The "State vector output coordinate frame" parameter in the "Orbit Propagator Numerical" block has two options: ICRF and Fixed-frame.
- International Celestial Reference Frame (ICRF) is a space-fixed inertial reference frame defined by the International Astronomical Union (IAU). The ICRF is centered at the barycenter of the solar system, not at the center of the Earth. The ICRF axes are not dependent on the motion or orientation of the Earth. It is designed to be a reference frame that does not rotate with respect to distant celestial objects. When the central body is Earth, the "ICRF" frame option can be treated as equal to the ECI coordinate system realized at the J2000 epoch. The ECI coordinate is centered at the Earth’s center and is aligned with the ICRF. When the central body is moon, the ICRF axes are oriented in a space-fixed manner, with its center located at the barycenter of the solar system at J2000 epoch. You can refer to the following documentation to understand more about the ECI coordinates: https://www.mathworks.com/help/releases/R2024b/aeroblks/about-aerospace-coordinate-systems.html#bqsh8ni-1
- Fixed-frame is a generic term for the coordinate system that is fixed to the central body (its axes rotate with the central body and are not fixed in inertial space). When the central body is moon, the fixed-frame coordinate system for the moon is defined based on whether the moon libration angles are provided as input or not. You can refer to the following documentation to know more about the difference when Fixed-frame coordinate system is used for Earth and Moon as central body: https://www.mathworks.com/help/releases/R2024b/aeroblks/orbitpropagatornumericalhighprecision.html#mw_3689e744-e4c3-4874-af9f-86088dc270d9_sep_mw_dfb1936f-1b7a-4669-af47-5fb507048330_head
I hope this answers your query.
