Understanding NORAD ID
How an object earns its number
A catalogue number is not handed out at launch. It is assigned once sensors of the US Space Surveillance Network — ground radar, optical telescopes and the phased-array Space Fence — have tracked an object long enough to fit a stable orbit and match it to a known launch. Only then does it receive the next free integer. Because faint fragments can take weeks to characterise, numbers follow launch order only roughly. Objects being tracked but not yet formally catalogued are given temporary 'analyst' numbers in the 80000–89999 band. This whole pipeline is part of space situational awareness — the business of knowing what is up there and where it is heading.
NORAD ID versus COSPAR ID
Every catalogued object actually carries two identifiers, and the difference is worth knowing. The NORAD Catalog Number is a plain running integer assigned by the US when the object enters the catalogue. The COSPAR ID (or International Designator) instead encodes the launch — the year, that year's launch number, and a letter for each separate piece — and is coordinated internationally. Both name the same hardware, as the table shows, and the low numbers reveal just how far the catalogue has come since 1957.
| Object | NORAD ID | COSPAR ID |
|---|---|---|
| Sputnik 1 rocket body (first catalogued) | 00001 | 1957-001A |
| Sputnik 1 satellite | 00002 | 1957-001B |
| Vanguard 1 (oldest still in orbit) | 00005 | 1958-002B |
| Hubble Space Telescope | 20580 | 1990-037B |
| ISS (Zarya module) | 25544 | 1998-067A |
| Tiangong (Tianhe core) | 48274 | 2021-035A |
Running out of digits: Alpha-5 and nine-digit numbers
The classic two-line element set reserves only five characters for the catalogue number, capping it at 99,999. As the catalogue climbed toward that ceiling, the US Space Force adopted Alpha-5: the leading character can become a letter, where 'A' means 10, 'B' means 11 and so on, with the letters I and O skipped to avoid confusion with 1 and 0. That stretches the five-character field to 339,999. The 100,000th number was issued in July 2026 — assigned to a Portuguese CubeSat — and in Alpha-5 that first six-digit value, 100000, is written 'A0000'. For the longer term the modern GP/OMM data formats, introduced in 2020, carry a full nine-digit catalogue number (up to 999,999,999), and newly catalogued high-number objects are increasingly published in those formats rather than the legacy TLE.