DTrajectory

Dynamic-dimension trajectory container for N-dimensional state data.

DTrajectory

DTrajectory()

Dynamic-dimension trajectory container.

Stores a sequence of N-dimensional states at specific epochs with support for interpolation and automatic state eviction policies. Dimension is determined at runtime.

Initialize instance.

__doc__ class-attribute

__doc__ = 'Dynamic-dimension trajectory container.\n\nStores a sequence of N-dimensional states at specific epochs with support\nfor interpolation and automatic state eviction policies. Dimension is\ndetermined at runtime.'

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'.

length property

length: int

Get the number of states in the trajectory.

Returns:

Name	Type	Description
int	int	Number of states in the trajectory

Example

import brahe as bh
import numpy as np

traj = bh.DTrajectory(6)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
print(f"Trajectory length: {traj.length}")

__getitem__ method descriptor

__getitem__(key: str) -> Any

Return self[key].

__iter__ method descriptor

__iter__() -> Any

Implement iter(self).

__len__ method descriptor

__len__() -> int

Return len(self).

__new__ builtin

__new__(*args, **kwargs)

Create and return a new object. See help(type) for accurate signature.

__repr__ method descriptor

__repr__() -> str

Return repr(self).

__str__ method descriptor

__str__() -> str

Return str(self).

add method descriptor

add(epoch: Epoch, state: ndarray) -> Any

Add a state to the trajectory.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Time of the state	required
state	ndarray	N-element state vector where N is the trajectory dimension	required

Example

import brahe as bh
import numpy as np

traj = bh.DTrajectory(6)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)

clear method descriptor

clear() -> Any

Clear all states from the trajectory.

dimension method descriptor

dimension() -> int

Get the trajectory dimension (method form).

Returns:

Name	Type	Description
int	int	Dimension of the trajectory

Example

import brahe as bh

traj = bh.DTrajectory(6)
print(f"Dimension: {traj.dimension()}")

end_epoch method descriptor

end_epoch() -> Any

Get end epoch of trajectory

epoch_at_idx method descriptor

epoch_at_idx(index: int) -> Epoch

Get epoch at a specific index

Parameters:

Name	Type	Description	Default
index	int	Index of the epoch	required

Returns:

Name	Type	Description
Epoch	Epoch	Epoch at index

Example

import brahe as bh
import numpy as np

traj = bh.DTrajectory(6)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
retrieved_epc = traj.epoch_at_idx(0)

first method descriptor

first() -> Tuple

Get the first (epoch, state) tuple in the trajectory, if any exists.

Returns:

Type	Description
Tuple	tuple or None: Tuple of (Epoch, numpy.ndarray) for first state, or None if empty

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
first_epc, first_state = traj.first()

from_data builtin

from_data(epochs: list[Epoch], states: ndarray, interpolation_method: InterpolationMethod = None) -> DTrajectory

Create a trajectory from existing data.

Parameters:

Name	Type	Description	Default
epochs	list[Epoch]	List of time epochs	required
states	ndarray	2D array of states with shape (num_epochs, dimension) where each row is a state vector	required
interpolation_method	InterpolationMethod	Interpolation method (default Linear)	None

Returns:

Name	Type	Description
DTrajectory	DTrajectory	New trajectory instance populated with data

get method descriptor

get(index: int) -> Tuple

Get both epoch and state at a specific index.

Parameters:

Name	Type	Description	Default
index	int	Index to retrieve	required

Returns:

Name	Type	Description
tuple	Tuple	Tuple of (Epoch, numpy.ndarray) for epoch and state at the index

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
ret_epc, ret_state = traj.get(0)

get_eviction_policy method descriptor

get_eviction_policy() -> str

Get current eviction policy.

Returns:

Name	Type	Description
str	str	String representation of eviction policy

Example

import brahe as bh

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
policy = traj.get_eviction_policy()

get_interpolation_method method descriptor

get_interpolation_method() -> InterpolationMethod

Get interpolation method.

Returns:

Name	Type	Description
InterpolationMethod	InterpolationMethod	Current interpolation method

Example

import brahe as bh

traj = bh.DTrajectory(6)
method = traj.get_interpolation_method()

index_after_epoch method descriptor

index_after_epoch(epoch: Epoch) -> int

Get the index of the state at or after the given epoch.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Target epoch	required

Returns:

Name	Type	Description
int	int	Index of the state at or after the target epoch

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc1 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc1, state)
epc2 = bh.Epoch.from_datetime(2024, 1, 1, 11, 59, 0.0, 0.0, bh.TimeSystem.UTC)
index = traj.index_after_epoch(epc2)

index_before_epoch method descriptor

index_before_epoch(epoch: Epoch) -> int

Get the index of the state at or before the given epoch.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Target epoch	required

Returns:

Name	Type	Description
int	int	Index of the state at or before the target epoch

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc1 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc1, state)
epc2 = bh.Epoch.from_datetime(2024, 1, 1, 12, 1, 0.0, 0.0, bh.TimeSystem.UTC)
index = traj.index_before_epoch(epc2)

interpolate method descriptor

interpolate(epoch: Epoch) -> ndarray

Interpolate state at a given epoch using the configured interpolation method.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Target epoch	required

Returns:

Type	Description
ndarray	numpy.ndarray: Interpolated state vector

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc1 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state1 = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc1, state1)
epc2 = bh.Epoch.from_datetime(2024, 1, 1, 12, 2, 0.0, 0.0, bh.TimeSystem.UTC)
state2 = np.array([bh.R_EARTH + 510e3, 0.0, 0.0, 0.0, 7650.0, 0.0])
traj.add(epc2, state2)
epc_mid = bh.Epoch.from_datetime(2024, 1, 1, 12, 1, 0.0, 0.0, bh.TimeSystem.UTC)
state_interp = traj.interpolate(epc_mid)

interpolate_linear method descriptor

interpolate_linear(epoch: Epoch) -> ndarray

Interpolate state at a given epoch using linear interpolation.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Target epoch	required

Returns:

Type	Description
ndarray	numpy.ndarray: Linearly interpolated state vector

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc1 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state1 = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc1, state1)
epc2 = bh.Epoch.from_datetime(2024, 1, 1, 12, 2, 0.0, 0.0, bh.TimeSystem.UTC)
state2 = np.array([bh.R_EARTH + 510e3, 0.0, 0.0, 0.0, 7650.0, 0.0])
traj.add(epc2, state2)
epc_mid = bh.Epoch.from_datetime(2024, 1, 1, 12, 1, 0.0, 0.0, bh.TimeSystem.UTC)
state_interp = traj.interpolate_linear(epc_mid)

is_empty method descriptor

is_empty() -> bool

Check if trajectory is empty.

Returns:

Name	Type	Description
bool	bool	True if trajectory contains no states, False otherwise

Example

import brahe as bh

traj = bh.DTrajectory(6)
print(f"Is empty: {traj.is_empty()}")

last method descriptor

last() -> Tuple

Get the last (epoch, state) tuple in the trajectory, if any exists.

Returns:

Type	Description
Tuple	tuple or None: Tuple of (Epoch, numpy.ndarray) for last state, or None if empty

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
last_epc, last_state = traj.last()

len method descriptor

len() -> int

Get the number of states in the trajectory (alias for length).

Returns:

Name	Type	Description
int	int	Number of states in the trajectory

Example

import brahe as bh
import numpy as np

traj = bh.DTrajectory(6)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
print(f"Number of states: {traj.len()}")

nearest_state method descriptor

nearest_state(epoch: Epoch) -> Tuple

Get the nearest state to a given epoch.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Target epoch	required

Returns:

Name	Type	Description
tuple	Tuple	Tuple of (Epoch, numpy.ndarray) containing the nearest state

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc1 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc1, state)
epc2 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 30.0, 0.0, bh.TimeSystem.UTC)
nearest_epc, nearest_state = traj.nearest_state(epc2)

remove method descriptor

remove(index: int) -> Tuple

Remove a state at a specific index.

Parameters:

Name	Type	Description	Default
index	int	Index of the state to remove	required

Returns:

Name	Type	Description
tuple	Tuple	Tuple of (Epoch, numpy.ndarray) for the removed epoch and state

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
removed_epc, removed_state = traj.remove(0)

remove_epoch method descriptor

remove_epoch(epoch: Epoch) -> ndarray

Remove a state at a specific epoch.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Epoch of the state to remove	required

Returns:

Type	Description
ndarray	numpy.ndarray: The removed state vector

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
removed_state = traj.remove_epoch(epc)

set_eviction_policy_max_age method descriptor

set_eviction_policy_max_age(max_age: float) -> Any

Set maximum age for trajectory states.

Parameters:

Name	Type	Description	Default
max_age	float	Maximum age in seconds relative to most recent state	required

set_eviction_policy_max_size method descriptor

set_eviction_policy_max_size(max_size: int) -> Any

Set maximum trajectory size.

Parameters:

Name	Type	Description	Default
max_size	int	Maximum number of states to retain	required

set_interpolation_method method descriptor

set_interpolation_method(method: InterpolationMethod) -> Any

Set interpolation method.

Parameters:

Name	Type	Description	Default
method	InterpolationMethod	New interpolation method	required

Example

import brahe as bh

traj = bh.DTrajectory(6)
method = bh.InterpolationMethod.LINEAR
traj.set_interpolation_method(method)

start_epoch method descriptor

start_epoch() -> Any

Get start epoch of trajectory

state_after_epoch method descriptor

state_after_epoch(epoch: Epoch) -> Tuple

Get the state at or after the given epoch.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Target epoch	required

Returns:

Name	Type	Description
tuple	Tuple	Tuple of (Epoch, numpy.ndarray) containing state at or after the target epoch

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc1 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc1, state)
epc2 = bh.Epoch.from_datetime(2024, 1, 1, 11, 59, 0.0, 0.0, bh.TimeSystem.UTC)
ret_epc, ret_state = traj.state_after_epoch(epc2)

state_at_idx method descriptor

state_at_idx(index: int) -> ndarray

Get state at a specific index

Parameters:

Name	Type	Description	Default
index	int	Index of the state	required

Returns:

Type	Description
ndarray	numpy.ndarray: State vector at index

Example

import brahe as bh
import numpy as np

traj = bh.DTrajectory(6)
epc = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc, state)
retrieved_state = traj.state_at_idx(0)

state_before_epoch method descriptor

state_before_epoch(epoch: Epoch) -> Tuple

Get the state at or before the given epoch.

Parameters:

Name	Type	Description	Default
epoch	Epoch	Target epoch	required

Returns:

Name	Type	Description
tuple	Tuple	Tuple of (Epoch, numpy.ndarray) containing state at or before the target epoch

Example

import brahe as bh
import numpy as np

traj = bh.OrbitTrajectory(bh.OrbitFrame.ECI, bh.OrbitRepresentation.CARTESIAN, None)
epc1 = bh.Epoch.from_datetime(2024, 1, 1, 12, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([bh.R_EARTH + 500e3, 0.0, 0.0, 0.0, 7600.0, 0.0])
traj.add(epc1, state)
epc2 = bh.Epoch.from_datetime(2024, 1, 1, 12, 1, 0.0, 0.0, bh.TimeSystem.UTC)
ret_epc, ret_state = traj.state_before_epoch(epc2)

timespan method descriptor

timespan() -> Any

Get time span of trajectory in seconds

to_matrix method descriptor

to_matrix() -> ndarray

Get all states as a numpy array

with_eviction_policy_max_age method descriptor

with_eviction_policy_max_age(max_age: float) -> DTrajectory

Set eviction policy to keep states within maximum age using builder pattern

Parameters:

Name	Type	Description	Default
max_age	float	Maximum age of states in seconds	required

Returns:

Name	Type	Description
DTrajectory	DTrajectory	Self with updated eviction policy

Example

import brahe as bh

traj = bh.DTrajectory(6)
traj = traj.with_eviction_policy_max_age(3600.0)

with_eviction_policy_max_size method descriptor

with_eviction_policy_max_size(max_size: int) -> DTrajectory

Set eviction policy to keep maximum number of states using builder pattern

Parameters:

Name	Type	Description	Default
max_size	int	Maximum number of states to retain	required

Returns:

Name	Type	Description
DTrajectory	DTrajectory	Self with updated eviction policy

Example

import brahe as bh

traj = bh.DTrajectory(6)
traj = traj.with_eviction_policy_max_size(1000)

with_interpolation_method method descriptor

with_interpolation_method(interpolation_method: InterpolationMethod) -> DTrajectory

Set interpolation method using builder pattern

Parameters:

Name	Type	Description	Default
interpolation_method	InterpolationMethod	Interpolation method to use	required

Returns:

Name	Type	Description
DTrajectory	DTrajectory	Self with updated interpolation method

Example

import brahe as bh

traj = bh.DTrajectory(6)
traj = traj.with_interpolation_method(bh.InterpolationMethod.LINEAR)

Overview

DTrajectory is a flexible trajectory container where the state dimension is determined at runtime. Use this when you need to store state vectors of varying sizes or when the dimension isn't known at compile time.

Module: brahe.trajectories

Key Features: - Runtime dimension specification - Automatic time-ordering of states - Configurable interpolation (Linear or Lagrange) - Eviction policies for memory management - Efficient state queries and interpolation

Creating a Trajectory

import brahe as bh

# Create with specified dimension
traj = bh.DTrajectory(dimension=6)  # For orbital states

# Create with specific interpolation method
traj = bh.DTrajectory(
    dimension=3,
    interpolation_method=bh.InterpolationMethod.LAGRANGE
)

# Create from existing data
import numpy as np
epochs = [epoch1, epoch2, epoch3]
states = np.array([[x1,y1,z1], [x2,y2,z2], [x3,y3,z3]])
traj = bh.DTrajectory.from_data(
    epochs,
    states,
    interpolation_method=bh.InterpolationMethod.LINEAR
)

Adding States

import brahe as bh
import numpy as np

traj = bh.DTrajectory(dimension=6)

# Add single state
epoch = bh.Epoch.from_datetime(2024, 1, 1, 0, 0, 0.0, 0.0, bh.TimeSystem.UTC)
state = np.array([7e6, 0, 0, 0, 7.5e3, 0])
traj.add(epoch, state)

# Add multiple states from propagation
prop = bh.KeplerianPropagator(...)
for i in range(100):
    future_epoch = epoch + i * 60.0  # Every minute
    state = prop.propagate(future_epoch)
    traj.add(future_epoch, state)

Querying States

# Interpolate at specific epoch
query_epoch = epoch + 1800.0  # 30 minutes later
interp_state = traj.interpolate(query_epoch)

# Get state at specific index
state_10 = traj.state(10)
epoch_10 = traj.epoch(10)

# Get first and last states
first_epoch, first_state = traj.first()
last_epoch, last_state = traj.last()

# Get state before/after epoch
before_epoch, before_state = traj.state_before_epoch(query_epoch)
after_epoch, after_state = traj.state_after_epoch(query_epoch)

# Get all data
all_states = traj.to_matrix()  # Returns numpy array (n_states, dimension)
all_epochs = traj.to_epochs()  # Returns list of Epochs

Eviction Policies

Control memory usage by automatically removing old states:

# Maximum age: keep only states within 1 hour of newest
traj.set_eviction_policy_max_age(3600.0)

# Maximum size: keep only last 1000 states
traj.set_eviction_policy_max_size(1000)

# No eviction (default)
traj.set_eviction_policy_no_eviction()

# Builder pattern (method chaining)
traj = bh.DTrajectory(dimension=6) \
    .with_eviction_policy_max_age(3600.0) \
    .with_interpolation_method(bh.InterpolationMethod.LAGRANGE)

Interpolation Methods

# Linear interpolation (faster, less accurate)
traj.set_interpolation_method(bh.InterpolationMethod.LINEAR)

# Lagrange interpolation (slower, more accurate)
traj.set_interpolation_method(bh.InterpolationMethod.LAGRANGE)

Trajectory Information

# Get dimension
dim = traj.dimension()  # Returns dimension of state vectors

# Get size
n_states = traj.len()  # Number of states stored

# Check if empty
is_empty = traj.is_empty()

# Get time span
span = traj.timespan()  # Duration in seconds from first to last

# Get start/end epochs
start = traj.start_epoch()
end = traj.end_epoch()

Clearing and Removing States

# Clear all states
traj.clear()

# Remove state at specific epoch
removed_state = traj.remove_epoch(epoch)

# Remove state at index
removed_epoch, removed_state = traj.remove_at(index)

Complete Example

import brahe as bh
import numpy as np
import matplotlib.pyplot as plt

# Set up propagator
epoch_start = bh.Epoch.from_datetime(2024, 1, 1, 0, 0, 0.0, 0.0, bh.TimeSystem.UTC)
elements = np.array([7000e3, 0.001, 98*bh.DEG2RAD, 0, 0, 0])
prop = bh.KeplerianPropagator(
    epoch=epoch_start,
    elements=elements,
    element_type=bh.OrbitRepresentation.MEAN_ELEMENTS,
    frame=bh.OrbitFrame.ECI
)

# Create trajectory with eviction policy
traj = bh.DTrajectory(dimension=6) \
    .with_interpolation_method(bh.InterpolationMethod.LINEAR) \
    .with_eviction_policy_max_size(1000)

# Propagate and store states
times = np.linspace(0, 86400, 1440)  # 1 day, 1-minute steps
for dt in times:
    epoch = epoch_start + dt
    state = prop.propagate(epoch)
    traj.add(epoch, state)

print(f"Stored {traj.len()} states")
print(f"Time span: {traj.timespan()/3600:.1f} hours")

# Interpolate at arbitrary times
query_times = np.linspace(0, 86400, 100)
altitudes = []
for dt in query_times:
    query_epoch = epoch_start + dt
    state = traj.interpolate(query_epoch)
    altitude = (np.linalg.norm(state[:3]) - bh.R_EARTH) / 1000  # km
    altitudes.append(altitude)

# Plot altitude profile
plt.plot(query_times/3600, altitudes)
plt.xlabel('Time (hours)')
plt.ylabel('Altitude (km)')
plt.title('Orbit Altitude Over 1 Day')
plt.grid(True)
plt.show()

See Also

• STrajectory6 - Fixed 6D trajectory (faster)
• OrbitTrajectory - Frame-aware orbital trajectory
• InterpolationMethod