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Mars Reference Frames

Brahe provides two Mars-centered reference frames: MCI (inertial) and MCMF (body-fixed). MCI is used as the integration frame for Mars-centered propagation; MCMF expresses a state relative to Mars's rotating surface using the IAU/WGCCRE pole and prime-meridian model1.

MCI (Mars-Centered Inertial)

MCI axes are ICRF-aligned (treated as equivalent to J2000, consistent with the rest of Brahe) and centered on the Mars body center (NAIF ID 499). No kernel is required for the MCI orientation itself. Converting between MCI and ECI requires Mars's position relative to Earth: the bundled de440s SPK kernel carries only the Mars system barycenter (NAIF ID 4), so the body-center leg from the barycenter to NAIF 499 is resolved through the mar099s satellite ephemeris kernel, which is auto-loaded on first use alongside de440s.

MCMF (Mars-Centered Mars-Fixed)

MCMF is the body-fixed frame defined by the IAU Working Group on Cartographic Coordinates and Rotational Elements (WGCCRE) pole and prime-meridian model for Mars1. Unlike the Moon's LFPA frame, no external kernel is required — the WGCCRE polynomial model is compiled directly into Brahe (see rotation_icrf_to_body_fixed_iau and iau_rotation_model_ids). It is equivalent to the IAU_MARS frame realized by SPICE.

Function Reference

Conversion Function
MCI → MCMF rotation_mci_to_mcmf, position_mci_to_mcmf, state_mci_to_mcmf
MCMF → MCI rotation_mcmf_to_mci, position_mcmf_to_mci, state_mcmf_to_mci
ECI ↔ MCI position_eci_to_mci/position_mci_to_eci, state_eci_to_mci/state_mci_to_eci

All rotation functions return a 3x3 direction cosine matrix; all position_*/state_* functions take and return SI units (m, m/s). See the Mars Frames API Reference for full signatures.

For propagating an orbit about Mars and reporting it in the MCMF frame, see Propagation Around Other Central Bodies.

See Also

  1. Archinal, B. A., Acton, C. H., A'Hearn, M. F., et al. (2018). Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015. Celestial Mechanics and Dynamical Astronomy, 130(3), 22. Brahe's embedded Mars pole/prime-meridian polynomial is taken from this report and matches SPICE's IAU_MARS realization. ↩↩