Orbital Eccentricity

Orbital eccentricity (e) is a dimensionless number that describes the shape of an orbit. A value of 0 is a perfect circle, values between 0 and 1 are ellipses, exactly 1 is a parabolic trajectory (escape), and values above 1 are hyperbolic. The ISS has an eccentricity of 0.0001 (nearly circular). GEO satellites are also nearly circular (e ≈ 0). Molniya orbits have high eccentricity (0.74). In TLE format, eccentricity is encoded as a decimal with an implied leading "0." — so "0001411" means e = 0.0001411.