A Very Brief Introduction to SPICE

The SPICE (Spacecraft Planets Instrument C- Matrix Events) information system uses ancillary data to provide solar system geometry information to scientists and engineers for planetary missions in order to plan and analyze scientific observations from space-born instruments.

A SPICE archive includes the complete set of SPICE data files (kernel files) for a given mission, which can be accessed using SPICE software. The SPICE data contain geometric and other ancillary information needed to recover the full value of science instrument data. In particular SPICE kernels provide spacecraft and planetary ephemerides, spacecraft and instrument orientation, instrument mounting alignments, data specifying target body size, shape and orientation, and data needed for relevant time conversions. Data in SPICE kernel files must be accessed using the software called the SPICE Toolkit produced and distributed by the Navigation and Ancillary Information Facility (NAIF) Node of the Planetary Data System.

The SPICE toolkit is available in FORTRAN, C at the NAIF web site. Interfaces to higher-level data analysis software in the Interactive Data Language (IDL), Matlab and JAVA are also provided. There are several other wrappers amongst which we highlight the Python wrapper SpiceyPy.

SPICE Kernels Organization

SPICE kernels in a SPICE archive are grouped into a set of subdirectories. Each subdirectory contains one specific kernel type; those types are briefly described here.

  • spk/ (Spacecraft Planet Kernel) files contain ephemerides (position and velocity) for spacecraft, planets, satellites, comets and asteroids as well as for moving or fixed spacecraft and instrument structures.

  • pck/ (Planetary Constants Kernel) files contain certain physical, dynamical and cartographic constants for target bodies, such as size and shape specifications, and orientation of the spin axis and prime meridian.

  • ik/ (Instrument Kernel) files contain instrument parameters relevant for computing an instrument’s geometry such as field-of-view definitions, CCD and optical distortion characteristics, and internal timing parameters.

  • ck/ (C-matrix Kernel) files contain time varying orientations for spacecraft, spacecraft structures, and articulating science instruments.

  • lsk/ (Leapseconds Kernel) files contain the leapseconds and the values of other constants required to perform a transformation between Universal Time Coordinated (UTC) and Ephemeris time (ET), which is also known as Barycentric Dynamical Time (TDB).

  • sclk/ (Spacecraft Clock Kernel) files contain on-board clock calibration data required to perform a transformation between Ephemeris time (ET) and spacecraft on-board time (SCLK).

  • fk/ (Frame definitions Kernel) files contain information required to define reference frames, sources of frame orientation data and connections between these frames and other frames supported within the SPICE system. The science instrument frame definitions provided in the FK files include mounting alignment information for the instruments.

  • dsk/ (Digital Shape Kernel) files contain detailed shape models for extended objects such as planets, natural satellites, asteroids, and comet nuclei.

A SPICE archive contains one additional subdirectory holding meta-kernels, described here.

  • mk/ (Meta-Kernel) files list sets of related SPICE kernels that should be used together, providing an easy way to make data from these kernel sets available to a SPICE-based application by loading meta-kernels into the program using the high level SPICE data loader routine FURNSH.