fix(sstv): fix inaccurate ISS orbit tracking — three root causes

1. iss_schedule() was importing TLE_SATELLITES directly from data/satellites.py
   (hardcoded, 446 days stale) instead of the live _tle_cache kept fresh by
   the 24h auto-refresh. Add get_cached_tle() to satellite.py and use it.

2. Ground track was a fake sine wave (inclination * sin(phase)) that mapped
   longitude offset directly to orbital phase, ignoring Earth's rotation under
   the satellite (~23° westward shift per orbit). Replace with a /sstv/iss-track
   endpoint that propagates the orbit via skyfield SGP4 over ±90 minutes, and
   update the frontend to call it. Past/future track rendered with separate
   polylines (dim solid vs bright dashed).

3. refresh_tle_data() updated _tle_cache in memory but never persisted back to
   data/satellites.py, so every restart reloaded the stale hardcoded TLE. Add
   _persist_tle_cache() called after each successful refresh.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

routes/sstv.py

@@ -16,6 +16,7 @@ from typing import Any
 from flask import Blueprint, Response, jsonify, request, send_file
 
 import app as app_module
+from routes.satellite import get_cached_tle
 from utils.event_pipeline import process_event
 from utils.logging import get_logger
 from utils.responses import api_error
@@ -26,13 +27,13 @@ from utils.sstv import (
     is_sstv_available,
 )
 
-logger = get_logger('intercept.sstv')
+logger = get_logger("intercept.sstv")
 
-sstv_bp = Blueprint('sstv', __name__, url_prefix='/sstv')
+sstv_bp = Blueprint("sstv", __name__, url_prefix="/sstv")
 
 # ISS SSTV runs on a fixed downlink; allow a small entry tolerance so users
 # can type nearby values and still land on the canonical center frequency.
-ISS_SSTV_MODULATION = 'fm'
+ISS_SSTV_MODULATION = "fm"
 ISS_SSTV_FREQUENCIES = (ISS_SSTV_FREQ,)
 ISS_SSTV_FREQ_TOLERANCE_MHZ = 0.05
 
@@ -59,7 +60,7 @@ _timescale_lock = threading.Lock()
 
 # Track which device is being used
 sstv_active_device: int | None = None
-sstv_active_sdr_type: str = 'rtlsdr'
+sstv_active_sdr_type: str = "rtlsdr"
 
 
 def _progress_callback(data: dict) -> None:
@@ -82,7 +83,7 @@ def _normalize_iss_frequency(frequency_mhz: float) -> float | None:
     return None
 
 
-@sstv_bp.route('/status')
+@sstv_bp.route("/status")
 def get_status():
     """
     Get SSTV decoder status.
@@ -94,24 +95,24 @@ def get_status():
     decoder = get_sstv_decoder()
 
     result = {
-        'available': available,
-        'decoder': decoder.decoder_available,
-        'running': decoder.is_running,
-        'iss_frequency': ISS_SSTV_FREQ,
-        'modulation': ISS_SSTV_MODULATION,
-        'image_count': len(decoder.get_images()),
-        'doppler_enabled': decoder.doppler_enabled,
+        "available": available,
+        "decoder": decoder.decoder_available,
+        "running": decoder.is_running,
+        "iss_frequency": ISS_SSTV_FREQ,
+        "modulation": ISS_SSTV_MODULATION,
+        "image_count": len(decoder.get_images()),
+        "doppler_enabled": decoder.doppler_enabled,
     }
 
     # Include Doppler info if available
     doppler_info = decoder.last_doppler_info
     if doppler_info:
-        result['doppler'] = doppler_info.to_dict()
+        result["doppler"] = doppler_info.to_dict()
 
     return jsonify(result)
 
 
-@sstv_bp.route('/start', methods=['POST'])
+@sstv_bp.route("/start", methods=["POST"])
 def start_decoder():
     """
     Start SSTV decoder.
@@ -133,20 +134,24 @@ def start_decoder():
         JSON with start status.
     """
     if not is_sstv_available():
-        return jsonify({
-            'status': 'error',
-            'message': 'SSTV decoder not available. Install numpy and Pillow: pip install numpy Pillow'
-        }), 400
+        return jsonify(
+            {
+                "status": "error",
+                "message": "SSTV decoder not available. Install numpy and Pillow: pip install numpy Pillow",
+            }
+        ), 400
 
     decoder = get_sstv_decoder()
 
     if decoder.is_running:
-        return jsonify({
-            'status': 'already_running',
-            'frequency': ISS_SSTV_FREQ,
-            'modulation': ISS_SSTV_MODULATION,
-            'doppler_enabled': decoder.doppler_enabled
-        })
+        return jsonify(
+            {
+                "status": "already_running",
+                "frequency": ISS_SSTV_FREQ,
+                "modulation": ISS_SSTV_MODULATION,
+                "doppler_enabled": decoder.doppler_enabled,
+            }
+        )
 
     # Clear queue
     while not _sstv_queue.empty():
@@ -157,43 +162,38 @@ def start_decoder():
 
     # Get parameters
     data = request.get_json(silent=True) or {}
-    sdr_type_str = data.get('sdr_type', 'rtlsdr')
+    sdr_type_str = data.get("sdr_type", "rtlsdr")
 
-    if sdr_type_str != 'rtlsdr':
-        return jsonify({
-            'status': 'error',
-            'message': f'{sdr_type_str.replace("_", " ").title()} is not yet supported for this mode. Please use an RTL-SDR device.'
-        }), 400
+    if sdr_type_str != "rtlsdr":
+        return jsonify(
+            {
+                "status": "error",
+                "message": f"{sdr_type_str.replace('_', ' ').title()} is not yet supported for this mode. Please use an RTL-SDR device.",
+            }
+        ), 400
 
-    frequency = data.get('frequency', ISS_SSTV_FREQ)
-    modulation = str(data.get('modulation', ISS_SSTV_MODULATION)).strip().lower()
-    device_index = data.get('device', 0)
-    latitude = data.get('latitude')
-    longitude = data.get('longitude')
+    frequency = data.get("frequency", ISS_SSTV_FREQ)
+    modulation = str(data.get("modulation", ISS_SSTV_MODULATION)).strip().lower()
+    device_index = data.get("device", 0)
+    latitude = data.get("latitude")
+    longitude = data.get("longitude")
 
     # Validate modulation (ISS mode is FM-only)
     if modulation != ISS_SSTV_MODULATION:
-        return jsonify({
-            'status': 'error',
-            'message': f'Modulation must be {ISS_SSTV_MODULATION} for ISS SSTV mode'
-        }), 400
+        return jsonify(
+            {"status": "error", "message": f"Modulation must be {ISS_SSTV_MODULATION} for ISS SSTV mode"}
+        ), 400
 
     # Validate frequency
     try:
         frequency = float(frequency)
         normalized_frequency = _normalize_iss_frequency(frequency)
         if normalized_frequency is None:
-            supported = ', '.join(f'{freq:.3f}' for freq in ISS_SSTV_FREQUENCIES)
-            return jsonify({
-                'status': 'error',
-                'message': f'Supported ISS SSTV frequency: {supported} MHz FM'
-            }), 400
+            supported = ", ".join(f"{freq:.3f}" for freq in ISS_SSTV_FREQUENCIES)
+            return jsonify({"status": "error", "message": f"Supported ISS SSTV frequency: {supported} MHz FM"}), 400
         frequency = normalized_frequency
     except (TypeError, ValueError):
-        return jsonify({
-            'status': 'error',
-            'message': 'Invalid frequency'
-        }), 400
+        return jsonify({"status": "error", "message": "Invalid frequency"}), 400
 
     # Validate location if provided
     if latitude is not None and longitude is not None:
@@ -201,20 +201,11 @@ def start_decoder():
             latitude = float(latitude)
             longitude = float(longitude)
             if not (-90 <= latitude <= 90):
-                return jsonify({
-                    'status': 'error',
-                    'message': 'Latitude must be between -90 and 90'
-                }), 400
+                return jsonify({"status": "error", "message": "Latitude must be between -90 and 90"}), 400
             if not (-180 <= longitude <= 180):
-                return jsonify({
-                    'status': 'error',
-                    'message': 'Longitude must be between -180 and 180'
-                }), 400
+                return jsonify({"status": "error", "message": "Longitude must be between -180 and 180"}), 400
         except (TypeError, ValueError):
-            return jsonify({
-                'status': 'error',
-                'message': 'Invalid latitude or longitude'
-            }), 400
+            return jsonify({"status": "error", "message": "Invalid latitude or longitude"}), 400
     else:
         latitude = None
         longitude = None
@@ -222,13 +213,9 @@ def start_decoder():
     # Claim SDR device
     global sstv_active_device, sstv_active_sdr_type
     device_int = int(device_index)
-    error = app_module.claim_sdr_device(device_int, 'sstv', sdr_type_str)
+    error = app_module.claim_sdr_device(device_int, "sstv", sdr_type_str)
     if error:
-        return jsonify({
-            'status': 'error',
-            'error_type': 'DEVICE_BUSY',
-            'message': error
-        }), 409
+        return jsonify({"status": "error", "error_type": "DEVICE_BUSY", "message": error}), 409
 
     # Set callback and start
     decoder.set_callback(_progress_callback)
@@ -245,28 +232,25 @@ def start_decoder():
         sstv_active_sdr_type = sdr_type_str
 
         result = {
-            'status': 'started',
-            'frequency': frequency,
-            'modulation': ISS_SSTV_MODULATION,
-            'device': device_index,
-            'doppler_enabled': decoder.doppler_enabled
+            "status": "started",
+            "frequency": frequency,
+            "modulation": ISS_SSTV_MODULATION,
+            "device": device_index,
+            "doppler_enabled": decoder.doppler_enabled,
         }
 
         # Include initial Doppler info if available
         if decoder.doppler_enabled and decoder.last_doppler_info:
-            result['doppler'] = decoder.last_doppler_info.to_dict()
+            result["doppler"] = decoder.last_doppler_info.to_dict()
 
         return jsonify(result)
     else:
         # Release device on failure
         app_module.release_sdr_device(device_int, sdr_type_str)
-        return jsonify({
-            'status': 'error',
-            'message': 'Failed to start decoder'
-        }), 500
+        return jsonify({"status": "error", "message": "Failed to start decoder"}), 500
 
 
-@sstv_bp.route('/stop', methods=['POST'])
+@sstv_bp.route("/stop", methods=["POST"])
 def stop_decoder():
     """
     Stop SSTV decoder.
@@ -283,10 +267,10 @@ def stop_decoder():
         app_module.release_sdr_device(sstv_active_device, sstv_active_sdr_type)
         sstv_active_device = None
 
-    return jsonify({'status': 'stopped'})
+    return jsonify({"status": "stopped"})
 
 
-@sstv_bp.route('/doppler')
+@sstv_bp.route("/doppler")
 def get_doppler():
     """
     Get current Doppler shift information.
@@ -299,27 +283,28 @@ def get_doppler():
     decoder = get_sstv_decoder()
 
     if not decoder.doppler_enabled:
-        return jsonify({
-            'status': 'disabled',
-            'message': 'Doppler tracking not enabled. Provide latitude/longitude when starting decoder.'
-        })
+        return jsonify(
+            {
+                "status": "disabled",
+                "message": "Doppler tracking not enabled. Provide latitude/longitude when starting decoder.",
+            }
+        )
 
     doppler_info = decoder.last_doppler_info
     if not doppler_info:
-        return jsonify({
-            'status': 'unavailable',
-            'message': 'Doppler data not yet available'
-        })
+        return jsonify({"status": "unavailable", "message": "Doppler data not yet available"})
 
-    return jsonify({
-        'status': 'ok',
-        'doppler': doppler_info.to_dict(),
-        'nominal_frequency_mhz': ISS_SSTV_FREQ,
-        'corrected_frequency_mhz': doppler_info.frequency_hz / 1_000_000
-    })
+    return jsonify(
+        {
+            "status": "ok",
+            "doppler": doppler_info.to_dict(),
+            "nominal_frequency_mhz": ISS_SSTV_FREQ,
+            "corrected_frequency_mhz": doppler_info.frequency_hz / 1_000_000,
+        }
+    )
 
 
-@sstv_bp.route('/images')
+@sstv_bp.route("/images")
 def list_images():
     """
     Get list of decoded SSTV images.
@@ -333,18 +318,14 @@ def list_images():
     decoder = get_sstv_decoder()
     images = decoder.get_images()
 
-    limit = request.args.get('limit', type=int)
+    limit = request.args.get("limit", type=int)
     if limit and limit > 0:
         images = images[-limit:]
 
-    return jsonify({
-        'status': 'ok',
-        'images': [img.to_dict() for img in images],
-        'count': len(images)
-    })
+    return jsonify({"status": "ok", "images": [img.to_dict() for img in images], "count": len(images)})
 
 
-@sstv_bp.route('/images/<filename>')
+@sstv_bp.route("/images/<filename>")
 def get_image(filename: str):
     """
     Get a decoded SSTV image file.
@@ -358,22 +339,22 @@ def get_image(filename: str):
     decoder = get_sstv_decoder()
 
     # Security: only allow alphanumeric filenames with .png extension
-    if not filename.replace('_', '').replace('-', '').replace('.', '').isalnum():
-        return api_error('Invalid filename', 400)
+    if not filename.replace("_", "").replace("-", "").replace(".", "").isalnum():
+        return api_error("Invalid filename", 400)
 
-    if not filename.endswith('.png'):
-        return api_error('Only PNG files supported', 400)
+    if not filename.endswith(".png"):
+        return api_error("Only PNG files supported", 400)
 
     # Find image in decoder's output directory
     image_path = decoder._output_dir / filename
 
     if not image_path.exists():
-        return api_error('Image not found', 404)
+        return api_error("Image not found", 404)
 
-    return send_file(image_path, mimetype='image/png')
+    return send_file(image_path, mimetype="image/png")
 
 
-@sstv_bp.route('/images/<filename>/download')
+@sstv_bp.route("/images/<filename>/download")
 def download_image(filename: str):
     """
     Download a decoded SSTV image file.
@@ -387,21 +368,21 @@ def download_image(filename: str):
     decoder = get_sstv_decoder()
 
     # Security: only allow alphanumeric filenames with .png extension
-    if not filename.replace('_', '').replace('-', '').replace('.', '').isalnum():
-        return api_error('Invalid filename', 400)
+    if not filename.replace("_", "").replace("-", "").replace(".", "").isalnum():
+        return api_error("Invalid filename", 400)
 
-    if not filename.endswith('.png'):
-        return api_error('Only PNG files supported', 400)
+    if not filename.endswith(".png"):
+        return api_error("Only PNG files supported", 400)
 
     image_path = decoder._output_dir / filename
 
     if not image_path.exists():
-        return api_error('Image not found', 404)
+        return api_error("Image not found", 404)
 
-    return send_file(image_path, mimetype='image/png', as_attachment=True, download_name=filename)
+    return send_file(image_path, mimetype="image/png", as_attachment=True, download_name=filename)
 
 
-@sstv_bp.route('/images/<filename>', methods=['DELETE'])
+@sstv_bp.route("/images/<filename>", methods=["DELETE"])
 def delete_image(filename: str):
     """
     Delete a decoded SSTV image.
@@ -415,19 +396,19 @@ def delete_image(filename: str):
     decoder = get_sstv_decoder()
 
     # Security: only allow alphanumeric filenames with .png extension
-    if not filename.replace('_', '').replace('-', '').replace('.', '').isalnum():
-        return api_error('Invalid filename', 400)
+    if not filename.replace("_", "").replace("-", "").replace(".", "").isalnum():
+        return api_error("Invalid filename", 400)
 
-    if not filename.endswith('.png'):
-        return api_error('Only PNG files supported', 400)
+    if not filename.endswith(".png"):
+        return api_error("Only PNG files supported", 400)
 
     if decoder.delete_image(filename):
-        return jsonify({'status': 'ok'})
+        return jsonify({"status": "ok"})
     else:
-        return api_error('Image not found', 404)
+        return api_error("Image not found", 404)
 
 
-@sstv_bp.route('/images', methods=['DELETE'])
+@sstv_bp.route("/images", methods=["DELETE"])
 def delete_all_images():
     """
     Delete all decoded SSTV images.
@@ -437,10 +418,10 @@ def delete_all_images():
     """
     decoder = get_sstv_decoder()
     count = decoder.delete_all_images()
-    return jsonify({'status': 'ok', 'deleted': count})
+    return jsonify({"status": "ok", "deleted": count})
 
 
-@sstv_bp.route('/stream')
+@sstv_bp.route("/stream")
 def stream_progress():
     """
     SSE stream of SSTV decode progress.
@@ -453,36 +434,38 @@ def stream_progress():
     Returns:
         SSE stream (text/event-stream)
     """
+
     def _on_msg(msg: dict[str, Any]) -> None:
-        process_event('sstv', msg, msg.get('type'))
+        process_event("sstv", msg, msg.get("type"))
 
     response = Response(
         sse_stream_fanout(
             source_queue=_sstv_queue,
-            channel_key='sstv',
+            channel_key="sstv",
             timeout=1.0,
             keepalive_interval=30.0,
             on_message=_on_msg,
         ),
-        mimetype='text/event-stream',
+        mimetype="text/event-stream",
     )
-    response.headers['Cache-Control'] = 'no-cache'
-    response.headers['X-Accel-Buffering'] = 'no'
-    response.headers['Connection'] = 'keep-alive'
+    response.headers["Cache-Control"] = "no-cache"
+    response.headers["X-Accel-Buffering"] = "no"
+    response.headers["Connection"] = "keep-alive"
     return response
 
 
-def _get_timescale():
-    """Return a cached skyfield timescale (expensive to create)."""
-    global _timescale
-    with _timescale_lock:
-        if _timescale is None:
-            from skyfield.api import load
-            _timescale = load.timescale(builtin=True)
-        return _timescale
+def _get_timescale():
+    """Return a cached skyfield timescale (expensive to create)."""
+    global _timescale
+    with _timescale_lock:
+        if _timescale is None:
+            from skyfield.api import load
+
+            _timescale = load.timescale(builtin=True)
+        return _timescale
 
 
-@sstv_bp.route('/iss-schedule')
+@sstv_bp.route("/iss-schedule")
 def iss_schedule():
     """
     Get ISS pass schedule for SSTV reception.
@@ -500,24 +483,23 @@ def iss_schedule():
     """
     global _iss_schedule_cache, _iss_schedule_cache_time, _iss_schedule_cache_key
 
-    lat = request.args.get('latitude', type=float)
-    lon = request.args.get('longitude', type=float)
-    hours = request.args.get('hours', 48, type=int)
+    lat = request.args.get("latitude", type=float)
+    lon = request.args.get("longitude", type=float)
+    hours = request.args.get("hours", 48, type=int)
 
     if lat is None or lon is None:
-        return jsonify({
-            'status': 'error',
-            'message': 'latitude and longitude parameters required'
-        }), 400
+        return jsonify({"status": "error", "message": "latitude and longitude parameters required"}), 400
 
     # Cache key: rounded lat/lon (1 decimal place) so nearby locations share cache
     cache_key = f"{round(lat, 1)}:{round(lon, 1)}:{hours}"
 
     with _iss_schedule_lock:
         now = time.time()
-        if (_iss_schedule_cache is not None
-                and cache_key == _iss_schedule_cache_key
-                and (now - _iss_schedule_cache_time) < ISS_SCHEDULE_CACHE_TTL):
+        if (
+            _iss_schedule_cache is not None
+            and cache_key == _iss_schedule_cache_key
+            and (now - _iss_schedule_cache_time) < ISS_SCHEDULE_CACHE_TTL
+        ):
             return jsonify(_iss_schedule_cache)
 
     try:
@@ -526,15 +508,10 @@ def iss_schedule():
         from skyfield.almanac import find_discrete
         from skyfield.api import EarthSatellite, wgs84
 
-        from data.satellites import TLE_SATELLITES
-
-        # Get ISS TLE
-        iss_tle = TLE_SATELLITES.get('ISS')
+        # Get ISS TLE from live cache (kept fresh by auto-refresh)
+        iss_tle = get_cached_tle("ISS")
         if not iss_tle:
-            return jsonify({
-                'status': 'error',
-                'message': 'ISS TLE data not available'
-            }), 500
+            return jsonify({"status": "error", "message": "ISS TLE data not available"}), 500
 
         ts = _get_timescale()
         satellite = EarthSatellite(iss_tle[1], iss_tle[2], iss_tle[0], ts)
@@ -549,7 +526,7 @@ def iss_schedule():
             alt, _, _ = topocentric.altaz()
             return alt.degrees > 0
 
-        above_horizon.step_days = 1/720
+        above_horizon.step_days = 1 / 720
 
         times, events = find_discrete(t0, t1, above_horizon)
 
@@ -588,23 +565,25 @@ def iss_schedule():
                         max_el = alt.degrees
 
                 if max_el >= 10:  # Min elevation filter
-                    passes.append({
-                        'satellite': 'ISS',
-                        'startTime': rise_time.utc_datetime().strftime('%Y-%m-%d %H:%M UTC'),
-                        'startTimeISO': rise_time.utc_datetime().isoformat(),
-                        'maxEl': round(max_el, 1),
-                        'duration': duration_minutes,
-                        'color': '#00ffff'
-                    })
+                    passes.append(
+                        {
+                            "satellite": "ISS",
+                            "startTime": rise_time.utc_datetime().strftime("%Y-%m-%d %H:%M UTC"),
+                            "startTimeISO": rise_time.utc_datetime().isoformat(),
+                            "maxEl": round(max_el, 1),
+                            "duration": duration_minutes,
+                            "color": "#00ffff",
+                        }
+                    )
 
             i += 1
 
         result = {
-            'status': 'ok',
-            'passes': passes,
-            'count': len(passes),
-            'sstv_frequency': ISS_SSTV_FREQ,
-            'note': 'ISS SSTV events are not continuous. Check ARISS.org for scheduled events.'
+            "status": "ok",
+            "passes": passes,
+            "count": len(passes),
+            "sstv_frequency": ISS_SSTV_FREQ,
+            "note": "ISS SSTV events are not continuous. Check ARISS.org for scheduled events.",
         }
 
         # Update cache
@@ -616,17 +595,11 @@ def iss_schedule():
         return jsonify(result)
 
     except ImportError:
-        return jsonify({
-            'status': 'error',
-            'message': 'skyfield library not installed'
-        }), 503
+        return jsonify({"status": "error", "message": "skyfield library not installed"}), 503
 
     except Exception as e:
         logger.error(f"Error getting ISS schedule: {e}")
-        return jsonify({
-            'status': 'error',
-            'message': str(e)
-        }), 500
+        return jsonify({"status": "error", "message": str(e)}), 500
 
 
 def _fetch_iss_position() -> dict | None:
@@ -644,14 +617,14 @@ def _fetch_iss_position() -> dict | None:
 
     # Try primary API: Where The ISS At
     try:
-        response = requests.get('https://api.wheretheiss.at/v1/satellites/25544', timeout=3)
+        response = requests.get("https://api.wheretheiss.at/v1/satellites/25544", timeout=3)
         if response.status_code == 200:
             data = response.json()
             cached = {
-                'lat': float(data['latitude']),
-                'lon': float(data['longitude']),
-                'altitude': float(data.get('altitude', 420)),
-                'source': 'wheretheiss',
+                "lat": float(data["latitude"]),
+                "lon": float(data["longitude"]),
+                "altitude": float(data.get("altitude", 420)),
+                "source": "wheretheiss",
             }
     except Exception as e:
         logger.warning(f"Where The ISS At API failed: {e}")
@@ -659,15 +632,15 @@ def _fetch_iss_position() -> dict | None:
     # Try fallback API: Open Notify
     if cached is None:
         try:
-            response = requests.get('http://api.open-notify.org/iss-now.json', timeout=3)
+            response = requests.get("http://api.open-notify.org/iss-now.json", timeout=3)
             if response.status_code == 200:
                 data = response.json()
-                if data.get('message') == 'success':
+                if data.get("message") == "success":
                     cached = {
-                        'lat': float(data['iss_position']['latitude']),
-                        'lon': float(data['iss_position']['longitude']),
-                        'altitude': 420,
-                        'source': 'open-notify',
+                        "lat": float(data["iss_position"]["latitude"]),
+                        "lon": float(data["iss_position"]["longitude"]),
+                        "altitude": 420,
+                        "source": "open-notify",
                     }
         except Exception as e:
             logger.warning(f"Open Notify API failed: {e}")
@@ -680,7 +653,7 @@ def _fetch_iss_position() -> dict | None:
     return cached
 
 
-@sstv_bp.route('/iss-position')
+@sstv_bp.route("/iss-position")
 def iss_position():
     """
     Get current ISS position from real-time API.
@@ -698,28 +671,25 @@ def iss_position():
     """
     from datetime import datetime
 
-    observer_lat = request.args.get('latitude', type=float)
-    observer_lon = request.args.get('longitude', type=float)
+    observer_lat = request.args.get("latitude", type=float)
+    observer_lon = request.args.get("longitude", type=float)
 
     pos = _fetch_iss_position()
     if pos is None:
-        return jsonify({
-            'status': 'error',
-            'message': 'Unable to fetch ISS position from real-time APIs'
-        }), 503
+        return jsonify({"status": "error", "message": "Unable to fetch ISS position from real-time APIs"}), 503
 
     result = {
-        'status': 'ok',
-        'lat': pos['lat'],
-        'lon': pos['lon'],
-        'altitude': pos['altitude'],
-        'timestamp': datetime.utcnow().isoformat(),
-        'source': pos['source'],
+        "status": "ok",
+        "lat": pos["lat"],
+        "lon": pos["lon"],
+        "altitude": pos["altitude"],
+        "timestamp": datetime.utcnow().isoformat(),
+        "source": pos["source"],
     }
 
     # Calculate observer-relative data if location provided
     if observer_lat is not None and observer_lon is not None:
-        result.update(_calculate_observer_data(pos['lat'], pos['lon'], observer_lat, observer_lon))
+        result.update(_calculate_observer_data(pos["lat"], pos["lon"], observer_lat, observer_lon))
 
     return jsonify(result)
 
@@ -743,7 +713,7 @@ def _calculate_observer_data(iss_lat: float, iss_lon: float, obs_lat: float, obs
     # Haversine for ground distance
     dlat = lat2 - lat1
     dlon = lon2 - lon1
-    a = math.sin(dlat/2)**2 + math.cos(lat1) * math.cos(lat2) * math.sin(dlon/2)**2
+    a = math.sin(dlat / 2) ** 2 + math.cos(lat1) * math.cos(lat2) * math.sin(dlon / 2) ** 2
     c = 2 * math.asin(math.sqrt(a))
     ground_distance = earth_radius * c
 
@@ -763,14 +733,60 @@ def _calculate_observer_data(iss_lat: float, iss_lon: float, obs_lat: float, obs
     azimuth = math.degrees(math.atan2(y, x))
     azimuth = (azimuth + 360) % 360
 
-    return {
-        'elevation': round(elevation, 1),
-        'azimuth': round(azimuth, 1),
-        'distance': round(slant_range, 1)
-    }
+    return {"elevation": round(elevation, 1), "azimuth": round(azimuth, 1), "distance": round(slant_range, 1)}
 
 
-@sstv_bp.route('/decode-file', methods=['POST'])
+@sstv_bp.route("/iss-track")
+def iss_track():
+    """
+    Return ISS ground track points propagated from TLE data.
+
+    Uses skyfield SGP4 propagation over ±90 minutes (roughly one full orbit)
+    to produce an accurate track that accounts for Earth's rotation.
+
+    Returns:
+        JSON with list of {lat, lon, past} points.
+    """
+    try:
+        from datetime import timedelta
+
+        from skyfield.api import EarthSatellite, wgs84
+
+        iss_tle = get_cached_tle("ISS")
+        if not iss_tle:
+            return jsonify({"status": "error", "message": "ISS TLE not available"}), 500
+
+        ts = _get_timescale()
+        satellite = EarthSatellite(iss_tle[1], iss_tle[2], iss_tle[0], ts)
+        now = ts.now()
+        now_dt = now.utc_datetime()
+
+        track = []
+        for minutes_offset in range(-90, 91, 1):
+            t_point = ts.utc(now_dt + timedelta(minutes=minutes_offset))
+            try:
+                geo = satellite.at(t_point)
+                sp = wgs84.subpoint(geo)
+                track.append(
+                    {
+                        "lat": round(float(sp.latitude.degrees), 4),
+                        "lon": round(float(sp.longitude.degrees), 4),
+                        "past": minutes_offset < 0,
+                    }
+                )
+            except Exception:
+                continue
+
+        return jsonify({"status": "ok", "track": track})
+
+    except ImportError:
+        return jsonify({"status": "error", "message": "skyfield not installed"}), 503
+    except Exception as e:
+        logger.error(f"Error computing ISS track: {e}")
+        return jsonify({"status": "error", "message": str(e)}), 500
+
+
+@sstv_bp.route("/decode-file", methods=["POST"])
 def decode_file():
     """
     Decode SSTV from an uploaded audio file.
@@ -780,23 +796,18 @@ def decode_file():
     Returns:
         JSON with decoded images.
     """
-    if 'audio' not in request.files:
-        return jsonify({
-            'status': 'error',
-            'message': 'No audio file provided'
-        }), 400
+    if "audio" not in request.files:
+        return jsonify({"status": "error", "message": "No audio file provided"}), 400
 
-    audio_file = request.files['audio']
+    audio_file = request.files["audio"]
 
     if not audio_file.filename:
-        return jsonify({
-            'status': 'error',
-            'message': 'No file selected'
-        }), 400
+        return jsonify({"status": "error", "message": "No file selected"}), 400
 
     # Save to temp file
     import tempfile
-    with tempfile.NamedTemporaryFile(suffix='.wav', delete=False) as tmp:
+
+    with tempfile.NamedTemporaryFile(suffix=".wav", delete=False) as tmp:
         audio_file.save(tmp.name)
         tmp_path = tmp.name
 
@@ -804,18 +815,11 @@ def decode_file():
         decoder = get_sstv_decoder()
         images = decoder.decode_file(tmp_path)
 
-        return jsonify({
-            'status': 'ok',
-            'images': [img.to_dict() for img in images],
-            'count': len(images)
-        })
+        return jsonify({"status": "ok", "images": [img.to_dict() for img in images], "count": len(images)})
 
     except Exception as e:
         logger.error(f"Error decoding file: {e}")
-        return jsonify({
-            'status': 'error',
-            'message': str(e)
-        }), 500
+        return jsonify({"status": "error", "message": str(e)}), 500
 
     finally:
         # Clean up temp file

static/js/modes/sstv.js

@@ -13,12 +13,14 @@ const SSTV = (function() {
     let issMap = null;
     let issMarker = null;
     let issTrackLine = null;
+    let issTrackPast = null;
     let issPosition = null;
-    let issUpdateInterval = null;
-    let countdownInterval = null;
-    let nextPassData = null;
-    let pendingMapInvalidate = false;
-    let locationListenersAttached = false;
+    let issUpdateInterval = null;
+    let issTrackInterval = null;
+    let countdownInterval = null;
+    let nextPassData = null;
+    let pendingMapInvalidate = false;
+    let locationListenersAttached = false;
 
     // ISS frequency
     const ISS_FREQ = 145.800;
@@ -93,12 +95,12 @@ const SSTV = (function() {
         if (latInput && storedLat) latInput.value = storedLat;
         if (lonInput && storedLon) lonInput.value = storedLon;
 
-        if (!locationListenersAttached) {
-            if (latInput) latInput.addEventListener('change', saveLocationFromInputs);
-            if (lonInput) lonInput.addEventListener('change', saveLocationFromInputs);
-            locationListenersAttached = true;
-        }
-    }
+        if (!locationListenersAttached) {
+            if (latInput) latInput.addEventListener('change', saveLocationFromInputs);
+            if (lonInput) lonInput.addEventListener('change', saveLocationFromInputs);
+            locationListenersAttached = true;
+        }
+    }
 
     /**
      * Save location from input fields
@@ -250,12 +252,19 @@ const SSTV = (function() {
         // Create ISS marker (will be positioned when we get data)
         issMarker = L.marker([0, 0], { icon: issIcon }).addTo(issMap);
 
-        // Create ground track line
+        // Past track (dimmer, solid)
+        issTrackPast = L.polyline([], {
+            color: '#00d4ff',
+            weight: 1.5,
+            opacity: 0.3,
+        }).addTo(issMap);
+
+        // Future track (brighter, dashed)
         issTrackLine = L.polyline([], {
             color: '#00d4ff',
             weight: 2,
-            opacity: 0.6,
-            dashArray: '5, 5'
+            opacity: 0.7,
+            dashArray: '6, 4'
         }).addTo(issMap);
 
         issMap.on('resize moveend zoomend', () => {
@@ -272,9 +281,12 @@ const SSTV = (function() {
      */
     function startIssTracking() {
         updateIssPosition();
-        // Update every 5 seconds
+        updateIssTrack();
         if (issUpdateInterval) clearInterval(issUpdateInterval);
         issUpdateInterval = setInterval(updateIssPosition, 5000);
+        // Track refreshes every 5 minutes — one orbit is ~93 min so this keeps it current
+        if (issTrackInterval) clearInterval(issTrackInterval);
+        issTrackInterval = setInterval(updateIssTrack, 5 * 60 * 1000);
     }
 
     /**
@@ -285,6 +297,52 @@ const SSTV = (function() {
             clearInterval(issUpdateInterval);
             issUpdateInterval = null;
         }
+        if (issTrackInterval) {
+            clearInterval(issTrackInterval);
+            issTrackInterval = null;
+        }
+    }
+
+    /**
+     * Fetch and render the ISS ground track from the backend (TLE-propagated).
+     */
+    async function updateIssTrack() {
+        try {
+            const response = await fetch('/sstv/iss-track');
+            const data = await response.json();
+            if (data.status !== 'ok' || !issTrackLine || !issTrackPast) return;
+
+            const pastPts = [], futurePts = [];
+            for (const pt of data.track) {
+                (pt.past ? pastPts : futurePts).push([pt.lat, pt.lon]);
+            }
+
+            // Split future track at antimeridian crossings to avoid long horizontal lines
+            const futureSegments = _splitAtAntimeridian(futurePts);
+            const pastSegments = _splitAtAntimeridian(pastPts);
+
+            issTrackLine.setLatLngs(futureSegments);
+            issTrackPast.setLatLngs(pastSegments);
+        } catch (err) {
+            console.error('Failed to fetch ISS track:', err);
+        }
+    }
+
+    /**
+     * Split an array of [lat, lon] points into segments at antimeridian crossings.
+     */
+    function _splitAtAntimeridian(points) {
+        const segments = [];
+        let current = [];
+        for (let i = 0; i < points.length; i++) {
+            if (i > 0 && Math.abs(points[i][1] - points[i - 1][1]) > 180) {
+                if (current.length > 1) segments.push(current);
+                current = [];
+            }
+            current.push(points[i]);
+        }
+        if (current.length > 1) segments.push(current);
+        return segments;
     }
 
     /**
@@ -486,55 +544,7 @@ const SSTV = (function() {
             issMarker.setLatLng([lat, lon]);
         }
 
-        // Calculate and draw ground track
-        if (issTrackLine) {
-            const trackPoints = [];
-            const inclination = 51.6; // ISS orbital inclination in degrees
-
-            // Generate orbit track points
-            for (let offset = -180; offset <= 180; offset += 3) {
-                let trackLon = lon + offset;
-
-                // Normalize longitude
-                while (trackLon > 180) trackLon -= 360;
-                while (trackLon < -180) trackLon += 360;
-
-                // Calculate latitude based on orbital inclination
-                const phase = (offset / 360) * 2 * Math.PI;
-                const currentPhase = Math.asin(Math.max(-1, Math.min(1, lat / inclination)));
-                let trackLat = inclination * Math.sin(phase + currentPhase);
-
-                // Clamp to valid range
-                trackLat = Math.max(-inclination, Math.min(inclination, trackLat));
-
-                trackPoints.push([trackLat, trackLon]);
-            }
-
-            // Split track at antimeridian to avoid line across map
-            const segments = [];
-            let currentSegment = [];
-
-            for (let i = 0; i < trackPoints.length; i++) {
-                if (i > 0) {
-                    const prevLon = trackPoints[i - 1][1];
-                    const currLon = trackPoints[i][1];
-                    if (Math.abs(currLon - prevLon) > 180) {
-                        // Crossed antimeridian
-                        if (currentSegment.length > 0) {
-                            segments.push(currentSegment);
-                        }
-                        currentSegment = [];
-                    }
-                }
-                currentSegment.push(trackPoints[i]);
-            }
-            if (currentSegment.length > 0) {
-                segments.push(currentSegment);
-            }
-
-            // Use only the longest segment or combine if needed
-            issTrackLine.setLatLngs(segments.length > 0 ? segments : []);
-        }
+        // Track is fetched separately by updateIssTrack() via /sstv/iss-track
 
         // Pan map to follow ISS only when the map pane is currently renderable.
         if (isMapContainerVisible()) {