What is an ORBNUM File?

For some of the orbiter-style missions NAIF has created a derived geometry product known as an Orbit Number File (ORBNUM). The primary purpose of such a file is to provide SPICE users a means to determine the time boundaries for each orbit. Some additional orbit geometry information is also provided. An accompanying text file named orbinfo.txt explains the contents of the ORBNUM files.

ORBNUM files are plain text files consisting of two header lines (column labels) followed by one line of data per orbit.

If an ORBNUM file has been made for a mission it is found within an .../extras/orbnum folder of the SPICE data set.

Unlike for kernel files for which there are "readers" provided within the SPICE Toolkit, there are no ORBNUM-specific readers. Some Toolkits provide assorted text I/O and string manipulation modules (APIs) that could be useful in accessing ORBNUM files within a program. The SPICE tutorial named "other_functions" provides information about these capabilities.