org.orekit.propagation.numerical
Interface AdditionalEquations

All Superinterfaces:

Serializable

All Known Implementing Classes:

AttitudeEquation, MassEquation, PartialDerivativesEquations

public interface AdditionalEquations
extends Serializable

This interface allows users to add their own differential equations to a numerical propagator.

In some cases users may need to integrate some problem-specific equations along with classical spacecraft equations of motions. One example is optimal control in low thrust where adjoint parameters linked to the minimized hamiltonian must be integrated. Another example is formation flying or rendez-vous which use the Clohessy-Whiltshire equations for the relative motion.

This interface allows users to add such equations to a numerical propagator. Users provide the equations as an implementation of this interface and register it to the propagator thanks to its NumericalPropagator.addAdditionalEquations(AdditionalEquations) method. Several such objects can be registered with each numerical propagator, but it is recommended to gather in the same object the sets of parameters which equations can interact on each others states.

The additional parameters are gathered in a simple p array. The additional equations compute the pDot array, which is the time-derivative of the p array. Since the additional parameters p may also have an influence on the equations of motion themselves (for example an equation linked to a complex thrust model may induce an acceleration and a mass change), the same time derivatives equations adder already shared by all force models to add their contributions is also provided to the additional equations implementation object. This means these equations can be used as an additional force model if needed. If the additional parameters have no influence at all on the spacecraft state, this adder can simply be ignored.

This interface is the numerical (read not already integrated) counterpart of the AdditionalStateProvider interface. It allows to append various additional state parameters to any numerical propagator.

Author:

Luc Maisonobe

See Also:

NumericalPropagator, AdditionalStateProvider

Method Summary

void	computeDerivatives(SpacecraftState s, TimeDerivativesEquations adder) Compute the derivatives related to the additional state parameters.
String	getName() Get the name of the additional state.

Method Detail

getName

String getName()

Get the name of the additional state.

Returns:

name of the additional state

computeDerivatives

void computeDerivatives(SpacecraftState s,
                        TimeDerivativesEquations adder)
                        throws OrekitException

Compute the derivatives related to the additional state parameters.

Parameters:

s - current state information: date, kinematics, attitude, additional states

adder - object where the contribution of the additional parameters to the orbit evolution (accelerations) should be added

Throws:

OrekitException - if some specific error occurs