Architecture Overview

SSG Tether Capture is a Bevy application that follows the Entity Component System (ECS) pattern. All simulation state lives in components attached to entities; logic runs as systems; shared mutable state is held in resources.

Entry point

main.rs  →  lib.rs::run()  →  App::new()

main.rs is a thin wrapper. All shared logic — including everything needed by the test harness — lives in lib.rs.

lib.rs exposes two functions:

Function	Purpose
run()	Full application entry point. Adds DefaultPlugins, UiPlugin, rendering setup, and startup systems, then calls app.run().
create_app()	Returns a partially-configured App with only shared plugins (physics, orbital mechanics, camera). Used by integration tests.

Module structure

src/
  constants.rs        — shared numeric constants and camera layer indices
  lib.rs              — run() and create_app() entry points
  main.rs             — binary entry point
  components/         — ECS components (data attached to entities)
  plugins/            — Bevy Plugin impls that register systems
  resources/          — global shared state (ECS Resources)
  systems/            — all system functions
  ui/                 — Bevy-native UI layer (plugin, screens, state, theme)
  tests/              — integration and unit tests

Plugin graph

The following plugins are added to the app:

PhysicsPlugins          (Avian3D rigid-body physics — on custom ManualPhysics schedule)
OrbitalMechanicsPlugin  (orbital init, physics stepping, capture algorithms)
OrbitCameraPlugin       (camera input + tracking — Update/PostUpdate)
GpuComputePlugin        (GPU compute pipeline for large orbital datasets)
UiPlugin                (UI camera, state machine, screen lifecycle)
DefaultPlugins          (Bevy standard — only added in run(), not in tests)

See Plugins for what each plugin registers.

System schedule

Schedule	Systems registered
OnEnter(UiScreen::Sim)	setup_lighting, setup_celestial, setup_tether, setup_entities, load_dataset_entities (chained)
First	init_orbitals
FixedUpdate	fixed_physics_step (drives the ManualPhysics schedule at FIXED_HZ)
Update	toggle_map_view, toggle_origin, toggle_capture_gizmos, change_time_warp, map_orbitals, floating_origin_update_visuals, dev_gizmos, capture_gizmos, camera input systems, UI update systems
PostUpdate	orbit_camera_track, GPU compute sync systems
ManualPhysics	cache_eci_states (First) → physics_bubble_add_remove, target_entity_reset_origin (Prepare) → Avian3D physics → capture_state_machine_update (Last)
Last	orbital_gizmos

External dependencies

Crate	Role
bevy	Game engine / ECS framework
avian3d	Rigid-body physics
brahe	Orbital mechanics (propagation, COE↔RV conversion)
nalgebra	6-element state vectors (Vector6) for ECI position/velocity