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>
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