Merge pull request #24 from Sceki/deep_propagation

Deep space module

Author: Sceki

README.md

@@ -121,7 +121,7 @@ print(states.shape)  # (2, 2, 3)
 - Time input (`tsince`) is in minutes from the TLE epoch.
 - Output units are km (position) and km/s (velocity).
 - Supported gravity constants: `wgs-72`, `wgs-84`, `wgs-72old`.
-- Deep-space propagation is currently not supported (periods above 225 minutes).
+- Deep-space propagation is supported.
 - Default torch dtype is set to `float64` when importing `dsgp4`.
 
 ## Development

doc/notebooks/deep_space_propagation.ipynb

@@ -0,0 +1,176 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "7d660414",
+   "metadata": {},
+   "source": [
+    "# Deep Space Propagation\n",
+    "\n",
+    "This notebook shows how to propagate TLEs with orbital period above 225 minutes (deep-space regime) and how to keep gradients enabled through propagation.\n",
+    "\n",
+    "In dSGP4, deep-space satellites are selected automatically when\\n\n",
+    "\\n\n",
+    "$$\\n\n",
+    "\\frac{2\\pi}{n_0} \\ge 225\\;\\text{minutes}\\n\n",
+    "$$\\n\n",
+    "\\n\n",
+    "where $n_0$ is the mean motion in rad/min."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "3e2e1e65",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import dsgp4\n",
+    "import numpy as np\n",
+    "import torch"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "5f44d3e7",
+   "metadata": {},
+   "source": [
+    "## 1. Load a deep-space TLE\n",
+    "\n",
+    "You can use any TLE with mean motion low enough to satisfy the 225-minute rule (for example geostationary satellites)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "45671b5d",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Replace these lines with your deep-space TLE lines.\n",
+    "line1 = \"1 41866U 16071A   24087.50000000 -.00000149  00000+0  00000+0 0  9990\"\n",
+    "line2 = \"2 41866   0.0171  87.5375 0001375 158.4767 157.4602  1.00270055 26844\"\n",
+    "\n",
+    "tle = dsgp4.tle.TLE([line1, line2])\n",
+    "\n",
+    "# Initialize (deep-space mode is selected automatically when applicable).\n",
+    "dsgp4.initialize_tle(tle, gravity_constant_name=\"wgs-84\")\n",
+    "\n",
+    "period_minutes = float(2.0 * np.pi / tle._no_unkozai)\n",
+    "print(\"method:\", tle._method)\n",
+    "print(\"orbital period [min]:\", period_minutes)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "d124e84d",
+   "metadata": {},
+   "source": [
+    "## 2. Propagate at one or multiple epochs"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "f2746b3d",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "tsince = torch.tensor([0.0, 360.0, 720.0, 1440.0])  # minutes since epoch\n",
+    "state = dsgp4.propagate(tle, tsince, initialized=True)\n",
+    "\n",
+    "# state shape: [N, 2, 3]\n",
+    "# row 0: position [km], row 1: velocity [km/s]\n",
+    "print(state.shape)\n",
+    "print(\"r(t0) [km]:\", state[0, 0])\n",
+    "print(\"v(t0) [km/s]:\", state[0, 1])"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "d0dd15f2",
+   "metadata": {},
+   "source": [
+    "## 3. Enable gradients through deep-space propagation\n",
+    "\n",
+    "To differentiate with respect to TLE parameters, initialize with `with_grad=True` and backpropagate from any scalar objective."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "e16a0407",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "tle = dsgp4.tle.TLE([line1, line2])\n",
+    "tle_elements = dsgp4.initialize_tle(\n",
+    "    tle,\n",
+    "    gravity_constant_name=\"wgs-84\",\n",
+    "    with_grad=True,\n",
+    ")\n",
+    "\n",
+    "tsince = torch.tensor(120.0)\n",
+    "state = dsgp4.propagate(tle, tsince, initialized=True)  # [2, 3]\n",
+    "\n",
+    "# Example objective: x-position at tsince=120 min\n",
+    "loss = state[0, 0]\n",
+    "loss.backward()\n",
+    "\n",
+    "# Gradient order in tle_elements:\n",
+    "# [bstar, ndot, nddot, ecco, argpo, inclo, mo, no_kozai, nodeo]\n",
+    "print(tle_elements.grad)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "5e026f59",
+   "metadata": {},
+   "source": [
+    "## 4. Batch propagation with mixed near-earth and deep-space objects\n",
+    "\n",
+    "If a batch contains deep-space members, dSGP4 automatically falls back to a per-satellite propagation path while preserving the same API."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "33cf0709",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "tles = [\n",
+    "    dsgp4.tle.TLE([line1, line2]),  # deep-space example\n",
+    "    dsgp4.tle.TLE([\n",
+    "        \"1 25544U 98067A   24087.49097222  .00016717  00000+0  10270-3 0  9993\",\n",
+    "        \"2 25544  51.6400  82.2420 0006290  58.9900  53.5550 15.50000000000000\",\n",
+    "    ]),\n",
+    "]\n",
+    "\n",
+    "_, initialized = dsgp4.initialize_tle(tles, gravity_constant_name=\"wgs-84\")\n",
+    "tsinces = torch.tensor([60.0, 60.0])\n",
+    "batch_state = dsgp4.propagate_batch(initialized, tsinces, initialized=True)\n",
+    "print(batch_state.shape)  # [2, 2, 3]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "7ff97818",
+   "metadata": {},
+   "source": [
+    "## Notes\n",
+    "\n",
+    "- Deep-space support is available in scalar propagation and in mixed batches.\n",
+    "- Gradients are supported through the deep-space scalar path.\n",
+    "- For reproducibility against external implementations, use the same gravity constants and operation mode."
+   ]
+  }
+ ],
+ "metadata": {
+  "language_info": {
+   "name": "python"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

doc/tutorials.rst

@@ -24,6 +24,7 @@ for more complex tasks.
 .. toctree::
   :maxdepth: 1
 
+  notebooks/deep_space_propagation.ipynb
   notebooks/covariance_transformation.ipynb
   notebooks/covariance_propagation.ipynb
   notebooks/gradient_based_optimization.ipynb