private double[] derivativesErrors(
PVCoordinatesProvider provider, AbsoluteDate date, Frame frame, OneAxisEllipsoid model)
throws OrekitException {
List<TimeStampedPVCoordinates> pvList = new ArrayList<TimeStampedPVCoordinates>();
List<TimeStampedPVCoordinates> groundPVList = new ArrayList<TimeStampedPVCoordinates>();
for (double dt = -0.25; dt <= 0.25; dt += 0.125) {
TimeStampedPVCoordinates shiftedPV = provider.getPVCoordinates(date.shiftedBy(dt), frame);
Vector3D p = model.projectToGround(shiftedPV.getPosition(), shiftedPV.getDate(), frame);
pvList.add(shiftedPV);
groundPVList.add(
new TimeStampedPVCoordinates(shiftedPV.getDate(), p, Vector3D.ZERO, Vector3D.ZERO));
}
TimeStampedPVCoordinates computed =
model.projectToGround(
TimeStampedPVCoordinates.interpolate(date, CartesianDerivativesFilter.USE_P, pvList),
frame);
TimeStampedPVCoordinates reference =
TimeStampedPVCoordinates.interpolate(date, CartesianDerivativesFilter.USE_P, groundPVList);
TimeStampedPVCoordinates pv0 = provider.getPVCoordinates(date, frame);
Vector3D p0 = pv0.getPosition();
Vector3D v0 = pv0.getVelocity();
Vector3D a0 = pv0.getAcceleration();
return new double[] {
Vector3D.distance(computed.getPosition(), reference.getPosition()) / p0.getNorm(),
Vector3D.distance(computed.getVelocity(), reference.getVelocity()) / v0.getNorm(),
Vector3D.distance(computed.getAcceleration(), reference.getAcceleration()) / a0.getNorm(),
};
}
/** {@inheritDoc} */
protected TimeStampedPVCoordinates getTargetPV(
final PVCoordinatesProvider pvProv, final AbsoluteDate date, final Frame frame)
throws OrekitException {
// transform from specified reference frame to spacecraft frame
final Transform refToSc =
new Transform(
date,
new Transform(date, pvProv.getPVCoordinates(date, frame).negate()),
new Transform(date, attitudeLaw.getAttitude(pvProv, date, frame).getOrientation()));
// transform from specified reference frame to body frame
final Transform refToBody = frame.getTransformTo(shape.getBodyFrame(), date);
// sample intersection points in current date neighborhood
final Transform scToBody = new Transform(date, refToSc.getInverse(), refToBody);
final double h = 0.1;
final List<TimeStampedPVCoordinates> sample = new ArrayList<TimeStampedPVCoordinates>();
sample.add(losIntersectionWithBody(scToBody.shiftedBy(-h)));
sample.add(losIntersectionWithBody(scToBody));
sample.add(losIntersectionWithBody(scToBody.shiftedBy(+h)));
// use interpolation to compute properly the time-derivatives
final TimeStampedPVCoordinates targetBody =
TimeStampedPVCoordinates.interpolate(date, CartesianDerivativesFilter.USE_P, sample);
// convert back to caller specified frame
return refToBody.getInverse().transformPVCoordinates(targetBody);
}
@Test
public void testGroundProjectionTaylor() throws OrekitException {
Frame itrf = FramesFactory.getITRF(IERSConventions.IERS_2010, true);
Frame eme2000 = FramesFactory.getEME2000();
OneAxisEllipsoid model =
new OneAxisEllipsoid(
Constants.WGS84_EARTH_EQUATORIAL_RADIUS, Constants.WGS84_EARTH_FLATTENING, itrf);
TimeStampedPVCoordinates initPV =
new TimeStampedPVCoordinates(
AbsoluteDate.J2000_EPOCH.shiftedBy(584.),
new Vector3D(3220103., 69623., 6449822.),
new Vector3D(6414.7, -2006., -3180.),
Vector3D.ZERO);
Orbit orbit = new EquinoctialOrbit(initPV, eme2000, Constants.EIGEN5C_EARTH_MU);
TimeStampedPVCoordinates pv0 = orbit.getPVCoordinates(orbit.getDate(), model.getBodyFrame());
PVCoordinatesProvider groundTaylor =
model.projectToGround(pv0, model.getBodyFrame()).toTaylorProvider(model.getBodyFrame());
TimeStampedPVCoordinates g0 =
groundTaylor.getPVCoordinates(orbit.getDate(), model.getBodyFrame());
Vector3D zenith = pv0.getPosition().subtract(g0.getPosition()).normalize();
Vector3D acrossTrack = Vector3D.crossProduct(zenith, g0.getVelocity()).normalize();
Vector3D alongTrack = Vector3D.crossProduct(acrossTrack, zenith).normalize();
for (double dt = -1; dt < 1; dt += 0.01) {
AbsoluteDate date = orbit.getDate().shiftedBy(dt);
Vector3D taylorP = groundTaylor.getPVCoordinates(date, model.getBodyFrame()).getPosition();
Vector3D refP =
model.projectToGround(
orbit.getPVCoordinates(date, model.getBodyFrame()).getPosition(),
date,
model.getBodyFrame());
Vector3D delta = taylorP.subtract(refP);
Assert.assertEquals(0.0, Vector3D.dotProduct(delta, alongTrack), 0.0015);
Assert.assertEquals(0.0, Vector3D.dotProduct(delta, acrossTrack), 0.0007);
Assert.assertEquals(0.0, Vector3D.dotProduct(delta, zenith), 0.00002);
}
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> accelerationDerivatives(
final SpacecraftState s, final String paramName) throws OrekitException {
complainIfNotSupported(paramName);
final AbsoluteDate date = s.getDate();
final Frame frame = s.getFrame();
final Vector3D position = s.getPVCoordinates().getPosition();
final Vector3D sunSatVector =
position.subtract(sun.getPVCoordinates(date, frame).getPosition());
final double r2 = sunSatVector.getNormSq();
// compute flux
final double rawP = kRef * getLightningRatio(position, frame, date) / r2;
final Vector3D flux = new Vector3D(rawP / FastMath.sqrt(r2), sunSatVector);
return spacecraft.radiationPressureAcceleration(
date, frame, position, s.getAttitude().getRotation(), s.getMass(), flux, paramName);
}
/** {@inheritDoc} */
public void addContribution(final SpacecraftState s, final TimeDerivativesEquations adder)
throws OrekitException {
final AbsoluteDate date = s.getDate();
final Frame frame = s.getFrame();
final Vector3D position = s.getPVCoordinates().getPosition();
final Vector3D sunSatVector =
position.subtract(sun.getPVCoordinates(date, frame).getPosition());
final double r2 = sunSatVector.getNormSq();
// compute flux
final double rawP = kRef * getLightningRatio(position, frame, date) / r2;
final Vector3D flux = new Vector3D(rawP / FastMath.sqrt(r2), sunSatVector);
final Vector3D acceleration =
spacecraft.radiationPressureAcceleration(
date, frame, position, s.getAttitude().getRotation(), s.getMass(), flux);
// provide the perturbing acceleration to the derivatives adder
adder.addAcceleration(acceleration, s.getFrame());
}
/**
* Get the useful angles for eclipse computation.
*
* @param position the satellite's position in the selected frame.
* @param frame in which is defined the position
* @param date the date
* @return the 3 angles {(satCentral, satSun), Central body apparent radius, Sun apparent radius}
* @exception OrekitException if the trajectory is inside the Earth
*/
private double[] getEclipseAngles(
final Vector3D position, final Frame frame, final AbsoluteDate date) throws OrekitException {
final double[] angle = new double[3];
final Vector3D satSunVector =
sun.getPVCoordinates(date, frame).getPosition().subtract(position);
// Sat-Sun / Sat-CentralBody angle
angle[0] = Vector3D.angle(satSunVector, position.negate());
// Central body apparent radius
final double r = position.getNorm();
if (r <= equatorialRadius) {
throw new OrekitException(OrekitMessages.TRAJECTORY_INSIDE_BRILLOUIN_SPHERE, r);
}
angle[1] = FastMath.asin(equatorialRadius / r);
// Sun apparent radius
angle[2] = FastMath.asin(Constants.SUN_RADIUS / satSunVector.getNorm());
return angle;
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> accelerationDerivatives(
final AbsoluteDate date,
final Frame frame,
final FieldVector3D<DerivativeStructure> position,
final FieldVector3D<DerivativeStructure> velocity,
final FieldRotation<DerivativeStructure> rotation,
final DerivativeStructure mass)
throws OrekitException {
final FieldVector3D<DerivativeStructure> sunSatVector =
position.subtract(sun.getPVCoordinates(date, frame).getPosition());
final DerivativeStructure r2 = sunSatVector.getNormSq();
// compute flux
final double ratio = getLightningRatio(position.toVector3D(), frame, date);
final DerivativeStructure rawP = r2.reciprocal().multiply(kRef * ratio);
final FieldVector3D<DerivativeStructure> flux =
new FieldVector3D<DerivativeStructure>(rawP.divide(r2.sqrt()), sunSatVector);
// compute acceleration with all its partial derivatives
return spacecraft.radiationPressureAcceleration(date, frame, position, rotation, mass, flux);
}
