Propagate STM Issue

Control flow commands, Target, Vary, Minimize, NonlinearConstraint, etc.

Propagate STM Issue

Postby tmoeller » Sat Apr 19, 2014 2:57 am

I am attempting to propagate the STM for one revolution of a quasi-periodic trajectory around a libration point; however, the script is getting stuck inside this command indefinitely. I am using a rotating coordinate system centered at the libration point.

Code: Select all
Propagate EarthMoonSun(STM_SC, STM) {STM_SC.ElapsedDays = Orbit_Period, StopTolerance = 1e-005};


Does anyone know what might be causing this issue?
tmoeller
 
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Re: Propagate STM Issue

Postby jjkparker » Tue Apr 22, 2014 2:04 pm

I don't see anything right off the bat. Can you provide your full script? I'm guessing something's going on with Orbit_Period, but that's just a guess.
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
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Re: Propagate STM Issue

Postby tmoeller » Tue Apr 22, 2014 4:59 pm

I think you were right that it was the Orbit_Period, because I changed the way this was calculated and no longer get stuck in this command.

However, as a broader GMAT issue, has the STM propagation been validated for non-standard coordinate systems? I am using an Earth-Moon rotating frame centered at L2, and I don't believe that the STM results that I am getting are correct. I say this because when I add small initial perturbations, dX0, to my initial state and propagate to the final state, the resulting final difference from the nominal trajectory, dXf, is not even close to the final state difference predicted by
dXf = STM*dX0
tmoeller
 
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Re: Propagate STM Issue

Postby jjkparker » Tue Apr 22, 2014 6:41 pm

Yes, our documentation is just wrong on this point. I gave myself a task to fix it.

The OrbitSTM parameter is always returned with respect to the MJ2000Eq axes (origin-independent). If you need it in a different coordinate system, you'll need to do the rotation manually in the script.

EDIT: See GMT-4532.
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
jjkparker
 
Posts: 617
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Location: NASA Goddard Space Flight Center, Greenbelt, MD


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