The Eccentricity of a satellite's orbit is defined as the ratio of the satellite orbit's focus distance (c) to the orbit's semi-major axis (a). It defines how elliptical (oval) the orbit is. Eccentricity is a unitless value. All of Earth's artificial satellites have orbit eccentricities of between 0 (perfectly circular orbit) and 1 (parabolic orbit). Within a TLE file, the eccentricity's decimal point is not present, but is always assumed to precede the first number. For the ISS TLE: "0007415" = 0.0007415 eccentricity, which implies a very nearly circular orbit shape. |
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Eccentricity Was Last Modified On May 23, 2010 |