Added orekit propagator and example.

examples/orekit_propagator.py

@@ -0,0 +1,76 @@
+"""Example for the orekit propagator with multiple drag coefficients."""
+
+from time import perf_counter as timer
+
+import orbitpy.orekitpropagator  # triggers decorator registration
+from orbitpy.propagator import PropagatorFactory
+from orbitpy.orbits import TwoLineElementSet
+
+from eosimutils.time import AbsoluteDate
+from eosimutils.base import WGS84_EARTH_EQUATORIAL_RADIUS
+
+import numpy as np
+import matplotlib.pyplot as plt
+
+specs = {
+    "propagator_type": "OREKIT_PROPAGATOR",
+    "stepSize": 10,
+}
+
+start_time = AbsoluteDate.from_dict(
+    {
+        "time_format": "Gregorian_Date",
+        "calendar_date": "2025-04-17T12:00:00",
+        "time_scale": "utc",
+    }
+)
+
+tle = TwoLineElementSet(
+    line0="0 LANDSAT 9",
+    line1="1 49260U 21088A   25106.07240456  .00000957  00000-0  22241-3 0  9997",
+    line2="2 49260  98.1921 177.4890 0001161  87.5064 272.6267 14.57121096188801",
+)
+
+duration_days = 0.25  # Propagate for 0.25 days
+
+# Drag coefficients to run
+drag_coeffs = [10000.0, 20000.0, 40000.0]
+colors = ["blue", "red", "green"]
+
+results = []
+
+print("Starting propagations...")
+for cd in drag_coeffs:
+    prop = PropagatorFactory.from_dict(specs)
+    prop.set_drag_coeff(cd)
+
+    sat_state_series = prop.execute(
+        t0=start_time, duration_days=duration_days, initial_state=tle
+    )
+
+    results.append((cd, sat_state_series))
+
+print("Finished propagation...")
+
+# Plot altitude over time
+fig, ax = plt.subplots(figsize=(10, 6))
+
+for (cd, series), color in zip(results, colors):
+    altitude = (
+        np.linalg.norm(series.data[0], axis=1) - WGS84_EARTH_EQUATORIAL_RADIUS
+    )
+
+    ax.plot(
+        series.time.ephemeris_time,
+        altitude,
+        color=color,
+        label=f"Cd = {cd}",
+    )
+
+plt.xlabel("Ephemeris Time (s)")
+plt.ylabel("Altitude (km)")
+plt.title("Orbit Altitude vs Time for Different Drag Coefficients")
+plt.legend()
+plt.grid(True)
+
+plt.show()