Wiki

App reference

Glossary

TLE / GP element set

A compact set of numbers describing a satellite's orbit at a specific reference time (its epoch) — inclination, eccentricity, mean motion, and so on. "TLE" (Two-Line Element) is the classic fixed-width text format; "GP" (General Perturbations) is the same underlying data in Space-Track's modern format. Both go stale as the satellite drifts from its last-known orbit, which is why fresh element sets matter.

SGP4

The standard orbital-propagation model used to turn a TLE/GP element set into a position and velocity at any given time, forward or backward from its epoch. Every position rendered on this site comes from an SGP4 propagation, not a stored coordinate.

NORAD ID / catalog number

The unique integer identifying a tracked object, assigned at cataloging and never reused.

COSPAR ID / international designator

The launch-based identifier in the form YYYY-NNNLLL (launch year, launch-of-year sequence, and a letter for each piece from that launch) — a different identity scheme from the NORAD ID, tied to the launch event rather than the object.

Orbital regime — LEO / MEO / HEO / GEO

Low, medium, highly-elliptical and geostationary/geosynchronous Earth orbit. On this site, regime is derived from an object's computed altitude, not a field Space-Track or CelesTrak reports directly.

Operator (derived)

The organization inferred to operate a satellite, guessed from its object name — not an authoritative registry field. Wherever it appears, it is labeled as derived; treat it as a best-effort label, not ground truth.

Mission

Not a distinct Space-Track field. The OBJECT_NAME search covers mission strings in practice, since most object names are the mission or payload name (for example, STARLINK-1234, LANDSAT 9). Searching "name, mission, intl designator, NORAD" returns the same results as name-only search.

Debris family

A group of tracked fragments attributed to a single breakup or collision event (for example, the Cosmos 2251 collision debris), grouped by their shared parent event rather than by operator.

Apogee / perigee

An orbit's highest and lowest points above Earth's surface, in kilometers — computed from the element set's eccentricity and semi-major axis.

RCS (radar cross-section)

A coarse size class (small / medium / large) describing how visible an object is to ground-based radar — used as a rough proxy for physical size, not a precise measurement.

Conjunction

A predicted close approach between two tracked objects. This site's conjunction screening is a derived, unofficial pass over public element sets — see the Conjunctions reference above.

Revs (orbital revolutions)

How many orbital periods of trajectory are drawn around a selected satellite — 1×, 3× or 5× its own orbital period, shown as past (dashed) and future (solid) arcs.

Time rate

How fast simulated time advances relative to real time on the globe pages — 1×, 10×, 100× or 1000× realtime, i.e. that many simulated seconds pass per real second.

Cohort

All catalog entries launched in the same decade, tracked as a group from that decade forward. Analytics' cohort survival chart shows, for each decade's cohort, how many are still on orbit today versus how many have since decayed.

Cumulative catalog entries vs. still on orbit today

Two different curves on Analytics' growth chart, deliberately never merged into one line. Cumulative catalog entries is a historical running total — every object ever catalogued, decayed objects included, so it never shrinks. Still on orbit today approximates the current population by subtracting a cumulative decay count from that same running total. Neither is a true historical on-orbit snapshot (the catalog doesn't hold one); treat the second series as an approximation.

Catalog entry vs. launch

A single launch often puts multiple trackable objects into orbit — a payload, its upper stage, and any shedding debris each get their own catalog entry. Counts described as catalog entries (for example, "recent launches" on the Brief, which is really new catalog entries filtered to OBJECT_TYPE = PAYLOAD) are a proxy for launch activity, not a one-to-one launch count.

Untyped (launch history)

In Analytics' launch-history table, the objects from a launch that Space-Track has not classified as PAYLOAD, ROCKET BODY or DEBRIS. This is normal for a recent launch — a catalog entry can exist before its OBJECT_TYPE is assigned — so a launch of seven objects may legitimately read "7 untyped" for a few days. The count is shown rather than hidden so the type breakdown always reconciles with the OBJECTS column; a breakdown that silently summed to less than the total would look like missing data instead of pending classification.

Altitude bin / inclination bin

A fixed-width range of altitude (or inclination) used to bucket objects into a histogram — for example, all objects between 500 and 550 km. Analytics' altitude and inclination histograms count only objects still on orbit (excluding decayed objects), unlike the catalog-growth chart on the same page, whose "cumulative catalog entries" series is a historical count that includes decayed objects.

Launch site code

A short code identifying the physical launch site (for example, AFETR for Cape Canaveral), sourced from Space-Track's static launch_site reference table — not derived or guessed. Where a code has no mapped name, this site shows the bare code rather than an invented one. Analytics' launch-history table resolves these to full site names through that table.