# Available Parameters

The framework discussed in the previous section explains how the parameter_settings list is populated. The goal of this section is to list the available parameters that can be used in the variational equations (and which are therefore available for estimation in a state estimation problem), what syntax they use, and explain to which environment models they are linked.

Single Parameters
• gravitational_parameter

Gravitational parameter of a body, linked to a GravityFieldModel object, which may be a point-mass or (time-dependent) spherical harmonic field. Parameter size: 1. Secondary identifer: None.

estimation_setup.parameter.gravitational_parameter( "Earth" )

• constant_drag_coefficient

Drag coefficient of a body that is constant, linked to a CustomAerodynamicCoefficientInterface object derived from AerodynamicCoefficientInterface, which must have 0 independent variables for the coefficients. Parameter size: 1. Secondary identifer: None.

estimation_setup.parameter.constant_drag_coefficient( "Spacecraft" )

• constant_rotation_rate

Rotation rate of a body around a fixed axis, linked to a SimpleRotationalEphemeris object derived from RotationalEphemeris. Parameter size: 1. Secondary identifer: None.

estimation_setup.parameter.constant_rotation_rate( "Earth" )

• radiation_pressure_coefficient

Constant radiation pressure coefficient of a body, linked to a RadiationPressureInterface object. Parameter size: 1. Secondary identifer: None.

estimation_setup.parameter.radiation_pressure_coefficient( "Spacecraft" )

• rotation_pole_position

Fixed rotation axis about which a body rotates with a fixed rotation rate, linked to a SimpleRotationalEphemeris object. Parameter size: 2 (denoting pole right ascension and declination). Secondary identifer: None.

estimation_setup.parameter.rotation_pole_position( "Earth" )

• ground_station_position

Fixed body-fixed position of a ground station on a body, linked to a GroundStationState object (requires a GroundStationState class). Parameter size: 3 (denoting body-fixed x, y and z Cartesian position). Secondary identifer: Ground station name.

estimation_setup.parameter.ground_station_position( "GroundStation" )

• ppn_parameter_gamma

Parameter $$\gamma$$ used in Parametric Post-Newtonian (PPN) framework, linked to a PPNParameterSet object (nominally the global relativity::ppnParameterSet variable). Parameter size: 1. Note that the name of the associated body should be "global_metric". Secondary identifer: None.

• ppn_parameter_beta

Parameter $$\beta$$ used in Parametric Post-Newtonian (PPN) framework, linked to a PPNParameterSet object (nominally the global relativity::ppnParameterSet variable). Parameter size: 1. Note that the name of the associated body should be "global_metric". Secondary identifer: None.

• equivalence_principle_lpi_violation_parameter

Parameter used to compute influence of a gravitational potential on proper time rate, equals 0 in general relativity, not linked to any object, but instead the equivalencePrincipleLpiViolationParameter global variable (in namespace relativity. Parameter size: 1. Note that the name of the associated body should be "global_metric". Secondary identifer: None.

Initial State Parameters

Warning

These functions return lists of parameters, which means that they can not be simply added in a list creation statement like [parameter_1, parameter_2, ...]. Instead, this list needs to be concatenated to a list of ‘simple’ parameters, e.g. by using the + operator: parameter_settings + estimation_setup.parameter.initial_states(...).

The factory function for initial states uses the propagator settings to determine which type is needed, e.g. if a translational propagator is defined, the function will automatically create the parameters for initial translational state.

• initial_translational_state

• initial_translational_state_from_ephemeris

• arc_wise_initial_translational_state

• arc_wise_initial_translational_state_from_ephemeris

• initial_rotational_state

estimation_setup.parameter.initial_states( propagator_settings, bodies )

Spherical Harmonic Parameters
• spherical_harmonics_c_coefficients

Considers the cosine coefficients in the spherical harmonics gravity model for a body. There are two ways to specify which coefficients are to be used: giving min/max settings for degree and order, or giving block indices. The latter constitutes a list of tuples, where the first value is the degree and the second the order of the coefficient to be used. The length of this list can be arbitrary, as long as the pairs are unique.

estimation_setup.parameter.spherical_harmonics_c_coefficients(
"Earth", minimum_degree, minimum_order, maximum_degree,
maximum_order )

block_indices = [(1, 1), (2, 2), (3, 3)]
estimation_setup.parameter.spherical_harmonics_c_coefficients(
"Earth", block_indices )

• spherical_harmonics_s_coefficients

Considers the sine coefficients in the spherical harmonics gravity model for a body. There are two ways to specify which coefficients are to be used: giving min/max settings for degree and order, or giving block indices:

estimation_setup.parameter.spherical_harmonics_s_coefficients(
"Earth", minimum_degree, minimum_order, maximum_degree,
maximum_order )

block_indices = [(1, 1), (2, 2), (3, 3)]
estimation_setup.parameter.spherical_harmonics_s_coefficients(
"Earth", block_indices )

Tidal Love Number Parameters
• full_degree_tidal_love_number

• single_degree_variable_tidal_love_number

Constant Observation Bias Parameters
• constant_additive_observation_bias

• arc_wise_constant_additive_observation_bias

• constant_relative_observation_bias

• arc_wise_constant_relative_observation_bias

Empirical Acceleration Parameters
• constant_empirical_acceleration_terms

estimation_setup.parameter.constant_empirical_acceleration_terms( body, central_body )

• empirical_acceleration_coefficients

• arc_wise_empirical_acceleration_coefficients