The leading letter tells you which object catalog the object belongs to, as follows:
|auxcat (Auxiliary catalog)
|csocat (Complementary catalog)
|deepcat (Deep space catalog)
|ftocat (Failed to orbit catalog)
|lcat (low altitude catalog)
|rcat (suborbital catalog)
|stdcat (Standard catalog)
|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.
|No (satcat) Number Assigned. Object should be in SATCAT but is not.
|No SATCAT number because remained attached to parent object
|No SATCAT number, component of complex object such as space station
|No SATCAT number because is an EVA spacesuit. These do not get recorded in SATCAT.
|No SATCAT number because object remained inside parent object
|No SATCAT number because completed less than one full orbit
|No SATCAT number because separated into marginally suborbital trajectory during parent reentry.
|No SATCAT number because launched into marginally suborbital trajectory
|Not in SATCAT because object was a separate object in orbit transiently, for only a few seconds (e.g. CORONA film capsule)
|Not in SATCAT because launch is a marginal orbit case
|No SATCAT number because suborbital
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.
Some debris objects have a string with RCS followed by a number in the PLName field. This refers to the radar cross section in square metres. The RCS values obtained from early 2000s era SATCAT releases are unreliable, but may indicate which objects are particularly small or large.
Some objects have a PLName beginning with the string `[UNID'. These objects are marked with an asterisk in the US SATCAT. They are unidentified debris objects; their piece designations (international designations) are believed to associate them with the wrong launch.For example, there are a lot of small component debris objects associated with Soviet Strela-2M communications satellites in rather similar orbits. When such an object is discovered years after its launch, the effects of drag and perturbations are such that while it is obvious from the orbit that the object comes from a Strela-2M, there's no way to tell exactly which Strela-2M it is from.
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.
Also, in some cases an asterisk is appended to the identifier. This is a flag that the launch designation in the Piece field is not what you'd expect from the launch designation of the parent. In the normal situation, for example, S45920 has Piece designation 2020-048A, and its parent S45921 has 2020-048B - both are 2020-048 launch pieces. But S45916 has Piece designation 1998-067RP, and its parent is A09547* with piece designation 2020-011, an apparent contradiction. In fact 2020-011 is the correct launch for both, with launch date 2020 Feb 15, but USSF assigns 1998-067 piece designations and a 1998 launch date for all objects released form the ISS. I added the asterisks to facilitate automatic checking: it lets you know to be careful about the launch date and launch information for this object.
The central body names are given in the Worlds file.
This UTC date (in Vague Date format) is the start time for the current phase. In the simplest cases, it is the time when the object separated from its parent.
The value of this field is a string representing the central body for the current phase. These strings are defined in the Worlds file. (Usually, the central body is Earth.)
This UTC date (in Vague Date format) is the end time for the current phase. In the simplest cases, it is the time when the object reentered the atmosphere. If blank, the phase is still in progress.
See the discussion on phases in the definitions section.
See the discussion on phases in the definitions section.
If the MassFlag is '?' then the value is an estimate, hopefully good to about 20 percent.
If the DryFlag is '?' then the value is an estimate, hopefully good to about 20 percent.
If the TotFlag is '?' then the value is an estimate, hopefully good to about 20 percent.
If LFlag is '?' the value is a guess, hopefully good to about 20 percent.