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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.
In astrodynamics, the vis-viva equation is one of the equations that model the motion of orbiting bodies.It is the direct result of the principle of conservation of mechanical energy which applies when the only force acting on an object is its own weight which is the gravitational force determined by the product of the mass of the object and the strength of the surrounding gravitational field.
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.
where is the orbital velocity when the orbital distance tends to infinity. Note that, since the kinetic energy is 1 2 m v 2 {\textstyle {\frac {1}{2}}mv^{2}} , C 3 is in fact equal to twice the magnitude of the specific orbital energy , ϵ {\textstyle \epsilon } , of the escaping object.
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.
In astrodynamics, an orbit equation defines the path of orbiting body around central body relative to , without specifying position as a function of time.Under standard assumptions, a body moving under the influence of a force, directed to a central body, with a magnitude inversely proportional to the square of the distance (such as gravity), has an orbit that is a conic section (i.e. circular ...
The orbital state vectors have now been found, the position (r 2) and velocity (v 2) vector for the second observation of the orbiting body. With these two vectors, the orbital elements can be found and the orbit determined.
Early results about relative orbital motion were published by George William Hill in 1878. [3] Hill's paper discussed the orbital motion of the moon relative to the Earth.. In 1960, W. H. Clohessy and R. S. Wiltshire published the Clohessy–Wiltshire equations to describe relative orbital motion of a general satellite for the purpose of designing control systems to achieve orbital rendezvous.