Linked Questions

6 votes
2 answers
3k views

Differences between SGP8 and the standard SGP4? Is it ever used in practice?

The Wikipedia article Two Line Element Set says: The SGP4 model was later extended with corrections for deep space objects, creating SDP4, which used the same TLE input data. Over the years a number ...
uhoh's user avatar
  • 149k
1 vote
2 answers
466 views

Can the deactivated satellites also be tracked through TLE?

TLE is used to track whether the satellites are in orbit or not. However, is it possible that a particular satellite is deactivated, decommissioned or deorbited yet its TLE is being updated regularly?
San Shaw's user avatar
8 votes
2 answers
2k views

Is SGP4 propagation necessarily more accurate near the epoch chosen for TLE generation?

This interesting answer includes a quote from Space-Track: From Space-Track.Org FAQ TLEs can contain future epochs. About 20 satellites are categorized as "multi-day objects" because ...
uhoh's user avatar
  • 149k
5 votes
1 answer
4k views

TLE SGP4 Coordinate Transformations

I am working on developing a user friendly SGP4 orbit propagator in C on a PIC24. I have extensively read Revisiting Spacetrack Report #3 and celestrak - there are a few outstanding questions I have. ...
Ashton Meginnis's user avatar
12 votes
3 answers
1k views

Why are Tiangong-1's Apogee and Perigee Graphs Wobbly?

The apogee and perigee graph of the Tiangong-1 space station, about to re-enter and break up Real Soon Now, is depicted in this graph (source: Wikipedia): Why are the graphs wobbly? Is it because the ...
Jens's user avatar
  • 1,696
5 votes
2 answers
1k views

Sun-synchronous satellite orbit propagation

I'm trying to propagate the orbit of a sun-synchronous satellite. The initial data is defined by the TLE. The orbit of the satellite is controlled by the operator ...
Tarlan Mammadzada's user avatar
21 votes
3 answers
25k views

How can I plot a satellite's orbit in 3D from a TLE using Python and Skyfield?

I have obtained a Two Line Element (TLE) of a satellite in Earth orbit from Celestrak at https://celestrak.org/NORAD/elements/ and I would like to use it to calculate an orbit. How can I calculate the ...
uhoh's user avatar
  • 149k
4 votes
2 answers
1k views

Has a TLE ever been issued for a spacecraft trajectory not bound to Earth orbit?

This excellent answer to the question Why has no TLE been published for the DSCOVR satellite and the Falcon 9 R/B? suggests that to the best of the writer's knowledge TLEs are only issued for ...
uhoh's user avatar
  • 149k
5 votes
2 answers
752 views

Why are Keplerian elements used in TLEs instead of Cartesian state vectors?

Propagating a state vector seems easier, you just account for the gravity, change the velocity and update the position. It also allows to easily apply perturbations, etc. Additionally, the ...
Mark's user avatar
  • 525
14 votes
4 answers
21k views

How to obtain UTC of the epoch time in a satellite TLE (two line element)?

I want to convert the epoch time of a TLE to UTC. At this moment I am less interested in explanations and history - I just want to know quantitatively, with certainty, how to convert. I'm confused ...
uhoh's user avatar
  • 149k

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