Implement spherical harmonic representation of planetary gravity
The Spherical Harmonic Gravity Model block implements the mathematical representation of spherical harmonic planetary gravity based on planetary gravitational potential. It provides a convenient way to describe a planet gravitational field outside of its surface in spherical harmonic expansion.
You can use spherical harmonics to modify the magnitude and direction of spherical gravity (-GM/r2). The most significant or largest spherical harmonic term is the second degree zonal harmonic, J2, which accounts for oblateness of a planet.
Use this block if you want more accurate gravity values than spherical gravity models. For example, nonatmospheric flight applications might require higher accuracy.
Specifies the parameter and output units:
Specify the degree of harmonic model. Recommended degrees are:
Specify if out-of-range input invokes a warning, error, or no action.
Specify the planetary model. From the list, select:
Earth — Is the latest Earth spherical harmonic gravitational model from National Geospatial-Intelligence Agency (NGA). This block provides the WGS-84 version of this gravitational model. You can use the EGM96 planetary model if you need to use the older standard for Earth.
Moon — Is best for lunar orbit determination based upon computational time required to compute orbits. This planet model was created in approximately the same year as LP165P with similar data.
Moon — Is best for extended lunar mission orbit accuracy. This planet model was created in approximately the same year as LP165P with similar data.
Enables you to specify your own planetary model. This option enables the Planet mat-file parameter.
Earth — Supports the gravity field model, EIGEN-GL04C (
When defining your own planetary model, the Degree parameter is limited to the maximum value for int16. When inputting a large degree, you might receive an out-of-memory error. For more information about avoiding out-of-memory errors in the MATLAB® environment, see Resolve “Out of Memory” Errors (MATLAB).
Specify a MAT-file that contains definitions for a custom planetary
aerogmm2b.mat file in the Aerospace Toolbox is
the default MAT-file for a custom planetary model.
This file must contain:
Scalar of planet equatorial radius in meters (m).
Scalar of planetary gravitational parameter in meters cubed per second squared (m3/s2)
Scalar of maximum degree.
(degree+1)-by-(degree+1) matrix containing normalized spherical harmonic coefficients matrix, C.
(degree+1)-by-(degree+1) matrix containing normalized spherical harmonic coefficients matrix, S.
When using a large value for Degree, you might receive an out-of-memory error. For more information about avoiding out-of-memory errors in the MATLAB environment, see Resolve “Out of Memory” Errors (MATLAB).
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