Openrocket Sim

OpenRocket Headless Simulation

Quick Start — rocket-sim CLI

The rocket-sim CLI at ~/broomva/experiments/rocket-tools/ wraps OpenRocket's headless core. All output is structured JSON.

# Prerequisites: Java 17
export JAVA_HOME=/opt/homebrew/opt/openjdk@17/libexec/openjdk.jdk/Contents/Home

ROCKET="~/broomva/experiments/openrocket/core/src/main/resources/datafiles/examples/A simple model rocket.ork"

# Inspect rocket design
rocket-sim info "$ROCKET"

# Run simulation → JSON with altitude, velocity, mach, events
rocket-sim run "$ROCKET"

# Parameter sweep (rod_angle, rod_length, launch_altitude, wind_speed, time_step)
rocket-sim sweep "$ROCKET" wind_speed 0,2,5,8,10

# Flight event timeline
rocket-sim events "$ROCKET"

Validated results (A simple model rocket, A8-3 motor):

• Max altitude: 50.7m | Max velocity: 29.3 m/s | Mach: 0.086 | Flight time: 15.9s
• Events: Launch→Ignition→Liftoff→Burnout→Apogee→Ejection→Parachute→Ground

Two stage high power rocket (multi-branch):

• Max altitude: 677.6m | Max velocity: 159.1 m/s | Mach: 0.469 | Flight time: 64.0s

AI Optimizer

At ~/broomva/experiments/rocket-ai/optimizer.py. Iterative loop: Claude analyzes simulation results, proposes parameter sweeps, evaluates trade-offs, converges.

export ANTHROPIC_API_KEY=sk-...
cd ~/broomva/experiments/rocket-ai
python3 optimizer.py "path/to/rocket.ork" \
    --goal "Maximize altitude while keeping ground hit velocity under 10 m/s" \
    --iterations 5

Loop: baseline sim → Claude analysis → sweep proposal → run sweep → feed results back → refine → converge.

Repository Layout

~/broomva/experiments/
├── openrocket/          # OpenRocket source (github.com/openrocket/openrocket)
│   ├── core/            # Headless simulation engine (Java 17, Gradle)
│   └── swing/           # GUI (optional)
├── rocket-tools/        # rocket-sim CLI (Gradle project, depends on core shadow JAR)
│   ├── rocket-sim       # Shell wrapper
│   └── src/main/java/rocket/cli/RocketCLI.java
└── rocket-ai/           # AI optimizer (Python + Anthropic SDK)
    └── optimizer.py

Build from Scratch

export JAVA_HOME=/opt/homebrew/opt/openjdk@17/libexec/openjdk.jdk/Contents/Home
export PATH="$JAVA_HOME/bin:$PATH"

# 1. Build OpenRocket core + shadow JAR
cd ~/broomva/experiments/openrocket
./gradlew build -x test && ./gradlew shadowJar

# 2. Build rocket-sim CLI
cd ~/broomva/experiments/rocket-tools
./gradlew jar

# 3. Install AI optimizer deps
cd ~/broomva/experiments/rocket-ai
pip install -r requirements.txt

Headless Java API

For programmatic use without the CLI, use OpenRocketCore.initialize():

import info.openrocket.core.startup.OpenRocketCore;

// One-line bootstrap (headless, no GUI)
OpenRocketCore.initialize();

// Load and simulate
var loader = new GeneralRocketLoader(new File("rocket.ork"));
var doc = loader.load();
var sim = doc.getSimulation(0);
sim.simulate();

FlightData data = sim.getSimulatedData();
data.getMaxAltitude();   // meters
data.getMaxVelocity();   // m/s
data.getFlightTime();    // seconds

System properties for faster startup:

System.setProperty("openrocket.bypass.presets", "true");   // skip component DB
System.setProperty("openrocket.bypass.motors", "true");    // skip motor DB

References

• API Reference — Components, SimulationOptions, FlightData, optimization framework, scripting
• Compounding Strategies — CLI, web API, AI optimization, design language, manufacturing pipeline, SaaS

Example .ork Files

At openrocket/core/src/main/resources/datafiles/examples/:

• A simple model rocket.ork — single stage, 5 motor configs
• Two stage high power rocket.ork — multi-stage, multi-branch sim
• Clustered motors.ork — parallel motor clusters
• Simulation extensions.ork — GraalVM JS scripting demo
• Dual parachute deployment.ork — recovery system demo
• Parallel booster staging.ork — side booster staging