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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.
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.
By contrast, subtracting equation (2) from equation (1) results in an equation that describes how the vector r = x 1 − x 2 between the masses changes with time. The solutions of these independent one-body problems can be combined to obtain the solutions for the trajectories x 1 ( t ) and x 2 ( t ) .
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.
A common problem in orbital mechanics is the following: Given a body in an orbit and a fixed original time , find the position of the body at some later time . For elliptical orbits with a reasonably small eccentricity, solving Kepler's Equation by methods like Newton's method gives excellent results.
In celestial mechanics, Lambert's problem is concerned with the determination of an orbit from two position vectors and the time of flight, posed in the 18th century by Johann Heinrich Lambert and formally solved with mathematical proof by Joseph-Louis Lagrange. It has important applications in the areas of rendezvous, targeting, guidance, and ...
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.
The problem of finding the separation of two bodies at a given time, given their separation and velocity at another time, is known as the Kepler problem. This section solves the Kepler problem for radial orbits. The first step is to determine the constant . Use the sign of to determine the orbit type.