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4. Software

The software includes:

• attidf.for - a FORTRAN subroutine to get a matrix M (named PA in the subroutine text) to transform any vector from the S/C coordinate system to the GSE coordinate system:

V_GSE = M * V_S/C

To transform a vector from the GSE coordinate system to the S/C coordinate system transpose the matrix M:

V_S/C = M^T * V_GSE

You can download subroutine.

Usage example

Here is an example of using the subroutine attidf.for

Let us suppose that we have a direction in the S/C frame:

V_S/C(x) = 0.866025
V_S/C(y) = 0.353553
V_S/C(z) = 0.353553

We want to know the direction of this vector in the GSE frame for date: 30.05.1997, time 1h.0min.0sec. ut.

We use the line in attitude coefficients arrays corresponding to an attitude coefficients data set for the given interval.

interval beginning: date 97.05.30, time 2.104 thousands of sec
interval duration:  4.594 thousands of sec.

Our time of interest (3.6 thousands of sec) is within the interval.

We use the subroutine {attidf}.
Our input parameters :

 ts=1.496 (which is 3.6 (the time of interest) minus 2.104 )

 A1=  -.288     B1=   .891      ω1=   53.1951
 A2=  6.104     B2= -3.159      ω2=   36.6355
 A3=  3.104     B3=  6.075      c1=    2.6714
 A4=  -.027     B4=  -.103      c2=  -53.1951
 A5=  -.036     B5=  -.077

The result is the matrix of transformation M:

      0.993484  -0.113452  0.010904
 M=  -0.112566  -0.991700 -0.062135 
      0.017862   0.060503 -0.998008

So the vector in the GSE system equals to V_GSE = M * V_S/C :

 Vgse(x)= 0.824126
 Vgse(y)=-0.470072
 Vgse(z)=-0.315989

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