Hot answers tagged

13 votes
Accepted

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

It's somewhat an issue of the cart driving the horse -- TLEs are generated explicitly for the purpose of being an input into the SGP4 propagator. The data used to generate them often comes from ...
Tristan's user avatar
  • 17.3k
9 votes
Accepted

How to generate TLE file?

In fact, your question is quite important. I will disagree with my colleagues who discourage the generation of custom TLEs. There are plenty of reasons to do so, mostly linked to the fact that most ...
Gustavo Boado's user avatar
7 votes

How to generate TLE file?

Do not make FAKE TLEs! Step 1: Read this answer. Step 2: Review all of the links in the answer. I'll repeat them here: Documentation webpage TLE format PDF Spacetrack report #3 PDF Revisiting ...
uhoh's user avatar
  • 149k
7 votes
Accepted

Why can't custom-made TLEs for the DSCOVR launch booster in orbit around Earth work with SDP4?

SDP4 has a lot of algorithmic nuances to handle objects in 12- and 24-hour orbits. You can get decent (km-level over a week or so) fits to the model. I see no evidence in the SDP4 algorithm that ...
Bill Gray's user avatar
  • 1,013
6 votes

What is/was legacy TLE ephemeris type 2? (TLE, line 1, column 63)

This has to do with ambiguities in the definitions used for certain terms, and software doing strange contortions to avoid breaking backwards compatibility. The USAF's family of Simplified General ...
Ryan C's user avatar
  • 7,882
6 votes
Accepted

SGP4 TEME frame to J2000 conversion

The problem is solved using the Skyfield and Astropy packages in python. ...
Tarlan Mammadzada's user avatar
6 votes

TLE SGP4 Coordinate Transformations

While this answer was written for a different question/project, it points out that the Two Line Element sets and the SGP4 propagator work together and each is designed specifically to work only with ...
uhoh's user avatar
  • 149k
6 votes
Accepted

Has Skyfield or any other SGP4-capable open-source Python package yet wrapped/implemented the new, improved SGP4 (version 8+)?

The new SGP4 library comes with a Python wrapper in the same zip archive file (also Java, Matlab, and Visual Basic, and documentation for the C API), but it's not at all idiomatically Pythonic, since ...
Ryan C's user avatar
  • 7,882
6 votes
Accepted

How is an input card for SGP4/other astro standards packages crafted?

I completely agree, the 6P card input is very annoying to use and its documentation is terrible. Here is an example of how to use it, as I did in preparing my answer to Failing at getting apogee and ...
Ryan C's user avatar
  • 7,882
6 votes

PseudoTLE creation

I would recommend against using Keplerian elements as TLEs are not Keplerian. If you do insist on doing so (not recommended), I would first make a 3DOF (or maybe even 6DOF) propagator that advances ...
David Hammen's user avatar
  • 74.2k
5 votes

SGP4 TEME frame to J2000 conversion

I have published a julia package called SatelliteToolbox.jl that has all the conversions related to IAU-76/FK5 model (ITRF, MOD, TOD, GCRF, PEF, etc.) and now I also added the support for TEME. ...
Ronan Arraes Jardim Chagas's user avatar
5 votes
Accepted

Generating TLEs with STK Using SGP4 Propagator;

First, the SGP4 propagator is meant to propagate TLEs. He takes a TLE and a time since the TLE's epoch as inputs and outputs a position and a velocity. By selecting several times, you get a trajectory....
Mefitico's user avatar
  • 1,947
4 votes

What is/was legacy TLE ephemeris type 2? (TLE, line 1, column 63)

I find Ryan C's answer interesting... but I've never actually interpreted the documentation that way. It's difficult to be certain, since all official TLEs have had ephem type 0. But I (and others ...
Bill Gray's user avatar
  • 1,013
4 votes

Onboard propagator in satellites SGP or J2

The first question you need to ask yourself is the following: does the spacecraft need to know its own position? Many, if not most, spacecraft do not need that information. The ground team simply ...
ChrisR's user avatar
  • 6,220
4 votes
Accepted

SGP4 on Systems Tool Kit (STK); how to check if SDP4 deep space correction is implemented?

I can confirm that the STK SGP4 propagator contains the deep space corrections in SDP4. Source: I worked at Analytical Graphics, Inc (AGI) for 25 years and the astro team sat 2 desks away from me :). ...
Tom Johnson's user avatar
4 votes
Accepted

STK SGP4 for Geostationary Satellite

As far as I can tell, this is nothing to worry. What goes into a TLE is a specific kind of average elements, which are meant to simplify short-term propagations. Here "mean" does not imply a time-...
Mefitico's user avatar
  • 1,947
4 votes
Accepted

SGP 4 for Geostationary Satellite

...but I can't find a source code for SDP4 on the internet. As discussed in the question How do “Deep space” corrections in SGP4 account for the Sun's and Moon's gravity? and according to Wikipedia: ...
uhoh's user avatar
  • 149k
4 votes

SGP4 gravity model accuracy

Is it possible that the blue plot shows the true shape of the radius vector, while the SGP4 plot show just an approximate shape? Just because SGP4 is indeed an approximation (a fairly low accuracy ...
David Hammen's user avatar
  • 74.2k
4 votes

In a 3D space defined by semimajor axis, eccentricity and inclination, what would be the shape of the space where SDP4 works better than SGP4?

I have no formal, mathematical answer to this. When I have to fit TLEs to a new object, I try SDP4; if it fails, I drop back to SGP4. It's an entirely empirical "gee, SDP4 didn't work here&...
Bill Gray's user avatar
  • 1,013
4 votes

In a 3D space defined by semimajor axis, eccentricity and inclination, what would be the shape of the space where SDP4 works better than SGP4?

The following is only a partial answer, but I will update as we make progress through this. I believe the on-going discussion in the comments at For any state vector of a satellite at an arbitrary ...
Rafa's user avatar
  • 1,750
4 votes

Track a satellite using python

It's the coordinate system. You need an additional tool to make the conversion. It's right there on the home page (https://pypi.org/project/sgp4/): Note that the SGP4 propagator returns raw x,y,z ...
Ryan C's user avatar
  • 7,882
4 votes

How is an input card for SGP4/other astro standards packages crafted?

I'm going to write out this answer for anyone else who might be furiously googling in the future: The first line of the input card for Sgp4Prop is a "6P card". It's parsed by timefunc.dll, ...
orbit-stuff's user avatar
4 votes
Accepted

Can I redistribute the SGP4 lib?

You can redistribute and even sell the software based on the terms of the "AIR FORCE SPACE COMMAND (AFSPC) OPEN SOURCE AGREEMENT for SGP4" as quoted in Ryan C's incorrect answer. Ryan was ...
Erin Anne's user avatar
  • 10.8k
4 votes
Accepted

In MATLAB, Computing a new TLE/orbit following a delta-v impulse?

You said, "I already work on this project for a week, and I still can not solve this problem by myself." No one could do it that fast, unless their solution was wrong. Getting it right ...
Ryan C's user avatar
  • 7,882
3 votes

How to generate TLE file?

What exactly do you mean by ‚generate‘? TLEs are mainly used by NORAD, you can find a specification on their website, telling you what exactly any particiluar character of the TLE means. That will be ...
Hans's user avatar
  • 3,566
3 votes

SGP4 TEME frame to J2000 conversion

Tarlan is spot on with his answer but I wanted to tag along for those not using python or using some other software not being discussed here. The general consensus is that converting directly between ...
aaastro's user avatar
  • 478
3 votes
Accepted

SGP4: propagation initialization by state vector

Indeed, SGP4 is not made to allow you to compute maneuvers. You can get a TLE, propagate up to maneuver time to obtain propagated position and velocity, then assume this instant is the new epoch, and ...
Mefitico's user avatar
  • 1,947
3 votes
Accepted

How do SDP4's "Deep space" corrections to SGP4 account for the Sun's and Moon's gravity?

I found Hujsak 1979 -- its title is "A Restricted Four Body Solution for Resonating Satellites Without Drag", but the linked pdf shows it is also Spacetrack Report #1. Four body means Earth,...
Ryan C's user avatar
  • 7,882
3 votes

How do SDP4's "Deep space" corrections to SGP4 account for the Sun's and Moon's gravity?

If you want a complete answer about how SGP4 (or SDP4) does it, you should read the original source: The Space Track Report #3. For the actual theory behind it, you should read the references by ...
Mefitico's user avatar
  • 1,947

Only top scored, non community-wiki answers of a minimum length are eligible