COMMIT_MSG.txt

feat: Initial commit - Phase 1 foundation (core infrastructure)

Implement production-grade foundation for GPU-accelerated physics simulation
engine targeting spacecraft dynamics, orbital mechanics, and N-body simulations.

This Phase 1 delivers enterprise-quality core infrastructure with modern C++20,
validated algorithms from IAU/CODATA standards, and comprehensive documentation.

Core Modules Implemented:
- Type system: Eigen-based Vec3/Quat/Mat3, State (6-DOF), Particle, bounding volumes
- Physical constants: CODATA 2018 universal constants, IAU 2015 solar system data
- Time systems: UTC↔TAI↔TT↔TDB conversions, Julian Date, GMST/GAST (IAU 2006)
- Reference frames: ECI↔ECEF, geodetic (WGS84), LVLH/RTN, topocentric coordinates
- Logging: spdlog-based infrastructure with rotating files and colored output

Build Infrastructure:
- Modern CMake 3.25+ with namespaced targets and installation rules
- vcpkg dependency manifest for reproducible builds
- Code quality: .clang-format (Google C++ style), .clang-tidy (modernize/performance)
- Convenience Makefile with build/test/format/lint targets
- Compiler flags: -O3 -march=native (Release), sanitizer support (Debug)

Code Quality:
- C++20 standard with modern features (concepts, constexpr, std::numbers)
- Comprehensive Doxygen documentation on all public APIs
- Const correctness throughout (all inputs const&)
- RAII resource management (no raw pointers)
- Production error handling with exceptions

Project Statistics:
- 2,313 lines of production C++ code
- 5 header files, 4 implementation files
- CMake configuration validated on macOS with AppleClang 17.0

Documentation:
- README.md: Feature overview, quickstart, dependencies, examples
- LICENSE: MIT (permissive for commercial use)
- PHASE1_COMPLETE.md: Detailed Phase 1 accomplishments
- PROJECT_STATUS.md: Roadmap for Phases 2-12

Standards Compliance:
- Physical constants: CODATA 2018 recommended values
- Solar system data: IAU 2015 / NASA JPL DE440 ephemeris
- Geodetic system: WGS84 ellipsoid with J2-J4 harmonics
- Time algorithms: Meeus "Astronomical Algorithms" (1998)
- Sidereal time: IAU 2006 precession model

Next Phase: Integration & Forces (RK4/RK45 integrators, gravity forces, tests)

Performance targets:
- Phase 3: 10,000 bodies @ 60 FPS (CPU direct)
- Phase 4: 100,000 bodies @ 60 FPS (CPU Barnes-Hut)
- Phase 5: 100,000+ bodies @ 60 FPS (GPU, RTX 3090)
- Phase 10: <10 km error vs NASA HORIZONS (1 year)