The North American Aerospace Defense Command (NORAD) developed the Two-Line Element (TLE) format for transmitting satellite Keplerian elements.
This is a structured format intended to be very compact.
It is, therefore, difficult to read unless you are familiar with the structure. Hence, the purpose of this page is to define the components of this structure as defined below.
United States Space Command (USSPACECOM) computes most of the publicly-available TLEs.
These data are released by NASA Goddard Space Flight Center (GSFC). In order to get accurate orbital predictions, you need to use the either USSPACECOM Simplified General
Perturbations (SGP) or the SGP Version 4 (SGP4)
orbit propagator. Using even an inherently more accurate prediction model will get degraded predictions because the TLEs released by GSFC are "mean" Keplerian elements produced by removing the long- and short-term periodic variations in a particular way. Complete details of the SGP/SGP4 orbit propagators are in Project Space Track, Models for the Propagation of NORAD Element Sets, Felix R. Hoots and Ronald L Roehrich, Spacetrack Report No. 3, December 1980. This
report is in Adobe Acrobat Portable Document Format (PDF). You can download the free Acrobat Reader software from the Adobe Web site.
The physical significance of each Keplerian orbital parameter is illustrated on the Orbital Description page.