NAME: spice_file_source PURPOSE: Provides a structure that contains information pertinent to the locaton (and downloading) of SPICE data files CALLING SEQUENCE: source=spice_file_source() TYPICAL USAGE: pathname = 'MAVEN/kernels/sclk/MVN_SCLKSCET.?????.tsc'' sclk_kernel = file_retrieve(pathname,_extra = spice_file_source() ,/last_version) INPUT: None required. If default_source is provided then the relevant structure elements are copied and used in the output KEYWORDS: SET : If set, then the values in DEFAULT_SOURCE are made permanent. OUTPUT: Structure: see FILE_RETRIEVE for a description of the elements $LastChangedBy: $ $LastChangedDate: $ $LastChangedRevision: $ $URL: $