Getting DC error message

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Getting DC error message

Postby JackCrenshaw » Wed Sep 11, 2013 3:56 pm

I'm working on a lunar mission, and getting an error message that says that (short form) the parameters in the Vary command(s) don't affect those in the Achieve command(s).

I'm trying to vary RAAN and AOP. But looking at your example missions, I see that they begin in LEO, and involve a delta-v to get to the (approximately) 2-body transfer ellipse. I know basically what ellipse I want, so I'm setting its parameters in Spacecraft.Orbit.

I'm guessing that the DCconsiders settings in the S/C to be constant, not eligible for variation. Is that correct?

Jack
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Re: Getting DC error message

Postby jjkparker » Wed Sep 11, 2013 4:03 pm

That usually means your changes (through the Vary commands) aren't actually being applied in a way that the Achieve command can see.

For example, you could be varying an orbit, but not propagating it. Or varying a maneuver, but not applying it. Varying spacecraft orbit parameters is definitely possible, we do it all the time!

If you send a script, we can take a look.

Joel
Joel J. K. Parker
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http://gmatcentral.org
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Re: Getting DC error message

Postby JackCrenshaw » Wed Sep 11, 2013 5:22 pm

Ok, here's the script. As you can see, I AM propagating the orbit.

Thanks for your help.

Jack
Attachments
CrenshawScript.m
(10.15 KiB) Downloaded 118 times
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Re: Getting DC error message

Postby shughes » Wed Sep 18, 2013 3:34 pm

Hi Jack,

There are a few issues with the script. The first is that the stopping condition is configured to propagate to Earth periapsis but it was intended to propagate to Lunar periapsis. The second issue is that you did not use a Maneuver command to apply the Maneuver named DefaultIB to the spacecraft. The result is that the targeter says the Jacobian cannot be inverted because the maneuver has no influence on the trajectory. Thirdly, the guess is poor, so even though I fixed those issues in the attachment, the targeter doesn't converge. You can better generate guesses using other scripts delivered with GMAT, especially the one called Ex_GivenEpochGoToTheMoon.

Hope this helps!

Steve
Attachments
CrenshawScript_DCIssues.m
(10.28 KiB) Downloaded 106 times
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