SGP Propagator¶

The SGP4/SDP4 propagator for satellite orbit propagation using Two-Line Element (TLE) data.

SGPPropagator ¶

SGPPropagator()

Python wrapper for SGPPropagator (replaces TLE) SGP4/SDP4 satellite propagator using TLE data.

The SGP (Simplified General Perturbations) propagator implements the SGP4/SDP4 models for propagating satellites using Two-Line Element (TLE) orbital data. This is the standard model used for tracking objects in Earth orbit.

Example

import brahe as bh

# ISS TLE data (example)
line1 = "1 25544U 98067A   24001.50000000  .00016717  00000-0  30000-3 0  9005"
line2 = "2 25544  51.6400 150.0000 0003000 100.0000 260.0000 15.50000000300000"

# Create propagator
prop = bh.SGPPropagator.from_tle(line1, line2, step_size=60.0)

# Propagate to a specific epoch
epc = bh.Epoch.from_datetime(2024, 1, 2, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state_eci = prop.state(epc)
print(f"Position: {state_eci[:3]}")
print(f"Velocity: {state_eci[3:]}")

# Propagate multiple epochs
epochs = [epc + i*60.0 for i in range(10)]  # 10 minutes
states = prop.states(epochs)

Initialize instance.

doc `class-attribute` ¶

__doc__ = 'Python wrapper for SGPPropagator (replaces TLE)\nSGP4/SDP4 satellite propagator using TLE data.\n\nThe SGP (Simplified General Perturbations) propagator implements the SGP4/SDP4 models\nfor propagating satellites using Two-Line Element (TLE) orbital data. This is the standard\nmodel used for tracking objects in Earth orbit.\n\nExample:\n    ```python\n    import brahe as bh\n\n    # ISS TLE data (example)\n    line1 = "1 25544U 98067A   24001.50000000  .00016717  00000-0  30000-3 0  9005"\n    line2 = "2 25544  51.6400 150.0000 0003000 100.0000 260.0000 15.50000000300000"\n\n    # Create propagator\n    prop = bh.SGPPropagator.from_tle(line1, line2, step_size=60.0)\n\n    # Propagate to a specific epoch\n    epc = bh.Epoch.from_datetime(2024, 1, 2, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)\n    state_eci = prop.state(epc)\n    print(f"Position: {state_eci[:3]}")\n    print(f"Velocity: {state_eci[3:]}")\n\n    # Propagate multiple epochs\n    epochs = [epc + i*60.0 for i in range(10)]  # 10 minutes\n    states = prop.states(epochs)\n    ```'

str(object='') -> str str(bytes_or_buffer[, encoding[, errors]]) -> str

Create a new string object from the given object. If encoding or errors is specified, then the object must expose a data buffer that will be decoded using the given encoding and error handler. Otherwise, returns the result of object.str() (if defined) or repr(object). encoding defaults to 'utf-8'. errors defaults to 'strict'.

module `class-attribute` ¶

__module__ = 'brahe._brahe'

str(object='') -> str str(bytes_or_buffer[, encoding[, errors]]) -> str

Create a new string object from the given object. If encoding or errors is specified, then the object must expose a data buffer that will be decoded using the given encoding and error handler. Otherwise, returns the result of object.str() (if defined) or repr(object). encoding defaults to 'utf-8'. errors defaults to 'strict'.

current_epoch `property` ¶

current_epoch: Epoch

Get current epoch.

Returns:

Name	Type	Description
`Epoch`	`Epoch`	Current propagator epoch.

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
propagator = bh.SGPPropagator.from_tle(line1, line2)
propagator.step()
print(f"Current epoch: {propagator.current_epoch}")

epoch `property` ¶

epoch: Epoch

Get TLE epoch.

Returns:

Name	Type	Description
`Epoch`	`Epoch`	Epoch of the TLE data.

id `property` ¶

id: int

Get the current numeric ID.

Returns:

Type	Description
`int`	int or None: The numeric ID, or None if not set.

name `property` ¶

name: str

Get the current name.

Returns:

Type	Description
`str`	str or None: The name, or None if not set.

norad_id `property` ¶

norad_id: int

Get NORAD ID.

Returns:

Name	Type	Description
`int`	`int`	NORAD catalog ID.

satellite_name `property` ¶

satellite_name: str

Get satellite name (if available).

Returns:

Type	Description
`str`	str or None: Satellite name if provided.

Example

import brahe as bh

name = "ISS (ZARYA)"
line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
propagator = bh.SGPPropagator.from_3le(name, line1, line2)
print(f"Satellite: {propagator.satellite_name}")

step_size `property` ¶

step_size: float

Get step size in seconds.

Returns:

Name	Type	Description
`float`	`float`	Step size in seconds.

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
propagator = bh.SGPPropagator.from_tle(line1, line2)
print(f"Step size: {propagator.step_size} seconds")

trajectory `property` ¶

trajectory: OrbitTrajectory

Get accumulated trajectory.

Returns:

Name	Type	Description
`OrbitalTrajectory`	`OrbitTrajectory`	The accumulated trajectory.

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
prop.propagate_steps(100)
traj = prop.trajectory
print(f"Trajectory has {traj.len()} states")

uuid `property` ¶

uuid: str

Get the current UUID.

Returns:

Type	Description
`str`	str or None: The UUID as a string, or None if not set.

repr `method descriptor` ¶

__repr__() -> str

Return repr(self).

str `method descriptor` ¶

__str__() -> str

Return str(self).

current_state `method descriptor` ¶

current_state() -> ndarray

Get current state vector.

Returns:

Type	Description
`ndarray`	numpy.ndarray: Current state vector in the propagator's output format.

from_3le `builtin` ¶

from_3le(name: str, line1: str, line2: str, step_size: float = 60.0) -> SGPPropagator

Create a new SGP propagator from 3-line TLE format (with satellite name).

Parameters:

Name	Type	Description	Default
`name`	`str`	Satellite name (line 0).	required
`line1`	`str`	First line of TLE data.	required
`line2`	`str`	Second line of TLE data.	required
`step_size`	`float`	Step size in seconds for propagation. Defaults to 60.0.	`60.0`

Returns:

Name	Type	Description
`SGPPropagator`	`SGPPropagator`	New SGP propagator instance.

from_tle `builtin` ¶

from_tle(line1: str, line2: str, step_size: float = 60.0) -> SGPPropagator

Create a new SGP propagator from TLE lines.

Parameters:

Name	Type	Description	Default
`line1`	`str`	First line of TLE data.	required
`line2`	`str`	Second line of TLE data.	required
`step_size`	`float`	Step size in seconds for propagation. Defaults to 60.0.	`60.0`

Returns:

Name	Type	Description
`SGPPropagator`	`SGPPropagator`	New SGP propagator instance.

generate_uuid `method descriptor` ¶

generate_uuid() -> Any

Generate a new UUID and set it in-place (mutating).

get_elements `method descriptor` ¶

get_elements(angle_format: AngleFormat) -> ndarray

Get Keplerian orbital elements from TLE data.

Extracts the Keplerian elements directly from the TLE lines used to initialize this propagator.

Parameters:

Name	Type	Description	Default
`angle_format`	`AngleFormat`	Format for angular elements (DEGREES or RADIANS).	required

Returns:

Type	Description
`ndarray`	numpy.ndarray: Keplerian elements [a, e, i, Ω, ω, M] where: - a: semi-major axis [m] - e: eccentricity [dimensionless] - i: inclination [rad or deg] - Ω: right ascension of ascending node [rad or deg] - ω: argument of periapsis [rad or deg] - M: mean anomaly [rad or deg]

Example

import brahe as bh

line1 = "1 25544U 98067A   08264.51782528 -.00002182  00000-0 -11606-4 0  2927"
line2 = "2 25544  51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537"
prop = bh.SGPPropagator.from_tle(line1, line2)

# Get elements in degrees
oe_deg = prop.get_elements(bh.AngleFormat.DEGREES)
print(f"Inclination: {oe_deg[2]:.4f} degrees")

# Get elements in radians
oe_rad = prop.get_elements(bh.AngleFormat.RADIANS)
print(f"Inclination: {oe_rad[2]:.4f} radians")

initial_state `method descriptor` ¶

initial_state() -> ndarray

Get initial state vector.

Returns:

Type	Description
`ndarray`	numpy.ndarray: Initial state vector in the propagator's output format.

propagate_steps `method descriptor` ¶

propagate_steps(num_steps: int) -> Any

Propagate forward by specified number of steps.

Parameters:

Name	Type	Description	Default
`num_steps`	`int`	Number of steps to take.	required

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2, step_size=60.0)
prop.propagate_steps(10)  # Advance by 10 steps (600 seconds)
print(f"After 10 steps: {prop.current_epoch}")

propagate_to `method descriptor` ¶

propagate_to(target_epoch: Epoch) -> Any

Propagate to a specific target epoch.

Parameters:

Name	Type	Description	Default
`target_epoch`	`Epoch`	The epoch to propagate to.	required

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
target = prop.epoch + 7200.0  # 2 hours later
prop.propagate_to(target)
print(f"Propagated to: {prop.current_epoch}")

reset `method descriptor` ¶

reset() -> Any

Reset propagator to initial conditions.

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
initial_epoch = prop.epoch
prop.propagate_steps(100)
prop.reset()
print(f"Reset to: {prop.current_epoch == initial_epoch}")

set_eviction_policy_max_age `method descriptor` ¶

set_eviction_policy_max_age(max_age: float) -> Any

Set trajectory eviction policy based on maximum age.

Parameters:

Name	Type	Description	Default
`max_age`	`float`	Maximum age in seconds to keep states in trajectory.	required

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
prop.set_eviction_policy_max_age(86400.0)  # Keep 1 day of history
print("Trajectory limited to 24 hours of states")

set_eviction_policy_max_size `method descriptor` ¶

set_eviction_policy_max_size(max_size: int) -> Any

Set trajectory eviction policy based on maximum size.

Parameters:

Name	Type	Description	Default
`max_size`	`int`	Maximum number of states to keep in trajectory.	required

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
prop.set_eviction_policy_max_size(1000)
print("Trajectory limited to 1000 states")

set_id `method descriptor` ¶

set_id(id: int or None) -> Any

Set the numeric ID in-place (mutating).

Parameters:

Name	Type	Description	Default
`id`	`int or None`	Numeric ID to assign, or None to clear.	required

set_identity `method descriptor` ¶

set_identity(name: str or None, uuid_str: str or None, id: int or None) -> Any

Set all identity fields in-place (mutating).

Parameters:

Name	Type	Description	Default
`name`	`str or None`	Optional name to assign.	required
`uuid_str`	`str or None`	Optional UUID string to assign.	required
`id`	`int or None`	Optional numeric ID to assign.	required

set_name `method descriptor` ¶

set_name(name: str or None) -> Any

Set the name in-place (mutating).

Parameters:

Name	Type	Description	Default
`name`	`str or None`	Name to assign, or None to clear.	required

set_output_format `method descriptor` ¶

set_output_format(frame: OrbitFrame, representation: OrbitRepresentation, angle_format: AngleFormat or None) -> Any

Set output format (frame, representation, and angle format).

Parameters:

Name	Type	Description	Default
`frame`	`OrbitFrame`	Output frame (ECI or ECEF).	required
`representation`	`OrbitRepresentation`	Output representation (Cartesian or Keplerian).	required
`angle_format`	`AngleFormat or None`	Angle format for Keplerian (None for Cartesian).	required

state `method descriptor` ¶

state(epoch: Epoch) -> ndarray

Compute state at a specific epoch.

Parameters:

Name	Type	Description	Default
`epoch`	`Epoch`	Target epoch for state computation.	required

Returns:

Type	Description
`ndarray`	numpy.ndarray: State vector in the propagator's current output format.

state_ecef `method descriptor` ¶

state_ecef(epoch: Epoch) -> ndarray

Compute state at a specific epoch in ECEF coordinates.

Parameters:

Name	Type	Description	Default
`epoch`	`Epoch`	Target epoch for state computation.	required

Returns:

Type	Description
`ndarray`	numpy.ndarray: State vector [x, y, z, vx, vy, vz] in ECEF frame.

state_eci `method descriptor` ¶

state_eci(epoch: Epoch) -> ndarray

Compute state at a specific epoch in ECI coordinates.

Parameters:

Name	Type	Description	Default
`epoch`	`Epoch`	Target epoch for state computation.	required

Returns:

Type	Description
`ndarray`	numpy.ndarray: State vector [x, y, z, vx, vy, vz] in ECI frame.

state_pef `method descriptor` ¶

state_pef(epoch: Epoch) -> ndarray

Compute state at a specific epoch in PEF coordinates.

Parameters:

Name	Type	Description	Default
`epoch`	`Epoch`	Target epoch for state computation.	required

Returns:

Type	Description
`ndarray`	numpy.ndarray: State vector [x, y, z, vx, vy, vz] in PEF frame.

states `method descriptor` ¶

states(epochs: list[Epoch]) -> List

Compute states at multiple epochs.

Parameters:

Name	Type	Description	Default
`epochs`	`list[Epoch]`	List of epochs for state computation.	required

Returns:

Type	Description
`List`	list[numpy.ndarray]: List of state vectors in the propagator's current output format.

states_eci `method descriptor` ¶

states_eci(epochs: list[Epoch]) -> List

Compute states at multiple epochs in ECI coordinates.

Parameters:

Name	Type	Description	Default
`epochs`	`list[Epoch]`	List of epochs for state computation.	required

Returns:

Type	Description
`List`	list[numpy.ndarray]: List of ECI state vectors.

step `method descriptor` ¶

step() -> Any

Step forward by the default step size.

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
prop.step()  # Advance by default step_size
print(f"Advanced to: {prop.current_epoch}")

step_by `method descriptor` ¶

step_by(step_size: float) -> Any

Step forward by a specified time duration.

Parameters:

Name	Type	Description	Default
`step_size`	`float`	Time step in seconds.	required

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
prop.step_by(120.0)  # Advance by 2 minutes
print(f"Advanced to: {prop.current_epoch}")

step_past `method descriptor` ¶

step_past(target_epoch: Epoch) -> Any

Step past a specified target epoch.

Parameters:

Name	Type	Description	Default
`target_epoch`	`Epoch`	The epoch to step past.	required

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2)
target = prop.epoch + 3600.0  # 1 hour later
prop.step_past(target)
print(f"Stepped past target")

with_id `method descriptor` ¶

with_id(id: int) -> SGPPropagator

Set the numeric ID and return self (consuming constructor pattern).

Parameters:

Name	Type	Description	Default
`id`	`int`	Numeric ID to assign to this propagator.	required

Returns:

Name	Type	Description
`SGPPropagator`	`SGPPropagator`	Self with ID set.

with_identity `method descriptor` ¶

with_identity(name: str or None, uuid_str: str or None, id: int or None) -> SGPPropagator

Set all identity fields at once and return self (consuming constructor pattern).

Parameters:

Name	Type	Description	Default
`name`	`str or None`	Optional name to assign.	required
`uuid_str`	`str or None`	Optional UUID string to assign.	required
`id`	`int or None`	Optional numeric ID to assign.	required

Returns:

Name	Type	Description
`SGPPropagator`	`SGPPropagator`	Self with identity set.

Example

import brahe as bh
import uuid

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
my_uuid = str(uuid.uuid4())
prop = bh.SGPPropagator.from_tle(line1, line2).with_identity("ISS", my_uuid, 25544)
print(f"Name: {prop.name}, ID: {prop.id}, UUID: {prop.uuid}")

with_name `method descriptor` ¶

with_name(name: str) -> SGPPropagator

Set the name and return self (consuming constructor pattern).

Parameters:

Name	Type	Description	Default
`name`	`str`	Name to assign to this propagator.	required

Returns:

Name	Type	Description
`SGPPropagator`	`SGPPropagator`	Self with name set.

Example

import brahe as bh

line1 = "1 25544U 98067A   21027.77992426  .00003336  00000-0  68893-4 0  9990"
line2 = "2 25544  51.6461 339.8014 0002571  24.9690  60.4407 15.48919393267689"
prop = bh.SGPPropagator.from_tle(line1, line2).with_name("My Satellite")
print(f"Name: {prop.name}")

with_new_uuid `method descriptor` ¶

with_new_uuid() -> SGPPropagator

Generate a new UUID, set it, and return self (consuming constructor pattern).

Returns:

Name	Type	Description
`SGPPropagator`	`SGPPropagator`	Self with new UUID set.

with_uuid `method descriptor` ¶

with_uuid(uuid_str: str) -> SGPPropagator

Set the UUID and return self (consuming constructor pattern).

Parameters:

Name	Type	Description	Default
`uuid_str`	`str`	UUID string to assign to this propagator.	required

Returns:

Name	Type	Description
`SGPPropagator`	`SGPPropagator`	Self with UUID set.

Overview¶

The SGP (Simplified General Perturbations) propagator implements the SGP4/SDP4 models for propagating satellites using TLE orbital data. This is the standard model used for tracking objects in Earth orbit and is maintained by NORAD/Space Force.

Key Features: - Industry-standard orbit propagation - Atmospheric drag modeling - Automatic selection between SGP4 (near-Earth) and SDP4 (deep-space) models - Compatible with standard TLE format

Module: brahe.orbits

Example Usage¶

import brahe as bh

# ISS TLE data (example)
line1 = "1 25544U 98067A   24001.50000000  .00016717  00000-0  30000-3 0  9005"
line2 = "2 25544  51.6400 150.0000 0003000 100.0000 260.0000 15.50000000300000"

# Create propagator from TLE
prop = bh.SGPPropagator.from_tle(line1, line2)

# Get current epoch
epoch = prop.epoch()

# Propagate to a specific time
future_epoch = epoch + 3600.0  # 1 hour later
state = prop.propagate(future_epoch)  # Returns [x, y, z, vx, vy, vz] in TEME frame

# Propagate to multiple times
import numpy as np
times = np.linspace(0, 86400, 100)  # 1 day in 100 steps
epochs = [epoch + dt for dt in times]
states = prop.propagate_multiple(epochs)  # Returns array of states

SGP Propagator¶

SGPPropagator ¶

__doc__ class-attribute ¶

__module__ class-attribute ¶

current_epoch property ¶

epoch property ¶

id property ¶

name property ¶

norad_id property ¶

satellite_name property ¶

step_size property ¶

trajectory property ¶

uuid property ¶

__repr__ method descriptor ¶

__str__ method descriptor ¶

current_state method descriptor ¶

from_3le builtin ¶

from_tle builtin ¶

generate_uuid method descriptor ¶

get_elements method descriptor ¶

initial_state method descriptor ¶

propagate_steps method descriptor ¶

propagate_to method descriptor ¶

reset method descriptor ¶

set_eviction_policy_max_age method descriptor ¶

set_eviction_policy_max_size method descriptor ¶

set_id method descriptor ¶

set_identity method descriptor ¶

set_name method descriptor ¶

set_output_format method descriptor ¶

state method descriptor ¶

state_ecef method descriptor ¶

state_eci method descriptor ¶

state_pef method descriptor ¶

states method descriptor ¶

states_eci method descriptor ¶

step method descriptor ¶

step_by method descriptor ¶

step_past method descriptor ¶

with_id method descriptor ¶

with_identity method descriptor ¶

with_name method descriptor ¶

with_new_uuid method descriptor ¶

with_uuid method descriptor ¶

Overview¶

Example Usage¶

See Also¶

doc `class-attribute` ¶

module `class-attribute` ¶

current_epoch `property` ¶

epoch `property` ¶

id `property` ¶

name `property` ¶

norad_id `property` ¶

satellite_name `property` ¶

step_size `property` ¶

trajectory `property` ¶

uuid `property` ¶

repr `method descriptor` ¶

str `method descriptor` ¶

current_state `method descriptor` ¶

from_3le `builtin` ¶

from_tle `builtin` ¶

generate_uuid `method descriptor` ¶

get_elements `method descriptor` ¶

initial_state `method descriptor` ¶

propagate_steps `method descriptor` ¶

propagate_to `method descriptor` ¶

reset `method descriptor` ¶

set_eviction_policy_max_age `method descriptor` ¶

set_eviction_policy_max_size `method descriptor` ¶

set_id `method descriptor` ¶

set_identity `method descriptor` ¶

set_name `method descriptor` ¶

set_output_format `method descriptor` ¶

state `method descriptor` ¶

state_ecef `method descriptor` ¶

state_eci `method descriptor` ¶

state_pef `method descriptor` ¶

states `method descriptor` ¶

states_eci `method descriptor` ¶

step `method descriptor` ¶

step_by `method descriptor` ¶

step_past `method descriptor` ¶

with_id `method descriptor` ¶

with_identity `method descriptor` ¶

with_name `method descriptor` ¶

with_new_uuid `method descriptor` ¶

with_uuid `method descriptor` ¶