openrocket-sim - SKILL.md Agent Skill

name: openrocket-sim description: "Headless rocket design, simulation, and optimization using OpenRocket's Java core engine. Includes rocket-sim CLI tool for batch simulations and parameter sweeps, plus an AI-driven optimization loop using Claude. Use when: (1) designing model rockets programmatically, (2) running headless flight simulations, (3) optimizing rocket designs for altitude/stability/velocity, (4) batch-processing .ork files, (5) parameter sweeps over launch conditions, (6) AI-driven design optimization, (7) building a simulation pipeline or API wrapper, (8) exporting designs for 3D printing or laser cutting, (9) user mentions 'openrocket', 'rocket simulation', 'flight sim', 'rocket design', 'model rocket', 'rocketry', 'apogee optimization', 'thrust curve', 'rocket-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