# Parameter Settings

The parameter estimation framework of Tudat allows an ever increasing variety of parameters to be estimated, examples of which include:

Initial translational and rotational states of any number of bodies,

Properties of a body, such as a gravitational parameter \(\mu\)

Properties of a ground station, such as its body-fixed position \(\mathbf{x}_{GS}^{(B)}\)

Global properties of the simulation, such a Parameterize Post_Newtonian (PPN) parameters \(\gamma\) and \(\beta\)

Acceleration model properties, such as empirical acceleration magnitudes

Observation model properties, such as absolute and relative observation biases

In Tudat, these parameters influence the simulation in a variety of manners, and during propagation and/or observation simulation. Nevertheless, a *unified* framework is provided for defining any type of parameter. Very similar to the manner in which, for instance, acceleration or dependent variable settings are defined, a user must supply a list of parameter settings.

When only wishing to propagate the state transition matrix \(\Phi(t,t_{0})\) (or depending on your use case, only estimate initial state parameters), the following line the relevant settings:

Required

Show/Hideparameter_settings = estimation_setup.parameter.initial_states( propagator_settings, bodies )

- language
cpp

which defines the initial state parameters to be fully consistent with the settings in the propagator_settings.

Note

Options exist to manually define initial state parameters. However, at present, the initial state parameters **must** be consistent with the propagator settings, and these additional options are not described here.

When wishing to propagate the sensitivity matrix \(S(t)\) (or depending on your use case, estimate parameters in addtion to initial state parameters), the set of parameters can be extended using the following:

Required

Show/Hideparameter_settings = estimation_setup.parameter.initial_states( propagator_settings, bodies ) parameter_settings.append( estimation_setup.parameter.gravitational_parameter("Earth") ) parameter_settings.append( estimation_setup.parameter.constant_drag_coefficient("Delfi-C3") ) parameter_settings.append( estimation_setup.parameter.radiation_pressure_coefficient("Delfi-C3") )

In the snippet above, parameters are created to estimate the initial states in the propagator_settings (presumably Delfi C-3 initial translational states), the gravitational parameter of the Earth, the constant drag and the radiation pressure coefficient of Delfi-C3.

For the full list of available parameters, see Available Parameters.