Knowra Vis-viva equation Vis-viva equation The vis-viva equation relates an orbiting body's speed to its distance from the central body, the orbit's semimajor axis, and the gravitational parameter.
Specific orbital energy : The mechanical energy of an orbiting body per unit mass, combining kinetic and gravitational potential energy. The equation expresses this conserved quantity through speed, radius, and semimajor axis.
Hohmann transfer orbit : An energy-efficient transfer between two circular, coplanar orbits using two engine burns. Vis-viva gives the speeds required at both ends of the transfer ellipse.
Orbital eccentricity : A dimensionless measure of how much an orbit departs from circular shape. Together with semimajor axis, it helps determine radius and speed around an ellipse.
Kepler's laws of planetary motion : Three laws describing planetary orbits, orbital areas, and the relation between period and orbit size. They describe orbital geometry and timing, while vis-viva specifies speed at a given radius.
Gravitational parameter : The product of a central body's gravitational constant and mass, commonly written μ. It sets the strength of gravity in the equation.
Orbital maneuver : A deliberate change to a spacecraft's trajectory, usually produced by thrust. Comparing vis-viva speeds before and after a maneuver estimates its velocity change.
True anomaly : The angle between an orbit's periapsis direction and an object's current position, measured at the central body. It locates the body along its orbit, where the equation gives its speed.
Orbital elements : A set of parameters that specifies the size, shape, orientation, and position of an orbit. Vis-viva uses only a subset of the information needed to define a complete orbit.
Semimajor axis : Half the longest diameter of an ellipse, defining its overall size. It determines the orbital energy and therefore the speed scale.
Escape velocity : The minimum speed needed to escape a body's gravitational field without further propulsion. It is the zero-energy boundary case of the vis-viva relation.
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