TDBScale.java

  1. /* Copyright 2002-2022 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.time;

  18. import org.hipparchus.CalculusFieldElement;
  19. import org.hipparchus.util.FastMath;
  20. import org.orekit.utils.Constants;

  21. /** Barycentric Dynamic Time.
  22.  * <p>Time used to take account of time dilation when calculating orbits of planets,
  23.  * asteroids, comets and interplanetary spacecraft in the Solar system. It was based
  24.  * on a Dynamical time scale but was not well defined and not rigorously correct as
  25.  * a relativistic time scale. It was subsequently deprecated in favour of
  26.  * Barycentric Coordinate Time (TCB), but at the 2006 General Assembly of the
  27.  * International Astronomical Union TDB was rehabilitated by making it a specific
  28.  * fixed linear transformation of TCB.</p>
  29.  * <p>By convention, TDB = TT + 0.001658 sin(g) + 0.000014 sin(2g)seconds
  30.  * where g = 357.53 + 0.9856003 (JD - 2451545) degrees.</p>
  31.  * @author Aude Privat
  32.  */
  33. public class TDBScale implements TimeScale {

  34.     /** Serializable UID. */
  35.     private static final long serialVersionUID = 20131209L;

  36.     /** Constant term for g angle. */
  37.     private static final double G0 = 357.53;

  38.     /** Slope term for g angle. */
  39.     private static final double G1 = 0.9856003;

  40.     /** Factor for sin(g). */
  41.     private static final double SIN_G_FACTOR = 0.001658;

  42.     /** Factor for sin(2g). */
  43.     private static final double SIN_2G_FACTOR = 0.000014;

  44.     /** TT time scale. */
  45.     private final TimeScale tt;

  46.     /** Reference Epoch. */
  47.     private final AbsoluteDate j2000Epoch;

  48.     /**
  49.      * Package private constructor for the factory.
  50.      *
  51.      * @param tt         TT time scale.
  52.      * @param j2000Epoch reference date for this time scale.
  53.      */
  54.     TDBScale(final TimeScale tt, final AbsoluteDate j2000Epoch) {
  55.         this.tt = tt;
  56.         this.j2000Epoch = j2000Epoch;
  57.     }

  58.     /** {@inheritDoc} */
  59.     @Override
  60.     public double offsetFromTAI(final AbsoluteDate date) {
  61.         final double dtDays = date.durationFrom(j2000Epoch) / Constants.JULIAN_DAY;
  62.         final double g = FastMath.toRadians(G0 + G1 * dtDays);
  63.         return tt.offsetFromTAI(date) + (SIN_G_FACTOR * FastMath.sin(g) + SIN_2G_FACTOR * FastMath.sin(2 * g));
  64.     }

  65.     /** {@inheritDoc} */
  66.     @Override
  67.     public <T extends CalculusFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
  68.         final T dtDays = date.durationFrom(j2000Epoch).divide(Constants.JULIAN_DAY);
  69.         final T g = dtDays.multiply(G1).add(G0).multiply(dtDays.getPi().divide(180));
  70.         return tt.offsetFromTAI(date).
  71.                         add(g.sin().multiply(SIN_G_FACTOR).add(g.multiply(2).sin().multiply(SIN_2G_FACTOR)));
  72.     }

  73.     /** {@inheritDoc} */
  74.     public String getName() {
  75.         return "TDB";
  76.     }

  77.     /** {@inheritDoc} */
  78.     public String toString() {
  79.         return getName();
  80.     }

  81. }