Please forgive my ignorance, I'm new to orbital dynamics. I am using Orekit [https://www.orekit.org/] for orbital propagation in order to determine rise and set times for a MEO satellite, and am having trouble getting the accuracy where I need it. I am given ephemeris in PV Coordinates for a day, and need to propagate the orbit for the next several days as accurately as I can, within reason. I say "within reason" because I'm not actually doing anything real with this, but would still like to get within a minute or two of actual rise/set times for a given point on the earth. I've found the learning curve on Orekit rather steep, and am really just hoping for high level pointers to get me started, maybe by helping me out with the following questions?

  • As I mentioned, I'm provided PV coordinates at 1-minute intervals for a full day, but can't get every day's ephemeris. I need to propagate as far as I can based on this day. I've been able to set up a event listeners and get rise/set times using this data, but when I try to propagate past my last ephemeris point things go south quickly. One approach I've tried is to take the "final state" of my ehpemeris propagator and use it as initial state in another propagator (A NumericalPropagator with a RungeKutta integrator). I found that accuracy here quickly degrades, and I end up several KM off after just an hour of propagation. Is there another approach I could use to propagate forward based on a day's worth of ephemeris?

  • I also can get the TLE for my satellite. I assumed that using actual ephemeris would make a more accurate propagator... is this not true?

  • In order of importance, what things should I try to get the error of a numerical propagator down? Which propagator should I use?

Thanks very much for any insight more experienced users can offer.

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    $\begingroup$ I have never used Orekit, so I can't answer those questions. I can answer the astrodynamical ones. A position and velocity state is significantly more accurate than a TLE (I don't even know why we still use those today). What's in your ephemeris? Just PV states and a datetime? If you're several km off after just an hour, that seems like a lot... does your truth data have spherical harmonics (it will if it's high fidelity)? And what model of the harmonics and Earth fixed frame? It may also include third body perturbations such as Moon, Sun and possibly Jupiter. $\endgroup$ – ChrisR Feb 3 at 20:54
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    $\begingroup$ Likewise, no experience with Orekit but you could try a LEO and GEO orbit to see how it behaves there, just as setting your self a learning process. Anyway, Welcome to Space Stack Exchange! Can I suggest that you clarify your first bullet - what is acting as the truth for what propagation? Presumably within a day you are comparing the first PV, propagated via Orekit, to the last PV of the day and you imply that this works ok (am I right?). Then if you propagate further what are you comparing the propagation with (so as to conclude that its gone south)? $\endgroup$ – Puffin Feb 3 at 21:15
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    $\begingroup$ Also, I don't see where the second propagator comes in. Then, to make an informed choice about the PV vs TLEs as "truth" you need to ask how the PV were created and browse this site for TLE accuracy. Lastly edit and park the last question (or even both 2nd and 3rd questions) and ask it as a separate one - this site works far better when there is one real question per OP, otherwise you will get all sorts of muddy responses addressing one bit but not another. $\endgroup$ – Puffin Feb 3 at 21:18
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    $\begingroup$ Hello Brian, Welcome to Space Exchange! I am an Orekit user, but not familiar with all of its features. Have you visited the Orekit forum? People there are very responsive. As long as you explain what progress you have done specifically, you will get the an accurate answer. Try to search for older similar problems there first. forum.orekit.org $\endgroup$ – Manny Feb 3 at 22:35
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    $\begingroup$ @Manny and then hopefully come back here and post an answer here summarizing what was found out there! $\endgroup$ – uhoh Feb 4 at 0:47

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