define the shape of an ellipse or hyperbola, orient it around its central body, and define the position of a satellite on the orbit. The classical orbital elements are:

p33a p33b
Kepler's three laws of motion

Any spacecraft launched into orbit obeys the same laws that govern the motions of the planets around our sun, and the moon around the Earth. Johannes Kepler formulated three laws that describe these motions:

p34a p34b
  1. Each planet revolves around the sun in an orbit that is an ellipse with the sun as its focus or primary body. Kepler postulated the lack of circular orbits--only elliptical ones--determined by gravitational perturbations and other factors. Gravitational pulls, according to Newton, extend to infinity, although their forces weaken with distance and eventually become impossible to detect. (See Newton's law of universal gravitation.) Spacecraft orbiting the Earth are primarily influenced by the Earth's gravity and anomalies in its composition, but they also are influenced by the moon and sun and possibly other planets.
  2. The radius vector--such as the line from the center of the sun to the center of a planet, from the center of Earth to the center of the moon, or from the center of Earth to the center of gravity of a satellite--sweeps out equal areas in equal periods of time.
  3. The square of a planet's orbital period is equal to the cube of its mean distance from the sun times a constant. As extended and generalized, this means that a satellite's orbital period increases with its mean distance from the planet. See Newton's law of universal gravitation and laws of motion.
kilometer (km)

Metric unit of distance equal to 3,280.8 feet or .621 statute miles.


Unit of speed of one nautical mile (6,076.1 feet) an hour.