Understanding COSPAR ID
How to read a COSPAR ID
Take the International Space Station's Zarya module, 1998-067A. Here 1998 is the launch year, 067 is the 67th launch of that year, and A identifies the object — in this case the primary payload. Later objects from the same launch take subsequent letters: on the flight that deployed Hubble, the orbiter Space Shuttle Discovery is 1990-037A and Hubble itself is 1990-037B. The piece letters run A–Z, then AA–AZ, BA–ZZ and beyond, always omitting I and O so they cannot be mistaken for the digits 1 and 0.
| Part | Example (1998-067A) | Meaning |
|---|---|---|
| Launch year | 1998 | Calendar year of the launch |
| Launch number | 067 | 67th launch of that year (three digits, leading zeros) |
| Piece letter | A | Object A from the launch — the primary payload |
COSPAR ID versus NORAD catalogue number
The two identifiers on every tracked object answer different questions. A COSPAR ID is launch-based, fixed at or near launch, and groups everything from one lift-off under a shared prefix. A NORAD ID — the Satellite Catalogue Number issued by US Space Command — is simply the next free number in the catalogue when an object is first tracked, and carries no launch information. The ISS, for instance, is 1998-067A yet NORAD 25544. You will see both side by side on Space-Track and in every TLE.
| COSPAR ID | NORAD ID | |
|---|---|---|
| Based on | Launch event | Order first catalogued |
| Example (ISS) | 1998-067A | 25544 |
| Groups a launch? | Yes — shared prefix | No — one per object |
| Standardised by | COSPAR (international) | US Space Command |
One launch, many objects
Because the ID is tied to a launch, one prefix can cover many catalogued objects. The ISS launch of 1998-067 is the classic example: alongside Zarya, a long tail of released hardware and debris shares the 1998-067 prefix, its piece codes running well into the multi-letter range. A fragmentation event — a break-up or collision — behaves the same way, scattering new pieces that all inherit their parent launch's year and number. That launch-first grouping is why it is natural to browse objects by mission in the satellite launch log.
A short history: from Greek letters to numbers
The current numeric scheme began in 1963. Before then, launches were labelled with the year and a Greek letter under the older 'Harvard' system: Sputnik 1, the first artificial satellite, was 1957 Alpha 2, and its brighter R-7 rocket body was 1957 Alpha 1. As launch rates rose, the Greek alphabet proved too small, so COSPAR adopted the year-and-number format still in use today — the first object named the new way was a Soviet Luna probe, 1963-001B.