Compute the current position of any cataloged Earth-orbiting satellite by NORAD catalog number (e.g. 25544 = ISS, 20580 = Hubble), using fresh Celestrak orbital elements propagated with SGP4. Returns sub-point latitude/longitude, altitude (km), and speed (km/s) for the requested instant (default: now; pass `at` as an ISO timestamp for any time within a few days of the elements' epoch). Supply observer `lat`/`lon` (and optional altKm) to also get look angles — azimuth, elevation, slant range, and whether the satellite is above your horizon — for visual/antenna pointing. Satellite tracking, pass prediction, ground-station planning. Public-domain orbital data; physical/mission metadata is not included.