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Questions tagged [sgp4]

The U.S. Space Force's Simplified General Perturbations software, version 4, must be used to correctly interpret the orbit data format known as TLE (Two-Line Elements).

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

The Simplified Perturbations model SGP4 is used to calculate Earth satellite state vectors (position and velocity) using standard ephemeris data encoded as TLEs (Two Line Elements). According to ...
uhoh's user avatar
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7 votes
3 answers
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How to generate TLE file?

Subsequently to this answer: What is the way of generation of TLE file for a satellite? How to deal with BSTAR drag term, mean orbital elements, etc.? The generated TLE will be used as the input for ...
Tarlan Mammadzada's user avatar
8 votes
2 answers
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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
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3 votes
1 answer
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Confused about SGP4 implementation published by celestrack

I was trying to understand how SGP4 computes the propagated position I had a look on the original publication paper but i have not found a satisfactory answer. So I had a look to the Matlab ...
Giacomo Curzi's user avatar
2 votes
1 answer
170 views

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

This fascinating answer to Why has no TLE been published for the DSCOVR satellite and the Falcon 9 R/B? presents links to custom-made TLEs for the Falcon 9 rocket body that put DSCOVR into orbit, and ...
uhoh's user avatar
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5 votes
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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?

@BillGray's answer to Why can't custom-made TLEs for the DSCOVR launch booster in orbit around Earth work with SDP4? is quite interesting and informative; I fail to do it justice by summarizing it as ...
uhoh's user avatar
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SGP 4 for Geostationary Satellite

I have read some sources that say that SGP4 is for satellite which have orbital period less than 225 minutes. For orbital period more than 225 minutes, we should use SDP4 instead. I need a ...
Elisa Fitri's user avatar
5 votes
2 answers
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How is an input card for SGP4/other astro standards packages crafted?

I've read through the SGP4 documentation at least 5 times, and I swear the only reference it makes to the construction of an input card is "just look at the examples". For Sgp4Prop, it ...
orbit-stuff's user avatar
4 votes
2 answers
423 views

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

I am doing orbit propagation for a geostationary satellite which requires the deep space corrections of SDP4. See my previous question SGP 4 for Geostationary Satellite. I am using SGP4 on STK, but, ...
Elisa Fitri's user avatar
3 votes
2 answers
925 views

How to correctly make a fake, counter-propagating TLE?

In this answer I have said: Do not make FAKE TLEs! I would now like to make a fake TLE. Specifically I'd like to generate a counter-propagating "twin" of an orbit by flipping inclination by 180° ...
uhoh's user avatar
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What is/was legacy TLE ephemeris type 2? (TLE, line 1, column 63)

Wikipedia's Two-Line Element Set entry for line 1, column 63 (1.12) says: Ephemeris type (internal use only - always zero in distributed TLE data)13 13Celestrak Frequently Asked Questions: Two-Line ...
uhoh's user avatar
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SGP4: propagation initialization by state vector

I'm using the SGP4 model to propagate the orbit, initialized by TLE from celestrak.com ...
Tarlan Mammadzada's user avatar
3 votes
2 answers
230 views

PseudoTLE creation

I am developing a script in python to obtain pseudo TLEs of a satellite, starting from its state vector. I have always used TLEs to propagate the satellite and predict its next pass over a ground ...
Luca Pizzuto's user avatar
1 vote
1 answer
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Has Skyfield or any other SGP4-capable open-source Python package yet wrapped/implemented the new, improved SGP4 (version 8+)?

The first release on Github was in 2014. I have noticed Brandon Rhodes has contributed quite a bit to the Skyfield source code, so I will tag him here and in a comment. EDIT: I changed the title to ...
tdMJN6B2JtUe's user avatar
6 votes
1 answer
2k views

Orbit Propagator with J2 perturbation has larger error compared with simple 2 body Propagator

I have developed an orbit propagator, taking J2 perturbation into account according to the formulation as shown: with Runge-Kutta 4th order, timestep of 1 second as the integrator. Formulation as ...
Chia Jiun Wei's user avatar
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
4 votes
4 answers
8k views

SGP4 TEME frame to J2000 conversion

I've got familiar with the SGP4 model. The problem which I faced is that, the results are in TEME frame. How to convert the TEME to J2000? Would be glad also, if you suggest a method in ...
Tarlan Mammadzada's user avatar
4 votes
0 answers
1k views

TLE/SGP4 state vector accuracy assessment

I’m using the Planet Labs state vectors downloadable from http://ephemerides.planet-labs.com/planet.states or http://ephemerides.planet-labs.com/planet_YYYYMMDD.states to assess the TLEs/SGP4 accuracy ...
Cristiano's user avatar
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4 votes
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Why did the Chinese put the Tiangong-2 so high?

The most obvious answer is that they don’t want to deorbit the station shortly, but why? Some calculations with the TLEs and SGP4 show the following Tiangong-2 / ISS close encounters: ...
Cristiano's user avatar
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4 votes
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What does it mean to ask for a date beyond epoch time?

I am fairly new to this industry. As I am playing around with a library on Python, ephem, I have encountered an error saying that: ...
Danial Kosarifa's user avatar
2 votes
1 answer
324 views

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

I have already worked on this project for a week, and I still can not solve this problem by myself. How can I update data for the SGP4 OrbitPropagator in Matlab's ...
Achilles chan's user avatar
2 votes
0 answers
192 views

How to use David Vallado's AstroLib to do reference frame conversions

Given a Keplerian Orbit description such as that in here: ...
ScottishTapWater's user avatar
1 vote
1 answer
281 views

Converting TLEs into the input data for SGP4

At face value this seems like a trivial question the TLE's are the input to SGP4, but my question is a little more specific. Given a TLE, the values are in specific units (eg. argument of perigee is ...
ThePlanMan's user avatar
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