CK kernels contain spacecraft orientation information, correlated to spacecraft clock times. The information in these files, in combination with frame and instrument data can determine exactly what a Spacecraft’s camera and other instruments were pointing at and when.
Because these files are correlated to the Spacecraft’s internal clock time, a SCLK kernel is required to correlate the observations back to a relevant solar system time.
More information can be found by downloading the CK Tutorial:
https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/pdf/individual_docs/20_ck.pdf
