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In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter (the combined center of mass) or, if one body is much more massive than the other bodies of the system combined, its speed relative to the center of mass of the most massive body.
Orbital position vector, orbital velocity vector, other orbital elements. In astrodynamics and celestial dynamics, the orbital state vectors (sometimes state vectors) of an orbit are Cartesian vectors of position and velocity that together with their time () uniquely determine the trajectory of the orbiting body in space.
The speed (or the magnitude of velocity) relative to the centre of mass is constant: [1]: 30 = = where: , is the gravitational constant, is the mass of both orbiting bodies (+), although in common practice, if the greater mass is significantly larger, the lesser mass is often neglected, with minimal change in the result.
The perifocal coordinate system can also be defined using the orbital parameters inclination (i), right ascension of the ascending node and the argument of periapsis (). The following equations convert from perifocal coordinates to equatorial coordinates and vice versa.
Orbital velocity may refer to the following: The orbital angular velocity; The orbital speed of a revolving body in a gravitational field. The velocity of particles due to wave motion, such as those in wind waves; The equivalent velocity of a bound electron needed to produce its orbital kinetic energy
For an elliptic orbit the specific orbital energy is the negative of the additional energy required to accelerate a mass of one kilogram to escape velocity (parabolic orbit). For a hyperbolic orbit , it is equal to the excess energy compared to that of a parabolic orbit.
Final v s, θ s and r must match the requirements of the target orbit as determined by orbital mechanics (see Orbital flight, above), where final v s is usually the required periapsis (or circular) velocity, and final θ s is 90 degrees. A powered descent analysis would use the same procedure, with reverse boundary conditions.
The orbital velocity of a body travelling along a parabolic trajectory can be computed as: = where: is the radial distance of the orbiting body from the central body,; is the standard gravitational parameter.