Rewrite: Modern Python architecture with type safety, units system, and visualization (v0.2)

[cmflannery]

Summary

Complete rewrite of OpenRocketEngine with a modern, type-safe architecture. This replaces the legacy codebase with a clean, explicit API designed for liquid rocket engine preliminary design.

What's New

Core Modules

• units.py - Custom Quantity class for type-safe physical quantities with unit conversion
• isentropic.py - Numba-accelerated isentropic flow equations (c*, Cf, Isp, Mach relations)
• engine.py - Immutable dataclasses (EngineInputs, EnginePerformance, EngineGeometry) with pure computation functions
• nozzle.py - Rao bell and conical nozzle contour generation with CSV export for CAD
• plotting.py - Publication-quality visualizations (cross-sections, altitude performance, dashboards)

Key Features

• Type safety: beartype runtime checking prevents parameter errors
• Units system: Custom Quantity class prevents dimensional analysis mistakes
• Performance: Numba JIT compilation for hot paths
• Explicit API: No magic properties - clear data flow from inputs → performance → geometry
• Visualization: Engine cross-sections, altitude performance curves, design dashboards

Breaking Changes

• Removed legacy Engine class from rocket.py
• Removed interface.py CLI (replaced with examples)
• Removed xlsxwriter dependency and Excel output
• Removed pandas, fire dependencies
• New API requires explicit unit-wrapped quantities

Example Usage

from openrocketengine import EngineInputs, design_engine
from openrocketengine.units import newtons, megapascals, kelvin, meters, pascals

inputs = EngineInputs(
    thrust=newtons(5000),
    chamber_pressure=megapascals(2.0),
    chamber_temp=kelvin(3200),
    exit_pressure=pascals(101325),
    molecular_weight=22.0,
    gamma=1.2,
    lstar=meters(1.0),
    mixture_ratio=2.0,
)

performance, geometry = design_engine(inputs)
print(f"Isp: {performance.isp.value:.1f} s")  # Isp: 280.3 s

Testing

• 155 tests passing covering units, isentropic equations, engine calculations, and nozzle generation
• Run with: uv run pytest tests/ -v