4
$\begingroup$

I'm propagating a Low Earth orbit using GMAT.

I 'm trying to make the propagation realistic, considering the zonal harmonics, Sun, Moon, Jupiter, Venus perturbations, tidal forces and solar radiation.

What I exactly need is to calculate the change in argument of perigee in 6 month.

What is the most realistic force model configuration for this purpose?

My configuration now is the following: enter image description here

Does it account for zonal harmonics?

Improve this question
$\endgroup$
1

1 Answer 1

Reset to default
4
$\begingroup$

The notion of "the most realistic" is quite debatable. In fact, if you want the most realistic, you should be including the a precise 3D model of your spacecraft which includes the albedo of each infinitesimal surface of the spacecraft, take into account the shadowing of some parts of the spacecraft with respect to others (which will affect the reflectivity and therefore the solar radiation pressure), but also include the spherical harmonics of all the planets, include all the planets, include the comets and asteroids, etc. etc.

However, to answer your question of the study of argument of periapsis changes over six months, I would recommend that you only take into account the spherical harmonics as these will have the greatest effect. More specifically, you will likely find it interesting to propagate a spacecraft with different orders of the harmonics. Hence, I encourage you to propagate the spacecraft with only two body dynamics (i.e. turn off harmonics, SRP, drag and all the other bodies), and compare the drift in AoP with a propagation which takes into account Earth's harmonics of degree 2 and order 0 (commonly known as the J2 effect), and with degree 4 and order 0. Then, increase the fidelity of the model, by switching to a 21 by 21 gravity field.

I hope this helps.

Improve this answer
$\endgroup$
21
  • 1
    $\begingroup$ @Leeloo if you want the most realistic by GMAT's capabilities, then yes, you should be using a degree of 70 by 70 and you should switch to JGM3 instead of JGM2. However, what I think you ought to be interested in, is seeing how the fidelity of the gravity model impacts the drift in AoP so you can compare the drift in different levels of fidelity. The higher the fidelity, the longer/harder the computation, so knowing how the AoP drifts depending on the fidelity allows you to perform rapid iteration with little loss in fidelity. $\endgroup$
    – ChrisR
    Jul 12, 2018 at 0:52
  • 1
    $\begingroup$ You don't generally have to worry about the tide settings unless you're doing geodesy. Same with the fog model. However, if you should turn on one of the drag models for a higher fidelity if you're in LEO. You'll notice that the drag effect isn't a secular drift since it continuously slows down the vehicle. $\endgroup$
    – ChrisR
    Jul 12, 2018 at 15:03
  • 1
    $\begingroup$ No, there's nothing special about 21 by 21. It's just the kind of gravity field which is good enough to plan spacecraft operations to a high fidelity. $\endgroup$
    – ChrisR
    Jul 13, 2018 at 18:46
  • 1
    $\begingroup$ With a 21 by 21 field, you've got a very good representation of the gravity of Earth. If you switch to a 70 by 70, or use EGM2008 and a 2192 order field, you'll have higher fidelity, but the simulation will take hours longer to run but the difference in propagation after 100 days might be a few hundred meters compared to a 21 by 21. When running simulations, we usually do Monte Carlo analysis, with thousands of runs, and analyzing outliers. We prefer to be able to analyze the results after only two or three days of simulation instead of waiting for a week if the results will be very similar. $\endgroup$
    – ChrisR
    Jul 14, 2018 at 20:19
  • 1
    $\begingroup$ 20 by 20 would also work. You just get a slightly lower fidelity, that's it. But it might be sufficient in many cases. For example, when we want to do a quick study, we often just used an 8 by 8, which has decent fidelity, but is significantly faster. $\endgroup$
    – ChrisR
    Jul 14, 2018 at 20:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.