# 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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### Conversion of osculating orbital elements to TLE mean elements

I am looking for a method to resample TLE data, so they are regularly sampled. I wanted to use physical propagation to calculate elements at given time. However, the propagation of TLE by SGP4 returns ...
1 vote
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### How does the Gpredict software algorithm track satellites?

I was wondering how Gpredict calculates the ground tracks, Lat, Long and elevation based on a ground station. If I understand correctly, Gpredict takes the values from a TLE (Two-Line Element) set, ...
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### GMAT SGP TLE Propagator and maneuver

So this time I try to use GMAT(2022 ver). I am using the SPICESGP4 TLE Propagator to simulator ISS's orbit. For now it work well. However when I try to use the burn to change its orbit altitude, it ...
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### 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 ...
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### 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 ...
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### Meaning of superscript letters in sidereal time calculation

I'm following along with Dr Kelso's columns on CelesTrack and I've come across this equation. $$θ_g(0^h)=24110^s.54841+8640184^s.812866T_u+0^s.093104T_u^2- 6.2\times10^{-6} T_u^3$$ As you can see, ...
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### TEME to J2000 conversion algorithm

I've asked a few questions to do with this in the last day or so and received answers that have led to more questions... How to use David Vallado's AstroLib to do reference frame conversions https:...
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### How to use David Vallado's AstroLib to do reference frame conversions

Given a Keplerian Orbit description such as that in here: ...
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### Can I redistribute the SGP4 lib?

I'm writing a C# library to make working with orbits easier. Given I plan on being able to input data from space-track elsats, which uses TEME SGP4 orbital elements, it's looking increasingly likely ...
1 vote
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### Issue with propagating TLE sets using SGP4

I am trying to make some analysis on conjunction events using the TLEs available from Celestrak's SOCRATES page. Take for example the following predicted event: Here's my issue: when I try to ...
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### Predicting Satellite Flyover Calculations by Hand

Recently I used transit-finder.com to get a really cool picture of the ISS transiting the sun. The prediction from the website was spot-on. Since then I'm absolutely fascinated by how the prediction ...
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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 ...
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### Track a satellite using python

I tried tracking a satellite - or rather confirming the data I got from the AMSAT pass prediction web page - using python, more precisly the sgp4 and navpy packages. Now I don't really now what I'm ...
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1 vote
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### Another look at orbits of near-Earth satellites. What is wrong in this interpretation?

In a cartesian reference frame (O,X,Y,Z), put two circles centered at the origin O, of radius a. The blue circle is perpendicular to Z. The red circle makes an angle i with the blue (cf. Fig below). ...
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### 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 ...
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### What is the rationale behind NORAD's use of TEME?

The most popular catalog of Earth-orbiting objects is NORAD’s. The catalog provides the so-called « two-line elements » (TLE) which essentially are computed orbital parameters of a catalogued object, ...
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1 vote
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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 ...
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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 ...
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### Is Vallado's Revisiting Spacetrack Report #3 still relevant today?

The title pretty much sums it up. I am reading David A. Vallado's Revisiting Spacetrack Report #3, which was published in 2006 and includes source code for the SGP model series. I was wondering, is ...
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### Understanding the paper "Determination of Satellite Orbital Elements by Means of On-Board GPS Receiver and Its Verification" by Yoshiwo Okamoto et. al

I have been assigned with implementing the algorithm proposed in the paper "Determination of Satellite Orbital Elements by Means of On-Board GPS Receiver and Its Verification" by Yoshiwo ...
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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 ...
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### Satellite tracking telescope integrated program in Matlab

How can I get a comprehensive, integrated MATLAB program to set up and capture SGP4 output for telescope mounting? I am currently receiving state vectors from the SGP4 program, which include the ...
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### 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 ...
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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 ...
1 vote
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### STK SGP4 for Geostationary Satellite

I am using SGP4 propagator in STK to propagate my GEO satellite. SGP4 need TLE as an input. In TLE, I found the inclination of my satellite is 0.048. But the inclination result of SGP4 is 0.15. The ...
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### Issue with SGP4 modelling from scratch in MATLAB

I am trying to develop the code from this source , this research paper and from this too as same as bibliography of that aforementioned source. So, here as you can see at page 14, they have defined ...
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### Generating TLEs with STK Using SGP4 Propagator;

STK has two methods for generating TLEs; Trajectory Sampling method and Single Point method. I have read the differences both of them at http://help.agi.com/stk/index.htm#stk/tools-10.htm but I am ...
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### 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, ...
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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 ...
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### How to implement SGP4 C++, satellite propagator?

I would like to ask about how to implement the SGP4 code in C++ by Vallado. How can I implement the libraries that are available in https://celestrak.org/software/vallado-sw.php. I think that are the ...
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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: ...
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### 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° ...
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### SGP4: the accumulation of error in radial, in-track and cross-track

I'm propagating the trajectories of 2 LEO satellites (altitude 700 km) in 7 days and calculating the radial, in-track and cross-track distances to determine the risk of collision. JSPoC states that ...
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### 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 ...
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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: ...
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### Onboard propagator in satellites SGP or J2

The Earth orbit propagator SGP4 (simplified general perturbation) was developed by NORAD to allow users to generate short-term prediction of satellite positions using two line element sets (TLEs) ...
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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 ...
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1 vote
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### Calculating t(E)

The mean radius vector of an elliptic orbit is equivalent to the semi-major axis. If I sample the radius vector of an unperturbed elliptic orbit as a function of the eccentric anomaly with at a ...
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### SGP4 gravity model accuracy

From a simulation, I obtain the instantaneous radius vector of the SFERA 2 satellite. If I compare that radius vector with the one obtained from the SGP4 propagator, I get very big differences. The ...
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1 vote
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### 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 ...
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### 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. ...
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### How to calculate a satellite LTAN on the basis of Cartesian coordinates in GCRS frame?

I have calculated the Cartesian coordinates of a satellite in GCRS frame using Skyfield package in python. Propagating the sun-synchronius orbit, I want to analyse the change in its LTAN. How could I ...
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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 ...
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### 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 ...