ympyrärataa

Ympyrärata, or circular orbit, is the orbital path of a body around a central mass in which its distance from the center remains constant. In the standard two-body gravitational model, a circular orbit occurs when the inward gravitational force exactly provides the centripetal acceleration required for circular motion.

Key relations. For a body of mass m orbiting a central mass M, the gravitational force F = GMm/r^2 must equal m v^2 / r, giving v = sqrt(GM/r). The angular momentum per unit mass is h = r v = sqrt(GMr). The specific orbital energy is ε = -GM/(2r). The orbital period is T = 2πr / v = 2π sqrt(r^3/(GM)). A perfect circle has eccentricity e = 0; in practice, most orbits have small eccentricities and are nearly circular.

Occurrences and usage. Circular orbits describe natural planetary and satellite orbits that are nearly circular, and they are a common design target for artificial satellites because they simplify communications planning and provide stable coverage. The geostationary orbit is a well-known circular, equatorial orbit with a period equal to Earth's rotation.

In spaceflight, achieving a circular orbit requires precise velocity at insertion; perturbations from other bodies, atmospheric drag (in low orbits), and Earth's non-spherical mass distribution can cause gradual deviations, often corrected with orbit maintenance maneuvers.