Initialization

note

You are responsible for providing OMM or TLE. See Get orbital elements.

json2satrec - From OMM (preferred for new applications)

import { json2satrec, OMMJsonObject } from 'satellite.js';

const omm: OMMJsonObject = {
  "CCSDS_OMM_VERS":"3.0",
  "OBJECT_NAME": "HELIOS 2A",
  "OBJECT_ID": "2004-049A",
  "EPOCH": "2025-03-26T05:19:34.116960",
  "MEAN_MOTION": 15.00555103,
  "ECCENTRICITY": 0.000583,
  "INCLINATION": 98.3164,
  "RA_OF_ASC_NODE": 103.8411,
  "ARG_OF_PERICENTER": 20.5667,
  "MEAN_ANOMALY": 339.5789,
  "EPHEMERIS_TYPE": 0,
  "CLASSIFICATION_TYPE": "U",
  "NORAD_CAT_ID": 28492,
  "ELEMENT_SET_NO": 999,
  "REV_AT_EPOCH": 8655,
  "BSTAR": 0.00048021,
  "MEAN_MOTION_DOT": 0.00005995,
  "MEAN_MOTION_DDOT": 0
};

const satrec = json2satrec(omm);

Returns a SatRec object, created from a JSON object that follows OMM format (see Orbit Data Messages standard). OMM is a preferred default method for new applications.

The function implementation is a bit more relaxed on the precense of required fields according to the OMM standard. This is because Celestrak and Space-Track do not follow the standard precisely.

The function currently supports OMM format version 3 (this is actually the first production version; previous ones were testing). The function parameter, OMMJsonObject, is hence fairly strict.

twoline2satrec - From TLE

import { twoline2satrec } from 'satellite.js';

const tleLine1 = '1 25544U 98067A   19156.50900463  .00003075  00000-0  59442-4 0  9992',
      tleLine2 = '2 25544  51.6433  59.2583 0008217  16.4489 347.6017 15.51174618173442';

const satrec = twoline2satrec(tleLine1, tleLine2);

Returns a SatRec object, created from the TLEs passed in. tleLine1 and tleLine2 are the two lines of the TLE, properly formatted (careful with spaces!).

SatRec

The SatRec object is immense and complex; it contains are the Keplerian Elements and the other values pulled from the TLE/OMM, along with calculated values for SGP4 algorithm. While it is vastly complicated, for the basic usage you don't have to do anything with it, except pass it around to propagation functions and access the error property.

Key properties

SatRec has dozens of properties; for the full list please check the interface in your editor. Below are some of the most commonly accessed properties.

Property	Description
error	The error code that is set by SGP4 algorithm in case when propagation fails (see SatRecError)
satnum	Unique satellite identifier, usually NORAD number
epochyr	Full four-digit year of this element set's epoch moment
epochdays	Fractional days into the year of the epoch moment
jdsatepoch	Julian date of the epoch (computed from epochyr and epochdays)
ndot	First time derivative of the mean motion, in radians/minute²
nddot	Second time derivative of the mean motion, in radians/minute³
bstar	Ballistic drag coefficient B* in inverse earth radii
inclo	Inclination in radians
nodeo	Right ascension of ascending node in radians
ecco	Eccentricity
argpo	Argument of perigee in radians
mo	Mean anomaly in radians
no	Mean motion in radians per minute