Content deleted Content added
fix typo |
Alpha-5 format |
||
Line 1:
{{Short description|Orbital data format}}
A '''two-line element set''' ('''TLE''', or more rarely '''2LE''') or '''three-line element set''' ('''3LE''') is a [[file format|data format]] encoding a list of [[orbital elements]] of an Earth-orbiting object for a given point in time, the ''epoch''. Using a suitable prediction formula, the [[Orbital state vectors|state]] (position and velocity) at any point in the past or future can be estimated to some accuracy. The TLE data representation is specific to the [[simplified perturbations models]] (SGP, [[SGP4]], [[SDP4]], SGP8 and SDP8), so any algorithm using a TLE as a data source must implement one of the SGP models to correctly compute the state at a time of interest. TLEs can describe the trajectories only of Earth-orbiting objects. TLEs are widely used as input for projecting the future orbital tracks of [[space debris]] for purposes of characterizing "future debris events to support [[risk analysis]], close approach analysis, [[Collision avoidance (spacecraft)|collision avoidance]] maneuvering" and [[forensic analysis]].<ref name=aiaa2008>
{{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><ref name=":0">{{cite web |title=Space-Track.org Basic Description of the Two Line Element (TLE) Format |url=https://www.space-track.org/documentation#/tle |access-date=18 June 2025 |website=www.space-track.org |publisher=[[Combined Force Space Component Command]]
The format was originally intended for [[punch card|punched card]]s, encoding a set of elements on two [[punched card#IBM 80-column format and character codes|standard 80-column cards]]. This format was eventually replaced by [[text file]]s as punch card systems became obsolete, with each set of elements written to two 69-column [[ASCII]] lines preceded by a title line. The [[United States Space 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 websites Space Track and Celestrak,<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.
Line 30:
2 25544 51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537
The meaning of this data is as follows:<ref
===Title line (optional)===
Line 127:
The activation of the [[Space Fence]] in 2020 resulted in a great increase in the number of objects being tracked as the Space Fence's [[S-band]] RADAR is more sensitive than the radars used by the [[Air Force Space Surveillance System]] that previously had generated the raw data used for TLEs.<ref name="CelesTrak"/> The increase in the number of objects tracked meant that [[Satellite Catalog Number]]s may no longer fit in the five-digit field available in traditional TLEs. A secondary cause for the increase in Satellite Catalog Numbers was the commercialization of space and break-up events and collisions that have created debris objects.<ref name="CelesTrak"/> Adaptations of the TLE were considered to extend the number of encodable Satellites within the TLE but instead a new format, the [[CCSDS]] OMM (Orbit Mean-Elements Message), started being used in 2020 that supports nine-digit Satellite Catalog Numbers. The legacy TLE format will continue to use five-digit Satellite Catalog Numbers.<ref name="CelesTrak">{{Cite web|title=CelesTrak: A New Way to Obtain GP Data|url=https://celestrak.com/NORAD/documentation/gp-data-formats.php|access-date=2020-07-29|website=celestrak.com}}</ref>
As a stop-gap measure for systems which can only take in five characters for the Satellite Catalog number, the Space Force developed the "Alpha-5" numbering scheme, where the highest digit can be replaced with an alphabetical character to represent higher numbers from 100000–339999. The letters "I" and "O" are skipped to avoid confusion with the numbers "1" and "0". For example, the number 100000 can be represented as "A0000" in the Alpha-5 format, 110000 is represented by "B0000", up to the highest number 339999 which is represented as "Z9999". However, using the nine-digit Satellite Catalog number is preferred.<ref name=":0" />
==References==
| |||