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Once the TLE data has been loaded, is there a way to retreive the TLEs for use in sgp4?

See original GitHub issue

What is the procedure to extract the individual TLEs using Skyfield for input into sgp4? I’ve been able to get Skyfield to load the data from Celestrack, but I’m having difficulty extracting the individual TLEs. The code I’m using follows.

from skyfield.api import Topos, load

import numpy    as np
import spiceypy

from datetime import datetime, timedelta
from sgp4.earth_gravity import wgs84
from sgp4.io import twoline2rv

# --------------------------------------------------------------------------
# --------------------------------------------------------------------------

stations_url = 'https://celestrak.com/satcat/tle.php?INTDES=1987%2D060'
TLEs = load.tle_file(stations_url)
print('Loaded', len(TLEs), 'satellites')

# --------------------------------------------------------------------------
# --------------------------------------------------------------------------

satnum_list = open('COSMOS_1867_Coolant_IDs.dat', 'r')

# --------------------------------------------------------------------------
# --------------------------------------------------------------------------

for satnum in satnum_list:
     by_number = {sat.model.satnum: sat for sat in TLEs}
     sat = by_number[int(satnum)]
     print(sat, sat.epoch.utc_jpl())

# --------------------------------------------------------------------------
# --------------------------------------------------------------------------

for line1, line2, line3 in TLEs:
     print(line1)
     print(line2)
     print(line3)

The resulting output follows.


================================================================================
July 23, 2020 at 04:12:30
~/COSMOS_1867_Coolant/skyfield_satcat.py
--------------------------------------------------------------------------------
Loaded 41 satellites
EarthSatellite 'COSMOS 1867' number=18187 epoch=2020-07-22T12:55:48Z A.D. 2020-Jul-22 12:55:47.6259 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39637 epoch=2020-07-22T08:19:57Z A.D. 2020-Jul-22 08:19:56.8039 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39638 epoch=2020-07-22T20:59:31Z A.D. 2020-Jul-22 20:59:30.9281 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39639 epoch=2020-07-22T08:42:26Z A.D. 2020-Jul-22 08:42:26.1680 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39640 epoch=2020-07-22T12:45:25Z A.D. 2020-Jul-22 12:45:24.5385 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39641 epoch=2020-07-22T12:43:18Z A.D. 2020-Jul-22 12:43:17.5486 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39642 epoch=2020-07-22T17:18:51Z A.D. 2020-Jul-22 17:18:51.3386 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39643 epoch=2020-07-22T20:35:18Z A.D. 2020-Jul-22 20:35:18.2633 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39644 epoch=2020-07-22T17:04:00Z A.D. 2020-Jul-22 17:03:59.8202 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39645 epoch=2020-07-19T00:04:25Z A.D. 2020-Jul-19 00:04:25.1339 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39646 epoch=2020-07-22T21:03:13Z A.D. 2020-Jul-22 21:03:13.4600 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39647 epoch=2020-07-22T21:15:30Z A.D. 2020-Jul-22 21:15:30.3345 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39654 epoch=2020-07-21T12:44:35Z A.D. 2020-Jul-21 12:44:35.1626 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39655 epoch=2020-07-22T16:57:59Z A.D. 2020-Jul-22 16:57:59.3948 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39656 epoch=2020-07-22T20:48:43Z A.D. 2020-Jul-22 20:48:42.5583 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39657 epoch=2020-07-22T20:46:58Z A.D. 2020-Jul-22 20:46:58.4187 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39658 epoch=2020-07-22T18:29:34Z A.D. 2020-Jul-22 18:29:34.4875 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39659 epoch=2020-07-22T12:50:08Z A.D. 2020-Jul-22 12:50:08.4135 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39660 epoch=2020-07-22T18:33:18Z A.D. 2020-Jul-22 18:33:17.5421 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39661 epoch=2020-07-22T06:30:46Z A.D. 2020-Jul-22 06:30:45.6794 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39662 epoch=2020-07-22T20:55:29Z A.D. 2020-Jul-22 20:55:29.0073 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39663 epoch=2020-07-22T20:58:05Z A.D. 2020-Jul-22 20:58:04.9852 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39664 epoch=2020-07-22T20:49:17Z A.D. 2020-Jul-22 20:49:16.6665 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39665 epoch=2020-07-22T18:40:48Z A.D. 2020-Jul-22 18:40:47.9401 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39666 epoch=2020-07-22T20:52:46Z A.D. 2020-Jul-22 20:52:46.0957 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39667 epoch=2020-07-22T20:52:14Z A.D. 2020-Jul-22 20:52:13.7787 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39668 epoch=2020-07-22T20:51:23Z A.D. 2020-Jul-22 20:51:22.8277 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39669 epoch=2020-07-22T20:37:41Z A.D. 2020-Jul-22 20:37:41.3461 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39670 epoch=2020-07-21T12:35:15Z A.D. 2020-Jul-21 12:35:14.5778 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39671 epoch=2020-07-22T21:01:29Z A.D. 2020-Jul-22 21:01:29.4136 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39672 epoch=2020-07-22T20:54:19Z A.D. 2020-Jul-22 20:54:18.9265 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39673 epoch=2020-07-22T17:58:06Z A.D. 2020-Jul-22 17:58:06.4911 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39674 epoch=2020-07-22T12:49:37Z A.D. 2020-Jul-22 12:49:37.0381 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39675 epoch=2020-07-22T12:05:24Z A.D. 2020-Jul-22 12:05:23.8488 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39676 epoch=2020-07-22T16:56:17Z A.D. 2020-Jul-22 16:56:17.1776 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=39677 epoch=2020-07-21T12:52:38Z A.D. 2020-Jul-21 12:52:37.5710 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=43324 epoch=2020-07-22T18:01:40Z A.D. 2020-Jul-22 18:01:40.0045 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=43325 epoch=2020-07-22T12:59:41Z A.D. 2020-Jul-22 12:59:40.6951 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=43326 epoch=2020-07-22T18:21:59Z A.D. 2020-Jul-22 18:21:59.3790 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=43327 epoch=2020-07-21T15:25:15Z A.D. 2020-Jul-21 15:25:14.7752 UT
EarthSatellite 'COSMOS 1867 COOLANT' number=43328 epoch=2020-07-22T00:16:23Z A.D. 2020-Jul-22 00:16:23.1361 UT
Traceback (most recent call last):
  File "/Users/user/COSMOS_1867_Coolant/skyfield_satcat.py", line 42, in <module>
    for line1, line2, line3 in TLEs:
TypeError: cannot unpack non-iterable EarthSatellite object

Please advise.

Issue Analytics

State:
Created 3 years ago
Comments:7 (4 by maintainers)

Top GitHub Comments

1reaction

craigimcommented, Oct 1, 2020

Never mind. Just found from sgp4.exporter import export_tle.

0reactions

craigimcommented, Oct 1, 2020

I actually have a use case for this, though it’s probably obscure enough that it may not be worth it to add.

I’m running skyfield on an air-gapped computer and want to store TLEs in a simple database rather than a big text file. I’d like to use the fact that skyfield already parses the epoch date and can handle both 2 and 3 line entries, and then insert the two lines into the database. Then, if I want a particular TLE, I can search on the NORAD ID and epoch date and then return the two lines to build my skyfield EarthSatellite object. Essentially, if possible, under model (or similar), I’d like to see two fields line1 and line2 that are just copies of the inputs.

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