Earth Gravity Models

gravmodel

Earth gravity models available for use

For details, see: http://icgem.gfz-potsdam.de/

jgm3 class-attribute

The "JGM3" gravity model

This model is used by default in the orbit propagators

jgm2 class-attribute

The "JGM2" gravity model

egm96 class-attribute

The "EGM96" gravity model

itugrace16 class-attribute

the ITU Grace 16 gravity model

gravity(pos, **kwargs)

Return acceleration due to Earth gravity at the input position

Parameters:

Name	Type	Description	Default
pos	list[float] | itrfcoord | ArrayLike[float]	Position as ITRF coordinate or numpy 3-vector representing ITRF position in meters	required

Other Parameters:

Name	Type	Description
model	gravmodel	The gravity model to use. Default is gravmodel.egm96
degree	int	Maximum degree of gravity model to use. Default is 6, maximum is 40
order	int	Maximum order of gravity model to use. Default is same as degree

Returns:

Type	Description
NDArray[float64]	acceleration in m/s^2 in the International Terrestrial Reference Frame (ITRF)

Notes

• For details of calculation, see Chapter 3.2 of: "Satellite Orbits: Models, Methods, Applications", O. Montenbruck and B. Gill, Springer, 2012.

Example

coord = satkit.itrfcoord(latitude_deg=42.44, longitude_deg=-71.15, altitude=0)
accel = satkit.gravity(coord)
print(accel)
# array with acceleration in m/s^2 in ITRF

gravity_and_partials(pos, **kwargs)

Gravity and partial derivatives of gravity with respect to Cartesian coordinates

Parameters:

Name	Type	Description	Default
pos	itrfcoord | ArrayLike[float]	Position as ITRF coordinate or numpy 3-vector representing ITRF position in meters	required

Other Parameters:

Name	Type	Description
model	gravmodel	The gravity model to use. Default is gravmodel.egm96
degree	int	Maximum degree of gravity model to use. Default is 6, maximum is 40
order	int	Maximum order of gravity model to use. Default is same as degree

Returns:

Type	Description
tuple[NDArray[float64], NDArray[float64]]	acceleration in m/s^2 and partial derivative of acceleration with respect to ITRF Cartesian coordinate in m/s^2 / m

For details of calculation, see Chapter 3.2 of: "Satellite Orbits: Models, Methods, Applications", O. Montenbruck and B. Gill, Springer, 2012.