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# Words begining with "K"

## 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:

• a: semi-major axis, gives the size of the orbit
• e: eccentricity, gives the shape of the orbit
• i: inclination angle, gives the angle of the orbit plane to the central body's equator
• (Uppercase Omega): right ascension of the ascending node, which gives the rotation of the orbit plane from reference axis
• (Lowercase Omega): argument of perigee is the angle from the ascending nodes to perigee point, measured along the orbit in the direction of the satellites motion
• (Uppercase Theta): true anomaly gives the location of the satellite on the orbit.

## 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:

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 Newtons 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 Newtons law of universal qravitation and laws of motion.

## kilohertz (kHz)

One thousand hertz, i.e., one thousand cycles per second.

## Kilometer (km)

Metric unit of distance equal to 3,280.8 feet or 0.621 statute miles.

## Knot

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

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