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

[William T Bridgman]

A tf file for the Van Allen probes has a different definition to build GSE:

       \begindata

       FRAME_GSE                    = -362930
       FRAME_-362930_NAME           = 'GSE'
       FRAME_-362930_CLASS          = 5
       FRAME_-362930_CLASS_ID       = -362930
       FRAME_-362930_CENTER         = 399
       FRAME_-362930_RELATIVE       = 'J2000'
       FRAME_-362930_DEF_STYLE      = 'PARAMETERIZED'
       FRAME_-362930_FAMILY         = 'TWO-VECTOR'
       FRAME_-362930_PRI_AXIS       = 'X'
       FRAME_-362930_PRI_VECTOR_DEF = 'OBSERVER_TARGET_POSITION'
       FRAME_-362930_PRI_OBSERVER   = 'EARTH'
       FRAME_-362930_PRI_TARGET     = 'SUN'
       FRAME_-362930_PRI_ABCORR     = 'NONE'
       FRAME_-362930_SEC_AXIS       = 'Z'
       FRAME_-362930_SEC_VECTOR_DEF = 'CONSTANT'
       FRAME_-362930_SEC_SPEC       = 'RECTANGULAR'
       FRAME_-362930_SEC_FRAME      = 'MEAN_ECLIP'
       FRAME_-362930_SEC_VECTOR     = (0, 0, 1)

       \begintext

It defines the secondary as z-axis rather than y-axis.  I suspect your 
y-axis is not quite perpendicular to your x-axis which might be 
projecting some velocity in the x-direction.

Tom

On 1/27/16 7:33 PM, Donald F. Linton wrote:
> 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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-- 
Dr. William T."Tom" Bridgman               Scientific Visualization Studio
Global Science & Technology, Inc.          NASA/Goddard Space Flight Center
Email: William.T.Bridgman at nasa.gov         Code 606.4
Phone: 301-286-1346                        Greenbelt, MD 20771
FAX:   301-286-1634                        http://svs.gsfc.nasa.gov/