The leading letter tells you which object catalog the object belongs to, as follows:
|A||auxcat (Auxiliary catalog)|
|C||csocat (Complementary catalog)|
|D||deepcat (Deep space catalog)|
|F||ftocat (Failed to orbit catalog)|
|L||lcat (low altitude catalog)|
|R||rcat (suborbital catalog)|
|S||stdcat (Standard catalog)|
|T||tmpcat (Temporary catalog)|
Note that there are no prefix letters associated with the ecat (event catalog), or the heliocentric and lunar-planetary registers, since they contain only objects already defined in the other catalogs.
Sequence numbers in the A, D, F, L, R, and S catalogs are assigned sequentially starting with 00001. However, occasional numbers may be missing due to deletions of spurious or reassigned entries.
Sequence numbers in the C and T catalogs are not assigned sequentially.
Sequence numbers in the S catalog are in one-to-one correspondence with the US SATCAT catalog numbers. Thus, S46112 corresponds to SATCAT satellite 46112 (2020-056A).
In exceptional cases, future releases of GCAT may reassign existing catalog numbers. Any such reassignments will be recorded explicitly in an accompanying table. However, users who have found earlier (pre-GCAT) JCAT catalog numbers that crept into my public files have no such guarantee - in partcular, auxcat numbers previously seen in public files may now refer to different objects.
However, one US SATCAT number can correspond to multiple GCAT objects which are attached to one another. For example, SATCAT number 00032 corresponds to GCAT objects S00032 (Discoverer 11 payload), A00046 (Agena 1055 rocket stage), and A00047 (TOD experiment attached to Agena stage). All these objects have 00032 in the Satcat field.
Objects which do NOT have US SATCAT entries instead have a string in this field explaining why they don't.
|NNA||No (satcat) Number Assigned. Object should be in SATCAT but is not.|
|NNA A||No SATCAT number because remained attached to parent object|
|NNA C||No SATCAT number, component of complex object such as space station|
|NNA E||No SATCAT number because is an EVA spacesuit. These do not get recorded in SATCAT.|
|NNA I||No SATCAT number because object remained inside parent object|
|NNA P||No SATCAT number because completed less than one full orbit|
|NNA R||No SATCAT number because separated into marginally suborbital trajectory during parent reentry.|
|NNA S||No SATCAT number because launched into marginally suborbital trajectory|
|NNA T||Not in SATCAT because object was a separate object in orbit transiently, for only a few seconds (e.g. CORONA film capsule)|
|NNA X||Not in SATCAT because launch is a marginal orbit case|
|NSO||No SATCAT number because suborbital|
|C||Component (see SatType explanation)|
|D||Debris (see SatType explanation)|
At a finer level the type string provides a lot more information for special cases. See the SatType definition for more details.
`X part' indicates that the object is an unidentified component that separated from X. `deb X' indicates the object is a debris object from the breakup of X.
The launch date is given in UTC, with 1 day precision. More accurate launch times are given in the launch lists. Usually you can map the object to a launch using the international designation, but see the discussion in the Parent field below for exceptions.
The parent object is an Extended JCAT Identifier - it's usually just a JCAT ID but sometimes there's a port location appended to make it more specific. See the documentation on the main satcat for more details.
This UTC date (in Vague Date format) is the time when the object first separated from its parent. Details of subsquent phases (dockings/undockings, etc) are not given in this catalog - see the main catalogs for details. This date is useful for determining when debris objects appeared in orbit, for example.
This UTC date (in Vague Date format) is the time when the object reentered the atmosphere or landed. If blank, the object is still in orbit.