📡 Space Glossary

Tracking & Space Surveillance

How satellites and debris are detected, catalogued, and monitored. From radar systems and tracking formats to the identification standards that underpin global space situational awareness. 32 terms, each explained in plain language with key data and links to live trackers.

A5 Alpha-5 How catalogue numbers grew past 99,999 without breaking the TLE 31,827 live100000–339999 AO Analyst Object Tracked, numbered — but not yet officially in the catalogue Unattributed originYes AD Angular Diameter How large an object looks in the sky, measured as an angle About 32′About 29′ to 34′ AM Apparent Magnitude How bright a satellite looks — lower is brighter ≈ +6≈ −4 A Appulse A close approach in the sky without one object crossing the other Minutes of arcAn orbital conjunction CI COSPAR ID International launch-based object identifier YYYY-NNNP1998-067A C Covariance The uncertainty cloud around every predicted position 6×6 matrixPrediction horizon CT Cross-Tagging When two satellites swap identities in the catalogue Batch deployments DSN DSN NASA's global array of antennas for communicating with distant spacecraft 70 m diameterNASA JPL ES Earth's Shadow The cone of darkness that makes satellites vanish LEO satellites EA Elevation Angle How high a satellite climbs above the horizon Above 40° ELSET Elset One snapshot of an orbit, packaged for a propagator 6 mean elements + dragSGP4 / SDP4 E Ephemeris Predicted position table for a space object over time TLE + SGP4OEM (numerical) GS Ground Station The Earth end of every satellite link ~5–12 min per passAntenna-as-a-service IF Iridium Flare The sky's most punctual spectacle — now history To magnitude −8+1997 → ~2019 NI NORAD ID Unique tracking number for every space object 31,827 live25544 PA Position Angle A direction on the sky, measured from north through east Celestial north (0°)Through east RCS RCS Measure of how detectable an object is to radar 400 m²0.01 m² SF Satellite Flare A satellite catching the Sun like a moving mirror Seconds100–1000× in seconds SS Satellite Streak The bright line a satellite draws through a photograph Darken · dodge · maskStreaks as census data ST Satellite Transit A satellite seen crossing the face of the Sun or the Moon About 0.5 to 2 secondsUp to about 1′ across SGP4 SGP4 The algorithm that predicts satellite positions from TLEs TLE data1 km (fresh TLE) SA Sky Arc The curved path a satellite traces across the sky Peak elevationSky-dome diagram SF Space Fence US Space Force radar for detecting small debris Kwajalein AtollS-band radar ST Space-Track US Space Force's public satellite catalogue 31,827 live SSA SSA Knowing what's in orbit and where it's going 31,827 liveUS SSN (18th SDS) ST Starlink Train That eerie line of lights crossing the night sky Tracking & Space Surveillance SV State Vector Position and velocity — an orbit in six numbers J2000 · TEME · ECEFMetres TLE TLE Standard format for satellite orbit data 31,827 live2 (+ optional name) TC Transit Corridor The strip of ground from which a satellite transit can be seen About 4 km20 km or more T Twilight The dusk/dawn window when satellites are visible Sun 0–6° below horizon UCT UCT A radar return that matches nothing in the catalogue Tracking & Space Surveillance

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