Orbital Mechanics
Orbit simulation is provided by 42, NASA's spacecraft dynamics simulator. 42 propagates orbits for every satellite in the constellation and models the space environment. It handles large constellations — 10,000+ satellites have been propagated successfully.
Orbit Propagation
42 supports multi-body orbital dynamics with seamless transition between two-body and three-body models. Orbits are defined using standard Keplerian elements. For the LeoDOS Walker Delta constellation, 42 propagates all satellites simultaneously, maintaining the correct relative geometry as the constellation evolves.
Space Environment
| Model | What it provides |
|---|---|
| EGM96 gravity (18th order) | Orbit perturbations at LEO altitude |
| IGRF magnetic field (10th order) | Magnetometer readings, magnetorquer control |
| MSIS-86 / Jacchia-Roberts atmosphere | Aerodynamic drag |
| Solar geometry | Sun position, eclipse/sunlight status per spacecraft |
| Celestial bodies (sun, 9 planets, 45 moons) | Third-body perturbations |
Published State
At each timestep, 42 publishes to the hardware simulators:
- Date and time
- Spacecraft position and velocity (inertial and rotating frames)
- Attitude quaternion and angular velocity
- Sun vector (inertial frame)
- Magnetic field vector at the spacecraft
- Eclipse/sunlight flag
- Angular momentum
Each simulator reads the subset it needs — GPS reads position, the magnetometer reads the magnetic field, sun sensors read the sun vector.