星历是指在GPS测量中，天体运行随时间而变的精确位置或轨迹表，它是时间的函数。Orekit提供的教程中提供了计算星历的方法。

注意，在使用Orekit库之前，我们需要读取Orekit文件，详细的读取步骤请移步下面的文章观看：

Orekit使用心得（一）——读取orekit数据https://blog.csdn.net/whq002/article/details/135258646?spm=1001.2014.3001.5501

下面是使用Orekit进行卫星星历计算的具体步骤：

（1）定义卫星的轨道六根数

// Initial orbit parameters

final double a = 24396159; // semi major axis in meters

final double e = 0.72831215; // eccentricity

final double i = FastMath.toRadians(7); // inclination

final double omega = FastMath.toRadians(180); // perigee argument

final double raan = FastMath.toRadians(261); // right ascension of ascending node

final double lM = 0; // mean anomaly

（2）定义坐标系类型

// Inertial frame

final Frame inertialFrame = FramesFactory.getEME2000();

（3）定义初始时间

卫星星历的时间按世界标准时间（UTC）计算。

// Initial date in UTC time scale

final TimeScale utc = TimeScalesFactory.getUTC();

final AbsoluteDate initialDate = new AbsoluteDate(2004, 01, 01, 23, 30, 00.000, utc);

（4）定义地球引力系数

// gravitation coefficient

final double mu = 3.986004415e+14;

（5）定义卫星轨道类型

// Orbit construction as Keplerian

final Orbit initialOrbit = new KeplerianOrbit(a, e, i, omega, raan, lM, PositionAngle.MEAN,inertialFrame, initialDate, mu);

（6）定义卫星的初始状态

// Initialize state

final SpacecraftState initialState = new SpacecraftState(initialOrbit);

（7）定义propagator并插入到卫星上

final double stepSize = 10;

final AbstractIntegrator integrator = new ClassicalRungeKuttaIntegrator(stepSize);

final NumericalPropagator propagator = new NumericalPropagator(integrator);



// Set the propagator to ephemeris mode

final EphemerisGenerator generator = propagator.getEphemerisGenerator();



// Initialize propagation

propagator.setInitialState(initialState);

（8）计算并输出星历

// Propagation with storage of the results in an integrated ephemeris

final SpacecraftState finalState = propagator.propagate(initialDate.shiftedBy(6000));



System.out.format(Locale.US, "Numerical propagation:%n  Final date: %s%n  %s%n",finalState.getDate(), finalState.getOrbit());



// Getting the integrated ephemeris

final BoundedPropagator ephemeris = generator.getGeneratedEphemeris();



System.out.format(Locale.US, "%nEphemeris defined from %s to %s%n",ephemeris.getMinDate(),ephemeris.getMaxDate());



System.out.format(Locale.US, "%nEphemeris propagation:%n");

final String format = "  %s  %s%n";

AbsoluteDate intermediateDate = initialDate.shiftedBy(3000);

SpacecraftState intermediateState = ephemeris.propagate(intermediateDate);

System.out.format(Locale.US, format, intermediateState.getDate(), intermediateState.getOrbit());



intermediateDate = finalState.getDate();

intermediateState = ephemeris.propagate(intermediateDate);

System.out.format(Locale.US, format, intermediateState.getDate(), intermediateState.getOrbit());



intermediateDate = initialDate.shiftedBy(-1000);

System.out.format(Locale.US, "%nAttempting to propagate to date %s which is OUT OF RANGE%n",intermediateDate);

System.out.println("This propagation attempt should fail, " +"so an error message shoud appear below, " +"this is expected and shows that errors are handled correctly");

intermediateState = ephemeris.propagate(intermediateDate);



// these two print should never happen as an exception should have been triggered

System.out.println("  date :  " + intermediateState.getDate());

System.out.println("  " + intermediateState.getOrbit());

输出结果：