CASPER stores spacecraft attitude information in the form of C matrices, or equivalently, quaternions.
A C matrix is a rotation matrix between spacecraft coordinates and inertial coordinates.  A C matrix
thus uniquely defines the spacecraft's attitude in inertial space.  A C kernel is simply a binary file
with time-tagged C matrices.  CASPER generates a C matrix for each footprint and false footprint
in a module.  When a C kernel is saved, the C matrices for each of those footprints (actually, a
quaternion), along with the time of the initial placement of that footprint, is saved in a Type 3
NAIF C kernel.

Important information about CASPER C matrix conventions and output:
CASPER saves C kernels following the NAIF convention.  Quaternions give the rotation
from inertial (J2000) coordinates to spacecraft body coordinates.  However, for historical
reasons, the CASPER Output File writes quaternions which represent the inverse
rotation: spacecraft body coordinates to inertial coordinates.  Because the CASPER
Output File cannot be read directly by any NAIF routines, and for the sake of
continued compatibility with user software which does read the current CASPER
Output File format, the quaternion format in the CASPER Output File will remain
the same: S/C to J2000 transformation.  Because C kernels are NAIF products,
the C kernels written by CASPER conform to NAIF standards and have
J2000 to S/C transformation.