Acceleration Model Setup

Acceleration models can be created through the factory function create_acceleration_models().

How to select accelerations

In Tudat, an acceleration acting on a body is defined by:

• the body undergoing acceleration;

• the body exerting the acceleration;

• the type and settings of the acceleration.

These settings are defined via factory functions for each acceleration in the simulation.

See also

A comprehensive list of all available acceleration models in Tudat and the manner in which to define them is given in Available Acceleration Models.

For a single body, the user-specified settings are organized in nested dictionaries dict[str,dict[str,list[AccelerationSettings]]], with the first str denoting the body undergoing acceleration, the second str denoting the body exerting the acceleration, and the list of AccelerationSettings objects is created using the functions in the acceleration module.

This nested dictionary will be supplied to the create_acceleration_models() function to create the acceleration models. This is illustrated in the example below.

Example

In this example, the following accelerations are exerted on the vehicle:

• by the Earth:

  • spherical harmonic gravitational acceleration (degree and order 5)

  • aerodynamic acceleration

• by the Sun:

  • point-mass gravity

• by the Moon:

  • point-mass gravity

The variable accelerations_settings_vehicle denotes the list of bodies exerting accelerations and the types of accelerations, while the variable acceleration_settings associates this list with the body undergoing the acceleration. The function create_acceleration_models() creates the list of models that compute the accelerations during the propagation.

Python

Required

from tudatpy.numerical_simulation import propagation_setup

# Define bodies that are propagated
bodies_to_propagate = ["Vehicle"]

# Define central bodies
central_bodies = ["Earth"]

# Define accelerations acting on Vehicle
accelerations_settings_vehicle = dict(
    Sun=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ],
    Moon=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ],
    Earth=
    [
        propagation_setup.acceleration.spherical_harmonic_gravity(5, 5),
        propagation_setup.acceleration.aerodynamic()
    ])

# Create global accelerations settings dictionary
acceleration_settings = {"Vehicle": accelerations_settings_vehicle}

# Create acceleration models
acceleration_models = propagation_setup.create_acceleration_models(
    bodies, acceleration_settings,  bodies_to_propagate, central_bodies)

When propagating multiple bodies, the same list of settings may be re-used for multiple bodies. Below, an example is given for the definition of acceleration_settings for multiple bodies (Vehicle1 and Vehicle2) which are undergoing identical accelerations:

Python

Required

from tudatpy.numerical_simulation import propagation_setup

# Define bodies that are propagated
bodies_to_propagate = ["Vehicle1", "Vehicle2"]

# Define central bodies
central_bodies = ["Earth", "Earth"]

# Define accelerations acting on both vehicles
accelerations_settings_vehicle = dict(
    Sun=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ],
    Moon=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ],
    Earth=
    [
        propagation_setup.acceleration.spherical_harmonic_gravity(5, 5),
        propagation_setup.acceleration.aerodynamic()
    ])

# Create global accelerations settings dictionary
acceleration_settings = {"Vehicle1": accelerations_settings_vehicle,
			             "Vehicle2": accelerations_settings_vehicle}

# Create acceleration models
acceleration_models = propagation_setup.create_acceleration_models(
    bodies, acceleration_settings,  bodies_to_propagate, central_bodies)

Alternatively, separate acceleration settings may be defined for separate bodies and then combined into an acceleration_settings variable. Below, an example for such a case is given when propagating the Earth and Moon:

Python

Required

from tudatpy.numerical_simulation import propagation_setup

# Define bodies that are propagated
bodies_to_propagate = ["Moon", "Earth"]

# Define central bodies
central_bodies = ["Sun", "Sun"]

# Define accelerations acting on Vehicle
accelerations_settings_moon = dict(
    Sun=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ],
    Earth=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ]
    )

accelerations_settings_earth = dict(
    Sun=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ],
    Moon=
    [
        propagation_setup.acceleration.point_mass_gravity()
    ]
    )


# Create global accelerations settings dictionary.
acceleration_settings = {"Moon": accelerations_settings_moon,
			            "Earth": accelerations_settings_earth}

# Create acceleration models
acceleration_models = propagation_setup.create_acceleration_models(
    bodies, acceleration_settings,  bodies_to_propagate, central_bodies)