| Status Message Facility (SMF) | writes error and log messages |
| Process Control (PC) | the primary interface to the main system |
| Generic Input/Output (IO_Gen) | open and close files |
| Memory Allocation (MEM) | track memory usage and allow sharing |
| Level 0 access (IO_L0) | access Level 0 data |
| Metadata (MET) | read or write metadata |
| spacecraft ephemeris and attitude access (EPH) | read ephemeris and attitude data |
| time and date (TD) | time conversions |
| ancillary data access (AA) | read ancillary data |
| celestial body position (CBP) | locates sun, moon and planets |
| coordinate system conversion (CSC) | makes coordinate system conversions |
| constant and unit conversion (CUC) | table of constants and unit conversions |
| digital elevation model (DEM) | access digital elevation model data |
Documented by Jasmine S. Bartlett, COAS, Oregon State University.