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AGI.Foundation.Propagators Namespace

Contains types used in producing the state of an object from a known element set.
Public classAuxiliaryStateScalar
Represents a scalar value which may depend on integrated quantities in the state and is evaluated and stored for output during propagation.
Public classAuxiliaryStateVector
An auxiliary state vector which is not integrated with the rest of the state but is evaluated for the propagation output during propagation.
Public classBallisticPropagator
This class calculates a ballistic trajectory (two body gravity only) between two locations on a CentralBody.
Public classBallisticTrajectoryInformation
An object with many metrics that describe a ballistic trajectory from an initial point to a target point.
Public classCartesianOnePointPropagator
Public classConstantStateStoppablePropagator
A StoppablePropagator that always returns the initial state passed in at propagation time. This can be useful when you are modeling a trajectory with multiple propagators strung together and one of those segments is in some way fixed for a time, such as landed or docked.
Public classDynamicStateStoppablePropagator
A StoppablePropagator that evaluates a StateEvaluatorT in time until a StoppingCondition is tripped. The initial state of this segment will only be used to evaluate the DynamicState at the date of the passed in state. The DynamicState does not have a way to initialize the values within it, so except for the date this propagator can not be initialized with an initial state at propagation time. As such this propagator does not need adapters.
Public classExceptionDuringPropagationEventArgs
Provides information about the exception during propagation event conditions.
Public classGpsRinexPropagator
GPS RINEX Propagator class propagates GPS orbits - providing GPS satellite positions based on RINEX broadcast ephemeris sets.
Public classCode exampleJ2Propagator
An analytic propagator that uses a first order J2 perturbation algorithm which models only the secular effects on the orbital elements.
Public classCode exampleJ4Propagator
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.
Public classLifetimeOrbitPropagator
Propagates a set of initial conditions using a long-term propagation technique to determine when the orbit is expected to decay, based on the evolution of the mean orbital elements under the effects of gravitational, atmospheric, and solar perturbations.
Public classNavstarISGps200DPropagator
Propagates the orbit of a Global Positioning System (GPS) satellite according to the propagation scheme defined in the Navstar Interface Specific (IS) GPS-200D.
Public classNumericalIntegrationInformation
Contains information about the behavior of an integrator in a given integration step.
Public classNumericalPropagationException
An exception that indicates an error was encountered during propagation. See the inner exception for details regarding the root cause.
Public classNumericalPropagationStateHistory
Contains a collection of data resulting from propagating the state over a span of time.
Public classNumericalPropagator

A propagator which can advance the state from initial conditions by either taking individual integration steps or by propagating over a given time span. Note that a given instance of a propagator is NOT thread safe. So if there is a need to propagate a given state in different threads, make sure to clone the propagator for another thread using CopyT(T).

A NumericalPropagator is created by configuring a NumericalPropagatorDefinition and then calling CreatePropagator.

Public classNumericalPropagatorDefinition

The definitional object that creates a NumericalPropagator.

It consists of the overall propagation state which represents individual scalar, vector, or custom parameters within IntegrationElements (which are integrated during propagation), and the AuxiliaryElements (which are not). It also contains StateCorrectors which correct the IntegrationElements and their derivatives in between propagation steps, the Epoch of the initial conditions, and the Integrator which integrates the IntegrationElements.

Call CreatePropagator in order to create the defined NumericalPropagator.

Public classNumericalPropagatorState
A state representing every propagated value in a particular NumericalPropagator.
Public classOrbitLifetimeResults
A set of results indicating the time at which an orbit is expected to decay and the time history of the mean elements. Note that these results may not always indicate a decayed orbit. Check the Status to see whether one of the limit conditions was met before finishing the calculation. In that case, the DateOfDecay will be equal to the ReferenceEpoch, indicating an unknown decay date.
Public classPropagationEventArgs
Provides information about the current propagation event conditions and provides a means of indicating how the propagation should continue.
Public classPropagationNewtonianPoint
An PropagationStateElement representing the position (and velocity) of a body with its second derivative defined by Newton's second law of motion: Acceleration = AppliedForce / Mass
Public classPropagationScalar
An PropagationStateElement representing a scalar value to be integrated over time.
Public classPropagationStateConverter
A converter which can take raw data from the output of propagation and turn it into useful data by using PropagationStateElement and AuxiliaryStateElement converter types to convert to their corresponding output types. For instance, a PropagationVector defines its values using Cartesian types. So if the user enters an element identification corresponding to a PropagationVector, it can convert the raw data into the Motion<Cartesian> data containing the vector value and its derivatives.
Public classPropagationVector
A PropagationStateElement representing a vector value to be integrated over time.
Public classPropagatorPoint
A point with its location computed by a propagator. To create an instance of this class, call a propagator method that returns an instance.
Public classSgp4Elements
A set of orbital elements intended to be propagated with the SGP4 propagator.
Public classSgp4ElementsSwitchByClosestApproach
An algorithm which determines when to switch from one element set to another by propagating each element set against the next to determine the time at which the range between the positions of the two orbits is the smallest. This may not represent the most accurate position for the orbit at all times. However, it will minimize discontinuities which may result from fitting the newer element set to the correct orbit.
Public classSgp4ElementsSwitchByEpoch
An algorithm which determines when to switch from one element set to another by comparing their respective Epoch values. The first element set is used up until the epoch of the second and the last element set is used after its epoch.
Public classSgp4ElementsSwitchByMidpoint
An algorithm which determines when to switch from one element set to another by comparing their respective Epoch values. The first element set is used up until the midpoint in time between the epoch of the first and the epoch of the second. The last element set is used from the midpoint in time between its epoch and the epoch of the set before it.
Public classSgp4ElementsSwitching
An algorithm for determining when to switch from one set of elements to another.
Public classCode exampleSgp4Propagator
Propagates an orbit using the NORAD SGP4/SDP4 model as defined by the Center for Space Standards and Innovation (CSSI). More information and the algorithm's code can be found at

Note that the SGP4 propagator performs its propagation using the TAI time standard. If the user asks for a propagation over an interval and timestep specified in UTC, the system interprets this to mean that the reported values should be in UTC. However, in order to compute the correct timespans (potentially propagating through leap seconds), the system will convert to TAI in order to compare times. Since the length of a second is different in various time standards, the stepsize is measured in the time standard the user specifies even though the comparisons and propagation occurs in TAI. If the length of a given time step is important, this may be a necessary calculation. However, the performance of the SGP4 propagation can be improved by specifying input times in TAI.

The acceleration returned from the SGP4Propagator is identical to the J4Propagator, which is an approximation used to prevent code using this propagator from being unable to provide analysis in the absence of acceleration. In STK Components, there are a number of places that expect or require acceleration information from propagators. In order to support this, the Sgp4Propagator will return an acceleration when asked. However, because the SGP4 theory does not explicitly contain a representation of the acceleration and the velocity of the SGP4 theory does not correspond exactly with the position, the acceleration returned for SGP4 is an approximation. Compared with numerical differentiation of the position, the velocity returned from the SGP4 theory can have a discrepancy anywhere from a few millimeters to several meters. Since the acceleration perturbations from drag and third body effects are several orders of magnitude less than gravitational effects, the J4 perturbations are used here to approximate the acceleration for SGP4.

Public classSgp4PropagatorSgp4EstimationInput
A class containing configuration information for the static estimation methods available on the Sgp4Propagator.
Public classSgp4PropagatorSgp4EstimationOutput
A class containing the estimated Sgp4Elements along with the associated information from the fit.
Public classSimpleAscentPropagator
Propagates a simple (point) launch vehicle from a CentralBody to a specified burnout motion.
Public classSimpleAscentPropagatorWarnings
The arguments passed to any event handlers listening for propagation warnings that may be produced when using the SimpleAscentPropagator.
Public classSinglePointStoppablePropagator
Samples a Point at a specified time step until a StoppingCondition is satisfied, returning the ephemeris computed and all events found by the StoppingConditions.
Public classSinglePointStoppablePropagatorDefinition
Provides the infrastructure to use a Point as a basis for propagating a trajectory that can be stopped with StoppingConditions. Note that this only propagates a single point; no other items will be propagated.
Public classSinglePointStoppablePropagatorResults
Public classStateTransitionMatrix

An extended state transition matrix, if consider parameters are not used then it functions as a normal state transition matrix: mapping the value of the state parameters from one time to another time.

The state transition matrix represents the transformation from the state at one time to the state at another time. This can be used as an alternative to propagating a state in time with NumericalPropagator, but is more often used in order to find the time-varying covariance of the state. This is because the construction of a StateTransitionMatrix entails the linearization of the state, and in most cases calculating the derivatives of the state transition matrix takes as long or longer as calculating the derivatives of the state.

To find the covariance of a state over time a StateTransitionMatrix is propagated with a NumericalPropagator and the resulting data is used to create the covariance information for the same period using PopulateCovarianceCollection(Matrix, DateMotionCollectionMatrix, TransitionType).

Public classStoppableNumericalPropagator
A StoppablePropagator that wraps a PropagatorDefinition and will find events and stop based on a set of StoppingConditions.
Public classStoppableNumericalPropagatorResults
Stores the ephemeris computed by a NumericalPropagator and information about how the propagation was stopped.
Public classStoppablePropagator
A propagator that wraps some type that generates states and will sample some derived value from those states searching for events and eventually an event that will stop propagation with StoppingConditionEvaluators.
Public classStoppablePropagatorDefinition
Defines a propagator that can propagate to arbitrary events and stop on any StoppingCondition. This type is intended to work by wrapping some other propagator and generate states until a StoppingCondition is tripped.
Public classStoppablePropagatorResults
The results of a StoppablePropagator. This type is designed to be extended with additional data computed during propagation.
Public classStoppablePropagatorStepTakenArgs
The data for the event that gets raised when a StoppablePropagatortakes a step or resteps.
Public classTwoBodyPropagator
Propagates an orbit using a simple two-body model.
Public classTwoBodyStoppablePropagator
A StoppablePropagator that propagates an orbit using a simple two-body model.
Public classCode exampleTwoLineElementSet
A NORAD two-line element set (TLE). Note that the precision of most TLEs is limited by the string representations in the TLE. The resulting ephemeris has a precision on the order of kilometers. When creating a TLE based on orbital elements, it is important to note that information will be lost when converting precise elements into a string representation.
Public classCode exampleWaypoint
Defines the characteristics at a waypoint.
Public classWaypointCollection
A collection of Waypoints.
Public classCode exampleWaypointPropagator
Propagates a path connecting waypoints relative to an ellipsoid.
Public structurePropagationStateArray
Provides a means of specifying an indexable object which represents a set of values mapping a subset of the overall state elements. The sub-elements are defined by a set of indices into the overall state.
Public interfaceIGpsElements
An interface to a GPS element set that contains data items needed for GPS ephemeris propagation. This interface provides data for one GPS satellite.
Public interfaceIPropagateCollectionFromOnePointTCollection
An interface that enables propagation over multiple dates by one-point evaluating each date and adding the results to the collection.
Public interfaceIUpdatePriorToStep
An interface to an object created by a PropagationStateElement that has special behavior that takes place each time step prior to propagation. The NumericalPropagator will call the UpdatePriorToStep(JulianDate, PropagationStateArray) method in this class to perform that behavior.
Public enumerationBallisticPropagatorSolutionType
Species the kind of solution that was calculated by a BallisticPropagator, IE whether the desired trajectory was successfully calculated, the propagator failed to converge on a solution, or the specified constraint was invalid.
Public enumerationLifetimeCalculationLimitType
Specifies how the LifetimeCalculation should behave when determining completion of the computation. This will limit the run time of the orbit lifetime computation.
Public enumerationLifetimeCalculationStatus
An indication of the final state of the LifetimeOrbitPropagator calculation.
Public enumerationPropagationEventIndication
An indication of how the propagator should proceed.
Public enumerationPropagationEventTrigger
Indicates which kind of propagation method triggered the StepTaken event.
Public enumerationPropagationStage
An enumerator that communicates the which stage of propagation an evaluator is called during.
Public enumerationSimpleAscentPropagatorAscentType
The type of spline to use in the SimpleAscentPropagator.
Public enumerationSimpleAscentPropagatorBurnoutVelocityFrame
Sets the CentralBody-relative frame used to specify the burnout velocity in SimpleAscentPropagator.
Public enumerationSortingFormat
An enumeration that defines the order in which entries in a NumericalPropagationStateHistory are sorted.
Public enumerationTransitionType
An enumeration that defines the format of transformation described by a StateTransitionMatrix.