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J4Propagator Class

An analytic propagator that uses a second order J2/J4 perturbation algorithm which models only the secular effects on the orbital elements. J2 effects are considered to the second order and J4 effects are considered to the first order.
Inheritance Hierarchy

Namespace:  AGI.Foundation.Propagators
Assembly:  AGI.Foundation.Models (in AGI.Foundation.Models.dll) Version: 24.2.419.0 (24.2.419.0)
Syntax
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public class J4Propagator : CartesianOnePointPropagator

The J4Propagator type exposes the following members.

Constructors
Properties
  NameDescription
Public propertyGravitationalParameter
Gets or sets the gravitational parameter of the central body around which to propagate.
Public propertyInitialConditions
Gets or sets the orbital elements from which to propagate. Setting the initial conditions on this property will also update GravitationalParameter.
Public propertyIsFrozen
Gets a value indicating whether this object is frozen. A frozen object cannot be modified and an ObjectFrozenException will be thrown if an attempt is made to do so.
(Inherited from DefinitionalObject.)
Public propertyJ2ZonalHarmonicCoefficient
Gets or sets the non-normalized J2 zonal harmonic coefficient of the central body around which to propagate.
Public propertyJ4ZonalHarmonicCoefficient
Gets or sets the non-normalized J4 zonal harmonic coefficient of the central body around which to propagate.
Public propertyOrbitEpoch
Gets or sets the Julian date at which the InitialConditions are specified.
Public propertyReferenceDistance
Gets or sets the reference distance (equatorial radius) associated with the J2 and J4 coefficients.
Public propertyReferenceFrame
Gets or sets the reference frame in which the ephemeris is produced.
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Methods
  NameDescription
Protected methodCheckForSameDefinition(CartesianOnePointPropagator)
Checks to determine if another instance has the same definition as this instance and returns if it does. Derived classes MUST override this method and check all new fields introduced by the derived class for definitional equivalence. It is NOT necessary to check base class fields because the base class will already have done that. When overriding this method, you should NOT call the base implementation because it will return for all derived-class instances. Derived classes should check the type of other to preserve the symmetric nature of IsSameDefinition(Object).
(Overrides CartesianOnePointPropagatorCheckForSameDefinition(CartesianOnePointPropagator).)
Protected methodCheckForSameDefinition(DefinitionalObject)
Checks to determine if another instance has the same definition as this instance and returns if it does. Derived classes MUST override this method and check all new fields introduced by the derived class for definitional equivalence. It is NOT necessary to check base class fields because the base class will already have done that. When overriding this method, you should NOT call the base implementation because it will return for all derived-class instances. Derived classes should check the type of other to preserve the symmetric nature of IsSameDefinition(Object).
(Inherited from CartesianOnePointPropagator.)
Protected methodCheckForSameDefinition(J4Propagator)
Checks to determine if another instance has the same definition as this instance and returns if it does. Derived classes MUST override this method and check all new fields introduced by the derived class for definitional equivalence. It is NOT necessary to check base class fields because the base class will already have done that. When overriding this method, you should NOT call the base implementation because it will return for all derived-class instances. Derived classes should check the type of other to preserve the symmetric nature of IsSameDefinition(Object).
Public methodClone
Clones this object using the specified context.
(Overrides DefinitionalObjectClone(CopyContext).)
Protected methodComputeCurrentDefinitionHashCode
Computes a hash code based on the current properties of this object. Derived classes MUST override this method and compute a hash code that combines: a unique hash code seed, the base implementation result, and the hash codes of all new fields introduced by the derived class which are used in the CheckForSameDefinition(DefinitionalObject) method.
(Overrides CartesianOnePointPropagatorComputeCurrentDefinitionHashCode.)
Public methodCreatePoint
Creates a Point that represents the motion produced by this propagator.
(Inherited from CartesianOnePointPropagator.)
Public methodEnumerateDependencies
Enumerates the dependencies of this object by calling EnumerateT(T) for each object that this object directly depends upon. Derived classes which contain additional dependencies MUST override this method, call the base implementation, and enumerate dependencies introduced by the derived class.
(Overrides DefinitionalObjectEnumerateDependencies(DependencyEnumerator).)
Public methodEquals
Determines whether the specified object is equal to the current object.
(Inherited from Object.)
Protected methodFinalize
Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.
(Inherited from Object.)
Public methodFreeze
Freezes this object. Further attempts to modify it will result in an ObjectFrozenException.
(Inherited from DefinitionalObject.)
Protected methodFreezeAggregatedObjects
Called by Freeze to also freeze any objects that are considered to be a part of this object. Derived classes which contain additional aggregated objects MUST override this method, call the base implementation, and freeze aggregated objects introduced by the derived class. The objects that need to be frozen in this method are frequently created in this object's constructor and are not settable via properties.
(Inherited from DefinitionalObject.)
Public methodGetDefinitionHashCode
Gets a hash code representing the definition of this object.
(Inherited from DefinitionalObject.)
Public methodGetEvaluator

Gets an evaluator that can propagate at individual dates.

This evaluator propagates the orbit state. The result of evaluating will be a MotionT corresponding to the orbital state at the given JulianDate expressed in the propagator's ReferenceFrame.

Note: when evaluating with this evaluator, it may be more efficient to specify times using an arithmetically safe TimeStandard to avoid the need to convert in order to perform the propagation. The length of a time step may be different in different TimeStandards. So be careful when specifying times.

(Inherited from CartesianOnePointPropagator.)
Public methodGetEvaluator(EvaluatorGroup)

Gets an evaluator that can propagate at individual dates.

This evaluator propagates the orbit state from InitialConditions at OrbitEpoch based on the GravitationalParameter, J2ZonalHarmonicCoefficient, J4ZonalHarmonicCoefficient, and ReferenceDistance. The result of evaluating will be a Motion<Cartesian> corresponding to the orbital position and velocity at the given JulianDate expressed in the propagator's ReferenceFrame.

(Overrides CartesianOnePointPropagatorGetEvaluator(EvaluatorGroup).)
Public methodGetHashCode
Serves as the default hash function.
(Inherited from Object.)
Protected methodGetMotionReferenceFrame
Gets the reference frame in which the motion is defined.
(Overrides CartesianOnePointPropagatorGetMotionReferenceFrame.)
Public methodGetType
Gets the Type of the current instance.
(Inherited from Object.)
Public methodIsSameDefinition
Determines if this object has the same definition as another object.
(Inherited from DefinitionalObject.)
Protected methodMemberwiseClone
Creates a shallow copy of the current Object.
(Inherited from Object.)
Public methodPropagate(JulianDate, JulianDate, Duration, Int32, ReferenceFrame)

Calculates position (and zero or more derivatives) for regular time steps over an interval.

Note: when propagating, it may be more efficient to specify times using an arithmetically safe TimeStandard to avoid the need to convert in order to perform the propagation. The length of a time step may be different in different TimeStandards. So be careful when specifying times.

(Inherited from CartesianOnePointPropagator.)
Public methodPropagate(JulianDate, JulianDate, Duration, Int32, ReferenceFrame, ITrackCalculationProgress)

Calculates position (and zero or more derivatives) for regular time steps over an interval.

Note: when evaluating with this evaluator, it may be more efficient to specify times using an arithmetically safe TimeStandard to avoid the need to convert in order to perform the propagation. The length of a time step may be different in different TimeStandards. So be careful when specifying times.

(Inherited from CartesianOnePointPropagator.)
Protected methodThrowIfFrozen
Throws ObjectFrozenException if this object IsFrozen. This method should be called from any method or property that modifies this object.
(Inherited from DefinitionalObject.)
Public methodToString
Returns a string that represents the current object.
(Inherited from Object.)
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Remarks
The analytical model reverts to two-body motion if any portion of the orbit falls within the reference distance specified for the gravity model.
Examples

The following example shows how to create a J4Propagator using the EGM96 gravitational model:

C#
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GregorianDate orbitEpoch = new GregorianDate(2007, 5, 30, 12, 0, 0);
JulianDate orbitEpochJD = new JulianDate(orbitEpoch);

Motion<Cartesian> elementsAtEpoch = new Motion<Cartesian>(
    new Cartesian(12000000.0, 0.0, 0.0),    // initial position
    new Cartesian(0.0, 5763.0, 0.0));       // initial velocity

J4Propagator propagator = new J4Propagator(
    orbitEpochJD,
    CentralBodiesFacet.GetFromContext().Earth.InertialFrame,
    elementsAtEpoch,
    EarthGravitationalModel1996.GravitationalParameter,
    EarthGravitationalModel1996.J2UnnormalizedValue,
    EarthGravitationalModel1996.J4UnnormalizedValue,
    EarthGravitationalModel1996.SemimajorAxis);
See Also