This documents the ephemeris_slice function

;* The "mouse views ephemeris" function calls up a window with a 3-D display of
;* the satellite orbit. For this PAPCO-compatible routines that read the
;* ephemeris data for a given satellite are needed. Currently only supported
;* for POLAR. The idea is to extend this to draw a physical model of the 
;* magnetosphere too, to be able to view this model + orbit + satellite 
;* position from any angle etc - definitely still under development! A simple 
;* orbit visualization is in place for POLAR (CEPPAD and HYDRA modules).
;* -> user defined interface routine needed, no template included in 
;* $PAPCO_modules/plot_type/papco_interface/plot_type_slice.pro
