/**
* Compute line of sight intersection with body.
*
* @param scToBody transform from spacecraft frame to body frame
* @return intersection point in body frame (only the position is set!)
* @exception OrekitException if line of sight does not intersect body
*/
private TimeStampedPVCoordinates losIntersectionWithBody(final Transform scToBody)
throws OrekitException {
// compute satellite pointing axis and position/velocity in body frame
final Vector3D pointingBodyFrame = scToBody.transformVector(satPointingVector);
final Vector3D pBodyFrame = scToBody.transformPosition(Vector3D.ZERO);
// Line from satellite following pointing direction
// we use arbitrarily the Earth radius as a scaling factor, it could be anything else
final Line pointingLine =
new Line(
pBodyFrame,
pBodyFrame.add(Constants.WGS84_EARTH_EQUATORIAL_RADIUS, pointingBodyFrame),
1.0e-10);
// Intersection with body shape
final GeodeticPoint gpIntersection =
shape.getIntersectionPoint(
pointingLine, pBodyFrame, shape.getBodyFrame(), scToBody.getDate());
final Vector3D pIntersection =
(gpIntersection == null) ? null : shape.transform(gpIntersection);
// Check there is an intersection and it is not in the reverse pointing direction
if ((pIntersection == null)
|| (Vector3D.dotProduct(pIntersection.subtract(pBodyFrame), pointingBodyFrame) < 0)) {
throw new OrekitException(OrekitMessages.ATTITUDE_POINTING_LAW_DOES_NOT_POINT_TO_GROUND);
}
return new TimeStampedPVCoordinates(
scToBody.getDate(), pIntersection, Vector3D.ZERO, Vector3D.ZERO);
}
/**
* Get the {@link TimeStampedPVCoordinates} in a specified frame.
*
* @param outputFrame frame in which the position/velocity coordinates shall be computed
* @return pvCoordinates in the specified output frame
* @exception OrekitException if transformation between frames cannot be computed
* @see #getPVCoordinates()
*/
public TimeStampedPVCoordinates getPVCoordinates(final Frame outputFrame) throws OrekitException {
if (pvCoordinates == null) {
pvCoordinates = initPVCoordinates();
}
// If output frame requested is the same as definition frame,
// PV coordinates are returned directly
if (outputFrame == frame) {
return pvCoordinates;
}
// Else, PV coordinates are transformed to output frame
final Transform t = frame.getTransformTo(outputFrame, date);
return t.transformPVCoordinates(pvCoordinates);
}
/** {@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);
}
/** {@inheritDoc} */
@Override
public double[] getShortPeriodicVariations(final AbsoluteDate date, final double[] meanElements)
throws OrekitException {
// Initialise the short periodic variations
final double[] shortPeriodicVariation = new double[] {0., 0., 0., 0., 0., 0.};
// Compute only if there is at least one non-resonant tesseral or
// only the m-daily tesseral should be taken into account
if (!nonResOrders.isEmpty() || mDailiesOnly) {
// Build an Orbit object from the mean elements
final Orbit meanOrbit =
OrbitType.EQUINOCTIAL.mapArrayToOrbit(
meanElements, PositionAngle.MEAN, date, provider.getMu(), this.frame);
// Build an auxiliary object
final AuxiliaryElements aux = new AuxiliaryElements(meanOrbit, I);
// Central body rotation angle from equation 2.7.1-(3)(4).
final Transform t = bodyFrame.getTransformTo(aux.getFrame(), aux.getDate());
final Vector3D xB = t.transformVector(Vector3D.PLUS_I);
final Vector3D yB = t.transformVector(Vector3D.PLUS_J);
final double currentTheta =
FastMath.atan2(
-f.dotProduct(yB) + I * g.dotProduct(xB), f.dotProduct(xB) + I * g.dotProduct(yB));
// Add the m-daily contribution
for (int m = 1; m <= maxOrderMdailyTesseralSP; m++) {
// Phase angle
final double jlMmt = -m * currentTheta;
final double sinPhi = FastMath.sin(jlMmt);
final double cosPhi = FastMath.cos(jlMmt);
// compute contribution for each element
for (int i = 0; i < 6; i++) {
shortPeriodicVariation[i] +=
tesseralSPCoefs.getCijm(i, 0, m, date) * cosPhi
+ tesseralSPCoefs.getSijm(i, 0, m, date) * sinPhi;
}
}
// loop through all non-resonant (j,m) pairs
for (final Map.Entry<Integer, List<Integer>> entry : nonResOrders.entrySet()) {
final int m = entry.getKey();
final List<Integer> listJ = entry.getValue();
for (int j : listJ) {
// Phase angle
final double jlMmt = j * meanElements[5] - m * currentTheta;
final double sinPhi = FastMath.sin(jlMmt);
final double cosPhi = FastMath.cos(jlMmt);
// compute contribution for each element
for (int i = 0; i < 6; i++) {
shortPeriodicVariation[i] +=
tesseralSPCoefs.getCijm(i, j, m, date) * cosPhi
+ tesseralSPCoefs.getSijm(i, j, m, date) * sinPhi;
}
}
}
}
return shortPeriodicVariation;
}
/** {@inheritDoc} */
@Override
public void initializeStep(final AuxiliaryElements aux) throws OrekitException {
// Equinoctial elements
a = aux.getSma();
k = aux.getK();
h = aux.getH();
q = aux.getQ();
p = aux.getP();
lm = aux.getLM();
// Eccentricity
ecc = aux.getEcc();
e2 = ecc * ecc;
// Retrograde factor
I = aux.getRetrogradeFactor();
// Equinoctial frame vectors
f = aux.getVectorF();
g = aux.getVectorG();
// Central body rotation angle from equation 2.7.1-(3)(4).
final Transform t = bodyFrame.getTransformTo(aux.getFrame(), aux.getDate());
final Vector3D xB = t.transformVector(Vector3D.PLUS_I);
final Vector3D yB = t.transformVector(Vector3D.PLUS_J);
theta =
FastMath.atan2(
-f.dotProduct(yB) + I * g.dotProduct(xB), f.dotProduct(xB) + I * g.dotProduct(yB));
// Direction cosines
alpha = aux.getAlpha();
beta = aux.getBeta();
gamma = aux.getGamma();
// Equinoctial coefficients
// A = sqrt(μ * a)
final double A = aux.getA();
// B = sqrt(1 - h² - k²)
final double B = aux.getB();
// C = 1 + p² + q²
final double C = aux.getC();
// Common factors from equinoctial coefficients
// 2 * a / A
ax2oA = 2. * a / A;
// B / A
BoA = B / A;
// 1 / AB
ooAB = 1. / (A * B);
// C / 2AB
Co2AB = C * ooAB / 2.;
// B / (A * (1 + B))
BoABpo = BoA / (1. + B);
// &mu / a
moa = provider.getMu() / a;
// R / a
roa = provider.getAe() / a;
// Χ = 1 / B
chi = 1. / B;
chi2 = chi * chi;
// mean motion n
meanMotion = aux.getMeanMotion();
}
