orts is an astrodynamics simulation platform — orbit and attitude dynamics with real-time 3D visualization, extensible WASM plugins, and in-browser analytics.

Features

• N-body orbital simulation with adaptive (DOP853, Dormand-Prince) and symplectic (Störmer-Verlet, Yoshida) integrators
• Propagation frames: SimpleEci (ERA-only Earth rotation) and Gcrs (IAU 2006/2000A CIO chain with observed IERS EOP, orts run --sat altitude=400 --frame gcrs --eop auto, or frame = "gcrs" in a config)
• Gravity models: point-mass, zonal harmonics (J2, J3, J4), full spherical-harmonic geopotential from ICGEM .gfc files (EGM96 / EGM2008 / EIGEN-class, Holmes–Featherstone, validated against Orekit to 1e-13 pointwise and ~1 m over 24 h at 70×70)
• Perturbations: atmospheric drag, solar radiation pressure, third-body gravity, constant thrust. Drag and SRP can be attitude-dependent, from a flat-panel surface that also produces disturbance torques
• Atmosphere models: Exponential, Harris-Priester, NRLMSISE-00
• Geomagnetic field: IGRF-14 spherical harmonic expansion + tilted-dipole approximation
• Space weather: CSSI and GFZ providers (F10.7, Ap, Kp)
• IAU 2006/2000A CIO-based Earth rotation with typed coordinate frames and EOP
• Celestial body ephemerides (Meeus analytic + JPL Horizons)
• Attitude dynamics and control: reaction wheels, magnetorquers, B-dot / PD controllers
• Sensor models: magnetometer, gyroscope, sun sensor, star tracker (with noise)
• WASM Component Model plugin runtime for guest controllers via wasmtime
• CLI with embedded 3D viewer, WebSocket telemetry, and format conversion
• Real-time charting with DuckDB-wasm + uPlot (uneri library)
• Rerun .rrd data format for recording and replay

Installation

# From source
cargo install orts-cli

# Pre-built binary (cargo-binstall)
cargo binstall orts-cli

Quick Start

# Run a simulation (auto-detects orts.toml in current directory)
orts run

# WebSocket server with embedded 3D viewer
orts serve --config orts.toml
# Open http://localhost:9001

# Replay a recorded simulation
orts replay output.rrd

# Convert between formats
orts convert output.rrd --format csv

Example config (orts.toml). It points at a controller plugin, so build one first. The plugin sources ship in this repository, so this part needs a checkout — from its root:

cargo install cargo-component
rustup target add wasm32-wasip1
cargo component build --release \
  --manifest-path plugin-sdk/examples/pd-rw-control/Cargo.toml

body = "earth"
dt = 0.01
duration = 120.0

[[satellites]]
id = "sat-1"
sensors = ["gyroscope", "star_tracker"]

[satellites.orbit]
type = "circular"
altitude = 400

[satellites.attitude]
inertia_diag = [10, 10, 10]
mass = 500

[satellites.reaction_wheels]
type = "three_axis"
inertia = 0.01
max_momentum = 5.0
max_torque = 0.5

# PD attitude control: hold the identity quaternion using the wheels.
[satellites.controller]
type = "wasm"
path = "plugin-sdk/examples/target/wasm32-wasip1/release/orts_example_plugin_pd_rw_control.wasm"

path is resolved against the working directory, so run orts from the repository root too, or make it absolute.

The controller is what reads the sensors and commands the wheels. Drop it and orts run propagates orbit and attitude, and warns that the sensors and reaction_wheels blocks have no effect.

WASM Plugin

Write satellite attitude controllers in any language that compiles to WebAssembly. Plugins receive sensor readings (magnetometer, gyroscope, star tracker, etc.) each tick and return actuator commands (reaction wheels, magnetorquers) — the simulator handles all dynamics and environment models.

The quick start above builds and wires up pd-rw-control. Its gains and the attitude it holds come from [satellites.controller.config], which every field defaults so it can be omitted:

[satellites.controller.config]
kp = 1.0
kd = 2.0
target_q = [1.0, 0.0, 0.0, 0.0]
sample_period = 0.1

See plugin-sdk/examples/ for more plugin examples, and examples/ for Apollo 11, Artemis 1, and orbital lifetime analysis demos.

Project Structure

Rust crates

Crate	Directory	Description
orts	orts/	Core simulation: dynamics, force/torque models, sensors, plugin host
orts-cli	cli/	CLI binary with embedded viewer + WebSocket server
orts-plugin-sdk	plugin-sdk/	SDK for writing WASM plugin guest controllers
arika (在処)	arika/	Coordinate frames, epochs, Earth rotation, ephemerides
utsuroi (移ろい)	utsuroi/	ODE integrators (RK4, DOP853, Störmer-Verlet, Yoshida)
tobari (帳)	tobari/	Atmosphere density, spherical-harmonic geopotential, IGRF geomagnetic field, space weather
rrd-wasm	rrd-wasm/	Rerun RRD decoder compiled to WebAssembly

TypeScript / npm packages

Package	Directory	Description
uneri (うねり)	uneri/	DuckDB-wasm + uPlot streaming time-series charts
orts-viewer	viewer/	Real-time 3D orbit viewer (React + @react-three/fiber)
starlight-rustdoc	starlight-rustdoc/	Astro/Starlight plugin for Rust API docs from rustdoc JSON

Example plugins (plugin-sdk/examples/)

Plugin	Style	Description
bdot-finite-diff	main-loop	B-dot detumbling via finite-difference dB/dt
pd-rw-control	callback	PD attitude control + reaction wheels
pd-rw-unloading	callback	PD control + magnetorquer RW unloading
detumble-nadir	callback	Detumble → nadir pointing mode transition

Documentation

• Docs site — API reference, examples, guides
• ARCHITECTURE.md / 日本語 — Top-level architecture overview
• DESIGN.md — Design document (Japanese)
• CHANGELOG.md — English changelog
• CHANGELOG.ja.md — Japanese changelog
• RELEASING.md — Release process

License

MIT