Force Models¶

Force models compute accelerations applied to a spacecraft during numerical propagation. Community models cover standard perturbations; Pro models add radiation effects.

Community Force Models¶

GravitationalAcceleration¶

Central-body two-body gravity. Always present as the primary force.

new GravitationalAcceleration(centralBody)

ThirdBodyPerturbation¶

Third-body gravitational perturbation using Battin's numerically stable formula to avoid catastrophic cancellation when the perturbing body is distant.

new ThirdBodyPerturbation(perturbingBody, centralBody)

AtmosphericDrag¶

Atmosphere-relative velocity with co-rotation of the central body's atmosphere.

new AtmosphericDrag(spacecraft, celestialBody)

Property	Default	Description
`DragCoefficient` (Cd)	2.2	Set on the `Spacecraft` constructor
`SectionalArea`	--	Cross-sectional area (m2)

SolarRadiationPressure¶

Cannonball SRP model with configurable reflectivity coefficient and continuous shadow fraction for penumbra transitions.

new SolarRadiationPressure(spacecraft, occultingBodies)

Property	Default	Description
`SolarRadiationCoeff` (Cr)	1.0	Set on the `Spacecraft` constructor

GeopotentialGravitationalField¶

EGM2008 spherical harmonics up to degree 70 with geodesy-normalized Legendre functions (no Condon-Shortley phase).

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

Thread Safety

GeopotentialGravitationalField is not thread-safe. Create one CelestialBody with geopotential per propagation task.

Pro Force Models¶

AlbedoRadiationPressure¶

Pro

AlbedoRadiationPressure is a Pro feature.

Models sunlight reflected off a celestial body using a Lambertian sphere approximation. The acceleration is:

a = (L_sun / 4*pi*c) * alpha * Cr * (A/m) * (2/3*pi) * (R_body / r_sun)^2 * f(phi) / r_sc^2

Where f(phi) = (pi - phi) * cos(phi) + sin(phi) is the Lambertian visibility function. Acceleration is zero on the dark side.

new AlbedoRadiationPressure(spacecraft, reflectingBody)

Configuration: Set albedo on the CelestialBody constructor, then call IncludeAlbedo() on the builder.

Body	Bond Albedo
Earth	0.306
Moon	0.12
Venus	0.77
Mars	0.25

ThermalRadiationPressure¶

Pro

ThermalRadiationPressure is a Pro feature.

Models infrared radiation emitted by a celestial body using an isotropic emitter model. Always present regardless of Sun geometry or eclipse state.

a = Cr * (A/m) * epsilon * sigma * T_eff^4 * R^2 / (c * r^2)

new ThermalRadiationPressure(spacecraft, emittingBody)

Configuration: Set thermalEffectiveTemperature (Kelvin) and thermalEmissivity on the CelestialBody constructor, then call IncludeThermalRadiation() on the builder.

Body	T_eff (K)	Emissivity
Earth	254	0.95
Moon	270	0.95

Atmosphere Models¶

Model	Description
`IAtmosphericModel`	Common interface for density queries
`EarthStandardAtmosphere`	Low-altitude analytical Earth model
`MarsStandardAtmosphere`	Simple Mars atmospheric model
`Nrlmsise00Model`	Time-varying Earth model for drag analysis (thread-safe)

Example¶

var earth = new CelestialBody(PlanetsAndMoons.EARTH,
    new GeopotentialModelParameters("Data/SolarSystem/EGM2008_to70_TideFree", 10),
    albedo: 0.306, thermalEffectiveTemperature: 254.0, thermalEmissivity: 0.95);