Two-line element set: Difference between revisions

Revision as of 10:52, 31 January 2021

Revision as of 08:43, 23 February 2021

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{{cite journal |last1=Carrico |first1=Timothy |last2=Carrico |first2=John |last3=Policastri |first3=Lisa |last4=Loucks |first4=Mike |title=Investigating Orbital Debris Events using Numerical Methods with Full Force Model Orbit Propagation |journal=American Institute of Aeronautics and Astronautics |date=2008 |issue=AAS 08–126 |url=http://www.applieddefense.com/wp-content/uploads/2012/12/2008-Carrico-Policastri-Investigating_Orbital_Debris_Events.pdf |url-status=dead |archive-url=https://web.archive.org/web/20141204122502/http://www.applieddefense.com/wp-content/uploads/2012/12/2008-Carrico-Policastri-Investigating_Orbital_Debris_Events.pdf |archive-date=2014-12-04 }}</ref>

The format was originally intended for [[punch card]]s, encoding a set of elements on two [[Punched_card#IBM_80-column_punched_card_format_and_character_codes|standard 80-column cards]]. This format was eventually replaced by [[text file]]s{{when|date=June 2019}} with each set of elements written to two 7069-column [[ASCII]] lines. The [[United States Air Force]] tracks all detectable objects in Earth orbit, creating a corresponding TLE for each object, and makes publicly available TLEs for many of the space objects on the website Space Track,<ref>{{cite web|url=https://www.space-track.org/|title=Introduction and sign in to Space-Track.Org|publisher=Space-track.org|access-date=28 November 2014}}</ref><ref>{{cite web|url=http://celestrak.com/|title=Celestrak homepage|publisher=Celestrak.com|access-date=28 November 2014}}</ref> holding back or obfuscating data on many military or [[Classified information|classified objects]]. The TLE format is a ''de facto'' standard for distribution of an Earth-orbiting object's orbital elements.

A TLE set may include a title line preceding the element data, so each listing may take up three lines in the file. The title is not required, as each data line includes a unique object identifier code.

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The internal format used three 80-column punch cards. Each card started with a card number, 1, 2 or 3, and ended with the letter "G". For this reason, the system was often known as the "G-card format". In addition to the orbital elements, the G-card included various flags like the launching country and orbit type (geostationary, etc.), calculated values like the [[perigee]] altitude and visual magnitude, and a 38-character comments field.

The transmission format is essentially a cut-down version of the G-card format, removing any data that is not subject to change on a regular basis, or data that can be calculated using other values. For instance, the perigee altitude from the G-card is not included as this can be calculated from the other elements. What remains is the set of data needed to update the original G-card data as additional measurements are made. The data is fit into 7069 columns and does not include a trailing character. TLEs are simply the transmission format data rendered as ASCII text.

An example TLE for the [[International Space Station]]: