Eccentricity vector

In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.wikipedia
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Kepler orbit

Keplerian orbitKeplerianKeplerian ellipse
In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.
For a "close to circular" orbit the concept "eccentricity vector" defined as is useful.

Osculating orbit

osculatingnon-Keplerianosculating elements
Its main use is in the analysis of almost circular orbits, as perturbing (non-Keplerian) forces on an actual orbit will cause the osculating eccentricity vector to change continuously.

Laplace–Runge–Lenz vector

Runge–Lenz vectorelsewhereLaplace-Runge-Lenz vector
The LRL vector has been re-discovered several times and is also equivalent to the dimensionless eccentricity vector of celestial mechanics.

Orbital eccentricity

eccentricityeccentriceccentricities
In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.
The eccentricity of an orbit can be calculated from the orbital state vectors as the magnitude of the eccentricity vector:

Argument of periapsis

argument of perihelionargument of perigeeargument of pericenter
For the eccentricity and argument of periapsis parameters, eccentricity zero (circular orbit) corresponds to a singularity.

Celestial mechanics

celestialcelestial dynamicscelestial mechanician
In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.

Dimensionless quantity

dimensionlessdimensionless numberdimensionless quantities
In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.

Euclidean vector

vectorvectorsvector addition
In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.

Apsis

perigeeperihelionapogee
In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.

Velocity

velocitiesvelocity vectorlinear velocity

Specific relative angular momentum

specific angular momentumangular momentum of planets and satellitesangular momentum per unit mass

Standard gravitational parameter

gravitational parametergeocentric gravitational constantheliocentric gravitational constant

Apse line

line of apsesline of apsidesline-of-apsides
An apse line, or line of apsides, is an imaginary line defined by an orbit's eccentricity vector.

Frozen orbit

frozenJ3 perturbationneeded an inclination of 63.4°
The perturbing force caused by the oblateness of the Earth will in general perturb not only the orbital plane but also the eccentricity vector of the orbit.

Perifocal coordinate system

Perifocal reference frames are most commonly used with elliptical orbits for the reason that the coordinate must be aligned with the eccentricity vector.