Added function json2satrec in io.js

src/constants.js

@@ -13,3 +13,4 @@ export const j3 = -0.00000253881;
 export const j4 = -0.00000165597;
 export const j3oj2 = j3 / j2;
 export const x2o3 = 2.0 / 3.0;
+export const xpdotp = 1440.0 / (2.0 * pi); // 229.1831180523293;

src/index.js

@@ -1,7 +1,7 @@
 import * as constants from './constants';
 
 import { jday, invjday } from './ext';
-import twoline2satrec from './io';
+import { twoline2satrec, json2satrec} from './io';
 import { propagate, sgp4, gstime } from './propagation';
 
 import dopplerFactor from './dopplerFactor';
@@ -20,13 +20,16 @@ import {
   ecfToLookAngles,
 } from './transforms';
 
+import { sunPos } from './sun';
+
 export {
   constants,
 
   // Propagation
   propagate,
   sgp4,
   twoline2satrec,
+  json2satrec,
 
   gstime,
   jday,
@@ -46,4 +49,7 @@ export {
   eciToEcf,
   ecfToEci,
   ecfToLookAngles,
+
+  // Sun Position
+  sunPos,
 };

src/indexUmd.js

@@ -1,7 +1,7 @@
 import * as constants from './constants';
 
 import { jday, invjday } from './ext';
-import twoline2satrec from './io';
+import { twoline2satrec, json2satrec} from './io';
 import { propagate, sgp4, gstime } from './propagation';
 
 import dopplerFactor from './dopplerFactor';
@@ -27,6 +27,7 @@ export default {
   propagate,
   sgp4,
   twoline2satrec,
+  json2satrec,
 
   gstime,
   jday,

src/io.js

@@ -1,12 +1,12 @@
-import { pi, deg2rad } from './constants';
+import { deg2rad, xpdotp } from './constants';
 
 import { jday, days2mdhms } from './ext';
 
 import sgp4init from './propagation/sgp4init';
 
 /* -----------------------------------------------------------------------------
  *
- *                           function twoline2rv
+ *                           function twoline2satrec
  *
  *  this function converts the two line element set character string data to
  *    variables and initializes the sgp4 variables. several intermediate varaibles
@@ -59,9 +59,8 @@ import sgp4init from './propagation/sgp4init';
  * to the algorithm.  If you want to turn some of these off and go
  * back into "afspc" mode, then set `afspc_mode` to `True`.
  */
-export default function twoline2satrec(longstr1, longstr2) {
+export function twoline2satrec(longstr1, longstr2) {
   const opsmode = 'i';
-  const xpdotp = 1440.0 / (2.0 * pi); // 229.1831180523293;
   let year = 0;
 
   const satrec = {};
@@ -146,3 +145,93 @@ export default function twoline2satrec(longstr1, longstr2) {
 
   return satrec;
 }
+
+/* -----------------------------------------------------------------------------
+ *
+ *                           function json2satrec
+ *
+ *  this function converts the OMM json data to variables and initializes the sgp4 
+ *    variables. several intermediate varaibles and quantities are determined. note 
+ *    that the result is a structure so multiple satellites can be processed 
+ *    simultaneously without having to reinitialize. the verification mode is an 
+ *    important option that permits quick checks of any changes to the underlying 
+ *    technical theory. this option works using a modified tle file in which the 
+ *    start, stop, and delta time values are included at the end of the second line
+ *    of data. this only works with the verification mode. the catalog mode simply 
+ *    propagates from -1440 to 1440 min from epoch and is useful when performing 
+ *    entire catalog runs.
+ *
+ *  author        : Hariharan Vitaladevuni                   18 Aug 2023
+ *                  Theodore Kruczek                         19 Aug 2023
+ *
+ *  inputs        :
+ *    jsonobj     - OMM json data
+ *    opsmode     - mode of operation afspc or improved 'a', 'i'. Default: 'i'.
+ *
+ *  outputs       :
+ *    satrec      - structure containing all the sgp4 satellite information
+ *
+ *  coupling      :
+ *    days2mdhms  - conversion of days to month, day, hour, minute, second
+ *    jday        - convert day month year hour minute second into julian date
+ *    sgp4init    - initialize the sgp4 variables
+ * 
+ *  warning       : the epoch date in OMM format is more accurate than TLE format!
+ *                  this will result in extremely close, but different 
+ *                  position/velocity values. Depending on your use case, it may
+ *                  be better to use twoline2satrec, but for the average user this
+ *                  will provide comparable results.
+ *
+ *  references    :
+ *    https://celestrak.org/NORAD/documentation/gp-data-formats.php
+ --------------------------------------------------------------------------- */
+export function json2satrec(jsonobj, opsmode = 'i') {
+  const satrec = {};
+  satrec.error = 0;
+
+  satrec.satnum = jsonobj.NORAD_CAT_ID.toString().padStart(5, '0');
+
+  const epoch = new Date(jsonobj.EPOCH + 'Z');
+  const year = epoch.getUTCFullYear();
+
+  satrec.epochyr = Number(year.toString().slice(-2));
+  satrec.epochdays =
+    (epoch - new Date(Date.UTC(year, 0, 1, 0, 0, 0))) / (86400 * 1000) + 1;
+
+  satrec.ndot = jsonobj.MEAN_MOTION_DOT;
+  satrec.nddot = jsonobj.MEAN_MOTION_DDOT;
+  satrec.bstar = jsonobj.BSTAR;
+
+  satrec.inclo = jsonobj.INCLINATION * deg2rad;
+  satrec.nodeo = jsonobj.RA_OF_ASC_NODE * deg2rad;
+  satrec.ecco = jsonobj.ECCENTRICITY;
+  satrec.argpo = jsonobj.ARG_OF_PERICENTER * deg2rad;
+  satrec.mo = jsonobj.MEAN_ANOMALY * deg2rad;
+  satrec.no = jsonobj.MEAN_MOTION / xpdotp;
+
+  // ----------------------------------------------------------------
+  // find sgp4epoch time of element set
+  // remember that sgp4 uses units of days from 0 jan 1950 (sgp4epoch)
+  // and minutes from the epoch (time)
+  // ----------------------------------------------------------------
+  const mdhmsResult = days2mdhms(year, satrec.epochdays);
+
+  const { mon, day, hr, minute, sec } = mdhmsResult;
+  satrec.jdsatepoch = jday(year, mon, day, hr, minute, sec);
+
+  //  ---------------- initialize the orbit at sgp4epoch -------------------
+  sgp4init(satrec, {
+    opsmode,
+    satn: satrec.satnum,
+    epoch: satrec.jdsatepoch - 2433281.5,
+    xbstar: satrec.bstar,
+    xecco: satrec.ecco,
+    xargpo: satrec.argpo,
+    xinclo: satrec.inclo,
+    xmo: satrec.mo,
+    xno: satrec.no,
+    xnodeo: satrec.nodeo,
+  });
+
+  return satrec;
+}

src/sun.js

@@ -0,0 +1,145 @@
+import { deg2rad, twoPi } from './constants';
+
+////////////////////////////////////////////////////////////////////////////////////
+/* Line by Line MATLAB-to-Javascript conversion of "sun.mat" from Vallado package */
+////////////////////////////////////////////////////////////////////////////////////
+/* -----------------------------------------------------------------------------
+ *
+ *                              function sunPos
+ *
+ *  this function calculates the geocentric equatorial position vector
+ *      the sun given the julian date.  this is the low precision formula and
+ *      is valid for years from 1950 to 2050.  accuaracy of apparent coordinates
+ *      is 0.01  degrees.  notice many of the calculations are performed in
+ *      degrees, and are not changed until later.  this is due to the fact that
+ *      the almanac uses degrees exclusively in their formulations.
+ * 
+ *  author        : david vallado                  719-573-2600    1 mar 2001
+ * 
+ *  inputs          description                       range / units
+ *      jd          - julian date                       days from 4713 bc
+ * 
+ *  outputs       :
+ *      rsun        - ijk position vector of the sun    au
+ *      rtasc       - right ascension                   rad
+ *      decl        - declination                       rad
+ * 
+ *  coupling      :
+ *      -
+ * 
+ *  references    :
+ *      VALLADO, DAVID A. (2022) ‘Computer software in MATLAB’, in Fundamentals of astrodynamics and applications. 5th edn.
+ *      Computer software in MATLAB: http://celestrak.org/software/vallado-sw.php 
+ *  --------------------------------------------------------------------------- */
+
+export function sunPos(jd) {
+
+    // -------------------------  implementation   -----------------
+    // -------------------  initialize values   --------------------
+    const tut1 = ( jd - 2451545.0  ) / 36525.0;
+
+    const meanlong = (280.460  + 36000.77 * tut1) % 360.0; //deg
+
+    const ttdb = tut1; // is this declaration required instead of replacing `ttdb` with `tut1`
+
+    if (meananomaly < 0.0 ) {
+        const meananomaly = twoPi + ((357.5277233  + 35999.05034 * ttdb) * deg2rad) % twoPi; //rad;
+    } else {
+        const meananomaly = ((357.5277233  + 35999.05034 * ttdb) * deg2rad) % twoPi; //rad;
+    }
+
+    const eclplong_raw = ((meanlong + 1.914666471 * Math.sin(meananomaly) + 0.019994643 * Math.sin(2.0 * meananomaly)) % 360.0) * deg2rad; //rad
+
+    const obliquity = (23.439291 - 0.0130042 * ttdb) * deg2rad; //rad
+
+    // --------- find magnitude of sun vector, and it's components ------
+    const magr = 1.000140612  - 0.016708617 * Math.cos( meananomaly ) - 0.000139589 * Math.cos( 2.0 * meananomaly ); // in au's
+
+    const rsun = [
+        magr*Math.cos(eclplong_raw), 
+        magr*Math.cos(obliquity)*Math.sin(eclplong_raw), 
+        magr*Math.sin(obliquity)*Math.sin(eclplong_raw)
+    ];
+
+    const rtasc_raw = Math.atan( Math.cos(obliquity) * Math.tan(eclplong_raw) );
+
+    // --- check that rtasc is in the same quadrant as eclplong_raw ----
+    if ( eclplong_raw < 0.0  ) {
+        const eclplong = eclplong_raw + twoPi;    // make sure it's in 0 to 2pi range
+    } else {
+        const eclplong = eclplong_raw;
+    }
+
+    if ( Math.abs( eclplong_raw - rtasc_raw ) > pi*0.5  ) {
+        const rtasc = rtasc_raw + 0.5 *pi*Math.round( (eclplong_raw - rtasc_raw)/(0.5 *pi));
+    } else {
+        const rtasc = rtasc_raw;
+    }
+
+    const decl = Math.asin( Math.sin(obliquity) * Math.sin(eclplong_raw) );
+
+    return {rsun, rtasc, decl}
+  }
+
+
+  /* Original MATLAB code for Sun position from Vallado package (sun.mat)  */
+  /*
+  function [rsun,rtasc,decl] = sun ( jd );
+
+          twopi      =     2.0*pi;
+          deg2rad    =     pi/180.0;
+          show = 'n';
+
+          % -------------------------  implementation   -----------------
+          % -------------------  initialize values   --------------------
+          tut1= ( jd - 2451545.0  )/ 36525.0;
+
+          if show == 'y'
+              fprintf(1,'tut1 %14.9f \n',tut1);
+          end
+
+          meanlong= 280.460  + 36000.77*tut1;
+          meanlong= rem( meanlong,360.0  );  %deg
+
+          ttdb= tut1;
+          meananomaly= 357.5277233  + 35999.05034 *ttdb;
+          meananomaly= rem( meananomaly*deg2rad,twopi );  %rad
+          if ( meananomaly < 0.0  )
+              meananomaly= twopi + meananomaly;
+          end
+
+          eclplong_raw= meanlong + 1.914666471 *sin(meananomaly) ...
+                      + 0.019994643 *sin(2.0 *meananomaly); %deg
+          eclplong_raw= rem( eclplong_raw,360.0  );  %deg
+
+          obliquity= 23.439291  - 0.0130042 *ttdb;  %deg
+
+          eclplong_raw = eclplong_raw *deg2rad;
+          obliquity= obliquity *deg2rad;
+
+          % --------- find magnitude of sun vector, )   components ------
+          magr= 1.000140612  - 0.016708617 *cos( meananomaly ) ...
+                                - 0.000139589 *cos( 2.0 *meananomaly );    % in au's
+
+          rsun(1)= magr*cos( eclplong_raw );
+          rsun(2)= magr*cos(obliquity)*sin(eclplong_raw);
+          rsun(3)= magr*sin(obliquity)*sin(eclplong_raw);
+
+          if show == 'y'
+              fprintf(1,'meanlon %11.6f meanan %11.6f eclplon %11.6f obli %11.6f \n', ...
+                      meanlong,meananomaly/deg2rad,eclplong_raw/deg2rad,obliquity/deg2rad);
+              fprintf(1,'rs %11.9f %11.9f %11.9f \n',rsun);
+              fprintf(1,'magr %14.7f \n',magr);
+          end
+
+          rtasc= atan( cos(obliquity)*tan(eclplong_raw) );
+
+          % --- check that rtasc is in the same quadrant as eclplong_raw ----
+          if ( eclplong_raw < 0.0  )
+              eclplong_raw= eclplong_raw + twopi;    % make sure it's in 0 to 2pi range
+          end
+          if ( abs( eclplong_raw-rtasc ) > pi*0.5  )
+              rtasc= rtasc + 0.5 *pi*round( (eclplong_raw-rtasc)/(0.5 *pi));
+          end
+          decl = asin( sin(obliquity)*sin(eclplong_raw) );
+  */

test/ext.test.js

@@ -1,7 +1,7 @@
 import compareVectors from './compareVectors';
 
 import { jday, invjday } from '../src/ext';
-import twoline2satrec from '../src/io';
+import { twoline2satrec } from '../src/io';
 import { propagate, gstime } from '../src/propagation';
 
 describe('Julian date / time', () => {

test/index.test.js

@@ -17,7 +17,7 @@ import {
 } from '../src/constants';
 
 import { jday, invjday } from '../src/ext';
-import twoline2satrec from '../src/io';
+import { twoline2satrec, json2satrec } from '../src/io';
 import { propagate, sgp4, gstime } from '../src/propagation';
 
 import dopplerFactor from '../src/dopplerFactor';
@@ -74,6 +74,7 @@ function checkTransforms(transforms) {
 function checkExports(namespace) {
   it('constants', () => checkConstants(namespace.constants));
   it('twoline2satrec', () => expect(namespace.twoline2satrec).toEqual(twoline2satrec));
+  it('json2satrec', () => expect(namespace.json2satrec).toEqual(json2satrec));
   it('propagate', () => expect(namespace.propagate).toEqual(propagate));
   it('sgp4', () => expect(namespace.sgp4).toEqual(sgp4));
   it('gstime', () => expect(namespace.gstime).toEqual(gstime));

test/io-edge.json

@@ -0,0 +1,34 @@
+[
+  {
+    "tleLine1": "1 00001U 57001B   21005.53831292 -.00000083  00000-0 -11575-3 0  9996",
+    "tleLine2": "2 00001  34.2508 325.6936 1846988 181.8107 177.4919 00.00000000227203",
+    "description": "Mean motion is zero and that is not allowed.",
+    "results": [{
+      "error": 2
+    }]
+  },
+  {
+    "tleLine1": "1 00002U 57001B   21005.53831292 -.00000083  00000-0 -11575-3 0  9996",
+    "tleLine2": "2 00002  34.2508 325.6936 1846988 181.8107 177.4919 00.00000001227203",
+    "description": "Eccentricity is way too high because mean motion is nearly zero.",
+    "results": [{
+      "error": 3
+    }]
+  },
+  {
+    "tleLine1": "1 00004U 57001B   21005.53831292 -.00000083  00000-0 -11575-3 0  9996",
+    "tleLine2": "2 00004  34.2508 325.6936 9999999 181.8107 177.4919 10.84863720227203",
+    "description": "Eccentricity is way too high.",
+    "results": [{
+      "error": 4
+    }]
+  },
+  {
+    "tleLine1": "1 00006U 57001B   21005.53831292 -.00000083  00000-0 -11575-3 0  9996",
+    "tleLine2": "2 00005  34.2508 325.6936 1846988 181.8107 177.4919 25.84863720227203",
+    "description": "Satellite should be decayed already.",
+    "results": [{
+      "error": 6
+    }]
+  }
+]