GALILEO

## Galileo EPD Handbook

### Chapter 2. EPD Software

LGA Processing Software for the Energetic Particles Detector (continued)

Source: C. Brull and S. Stone, December 19, 1998

Appendix B. Coordinate Systems (continued)

B.2 SPICE

All of the necessary physical data and ephemeris information necessary to compute the coordinate transformations described above is contained in the SPICE kernel files. Subroutines in the SPICE Toolkit provide access to the data contained in the kernel files. The SPICE Toolkit also contains subroutines to do vector and matrix operations.

B.2.1 Required Kernels

Three kernels are necessary to complete the coordinate transformations described in the previous section.

- Leapseconds Kernel
The kernel contains information necessary to convert time strings into ephemeris seconds past epoch J2000.

- Planetary Constants Kernel
The kernel contains information regarding constants associated with various planets. The orientationof Jupiter's rotation axis along with the system III rotational rate are contained in this kernel. The routine BODMAT uses this information to create the conversion between inertial and body-fixed coordinates.

- Spacecraft and Planetary Kernel
The SP kernel contains position and velocity information for given planets, moons, and spacecraft for a range of time. The SPKEZ routine reads these kernels to determine the state of a target body.

B.2.2 Toolkit Routines

The following list describes the toolkit routines used in the above code segments. The descriptions are extracted from the subroutine library.

BODMAT Return the J2000 to body equator and prime meridian coordinate transformation matrix for a specified body.

GSETRN_G Return the matrix that transforms coordinates from a specified inertial reference frame to planetocentric solar ecliptic coordinates.

LATREC Convert from latitudinal coordinates to rectangular coordinates.

MXM Multiply two 3x3 matrices.

MXV Multiply a 3x3 double precision matrix with a 3-dimensional double precision vector.

ROTATE Calculate the 3x3 rotation matrix generated by a rotation of a specified angle about a specified axis. This rotation is thought of as rotating the coordinate system.

RPD Return the number of radians per degree.

SPKEZ Return the apparent state (position and velocity) of a target body relative to an observing body, optionally corrected for planetary (light time) and stellar aberrations.