Ecliptic frame, J2000 sun-centric

1

Hello,
I would like to use ecliptic coordinate system centered in Sun, and its direction to be Mean equinox of a standard epoch (J2000).

How would you construct such coordinate system?
What I am doing now is:
-get EME2000 geocentric frame
-use EclitpicProvider to align it with ecliptic
-use translation transform to change origin of such frame from geocentric to suncentric (I calculate translation between Earth and Sun).

Is there a better approach? I also wonder if mine does not introduce some errors.
Thank you for any help provided.
Regards,

2

Sorry for double post, but I would like to make my question more precise.
I am looking for IAU76/J2000 heliocentric ecliptic frame implementation. Are we able to get it in Orekit?
JPL Horizons web interface is providing orbital parameters in this frame:

Initial IAU76/J2000 heliocentric ecliptic osculating elements (au, days, deg.):

The problem with my previous approach is that EclipticProvider is aligning MOD with ecliptic. I would need a provider that aligns EME2000 with ecliptic.

Regards,

3

Hi, I don’t think that frame is available out of the box, though you might be able to construct it using the existing transform providers. Contributions are always welcome.

4

Here is what worked for me :

/**
  • Heliocentric Aries (J2000) ecliptic frame
  • This system has its Z axis perpendicular to the plane of the Earth’s orbit
  • around the Sun (positive North) and its X axis towards the First Point of
  • Aries (the direction in space defined by the intersection between the Earth’s
  • equatorial plane and the plane of its orbit around the Sun (the plane of the
  • ecliptic). This system is (to first order) fixed with respect to the distant
  • stars.

*/
public final class EclipticFrame extends Frame {

/** Serializable UID */
private static final long serialVersionUID = -2626811243057956275L;

/** Ecliptic frame name */
private static final String FRAME_NAME = "HELIOCENTRIC ECLIPTIC J2000";

/** Parent frame */
private static final Frame PARENT_FRAME = FramesFactory.getEME2000();

/** Instance */
private static EclipticFrame instance;

/**
 * Constructor
 */
private EclipticFrame() {
	super(PARENT_FRAME, new LocalTransformProvider(), FRAME_NAME);
}

/**
 * @return Instance of Ecliptic frame
 */
public static EclipticFrame getInstance() {
	if (instance == null) {
		instance = new EclipticFrame();
	}
	return instance;
}

/**
 * {@inheritDoc}
 */
@Override
public boolean isPseudoInertial() {
	return true;
}


private static class LocalTransformProvider implements TransformProvider {

	/** Serializable UID */
	private static final long serialVersionUID = -9133094479942135342L;

	/**
	 * {@inheritDoc}
	 */
	@Override
	public Transform getTransform(final AbsoluteDate date) throws OrekitException {
		// translation to Sun
		Vector3D sunCoords = PARENT_FRAME
				.getTransformTo(CelestialBodyFactory.getSun().getInertiallyOrientedFrame(), date).getTranslation();
		Transform translation = new Transform(date, sunCoords);
		// Ecliptic frame is based on MOD, so it has to be fixed on J2000 epoch where
		// EME2000 = MOD
		Transform rotation = PARENT_FRAME.getTransformTo(FramesFactory.getEcliptic(IERSConventions.IERS_2010),
				AbsoluteDate.J2000_EPOCH);

		return new Transform(date, translation, rotation);
	}


	@Override
	public <T extends org.hipparchus.RealFieldElement<T>> FieldTransform<T> getTransform(
			final FieldAbsoluteDate<T> date) throws OrekitException {
		// method not implemented
		return null;
	}
}

}