hammerhead-ecosystem

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HAMMERHEAD-Space Julia astrodynamics ecosystem overview and cross-cutting patterns. Use when working on any HAMMERHEAD-Space repository, when asking about package interdependencies, or when creating new packages in the ecosystem.

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HAMMERHEAD-Space Astrodynamics Ecosystem

Package Dependency Graph

QLaw.jl ──> AstroPropagators.jl ──> AstroForceModels.jl ──> AstroCoords.jl
                                                          ├─> SatelliteToolbox ecosystem
SimsFlanagan.jl ──> Lambert.jl ──> AstroCoords.jl
AstroMeasurements.jl ──> AstroCoords.jl

Shared Conventions

Convention	Standard
Julia versions	1.10, 1.11
Formatter	JuliaFormatter BlueStyle (`style = "blue"`)
Static arrays	`StaticArrays` / `StaticArraysCore` everywhere
AD support	ForwardDiff, Enzyme, Mooncake, Zygote, PolyesterForwardDiff
Allocation testing	AllocCheck.jl on all hot-path functions
Type stability	JET.jl on all packages
Package quality	Aqua.jl on all packages
Struct constructors	`@with_kw` from Parameters.jl
SciML interface	`solve(Problem, Algorithm)` pattern from SciMLBase
Default branch	`master` (not `main`)

Core Design Principles

AD-first: All code must be differentiable. Use promote_type, avoid mutation, use SVector returns.
Zero allocations: Hot-path functions (acceleration, EOM) must pass @check_allocs.
Type stability: All exported functions must pass JET analysis.
SciML composability: Follow Problem/Solution/Algorithm pattern.
Multiple dispatch: Use type dispatch over if/else branching.

Standard State Representation

Position/velocity: [rx, ry, rz, vx, vy, vz] km, km/s in J2000 ECI
Parameters: ComponentVector(; JD=epoch_jd, μ=gravitational_param)
Time: elapsed seconds since epoch; Julian Date = p.JD + t / 86400.0

New Package Checklist

When creating a new package in this ecosystem:

Add .JuliaFormatter.toml with style = "blue"
Add typos.toml for spell checking
Set up Aqua.jl, JET.jl, AllocCheck tests
Use StaticArraysCore (not full StaticArrays) for minimal deps
Support Julia 1.10+ in compat
Follow AbstractX base type pattern
Document with # Arguments, # Returns, # References sections
Add AD differentiability tests against FiniteDiff