Access to ephemeris of celestial bodies

Spacecraft, Thruster, Tank, Propagator, CoordinateSystem, etc.

Re: Access to ephemeris of celestial bodies

Postby marchand » Wed May 08, 2013 7:38 pm

That only fixes the state print line, it does not fix the problem about accessing eccentricity. Internally , GMAT still thinks that X, Y, Z, VX, VY, and VZ are zeros. So, it can't compute eccentricity.

For example, even with your fix to the previous print line, if I uncomment the line:

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Report rf helioEarthSC.ECC


I still get the error that says

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"Parameter exception: *** Error *** Cannot convert from Cartesian to Keplerian because position vector is a zero vector".


I can't link the eccentricity calculation directly to the SunMJ2000Eq state, apparently, because this line:

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Report rf helioEarthSC.SunMJ2000Eq.ECC


gives this error:

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1: **** ERROR **** Interpreter Exception: Invalid dependency name "SunMJ2000Eq" found for Parameter type "ECC" in line:
   "  81: Report rf helioEarthSC.SunMJ2000Eq.ECC;"

Clearly it's computing the eccentricity based on helioEarthSC.X, helioEarthSC.Y, helioEarthSC.Z, helioEarthSC.VX, helioEarthSC.VY, and helioEarthSC.VZ, without the coordinate frame specification. However, since GMAT thinks those are zero, it's not able to compute the eccentricity.
marchand
 
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Re: Access to ephemeris of celestial bodies

Postby jjkparker » Thu May 09, 2013 4:50 pm

Just to be clear, are you trying to report the Sun-centered eccentricity of Earth?

This line seems to give that:
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Report rf earthSC.Sun.ECC;

earthSC is the Earth analog, and the ECC parameter takes a celestial body as a dependency (hence Sun).
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
jjkparker
 
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Location: NASA Goddard Space Flight Center, Greenbelt, MD

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