[Spice_discussion] spkezr vs Geocentric Solar Ecliptic (GSE) Frame

Donald F. Linton lintond at gmail.com
Wed Jan 27 16:33:48 PST 2016


I implemented the Geocentric Solar Ecliptic (GSE) Frame in the Frames
<http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/frames.html#Specifying
a New Frame> reference:

\begindata
   FRAME_GSE                       =  314101
   FRAME_314101_NAME           = 'GSE'
   FRAME_314101_CLASS          =  5
   FRAME_314101_CLASS_ID       =  314101
   FRAME_314101_CENTER         =  399
   FRAME_314101_RELATIVE       = 'J2000'
   FRAME_314101_DEF_STYLE      = 'PARAMETERIZED'
   FRAME_314101_FAMILY         = 'TWO-VECTOR'
   FRAME_314101_PRI_AXIS       = 'X'
   FRAME_314101_PRI_VECTOR_DEF = 'OBSERVER_TARGET_POSITION'
   FRAME_314101_PRI_OBSERVER   = 'EARTH'
   FRAME_314101_PRI_TARGET     = 'SUN'
   FRAME_314101_PRI_ABCORR     = 'NONE'
   FRAME_314101_SEC_AXIS       = 'Y'
   FRAME_314101_SEC_VECTOR_DEF = 'OBSERVER_TARGET_VELOCITY'
   FRAME_314101_SEC_OBSERVER   = 'EARTH'
   FRAME_314101_SEC_TARGET     = 'SUN'
   FRAME_314101_SEC_ABCORR     = 'NONE'
   FRAME_314101_SEC_FRAME      = 'J2000'
\begintext

Using the epoch: 2017-07-01T00:00:00
et = 5.521392681841135e8

sv = spkezr( "SUN", et, "J2000", "NONE", "EARTH" )

 -2.41323e7  1.37774e8  5.97261e7  -28.9257  -4.24521  -1.83927

then

M = sxform("J2000", "GSE", et )

 -0.158671     0.905874      0.392703     0.0          0.0        0.0
 -0.987331    -0.145594     -0.0630798    0.0          0.0        0.0
  3.26993e-5  -0.397737      0.9175       0.0          0.0        0.0
 -1.90166e-7  -2.80422e-8   -1.21495e-8  -0.158671     0.905874   0.392703
  3.0561e-8   -1.7445e-7    -7.56986e-8  -0.987331    -0.145594  -0.0630798
 -6.6631e-11  -9.82553e-12  -4.257e-12    3.26993e-5  -0.397737   0.9175

M*SV yields

 1.5209e8
 2.79397e-9
 7.45058e-9
 0.0217735
 6.64746e-15
 2.22045e-16

I don't understand why I see 21.77 m/s of sunward velocity
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