Perifocal coordinate system
Encyclopedia
The perifocal frame is the two-dimensional frame of reference
for an orbit
. It is centered at the focus of the orbit, i.e. the planet
about which the orbit is centered. Its plane is given the coordinates p and q, where the p axis is directed toward the periapsis of the elliptical orbit (in the direction of the eccentricity vector
). The third dimension of this orbit, w, is composed of the normalized angular momentum
vector, which is the radius vector crossed
with the velocity vector.
Frame of reference
A frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer.It may also refer to both an...
for an orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
. It is centered at the focus of the orbit, i.e. the planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
about which the orbit is centered. Its plane is given the coordinates p and q, where the p axis is directed toward the periapsis of the elliptical orbit (in the direction of the eccentricity vector
Eccentricity vector
In astrodynamics, the eccentricity vector of a Kepler orbit is the vector pointing towards the periapsis having a magnitude equal to the orbit's scalar eccentricity. The magnitude is unitless. For Kepler orbits the eccentricity vector is a constant of motion...
). The third dimension of this orbit, w, is composed of the normalized angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
vector, which is the radius vector crossed
Dot product
In mathematics, the dot product or scalar product is an algebraic operation that takes two equal-length sequences of numbers and returns a single number obtained by multiplying corresponding entries and then summing those products...
with the velocity vector.
See also
- Celestial coordinate systemCelestial coordinate systemIn astronomy, a celestial coordinate system is a coordinate system for mapping positions on the celestial sphere.There are different celestial coordinate systems each using a system of spherical coordinates projected on the celestial sphere, in analogy to the geographic coordinate system used on...
- Polar distance (astronomy)Polar distance (astronomy)Polar distance is an astronomical term associated with the celestial equatorial coordinate system Σ and it is an angular distance of a celestial object on its meridian measured from the celestial pole, similar as declination is measured from the celestial equator:-Definition:Polar distace = 90°...
- Geocentric coordinatesGeocentric coordinatesGeocentric coordinates are an Earth-centered system of locating objects in the solar system in three-dimensions along the Cartesian X, Y and Z axes. They are differentiated from topocentric coordinates which use the observer's location as the reference point for bearings in altitude and azimuth...
- Heliocentric orbitHeliocentric orbitA heliocentric orbit is an orbit around the Sun. All planets, comets, and asteroids in our Solar System are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits as they orbit their respective planet...