lambert-rs 0.0.11

Rust + PyO3 implementation of the Izzo Lambert solver

lambert_rs

High-performance Rust + PyO3 implementation of the Izzo Lambert solver with advanced optimization capabilities.

Installation

From PyPI

pip install lambert-rs

Dependencies: The package automatically installs polars>=0.20.0 as a dependency (required for optimize_lambert_nm_multi_array).

Features

• Fast Lambert Problem Solving: Vectorized batch processing with parallel execution
• Multiple Solution Methods: Single solutions, grid search, and Nelder-Mead optimization
• Delta-V Calculations: Automatic computation of transfer impulses
• Two-Body Propagation: Universal variable formulation for orbit propagation
• Transfer Optimization: Find optimal departure/arrival times minimizing delta-v
• Rendezvous Optimization: Optimize for full rendezvous (two burns) or transfer only (one burn)

Quick Start

Basic Lambert Problem

Solve a single Lambert problem:

import numpy as np
import lambert_rs

# Initial and final positions (km)
r1 = np.array([7000., 0., 0.])
r2 = np.array([0., -8000., 0.])

# Time of flight (seconds)
tof = 3600.0

# Solve Lambert problem
sol = lambert_rs.lambert_izzo_single(
    r1, r2, tof,
    max_rev=0,        # Maximum number of revolutions
    retrograde=False, # Prograde transfer
    mu=398600.4418,  # Earth's gravitational parameter (km^3/s^2)
    tol=1e-8,        # Tolerance
    maxiter=50       # Maximum iterations
)

# Get the first valid solution
if sol.valid[0]:
    v1 = sol.v1[0]
    v2 = sol.v2[0]
    print(f"v1: {v1} km/s")
    print(f"v2: {v2} km/s")

Batch Processing

Process multiple Lambert problems in parallel:

import numpy as np
import lambert_rs

# Multiple position pairs: shape (N, 3)
r1_batch = np.array([
    [7000., 0., 0.],
    [8000., 0., 0.],
    [9000., 0., 0.],
])

r2_batch = np.array([
    [0., -8000., 0.],
    [0., -9000., 0.],
    [0., -10000., 0.],
])

# Multiple time-of-flight values
tof_array = np.array([3600., 7200., 10800.])

# Solve all combinations
sol = lambert_rs.lambert_izzo_vec(
    r1_batch, r2_batch, tof_array,
    max_rev=0,
    retrograde=False,
    mu=398600.4418,
    tol=1e-8,
    maxiter=50
)

# Results shape: (N, num_tof, num_solutions, 3)
print(f"v1 shape: {sol.v1.shape}")
print(f"v2 shape: {sol.v2.shape}")
print(f"valid shape: {sol.valid.shape}")

Delta-V Calculations

Calculate transfer impulses for rendezvous:

import numpy as np
import lambert_rs

# Initial and target states: [x, y, z, vx, vy, vz]
s1 = np.array([7000., 0., 0., 0., 7.5, 0.])  # Initial state
s2 = np.array([0., -8000., 0., 8.0, 0., 0.])  # Target state

# Time of flight
tof = 3600.0

# Calculate delta-v for all solutions
dv1_mag, dv2_mag, dv_total, valid, dv1_vec, dv2_vec = lambert_rs.lambert_izzo_vec_dv(
    s1, s2, tof,
    max_rev=0,
    retrograde=False,
    mu=398600.4418,
    tol=1e-8,
    maxiter=50
)

# Find best solution (minimum total delta-v)
if np.any(valid):
    best_idx = np.nanargmin(dv_total[valid])
    print(f"Best delta-v: {dv_total[best_idx]:.3f} km/s")
    print(f"First burn: {dv1_vec[best_idx]} km/s")
    print(f"Second burn: {dv2_vec[best_idx]} km/s")

Reentry Check

Filter out solutions that would reenter Earth's atmosphere:

import numpy as np
import lambert_rs

# Positions that might result in a reentry trajectory
r1 = np.array([7000., 0., 0.])  # km
r2 = np.array([0., -8000., 0.])  # km
tof = 1800.0  # Short time of flight might cause reentry

# Solve without reentry check
sol_no_check = lambert_rs.lambert_izzo_single(
    r1, r2, tof,
    max_rev=0,
    retrograde=False,
    mu=398600.4418,
    reentry_check=False  # Default: don't check for reentry
)

# Solve with reentry check enabled
sol_with_check = lambert_rs.lambert_izzo_single(
    r1, r2, tof,
    max_rev=0,
    retrograde=False,
    mu=398600.4418,
    reentry_check=True  # Filter out solutions that would reenter
)

print(f"Solutions without check: {np.sum(sol_no_check.valid)} valid")
print(f"Solutions with check: {np.sum(sol_with_check.valid)} valid")

# The reentry check marks solutions as invalid if the perigee radius
# would be below Earth's surface (6378.137 km)

Find Best Delta-V Solution

Automatically find the best solution (prograde or retrograde):

import numpy as np
import lambert_rs

# States: shape (..., 6) for batch processing
s1 = np.array([7000., 0., 0., 0., 7.5, 0.])
s2 = np.array([0., -8000., 0., 8.0, 0., 0.]) 

# Time of flight (can be scalar or array)
tof = np.array([3600., 7200., 10800.])

# Full rendezvous: minimize total delta-v (dv1 + dv2)
# Use this when you need to match both position AND velocity at the target
dv1_rend, dv2_rend, dv_total_rend, valid_rend, dv1_vec_rend, dv2_vec_rend = lambert_rs.lambert_izzo_best_dv(
    s1, s2, tof,
    max_rev=0,
    mu=398600.4418,
    tol=1e-8,
    maxiter=50,
    rendezvous=True  # Default: minimize dv1 + dv2
)

# Transfer-only: minimize first impulse (dv1 only)
# Use this when you only need to reach the target position (not matching velocity)
dv1_trans, dv2_trans, dv_total_trans, valid_trans, dv1_vec_trans, dv2_vec_trans = lambert_rs.lambert_izzo_best_dv(
    s1, s2, tof,
    max_rev=0,
    mu=398600.4418,
    tol=1e-8,
    maxiter=50,
    rendezvous=False  # Minimize dv1 only
)

# Automatically selects best solution (prograde or retrograde)
print(f"Rendezvous total delta-v: {dv_total_rend} km/s")
print(f"Transfer-only total delta-v: {dv1_trans} km/s")

Two-Body Orbit Propagation

Propagate an orbit using universal variable formulation:

import numpy as np
import lambert_rs

# Initial state: [x, y, z, vx, vy, vz] (km, km/s)
initial_state = np.array([7000., 0., 0., 0., 7.5, 0.])

# Propagation time (seconds)
dt = 3600.0

# Propagate
r_final, v_final = lambert_rs.kepler_universal_2body_py(initial_state, dt)

print(f"Final position: {r_final} km")
print(f"Final velocity: {v_final} km/s")

Transfer Optimization (Grid Search)

Find optimal departure and arrival times using grid search:

import numpy as np
import lambert_rs

# Source and target initial states
source_state = np.array([7000., 0., 0., 0., 7.5, 0.])
target_state = np.array([0., -8000., 0., 8.0, 0., 0.]) 

# Time bounds: (min_departure, max_arrival) in seconds
time_bounds = (0., 86400.)  # 24 hours
dt_step = 3600.0  # 1 hour steps

# Find optimal transfer
sol = lambert_rs.optimize_lambert_transfer_py(
    source_state, target_state,
    time_bounds, dt_step,
    # mu=398600.4418,  # Optional: default is 398600.4418 (Earth)
    # retrograde=False  # Optional: default is False
)

print(f"Optimal departure time: {sol.t0:.1f} s")
print(f"Optimal arrival time: {sol.tf:.1f} s")
print(f"Minimum delta-v: {sol.cost:.3f} km/s")
print(f"First burn: {sol.dv1} km/s")
print(f"Second burn: {sol.dv2} km/s")

Transfer Grid (All Solutions)

Get all transfer solutions in a time window:

import numpy as np
import lambert_rs

source_state = np.array([7000., 0., 0., 0., 7.5, 0.])
target_state = np.array([0., -8000., 0., 8.0, 0., 0.]) 

time_bounds = (0., 86400.)
dt_step = 3600.0

# Get all solutions
sols = lambert_rs.optimize_lambert_transfer_grid_py(
    source_state, target_state,
    time_bounds, dt_step,
    # mu=398600.4418,  # Optional: default is 398600.4418 (Earth)
    # retrograde=False  # Optional: default is False
)

# Plot or analyze all solutions
import matplotlib.pyplot as plt
plt.scatter(sols.t0, sols.tf, c=sols.cost, cmap='viridis')
plt.colorbar(label='Delta-V (km/s)')
plt.xlabel('Departure Time (s)')
plt.ylabel('Arrival Time (s)')
plt.show()

Nelder-Mead Optimization

Use gradient-free optimization to find optimal transfer:

import numpy as np
import lambert_rs

source_state = np.array([7000., 0., 0., 0., 7.5, 0.])
target_state = np.array([0., -8000., 0., 8.0, 0., 0.]) 

time_bounds = (0., 86400.)

# Optimize for transfer (single burn)
# Automatically selects best solution from both prograde and retrograde
sol = lambert_rs.optimize_lambert_nm_py(
    source_state, target_state,
    time_bounds,
    max_rev=0,
    optimize_rendezvous=False  # Transfer only (one burn)
    # mu=398600.4418,  # Optional: default is 398600.4418 (Earth)
    # max_iters=None,  # Optional: default is None (uses 1000 internally)
    # initial_guess=None  # Optional: (t0, tf) guess
)

print(f"Optimal times: t0={sol.t0:.1f} s, tf={sol.tf:.1f} s")
print(f"Cost (delta-v): {sol.cost:.3f} km/s")
print(f"First burn: {sol.dv1} km/s")

# Optimize for rendezvous (two burns)
# Automatically selects best solution from both prograde and retrograde
sol = lambert_rs.optimize_lambert_nm_py(
    source_state, target_state,
    time_bounds,
    max_rev=0,
    optimize_rendezvous=True,  # Full rendezvous (two burns)
    # mu=398600.4418,  # Optional: default is 398600.4418 (Earth)
    # max_iters=None,  # Optional: default is None (uses 1000 internally)
)

print(f"Rendezvous cost: {sol.cost:.3f} km/s")
print(f"First burn: {sol.dv1} km/s")
print(f"Second burn: {sol.dv2} km/s")

Multi-Start Optimization

Find multiple local optima using parallel multi-start optimization:

import numpy as np
import lambert_rs

source_state = np.array([7000., 0., 0., 0., 7.5, 0.])
target_state = np.array([0., -8000., 0., 8.0, 0., 0.]) 

time_bounds = (0., 86400.)

# Run multiple optimizers in parallel
# Automatically selects best solution from both prograde and retrograde for each optimizer
sols = lambert_rs.optimize_lambert_nm_multi_py(
    source_state, target_state,
    time_bounds,
    max_rev=0,
    optimize_rendezvous=True,
    num_solvers=10,        # Number of parallel optimizers
    return_best_only=False, # Return all solutions
    remove_duplicates=True,  # Remove duplicate solutions
    # mu=398600.4418,  # Optional: default is 398600.4418 (Earth)
    # max_iters=None,  # Optional: default is None (uses 1000 internally)
)

# Analyze all solutions
print(f"Found {len(sols.cost)} solutions")
print(f"Best cost: {np.min(sols.cost):.3f} km/s")
print(f"Worst cost: {np.max(sols.cost):.3f} km/s")

# Get the best solution
best_idx = np.argmin(sols.cost)
print(f"\nBest solution:")
print(f"  Times: t0={sols.t0[best_idx]:.1f} s, tf={sols.tf[best_idx]:.1f} s")
print(f"  Cost: {sols.cost[best_idx]:.3f} km/s")
print(f"  First burn: {sols.dv1[best_idx]} km/s")
print(f"  Second burn: {sols.dv2[best_idx]} km/s")

Array-based Multi-Start Optimization

For analyzing multiple source and target states simultaneously, use optimize_lambert_nm_multi_array:

import numpy as np
import polars as pl
import lambert_rs

# Generate arrays of source and target states
# Example: 100 source states and 20 target states
num_sources = 100
num_targets = 20

# Create random orbital states (in practice, these would be your actual states)
source_states = np.random.randn(num_sources, 6) * 1000  # [N, 6] array
target_states = np.random.randn(num_targets, 6) * 1000  # [M, 6] array

# Time bounds for optimization
time_bounds = (0.0, 86400.0)  # 0 to 1 day in seconds

# Run optimization for all combinations
# This will compute 100 * 20 = 2000 combinations
df = lambert_rs.optimize_lambert_nm_multi_array(
    source_states, target_states,
    time_bounds,
    max_rev=0,
    optimize_rendezvous=True,
    num_solvers=10,        # Number of parallel optimizers per combination
    return_best_only=True, # Return only best solution per [i,j] combination
    remove_duplicates=True,
    # mu=398600.4418,  # Optional: default is 398600.4418 (Earth)
    # max_iters=None,  # Optional: default is None (uses 1000 internally)
)

# df is a Polars DataFrame with columns:
# - source_idx: index of source state (0 to num_sources-1)
# - target_idx: index of target state (0 to num_targets-1)
# - t0: departure time [s]
# - tf: arrival time [s]
# - cost: total delta-v [km/s]
# - dv1_x, dv1_y, dv1_z: first burn impulse components [km/s]
# - dv2_x, dv2_y, dv2_z: second burn impulse components [km/s]

# Analyze results with Polars
print(f"Total solutions: {len(df)}")
print(f"\nBest solution:")
best = df.sort("cost").head(1)
print(best)

# Find best solution for each source state
best_per_source = df.sort("cost").group_by("source_idx").first()
print(f"\nBest solution per source state:")
print(best_per_source)

# Find best solution for each target state
best_per_target = df.sort("cost").group_by("target_idx").first()
print(f"\nBest solution per target state:")
print(best_per_target)

# Filter solutions with cost < 5 km/s
low_cost = df.filter(pl.col("cost") < 5.0)
print(f"\nSolutions with cost < 5 km/s: {len(low_cost)}")

# When return_best_only=False, you can get multiple solutions per [i,j] combination
df_all = lambert_rs.optimize_lambert_nm_multi_array(
    source_states, target_states,
    time_bounds,
    max_rev=0,
    optimize_rendezvous=True,
    num_solvers=10,
    return_best_only=False, # Return all solutions per [i,j] combination
    remove_duplicates=True,
    # mu=398600.4418,  # Optional: default is 398600.4418 (Earth)
    # max_iters=None,  # Optional: default is None (uses 1000 internally)
)

# Now you can analyze all solutions for a specific source-target pair
source_0_target_5 = df_all.filter(
    (pl.col("source_idx") == 0) & (pl.col("target_idx") == 5)
)
print(f"\nAll solutions for source[0] -> target[5]:")
print(source_0_target_5.sort("cost"))

API Reference

Core Functions

• lambert_izzo_single(r1, r2, tof, max_rev, retrograde, mu, tol, maxiter)

  • Solve a single Lambert problem
  • Returns: LambertSolutionArray object with fields:
    • v1: Velocity at r1 [km/s] - shape (n, 3)
    • v2: Velocity at r2 [km/s] - shape (n, 3)
    • tof: Time of flight [s] - shape (n,)
    • num_revs: Number of revolutions - shape (n,)
    • path_flag: Path flag - shape (n,)
    • valid: Whether solution is valid - shape (n,)
    • retrograde: Whether solution uses retrograde motion - shape (n,)

• lambert_izzo_vec(r1, r2, tof, max_rev, retrograde, mu, tol, maxiter)

  • Vectorized batch processing
  • Returns: LambertSolutionArray object with same fields as above

• lambert_izzo_vec_dv(s1, s2, tof, max_rev, retrograde, mu, tol, maxiter)

  • Calculate delta-v for transfers
  • Returns: (dv1_mag, dv2_mag, dv_total, valid, dv1_vec, dv2_vec)

• lambert_izzo_best_dv(s1, s2, tof, max_rev, mu, tol, maxiter, rendezvous)

  • Automatically find best solution (prograde or retrograde)
  • rendezvous=True (default): Minimize total delta-v (dv1 + dv2) for full rendezvous
  • rendezvous=False: Minimize first impulse (dv1) for transfer-only missions
  • Returns: (dv1_mag, dv2_mag, dv_total, valid, dv1_vec, dv2_vec)

Propagation

• kepler_universal_2body_py(init_state_vec, dt_sec)
  • Two-body orbit propagation using universal variables
  • Returns: (r_final, v_final)

Optimization

• optimize_lambert_transfer_py(source_state, target_state, time_bounds, dt_step, mu=398600.4418, retrograde=False)

  • Grid search for optimal transfer
  • Parameters:
    • source_state: Initial state vector [6] (position + velocity)
    • target_state: Target state vector [6] (position + velocity)
    • time_bounds: Tuple (min_departure_time, max_arrival_time) [s]
    • dt_step: Time step for grid search [s]
    • mu: Gravitational parameter [km³/s²] (default: 398600.4418 for Earth)
    • retrograde: Whether to allow retrograde transfers (default: False)
  • Returns: OptimizedLambertSolutionPy object with fields:
    • t0: Departure time [s]
    • tf: Arrival time [s]
    • cost: Total delta-v [km/s]
    • dv1: First burn impulse [km/s] - shape (3,)
    • dv2: Second burn impulse [km/s] - shape (3,)

• optimize_lambert_transfer_grid_py(source_state, target_state, time_bounds, dt_step, mu=398600.4418, retrograde=False)

  • Get all grid search solutions
  • Parameters: Same as optimize_lambert_transfer_py
  • Returns: OptimizedLambertSolutionArray object with fields:
    • t0: Departure times [s] - shape (n,)
    • tf: Arrival times [s] - shape (n,)
    • cost: Total delta-v [km/s] - shape (n,)
    • dv1: First burn impulses [km/s] - shape (n, 3)
    • dv2: Second burn impulses [km/s] - shape (n, 3)

• optimize_lambert_nm_py(source_state, target_state, time_bounds, max_rev, optimize_rendezvous, mu=398600.4418, max_iters=None, initial_guess=None)

  • Nelder-Mead optimization
  • Automatically selects best solution from both prograde and retrograde transfers
  • Parameters:
    • source_state: Initial state vector [6] (position + velocity)
    • target_state: Target state vector [6] (position + velocity)
    • time_bounds: Tuple (min_departure_time, max_arrival_time) [s]
    • max_rev: Maximum number of revolutions to consider
    • optimize_rendezvous: If True, optimize for full rendezvous (both burns); if False, optimize for transfer only (first burn)
    • mu: Gravitational parameter [km³/s²] (default: 398600.4418 for Earth)
    • max_iters: Maximum iterations (default: None, uses 1000 internally)
    • initial_guess: Optional tuple (t0, tf) for initial guess [s]
  • Returns: OptimizedLambertSolutionPy object (same fields as optimize_lambert_transfer_py)

• optimize_lambert_nm_multi_py(source_state, target_state, time_bounds, max_rev, optimize_rendezvous, num_solvers, return_best_only, remove_duplicates, mu=398600.4418, max_iters=None)

  • Multi-start parallel optimization
  • Automatically selects best solution from both prograde and retrograde transfers for each optimizer
  • Parameters:
    • source_state: Initial state vector [6] (position + velocity)
    • target_state: Target state vector [6] (position + velocity)
    • time_bounds: Tuple (min_departure_time, max_arrival_time) [s]
    • max_rev: Maximum number of revolutions to consider
    • optimize_rendezvous: If True, optimize for full rendezvous (both burns); if False, optimize for transfer only (first burn)
    • num_solvers: Number of parallel optimizers to spawn
    • return_best_only: If True, return only the best solution; if False, return all solutions
    • remove_duplicates: If True, remove duplicate solutions that converged to the same point
    • mu: Gravitational parameter [km³/s²] (default: 398600.4418 for Earth)
    • max_iters: Maximum iterations (default: None, uses 1000 internally)
  • Returns: OptimizedLambertSolutionArray object (same fields as optimize_lambert_transfer_grid_py)

• optimize_lambert_nm_multi_array(source_state, target_state, time_bounds, max_rev, optimize_rendezvous, num_solvers, return_best_only, remove_duplicates, mu=398600.4418, max_iters=None)

  • Array-based multi-start optimization for multiple source and target states
  • Note: Requires polars package (automatically installed as a dependency)
  • Parameters:
    • source_state: Array of shape [N, 6] where N is any number of source states
    • target_state: Array of shape [M, 6] where M is any number of target states
    • time_bounds: Tuple (min_departure_time, max_arrival_time) [s]
    • max_rev: Maximum number of revolutions to consider
    • optimize_rendezvous: If True, optimize for full rendezvous (both burns); if False, optimize for transfer only (first burn)
    • num_solvers: Number of parallel optimizers to spawn per combination
    • return_best_only: If True, return only the best solution per [i,j] combination; if False, return all solutions
    • remove_duplicates: If True, remove duplicate solutions that converged to the same point
    • mu: Gravitational parameter [km³/s²] (default: 398600.4418 for Earth)
    • max_iters: Maximum iterations (default: None, uses 1000 internally)
  • Computes all N×M combinations in parallel
  • Automatically selects best solution from both prograde and retrograde transfers for each optimizer
  • Returns: Polars DataFrame with columns:
    • source_idx: Index of source state (0 to N-1)
    • target_idx: Index of target state (0 to M-1)
    • t0: Departure time [s]
    • tf: Arrival time [s]
    • cost: Total delta-v [km/s]
    • dv1_x, dv1_y, dv1_z: First burn impulse components [km/s]
    • dv2_x, dv2_y, dv2_z: Second burn impulse components [km/s]
  • When return_best_only=True: One row per [i,j] source-target combination
  • When return_best_only=False: Multiple rows per [i,j] combination (all solutions)

Performance

• Parallel Processing: Automatically uses N-1 CPU cores for batch operations
• Vectorized Operations: Efficient NumPy array operations
• Rust Performance: Core algorithms implemented in Rust for maximum speed

Units

• Positions: kilometers (km)
• Velocities: kilometers per second (km/s)
• Time: seconds (s)
• Gravitational Parameter (mu): km³/s²
  • Earth: 398600.4418 km³/s²