add orbit determination test case for flight path angle

tests/orbit_test.cpp

@@ -44,6 +44,36 @@ TEST_CASE("orbit determination, example 2.1", "[orbits]")
 	REQUIRE_THAT(e, WithinAbs(0.4024, 1e-4));
 }
 
+TEST_CASE("Chandra X-ray Observatory orbit, example 2.3", "[orbits]")
+{
+	double r_periapsis = 20686;
+	double r_apoapsis = 140906;
+	double mu = EARTH_GRAVITATIONAL_PARAMETER;
+	EllipseParameters ep = ellipseInitAE(
+			(r_periapsis + r_apoapsis) / 2,
+			(r_apoapsis - r_periapsis) / (r_periapsis + r_apoapsis));
+	double a = ep.a, e = ep.e, p = ep.p;
+	REQUIRE_THAT(a, WithinAbs(80796, 1));
+	REQUIRE_THAT(e, WithinAbs(0.7440, 1e-4));
+	REQUIRE_THAT(p, WithinAbs(36075.81, 1e-2));
+
+	double h = orbitGetAngularMomentum(p, mu);
+	REQUIRE_THAT(h, WithinAbs(119915.89, 0.5));
+
+	double epsilon = orbitGetSpecificEnergy(a, mu);
+	REQUIRE_THAT(epsilon, WithinAbs(-2.4667, 1e-4));
+
+	double theta = DEG2RAD(120);
+	double r_theta = orbitGetRadialDistance(e, p, theta);
+	REQUIRE_THAT(r_theta, WithinAbs(57444.31, 1e-2));
+
+	double v_theta = orbitGetVelocity(epsilon, mu, r_theta);
+	REQUIRE_THAT(v_theta, WithinAbs(2.9907, 1e-4));
+
+	double gamma = orbitGetFlightPathAngle(e, theta);
+	REQUIRE_THAT(gamma, WithinAbs(DEG2RAD(45.73), 1e-2));
+}
+
 TEST_CASE("state vectors to orbital elements, example 3.1", "[orbits]")
 {
 	double mu = EARTH_GRAVITATIONAL_PARAMETER;