Module: sphericalHarmonicsGravityModel

class SphericalHarmonicsGravityModel : public GravityModel

#include <sphericalHarmonicsGravityModel.h>

The Spherical Harmonics gravity model

Public Functions

std::optional<std::string> initializeParameters() override

Initialize all parameters necessary for the computation of gravity.

The attributes muBodyand radEquator must be set separately.

Will return an error message (string) if cBar or sBar were not set. Otherwise, returns an empty optional.

std::optional<std::string> initializeParameters(const GravBodyData&) override

Initialize all parameters necessary for the computation of gravity.

The attributes muBodyand radEquator are read from the given GravBodyData.

Will return an error message (string) if cBar or sBar were not set. Otherwise, returns an empty optional.

Eigen::Vector3d computeField(const Eigen::Vector3d &position_planetFixed) const override

Returns the gravity acceleration at a position around this body.

The position is given in the body-fixed reference frame. Likewise, the resulting acceleration should be given in the body-fixed reference frame.

Eigen::Vector3d computeField(const Eigen::Vector3d &position_planetFixed, size_t degree, bool include_zero_degree) const

Returns the gravity acceleration at a position around this body.

The position is given in the body-fixed reference frame. Likewise, the resulting acceleration should be given in the body-fixed reference frame.

If the given degree is smaller than the maximum degree stored in this class, then the field is computed using only degrees up to degree. If the requested degree is higher than the available one, an error is thrown.

If include_zero_degree is false the degree that corresponds to the spherical term (point-mass) of the gravity is ignored.

double computePotentialEnergy(const Eigen::Vector3d &positionWrtPlanet_N) const override

Returns the gravitational potential energy at a position around this body.

The current implementation returns the potential energy of a point-mass (the spherical harmonics coefficients of the body are ignored)

The position is given relative to the body and in the inertial reference frame.

Public Members

double radEquator = 0

[m] Reference radius for the planet

double muBody = 0

[m^3/s^2] Gravitation parameter for the planet

size_t maxDeg = 0

The maximum degree of Spherical Harmonics to use

A value of maxDeg greater than the size of cBar or sBar will cause an error. A value that is lower will truncate the spherical harmonics, ignoring any parameters in cBar/sBar with degree greater than maxDeg.

std::vector<std::vector<double>> cBar

The normalized “C” spherical harmonics coefficients

std::vector<std::vector<double>> sBar

The normalized “S” spherical harmonics coefficients

Private Members

mutable std::vector<std::vector<double>> aBar

The following parameters are used internally to compute the gravity.

They are coefficients used in the method of Pines for the gravity due to SH. For their definition, see the ‘Basilisk-GravityEffector’ documentation. [-] Eq. 61

std::vector<std::vector<double>> n1

[-] Eq. 63

std::vector<std::vector<double>> n2

[-] Eq. 64

std::vector<std::vector<double>> nQuot1

[-] Eq. 79

std::vector<std::vector<double>> nQuot2

[-] Eq. 80