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High-Fidelity Propagation

The CentralBodyPropagatorBuilder fluent API assembles a propagator with the full suite of force models in a single declarative setup.

Full Force Model Assembly

// Central body with geopotential, atmosphere, albedo, and thermal properties
var earth = new CelestialBody(PlanetsAndMoons.EARTH,
    new GeopotentialModelParameters("Data/SolarSystem/EGM2008_to70_TideFree", 10),
    new Nrlmsise00Model(SpaceWeather.Nominal),
    albedo: 0.306, thermalEffectiveTemperature: 254.0, thermalEmissivity: 0.95);

// Adaptive integrator
var integrator = new RK78Integrator(
    absoluteTolerance: 1e-10,
    relativeTolerance: 1e-10,
    initialStepSize: 30.0);

// Assemble propagator with all perturbations
using var propagator = new CentralBodyPropagatorBuilder(window, spacecraft, integrator, deltaT)
    .WithPerturbingBody(Stars.SUN_BODY)
    .WithPerturbingBody(PlanetsAndMoons.MOON_BODY)
    .IncludeAtmosphericDrag()
    .IncludeSolarRadiationPressure()
    .IncludeAlbedo(earth)
    .IncludeThermalRadiation(earth)
    .Build();

var solution = propagator.Propagate();

Force Models

The builder supports the following perturbations:

Method Force Model
(automatic) Central-body gravity
WithPerturbingBody(body) Third-body perturbation
IncludeAtmosphericDrag() Atmospheric drag
IncludeSolarRadiationPressure() Direct solar radiation pressure
IncludeAlbedo(body) Reflected sunlight (Lambertian sphere)
IncludeThermalRadiation(body) Infrared emission (isotropic emitter)

Geopotential Degree Guidance

Degree Use Case
2 Fast J2-only preliminary analysis
10 Good LEO production baseline
20-30 Higher-fidelity geodesy and mission analysis
70 Maximum supported EGM2008 fidelity

Performance trade-off

Higher geopotential degree increases computation time significantly. Degree 10 is sufficient for most LEO missions. Reserve degree 70 for geodetic satellites or when matching external high-fidelity references.

Typical Acceleration Magnitudes (LEO)

For context, approximate acceleration magnitudes at 400 km altitude:

  • Direct SRP: ~4.5e-8 m/s^2 (reference)
  • Albedo: ~10-20x smaller than direct SRP
  • Thermal (IR): ~15% of direct SRP, always present regardless of eclipse

See Also