Agent skill

astrocoords-jl

Develop and maintain AstroCoords.jl, a Julia library for orbital coordinate representations and transformations. Use when working on AstroCoords.jl, adding new coordinate sets, implementing coordinate transformations, or converting between orbital elements.

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SKILL.md

AstroCoords.jl

High-performance, non-allocating Julia library for orbital coordinate representations and transformations. Repo: HAMMERHEAD-Space/AstroCoords.jl

Architecture

Type Hierarchy

Coordinate{N,T} <: StaticVector{N,T}
├── AstroCoord{N,T}           # Orbital coordinate sets
│   ├── Cartesian{T}          # (x, y, z, dx, dy, dz)
│   ├── Keplerian{T}          # (a, e, i, RAAN, ω, ν)
│   ├── Delaunay{T}
│   ├── ModEq{T}              # Modified equinoctial
│   ├── ModEqN{T}             # Generalized modified equinoctial
│   ├── Spherical{T}
│   ├── Cylindrical{T}
│   ├── USM7{T}, USM6{T}, USMEM{T}  # Unified State Models
│   ├── Milankovich{T}
│   ├── J2EqOE{T}             # J2 modified equinoctial
│   ├── EDromo{T}
│   ├── KustaanheimoStiefel{T}
│   └── StiefelScheifele{T}
└── AttitudeCoord{N,T}        # Attitude coordinates

All coordinates are StaticVector subtypes -- they support indexing, broadcasting, and all StaticArrays operations.

Source Layout

src/
  AstroCoords.jl             # Module, includes, exports, alias dictionary
  core_types.jl              # Abstract types, Transformation hierarchy
  anomalies.jl               # Kepler solver, true/eccentric/mean anomaly conversions
  quantities.jl              # meanMotion, orbitalPeriod, orbitalNRG, angularMomentum
  regularized_config.jl      # Config for regularized coords (EDromo, KS, SS)
  transformations.jl         # BFS graph, macro-generated transformation pairs
  utils.jl
  coordinate_sets/           # One file per coordinate type
  coordinate_changes/        # Conversion math between coordinate systems
ext/
  AstroCoordsZygoteExt.jl   # Zygote AD extension

Key Patterns

Coordinate Construction (3 forms per type)

julia
# Field-by-field
cart = Cartesian(x, y, z, dx, dy, dz)

# From vector
cart = Cartesian(vec)

# Convert from another coordinate (auto-finds path via BFS graph)
cart = Cartesian(kep, μ)

Extract Raw Data

julia
params(cart)   # -> SVector{6,T}
cart.r          # -> SVector{3,T} position (Cartesian only)
cart.v          # -> SVector{3,T} velocity (Cartesian only)

Transformation System

  • @define_transformation_pair macro generates forward/inverse transforms
  • BFS graph finds shortest conversion path between any two coordinate types
  • Transformations composable via compose() / Base.:∘
  • All transforms: (coord, μ, args...) signature

Orbital Quantities

julia
meanMotion(a, μ)          # or meanMotion(kep, μ)
orbitalPeriod(a, μ)
orbitalNRG(a, μ)
angularMomentumVector(cart, μ)

Note: functions use camelCase (project convention for orbital quantities).

Anomaly Conversions

julia
KeplerSolver(M, e)  # Mean -> Eccentric anomaly

Adding a New Coordinate Set

  1. Create src/coordinate_sets/newcoord.jl with struct NewCoord{T} <: AstroCoord{N,T}
  2. Implement Tuple(::Type{NewCoord}) for field names
  3. Add transformations in src/coordinate_changes/ to/from at least Cartesian
  4. Register with @define_transformation_pair in transformations.jl
  5. Add to _COORDINATE_SETS test array
  6. Tests: construction, round-trip conversions, AD with all backends, @check_allocs

Dependencies

  • LinearAlgebra (stdlib), StaticArrays 1.9
  • Weak dep: Zygote (0.6, 0.7) via package extension
  • Julia 1.10, 1.11

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