A small, educational physics-based rocket trajectory simulation library for Python. Simulate vertical rocket launches with altitude-dependent gravity, visualize trajectories, and compare real-world rockets.
- Altitude-dependent gravity using Newton's inverse-square law
- 13 pre-configured rockets including Saturn V, Falcon 9, Starship, and more
- Custom rockets — create and simulate your own designs
- Multiple celestial bodies — Earth, Moon, and Mars, or roll your own
- Plots with multiple matplotlib styles (trajectory, velocity, dashboard, comparison)
- CLI & library — use as a command-line tool or import as a Python library
- Type-safe — full type hints throughout the public API
- Well-tested — pytest suite covering physics and simulation logic
This is a deliberately simplified educational model:
- Motion is 1-D vertical only (no pitch-over, no horizontal velocity, no orbital insertion).
- Mass is constant during flight; propellant burn is not modelled.
- No atmospheric drag is applied to trajectories. (
Physics.atmospheric_densityandPhysics.drag_forceare exposed as standalone utilities for users doing their own analyses.)
For a realistic 6-DOF aerospace simulation, see tools like RocketPy.
pip install rocket-simOr, for development:
git clone https://github.com/rramboer/rocket-sim.git
cd rocket-sim
pip install -e ".[dev]"# Simulate a preset rocket
rocket-sim --preset "Falcon 9" -o falcon9.png
# Simulate all presets
rocket-sim --all-presets -o comparison.png
# Custom rocket
rocket-sim --mass 50000 --thrust 1000000 --burn-time 120 --name "My Rocket"
# Interactive mode
rocket-sim --interactive
# List available presets
rocket-sim --list-presetsfrom rocket_sim import RocketSimulation, get_preset, Plotter
# Simulate a Falcon 9 launch
config = get_preset("Falcon 9")
sim = RocketSimulation(config)
result = sim.run()
# Print results
print(f"Max Altitude: {result.max_altitude_km:.2f} km")
print(f"Max Velocity: {result.max_velocity:.2f} m/s")
print(f"Flight Time: {result.flight_time:.2f} s")
# Create visualization
plotter = Plotter()
plotter.plot_trajectory(result, filename="falcon9.png")from rocket_sim import simulate_multiple, get_preset, Plotter, list_presets
# Get all preset configurations
configs = [get_preset(name) for name in list_presets()]
# Run simulations
results = simulate_multiple(configs)
# Compare trajectories
plotter = Plotter()
plotter.plot_multiple_trajectories(results, filename="comparison.png")from rocket_sim import RocketConfig, RocketSimulation, Plotter
# Define custom rocket
config = RocketConfig(
mass=100_000, # 100 tons
thrust=2_000_000, # 2 MN thrust
burn_time=180, # 3 minute burn
name="My Custom Rocket"
)
# Check thrust-to-weight ratio
print(f"T/W Ratio: {config.thrust_to_weight_ratio:.2f}")
# Simulate and plot
sim = RocketSimulation(config)
result = sim.run()
plotter = Plotter()
plotter.plot_dashboard(result, filename="dashboard.png")| Rocket | Mass (kg) | Thrust (N) | Burn Time (s) | T/W Ratio |
|---|---|---|---|---|
| Saturn V | 2,900,000 | 33,800,000 | 165 | 1.19 |
| SpaceX Starship | 5,000,000 | 72,000,000 | 200 | 1.47 |
| Falcon 9 | 549,054 | 7,607,000 | 162 | 1.41 |
| Space Shuttle | 2,030,000 | 30,600,000 | 510 | 1.54 |
| Delta IV Heavy | 733,000 | 17,840,000 | 360 | 2.48 |
| Atlas V | 584,000 | 10,500,000 | 270 | 1.83 |
| Ariane 5 | 777,000 | 11,600,000 | 540 | 1.52 |
| Soyuz-2 | 308,000 | 4,150,000 | 290 | 1.37 |
| Long March 5 | 867,000 | 10,600,000 | 480 | 1.25 |
| Vega | 137,000 | 2,310,000 | 110 | 1.72 |
| Electron | 12,550 | 240,000 | 150 | 1.95 |
| New Shepard † | 75,000 | 490,000 | 110 | 0.67 |
| Vulcan Centaur | 546,700 | 11,340,000 | 180 | 2.11 |
† New Shepard's listed first-stage thrust gives T/W < 1 at the masses shown, so the simulator reports immediate landing. The numbers reflect public BE-3 specs; treat the result as a sanity-check signal, not a flight prediction.
The simulation uses realistic physics including:
-
Gravity: Newton's law of universal gravitation with inverse-square falloff
g(h) = GM / (R + h)² -
Escape Velocity: Minimum velocity to escape gravitational field
v_esc = √(2GM / (R + h)) -
Atmospheric Density (utility, not applied to trajectories): Exponential atmosphere model exposed via
Physics.atmospheric_density(...)ρ(h) = ρ₀ × exp(-h / H)
Where:
G= 6.674×10⁻¹¹ m³/kg/s² (gravitational constant)M= 5.972×10²⁴ kg (Earth's mass)R= 6.371×10⁶ m (Earth's radius)ρ₀= 1.225 kg/m³ (sea level air density)H= 8,500 m (scale height)
rocket-sim/
├── src/rocket_sim/
│ ├── __init__.py # Package exports
│ ├── physics.py # Physics calculations
│ ├── models.py # Rocket and Engine classes
│ ├── simulation.py # Simulation engine
│ ├── visualization.py # Plotting tools
│ ├── presets.py # Rocket configurations
│ ├── config.py # Configuration management
│ └── cli.py # Command-line interface
├── tests/ # Test suite
├── docs/ # Documentation
├── examples/ # Example scripts
├── pyproject.toml # Project configuration
└── README.md
# Clone and install with dev dependencies
git clone https://github.com/rramboer/rocket-sim.git
cd rocket-sim
pip install -e ".[dev]"
# Install pre-commit hooks
pre-commit install# Run all tests
pytest
# Run with coverage
pytest --cov=rocket_sim --cov-report=html
# Run specific test file
pytest tests/test_physics.py# Lint and format (Ruff handles both)
ruff check --fix src tests
ruff format src tests
# Type checking
mypy srcContributions are welcome! Please see CONTRIBUTING.md for guidelines.
- Fork the repository
- Create a feature branch (
git checkout -b feature/amazing-feature) - Make your changes
- Run tests (
pytest) - Commit your changes (
git commit -m 'Add amazing feature') - Push to the branch (
git push origin feature/amazing-feature) - Open a Pull Request
This project is licensed under the MIT License - see the LICENSE file for details.
- Rocket specifications sourced from public NASA and SpaceX data
- Physics equations based on classical orbital mechanics
- Inspired by NASA's trajectory simulation tools