Package org.orekit.forces.gravity

Class J2OnlyPerturbation

java.lang.Object
org.orekit.forces.gravity.J2OnlyPerturbation
All Implemented Interfaces:
ForceModel, EventDetectorsProvider, ParameterDriversProvider
public class J2OnlyPerturbation extends Object implements ForceModel
J2-only force model. This class models the oblateness part alone of the central body's potential (degree 2 and order 0), whilst avoiding the computational overhead of generic NxM spherical harmonics.

This J2 coefficient has same magnitude and opposite sign than the so-called unnormalized C20 coefficient.

This class should not be used in combination of HolmesFeatherstoneAttractionModel, otherwise the J2 term would be taken into account twice.

Author:
Romain Serra

  • Constructor Details

    • J2OnlyPerturbation

      public J2OnlyPerturbation(double mu, double rEq, TimeScalarFunction j2OverTime, Frame frame)
      Constructor with TimeScalarFunction. It is the user's responsibility to make sure the Field and double versions are consistent with each other.
      Parameters:
      mu - central body's gravitational constant
      rEq - central body's equatorial radius
      j2OverTime - J2 coefficient as a function of time.
      frame - frame where J2 applies

    • J2OnlyPerturbation

      public J2OnlyPerturbation(double mu, double rEq, double constantJ2, Frame frame)
      Constructor with constant J2.
      Parameters:
      mu - central body gravitational constant
      rEq - central body's equatorial radius
      constantJ2 - constant J2 coefficient
      frame - frame where J2 applies

    • J2OnlyPerturbation

      public J2OnlyPerturbation(UnnormalizedSphericalHarmonicsProvider harmonicsProvider, Frame frame)
      Constructor with spherical harmonics provider.
      Parameters:
      harmonicsProvider - spherical harmonics provider of unnormalized coefficients
      frame - frame where J2 applies

  • Method Details

    • getMu

      public double getMu()
      Getter for mu.
      Returns:
      mu

    • getrEq

      public double getrEq()
      Getter for equatorial radius.
      Returns:
      equatorial radius

    • getFrame

      public Frame getFrame()
      Getter for frame.
      Returns:
      frame

    • getJ2

      public double getJ2(AbsoluteDate date)
      Return J2 at requested date.
      Parameters:
      date - epoch at which J2 coefficient should be retrieved
      Returns:
      J2 coefficient

    • getJ2

      public <T extends CalculusFieldElement<T>> T getJ2(FieldAbsoluteDate<T> date)
      Return J2 at requested date (Field version).
      Type Parameters:
      T - field
      Parameters:
      date - epoch at which J2 coefficient should be retrieved
      Returns:
      J2 coefficient

    • dependsOnPositionOnly

      public boolean dependsOnPositionOnly()
      Check if force model depends on position only at a given, fixed date.
      Specified by:
      dependsOnPositionOnly in interface ForceModel
      Returns:
      true if force model depends on position only, false if it depends on mass or velocity, either directly or due to a dependency on attitude

    • acceleration

      public Vector3D acceleration(SpacecraftState state, double[] parameters)
      Compute acceleration.
      Specified by:
      acceleration in interface ForceModel
      Parameters:
      state - current state information: date, kinematics, attitude
      parameters - values of the force model parameters at state date, only 1 value for each parameterDriver
      Returns:
      acceleration in same frame as state

    • computeAccelerationInJ2Frame

      public static Vector3D computeAccelerationInJ2Frame(Vector3D positionInJ2Frame, double mu, double rEq, double j2)
      Compute acceleration in J2 frame.
      Parameters:
      positionInJ2Frame - position in J2 frame@
      mu - gravitational parameter
      rEq - equatorial radius
      j2 - J2 coefficient
      Returns:
      acceleration in J2 frame

    • acceleration

      public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(FieldSpacecraftState<T> state, T[] parameters)
      Compute acceleration.
      Specified by:
      acceleration in interface ForceModel
      Type Parameters:
      T - type of the elements
      Parameters:
      state - current state information: date, kinematics, attitude
      parameters - values of the force model parameters at state date, only 1 value for each parameterDriver
      Returns:
      acceleration in same frame as state

    • computeAccelerationInJ2Frame

      public static <T extends CalculusFieldElement<T>> FieldVector3D<T> computeAccelerationInJ2Frame(FieldVector3D<T> positionInJ2Frame, double mu, double rEq, T j2)
      Compute acceleration in J2 frame. Field version.
      Type Parameters:
      T - field type
      Parameters:
      positionInJ2Frame - position in J2 frame@
      mu - gravitational parameter
      rEq - equatorial radius
      j2 - J2 coefficient
      Returns:
      acceleration in J2 frame

    • getParametersDrivers

      public List<ParameterDriver> getParametersDrivers()
      Get the drivers for parameters.
      Specified by:
      getParametersDrivers in interface ParameterDriversProvider
      Returns:
      drivers for parameters