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Force Model Configuration

Configuration classes for numerical orbit propagation force models. ForceModelConfig provides factory methods for common configurations and allows customization of gravity, atmospheric drag, solar radiation pressure, and third-body perturbations.

Note

For conceptual explanations and usage examples, see Force Models in the User Guide.

ForceModelConfig

ForceModelConfig 

ForceModelConfig(gravity: GravityConfiguration = None, drag: DragConfiguration = None, srp: SolarRadiationPressureConfiguration = None, third_body: ThirdBodyConfiguration = None, relativity: bool = False, mass: ParameterSource = None)

Force model configuration for numerical orbit propagation.

Defines all perturbation forces to be included: gravity, drag, SRP, third-body, relativity.

Parameters:

Name Type Description Default
gravity GravityConfiguration

Gravity model configuration. Default is point mass gravity.

 None
drag DragConfiguration

Atmospheric drag configuration. Default is None (disabled).

 None
srp SolarRadiationPressureConfiguration

Solar radiation pressure configuration. Default is None (disabled).

 None
third_body ThirdBodyConfiguration

Third-body perturbations configuration. Default is None (disabled).

 None
relativity bool

Enable relativistic corrections. Default is False.

 False
mass ParameterSource

Spacecraft mass source. Default is None.

 None

Attributes:

Name Type Description
gravity GravityConfiguration

Gravity model configuration
drag DragConfiguration or None

Atmospheric drag configuration
srp SolarRadiationPressureConfiguration or None

Solar radiation pressure configuration
third_body ThirdBodyConfiguration or None

Third-body perturbations configuration
relativity bool

Enable relativistic corrections
mass ParameterSource or None

Spacecraft mass source
Example 
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import brahe as bh

# Create with explicit parameters
config = bh.ForceModelConfig(
    gravity=bh.GravityConfiguration(degree=20, order=20),
    relativity=True,
)

# Or use convenience class methods
config = bh.ForceModelConfig.default()
config = bh.ForceModelConfig.two_body()

Initialize instance.

drag property 

drag: Any

Get the drag configuration (None if disabled).

gravity property 

gravity: Any

Get the gravity configuration.

mass property 

mass: Any

Get the mass parameter source (None if not required).

relativity property 

relativity: Any

Get whether relativistic corrections are enabled.

srp property 

srp: Any

Get the solar radiation pressure configuration (None if disabled).

third_body property 

third_body: Any

Get the third-body configuration (None if disabled).

conservative_forces builtin 

conservative_forces() -> ForceModelConfig

Create a conservative forces configuration (gravity + third-body + relativity, no drag/SRP).

default builtin 

default() -> ForceModelConfig

Create a default force model configuration.

Includes: - 20x20 EGM2008 gravity - Harris-Priester atmospheric drag - Solar radiation pressure with conical eclipse - Sun and Moon third-body perturbations

Requires parameter vector: [mass, drag_area, Cd, srp_area, Cr]

earth_gravity builtin 

earth_gravity() -> ForceModelConfig

Create an Earth gravity-only configuration (no drag, SRP, or third-body).

Uses 20x20 EGM2008 gravity. No parameter vector required.

geo_default builtin 

geo_default() -> ForceModelConfig

Create a configuration suitable for GEO satellites.

Includes SRP and third-body perturbations, omits drag. Requires parameter vector: [mass, , , srp_area, Cr]

high_fidelity builtin 

high_fidelity() -> ForceModelConfig

Create a high-fidelity force model configuration.

Includes: - 120x120 EGM2008 gravity - NRLMSISE-00 atmospheric model - SRP with conical eclipse - Sun, Moon, and all planets (DE440s ephemerides) - Relativistic corrections

Requires parameter vector: [mass, drag_area, Cd, srp_area, Cr]

leo_default builtin 

leo_default() -> ForceModelConfig

Create a configuration suitable for LEO satellites.

Includes drag and higher-order gravity, plus SRP and third-body. Requires parameter vector: [mass, drag_area, Cd, srp_area, Cr]

requires_params method descriptor 

requires_params() -> Any

Check if this configuration requires a parameter vector.

two_body builtin 

two_body() -> ForceModelConfig

Create a two-body (point mass) gravity configuration.

Uses only central body gravity with no perturbations. Produces results equivalent to Keplerian propagation. No parameter vector required.

Configuration Components

GravityConfiguration 

GravityConfiguration(degree: int = None, order: int = None, model_type: GravityModelType = None, use_global: bool = False)

Gravity model configuration.

Specifies the gravity model: point mass or spherical harmonic expansion.

Parameters:

Name Type Description Default
degree int

Maximum degree of spherical harmonic expansion. If None, uses point mass gravity.

 None
order int

Maximum order of spherical harmonic expansion. If None, uses point mass gravity.

 None
model_type GravityModelType

Gravity model to use. Defaults to EGM2008_360.

 None
use_global bool

If True, use global gravity model. Defaults to False.

 False
Example 
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import brahe as bh

# Simple two-body point mass gravity (default)
gravity = bh.GravityConfiguration()

# Spherical harmonic with 20x20 degree/order
gravity = bh.GravityConfiguration(degree=20, order=20)

# Spherical harmonic with specific model
gravity = bh.GravityConfiguration(
    degree=20, order=20, model_type=bh.GravityModelType.GGM05S
)

# Alternative: use class methods
gravity = bh.GravityConfiguration.point_mass()
gravity = bh.GravityConfiguration.spherical_harmonic(degree=20, order=20)

Initialize instance.

get_degree method descriptor 

get_degree() -> int

Get the degree (for spherical harmonic).

Returns:

Type Description
int

int or None: Degree if spherical harmonic, None otherwise.

get_order method descriptor 

get_order() -> int

Get the order (for spherical harmonic).

Returns:

Type Description
int

int or None: Order if spherical harmonic, None otherwise.

is_point_mass method descriptor 

is_point_mass() -> Any

Check if this is point mass gravity.

is_spherical_harmonic method descriptor 

is_spherical_harmonic() -> Any

Check if this is spherical harmonic gravity.

point_mass builtin 

point_mass() -> GravityConfiguration

Create a point mass gravity configuration.

Returns:

Name Type Description
GravityConfiguration GravityConfiguration

Point mass (two-body) gravity.

spherical_harmonic builtin 

spherical_harmonic(degree: int, order: int, model_type: GravityModelType = None, use_global: bool = False) -> GravityConfiguration

Create a spherical harmonic gravity configuration.

Parameters:

Name Type Description Default
degree int

Maximum degree of expansion.

 required
order int

Maximum order of expansion.

 required
model_type GravityModelType

Gravity model to use. Defaults to EGM2008_360.

 None
use_global bool

If True, use global gravity model. Defaults to False.

 False

Returns:

Name Type Description
GravityConfiguration GravityConfiguration

Spherical harmonic gravity.
Example 
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import brahe as bh

# Default (EGM2008)
gravity = bh.GravityConfiguration.spherical_harmonic(degree=20, order=20)

# With specific model
gravity = bh.GravityConfiguration.spherical_harmonic(
    degree=20, order=20, model_type=bh.GravityModelType.GGM05S
)

DragConfiguration 

DragConfiguration(model: AtmosphericModel, area: ParameterSource, cd: ParameterSource)

Atmospheric drag configuration.

Defines the atmospheric model and drag parameters.

Parameters:

Name Type Description Default
model AtmosphericModel

Atmospheric density model.

 required
area ParameterSource

Drag cross-sectional area source [m²].

 required
cd ParameterSource

Drag coefficient source (dimensionless).

 required

Attributes:

Name Type Description
model AtmosphericModel

Atmospheric density model
area ParameterSource

Drag area source
cd ParameterSource

Drag coefficient source
Example 
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import brahe as bh

drag = bh.DragConfiguration(
    model=bh.AtmosphericModel.HARRIS_PRIESTER,
    area=bh.ParameterSource.parameter_index(1),
    cd=bh.ParameterSource.value(2.2)
)

Initialize instance.

area property 

area: Any

Get the drag area parameter source.

cd property 

cd: Any

Get the drag coefficient parameter source.

model property 

model: Any

Get the atmospheric model.

SolarRadiationPressureConfiguration 

SolarRadiationPressureConfiguration(area: ParameterSource, cr: ParameterSource, eclipse_model: EclipseModel)

Solar radiation pressure configuration.

Defines the SRP parameters and eclipse model.

Parameters:

Name Type Description Default
area ParameterSource

SRP cross-sectional area source [m²].

 required
cr ParameterSource

Coefficient of reflectivity source (dimensionless).

 required
eclipse_model EclipseModel

Eclipse model for shadow effects.

 required

Attributes:

Name Type Description
area ParameterSource

SRP area source
cr ParameterSource

Reflectivity coefficient source
eclipse_model EclipseModel

Eclipse model
Example 
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import brahe as bh

srp = bh.SolarRadiationPressureConfiguration(
    area=bh.ParameterSource.parameter_index(3),
    cr=bh.ParameterSource.parameter_index(4),
    eclipse_model=bh.EclipseModel.CONICAL
)

Initialize instance.

area property 

area: Any

Get the SRP area parameter source.

cr property 

cr: Any

Get the coefficient of reflectivity parameter source.

eclipse_model property 

eclipse_model: Any

Get the eclipse model.

ThirdBodyConfiguration 

ThirdBodyConfiguration(ephemeris_source: EphemerisSource, bodies: list[ThirdBody])

Third-body perturbations configuration.

Defines which celestial bodies to include and ephemeris source.

Parameters:

Name Type Description Default
ephemeris_source EphemerisSource

Source for celestial body ephemerides.

 required
bodies list[ThirdBody]

List of bodies to include as perturbers.

 required

Attributes:

Name Type Description
ephemeris_source EphemerisSource

Ephemeris source
bodies list[ThirdBody]

List of perturbing bodies
Example 
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import brahe as bh

third_body = bh.ThirdBodyConfiguration(
    ephemeris_source=bh.EphemerisSource.DE440s,
    bodies=[bh.ThirdBody.SUN, bh.ThirdBody.MOON]
)

Initialize instance.

bodies property 

bodies: Any

Get the list of third bodies.

ephemeris_source property 

ephemeris_source: Any

Get the ephemeris source.

Enumerations

AtmosphericModel 

AtmosphericModel()

Atmospheric density model selection.

Example 
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import brahe as bh

model = bh.AtmosphericModel.HARRIS_PRIESTER
model = bh.AtmosphericModel.NRLMSISE00

Initialize instance.

HARRIS_PRIESTER class-attribute 

HARRIS_PRIESTER: Any = AtmosphericModel(HarrisPriester)

Atmospheric density model selection.

Example 
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import brahe as bh

model = bh.AtmosphericModel.HARRIS_PRIESTER
model = bh.AtmosphericModel.NRLMSISE00

NRLMSISE00 class-attribute 

NRLMSISE00: Any = AtmosphericModel(NRLMSISE00)

Atmospheric density model selection.

Example 
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import brahe as bh

model = bh.AtmosphericModel.HARRIS_PRIESTER
model = bh.AtmosphericModel.NRLMSISE00

exponential builtin 

exponential(scale_height: float, rho0: float, h0: float) -> AtmosphericModel

Create exponential atmosphere model with custom parameters.

Parameters:

Name Type Description Default
scale_height float

Scale height in meters.

 required
rho0 float

Reference density in kg/m³.

 required
h0 float

Reference altitude in meters.

 required

EclipseModel 

EclipseModel()

Eclipse model for solar radiation pressure calculations.

Example 
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import brahe as bh

eclipse = bh.EclipseModel.CONICAL
eclipse = bh.EclipseModel.CYLINDRICAL

Initialize instance.

CONICAL class-attribute 

CONICAL: Any = EclipseModel.Conical

Eclipse model for solar radiation pressure calculations.

Example 
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import brahe as bh

eclipse = bh.EclipseModel.CONICAL
eclipse = bh.EclipseModel.CYLINDRICAL

CYLINDRICAL class-attribute 

CYLINDRICAL: Any = EclipseModel.Cylindrical

Eclipse model for solar radiation pressure calculations.

Example 
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import brahe as bh

eclipse = bh.EclipseModel.CONICAL
eclipse = bh.EclipseModel.CYLINDRICAL

NONE class-attribute 

NONE: Any = EclipseModel.None

Eclipse model for solar radiation pressure calculations.

Example 
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import brahe as bh

eclipse = bh.EclipseModel.CONICAL
eclipse = bh.EclipseModel.CYLINDRICAL

ThirdBody 

ThirdBody()

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

Example 
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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

Initialize instance.

JUPITER class-attribute 

JUPITER: Any = ThirdBody.JUPITER

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

Example 
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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

MARS class-attribute 

MARS: Any = ThirdBody.MARS

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

Example 
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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

MERCURY class-attribute 

MERCURY: Any = ThirdBody.MERCURY

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

Example 
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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

MOON class-attribute 

MOON: Any = ThirdBody.MOON

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

Example 
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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

NEPTUNE class-attribute 

NEPTUNE: Any = ThirdBody.NEPTUNE

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

SATURN class-attribute 

SATURN: Any = ThirdBody.SATURN

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

SUN class-attribute 

SUN: Any = ThirdBody.SUN

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

URANUS class-attribute 

URANUS: Any = ThirdBody.URANUS

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

VENUS class-attribute 

VENUS: Any = ThirdBody.VENUS

Third-body perturber.

Celestial bodies that can act as gravitational perturbers.

Example 
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import brahe as bh

sun = bh.ThirdBody.SUN
moon = bh.ThirdBody.MOON

ParameterSource 

ParameterSource()

Source for a parameter value (fixed or from parameter vector).

Allows specifying whether a parameter comes from a fixed value or from an index in the parameter vector.

Example 
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import brahe as bh

# Fixed drag coefficient
cd = bh.ParameterSource.value(2.2)

# Variable mass from parameter vector index 0
mass = bh.ParameterSource.parameter_index(0)

Initialize instance.

get_index method descriptor 

get_index() -> int

Get the parameter index (if this is a ParameterIndex source).

Returns:

Type Description
int

int or None: The parameter index, or None if this is a Value.

get_value method descriptor 

get_value() -> float

Get the fixed value (if this is a Value source).

Returns:

Type Description
float

float or None: The fixed value, or None if this is a ParameterIndex.

is_parameter_index method descriptor 

is_parameter_index() -> Any

Check if this source references a parameter index.

is_value method descriptor 

is_value() -> Any

Check if this source is a fixed value.

parameter_index builtin 

parameter_index(index: int) -> ParameterSource

Create a parameter index source.

Parameters:

Name Type Description Default
index int

Index into the parameter vector.

 required

Returns:

Name Type Description
ParameterSource ParameterSource

A parameter source referencing a parameter vector index.

value builtin 

value(value: float) -> ParameterSource

Create a fixed value parameter source.

Parameters:

Name Type Description Default
value float

The fixed parameter value.

 required

Returns:

Name Type Description
ParameterSource ParameterSource

A parameter source with a fixed value.

See Also