New Coordinate Systems for Solar System Bodies
The International Astronomical Union (IAU) has published a new report with their latest recommendations for the cartographic coordinates and rotational elements of planetary bodies. The new guidelines, equations, and coefficients have been updated based on the latest data (including from interplanetary missions such as MESSENGER, Dawn, Rosetta, and Stardust-NExT).
One difference from the previous reports is that the low-fidelity Earth and Moon frames have been removed "in order to avoid confusion", since high-accuracy Earth and Moon frames are available. I mentioned the IAU_EARTH and IAU_MOON frames in a previous post. They are available in SPICE and the Fortran Astrodynamics Toolkit. I think it's unfortunate that they were removed. It's true that these are not ultra-precise frames (see, for example, this tutorial from JPL). However, low-to-medium fidelity frames are still very useful for many applications, including spacecraft trajectory optimization. A frame that is good enough, is very fast to compute, is continuous and differentiable for all time, and can be implemented in a few lines of code is often preferable to having to deal with thousands of lines of SOFA or SPICE code, leap second confusion, binary kernel files, etc. that are required to get the high-accuracy frames to work.
See also
- New Coordinate Systems for Solar System Bodies, IAU Announcement ann18010, Feb 27, 2018.
- B. A. Archinal, et. al., "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015", Celestial Mechanics and Dynamical Astronomy, Vol 130, Number 3, Feb 23, 2018.
- "High Accuracy" Orientation and Body-fixed Frames for the Moon and Earth, NAIF/JPL, January 2018.