What is a NORAD catalog number?

Where the numbers start

Number 1 is not Sputnik 1. It is the rocket body that launched it, catalogued first because it was the larger and brighter object in 1957. Sputnik 1 itself is number 2.

From there the numbers run in the order objects were catalogued. That is not always the order of launch: a fragment from a breakup years later gets a new number when it is first tracked, so a piece of an old satellite can carry a much higher number than its parent.

A few worth recognising

Number	Object
1	Sputnik 1 rocket body
2	Sputnik 1
20580	Hubble Space Telescope
25544	International Space Station (the Zarya module)

The Space Station's number belongs to its first module. Everything bolted on since shares it, because the tracked object is the whole station.

NORAD number versus international designator

Objects also carry an international designator, sometimes called a COSPAR ID, in the form year - launch number - piece. The Space Station's is 1998-067A: the 67th launch of 1998, piece A.

The two are complementary. The international designator tells you which launch something came from, which makes it useful for grouping a launch and its debris. The NORAD number is a single short key for one object, which is why trackers and element sets lead with it.

Why search by number instead of name

Names are unreliable. They are shortened to fit fixed-width fields, spelled differently between sources, reused for successive satellites in a series, and changed after launch. "Starlink" alone matches thousands of objects.

A catalogue number matches exactly one. If you have it, type it rather than the name.

The five-digit problem

The classic TLE format has room for five digits, so it tops out at 99999, and the catalogue is closing in on that limit. Newer formats such as the OMM carry larger numbers without trouble; the older text format uses a workaround that swaps the first digit for a letter.