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Two-line element set (TLE) data format parser

Two-line element set (TLE)

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Two-line element set (TLE) data format parser

A two-line element set (TLE) is a data format used to convey sets of orbital elements that describe the orbits of Earth-orbiting satellites. A computer program called a model can use the TLE to compute the position of a satellite at a particular time. The TLE is a format specified by NORAD and used by NORAD and NASA. The TLE can be used directly by the SGP4 model (or one of the SGP8, SDP4, SDP8 models). Orbital elements are determined for many thousands of space objects by NORAD and are freely distributed on the Internet in the form of TLEs. A TLE consists of a title line followed by two lines of formatted text.

— From Wikipedia

Install via npm

$ npm install --save tle


More, detailed information is available at NASA Human Space Flight:

Definition of Two-line Element Set Coordinate System

Some data to play around with can be found at Celestrak and in Celestrak's Master Index.


var TLE = require( 'tle' )

Parsing a single set

var set = 'ISS (ZARYA)\n' +
  '1 25544U 98067A   08264.51782528 -.00002182  00000-0 -11606-4 0  2927\n' +
  '2 25544  51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537'
var tle = TLE.parse( set )
  name: 'ISS (ZARYA)',
  number: 25544,
  class: 'U',
  id: '98067A',
  date: Date<'2008-09-20T12:25:40.104Z'>,
  fdmm: -0.00002182,
  sdmm: 0,
  drag: -1.1606,
  ephemeris: 0,
  esn: 292,
  inclination: 51.6416,
  ascension: 247.4627,
  eccentricity: 0.0006703,
  perigee: 130.536,
  anomaly: 325.0288,
  motion: 15.721253915,
  revolution: 6353

Parsing a stream

var parser = new TLE.Parser( options ) // OR 
var parser = TLE.createParser( options )
fs.createReadStream( FILEPATH )
  .pipe( new TLE.Parser() )
  .on( 'data', function( tle ) {
    // ... 

Creating a TLE instance from existing data

// From a JSON string 
var tle = TLE.fromJSON( '{"name":"ISS (ZARYA)","number":25544,"class":"U","id":"98067A","date":"2008-09-20T12:25:40.104Z","fdmm":-0.00002182,"sdmm":0,"drag":-1.1606,"ephemeris":0,"esn":292,"inclination":51.6416,"ascension":247.4627,"eccentricity":0.0006703,"perigee":130.536,"anomaly":325.0288,"motion":15.721253915,"revolution":6353}' )
// From an object 
var tle = TLE.fromJSON({
  name: 'FENGYUN 1C DEB',
  class: 'U',
  id: '29740',


It can read, stream & parse ~2500 TLEs from the file system in about 100ms.

node example/fs-stream.js
Parser: 2517 TLEs, 108ms, 23306 op/s
Parser: 23 op/ms


See examples folder for runnable examples:

node examples/fs-stream.js
node examples/http-stream.js