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

Are J2 and J4 cases of EGM2008 and other spherical harmonics models?

$J_2$, $J_3$, $J_4$, ... correspond exactly to specific terms in a spherical harmonics expansion. For example, $J_2 = -\sqrt{5}\,C_{2,0}$. Similarly, higher order $J_n$ values are equal to the product ...
David Hammen's user avatar
  • 74.2k
6 votes

For any state vector of a satellite at an arbitrary time T1, is there another state vector at a given time T2 that will result in the same orbit?

Partial answer because this is a hard question and because clarifying some of the terms may require more than the exchange of a few comments in this particular case. Kudos for taking on a challenge! ...
uhoh's user avatar
  • 149k
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
5 votes

Draper Semianalytical Satellite Theory (DSST) C/C++ version

The way I read the literature, the Java Orekit version is the only publicly accessible version. If I am wrong, someone please tell me! The C++ conversion was done later (2017-2020 vs. 2012-2015), by ...
Ryan C's user avatar
  • 7,882
5 votes

Accuracy of converting from TLE/Orbital Elements to Cartesian if used for other propagator?

If a two line element represented the exact state of a satellite at the epoch time of the element set, there would be zero penalty in applying the SGP4 algorithm to cartesian coordinates, which are in ...
David Hammen's user avatar
  • 74.2k
4 votes
Accepted

Usage of the coordinate systems in orbit propagation

Let us note $^A\vec\gamma$ a vector of magnitude $|\vec\gamma|=\gamma$ defined in the frame $A$. Let $A$ and $B$ be two distinct frames, $|^A\vec\gamma| = |^B\vec\gamma|$. Moreover, it may be useful ...
ChrisR's user avatar
  • 6,220
4 votes

Ноw to configure mission sequence for propagate until desired date in GMAT?

One way to do this is through some built-in GMAT function code. Here's a snip from a functional script: ...
djcinsb's user avatar
  • 96
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

How to propagate the orbit of a satellite analytically using Lagrange planetary equations/VOPs and compare them with numerically propagated solution?

In addition to the Lagrange planetary equations, there are lots of other SomeFamousPerson (no derogation intended) planetary equations. Examples include the Gauss planetary equations, the Delaunay ...
David Hammen's user avatar
  • 74.2k
4 votes

How to propagate the orbit of a satellite analytically using Lagrange planetary equations/VOPs and compare them with numerically propagated solution?

The question is about orbit-integration problems using Lagrange planetary equations and methods of variation of parameters (VP), especially for (earth-)satellite orbits. It's worth noting first the ...
terry-s's user avatar
  • 1,102
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
Accepted

Orbit Determination from Position and Velocity

First, some caveats: Always use the gravitational mass parameter $\mu_\text{body}$ rather than the product $GM_\text{body}$. The gravitational mass parameter $\mu_\text{body}$ conceptually is the ...
David Hammen's user avatar
  • 74.2k
3 votes
Accepted

Reducing degree of ICGEM's Gravity Field Models for orbit propagation

Regarding EGM2008 versus other models Your goal is orbit propagation. You do not need a 2190x2159 Earth gravitation model for orbit propagation. It's worse than pointless unless your field of study is ...
David Hammen's user avatar
  • 74.2k
3 votes
Accepted

How might an "imminent Starlink reentry in your area" alerting script work?

Well, I can't give a great definitive answer, but I can at least relate my experiences writing my own Starlink reentry analysis script. There are several challenges that make it difficult to create a ...
DuffBeerBaron's user avatar
3 votes

Ноw to configure mission sequence for propagate until desired date in GMAT?

Oh, I found what was wrong. In GMAT integrated help mentioned, that GMAT used non-standart MJD offset. For standart MJD, offset is 2400000.5, for GMAT MJD offset is 2430000.0.
Даниил Галахов's user avatar
3 votes
Accepted

Obtaining position of GPS and GLONASS satellites from RINEX navigation files

After insightful discussion about clock corrections of both GPS and GLONASS in Ephemeris time and clock corrections in RINEX navigation files, I understood better how to deal with the information ...
Rafa's user avatar
  • 1,750
3 votes
Accepted

Modeling satellite attitude for propagation of orbit

The most extensive attitude modeling I've ever seen is for GPS, but that's for calculating solar radiation pressure. There is a vast literature on the topic, ranging from the Proceedings of the First ...
Ryan C's user avatar
  • 7,882
2 votes

Accuracy of converting from TLE/Orbital Elements to Cartesian if used for other propagator?

Edited in response to very constructive criticism from @DavidHammen and @CallMeTom. I agree with them, but I didn't say those things in my initial answer, and I should have. If the only source of ...
Ryan C's user avatar
  • 7,882
2 votes
Accepted

GMAT: What causes the error "ArrayTemplate error : dimension error"?

The GMAT source code is written in C++. Those are C++ exceptions. They are invoked by a throw ArrayTemplateExceptions::DimensionError(); statement in the C++ source....
David Hammen's user avatar
  • 74.2k
2 votes

Implemented analytical orbit propagator

You can check out orekit.org,which basically is an open source java library for orbital mechanics. They have implemented various analytical propagators, all inheriting from an ...
tensorBoy's user avatar
1 vote

What would the TLE data (Mean Motion, Eccentricity, Inclination, RAAN, Argument of Pericenter) of GEO and PO be like?

You should never make your own TLEs. Even if you did manage it, the test conditions you state are incorrect, because you can't use TLEs that way. The effect of earth gravity nonuniformity, gravity of ...
Ryan C's user avatar
  • 7,882
1 vote

Optimizing trajectories with GMAT: how to understand the "Vary" parameters, and how to know what values to use for them?

In my experience with GMAT, sometimes I found it easier to initially start with a Targeting problem then refine from there, as a successful targeting problem will give you good convergent bounds to ...
dec's user avatar
  • 49
1 vote

NASA GMAT: Any good tutorials or methods to learn how to use patch points and control points to come up with viable and optimal trajectories?

I started using GMAT last week and I am roughly at the same point you were when you posted this message. I am trying to create a Low Energy transfer to the moon and trying to get the optimum launch ...
user48296's user avatar
1 vote

Wrong position during orbit propagation in Unity

If you want high fidelity orbit propagation, you should store the orbit in Cartesian form because it's a non-singular orbit representation. It's also the simplest form to account for extra forces on ...
ChrisR's user avatar
  • 6,220
1 vote

For any state vector of a satellite at an arbitrary time T1, is there another state vector at a given time T2 that will result in the same orbit?

I feel that I understand what you are trying to solve but there are many « loose ends » in your statement of problem that it is difficult to be affirmative. So, this is not really an answer, but ...
Ng Ph's user avatar
  • 2,724

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