TITLE

Astro::SpaceTrack::BulkData - Reconstructing Space Track bulk data downloads

SUMMARY

The purpose of this document is to examine the feasibility of duplicating the Space Track bulk data downloads through the REST interface after the bulk data functionality is removed. The short answer is:

Reasonable (and even trivial) queries appear to exist for "full", "geosynchronous", "iridium", "orbcomm", "globalstar", "intelsat", and "inmarsat".

Reasonable queries do not appear to exist for "navigation", "weather", "amateur", and "special". The only way I can see to get them is with a list of OIDs, which would have to be maintained.

The "visible" data set is a special case. It might be thought possible to come up with a reasonable facsimile of the list by selecting on "RCSVALUE", but in practice this does not seem to work. The Celestrak "visual" list might be an acceptable alternative.

DETAILS

There are, in general, three possibilities, for duplicating the Space Track bulk data, of which not all are exclusive:

1) there is an obvious SATCAT query to get the OIDs involved;
2) there is a Celestrak list of the OIDs involved;
3) there is no known source of the OIDs involved.

The SATCAT queries would specify at least "/basicspacedata/query/class/satcat/CURRENT/Y/DECAY/null-val". Except for the "full" and "geosynchronous" catalogs, "/OBJECT_TYPE/PAYLOAD" would also be specified. Predicates could be limited to "/predicates/NORAD_CAT_ID", though the construction of NASA-format TLEs will require predicate "SATNAME" as well.

The "full" and "geosynchronous" queries could be satisfied directly from class "tle_current" provided satellite names were not needed.

The individual bulk data sets are:

full - Full catalog

This is case (1) above, with no additional query arguments. The 'full' data set includes rocket bodies and debris. In theory this query could be satisfied from class "tle_current" if no names were needed.

Interestingly, the obvious query retrieves 15773 bodies, whereas the prebuilt data set has only 14908. The query as it currently stands took three or four minutes, but that was going through class "satcat". This will be required if common names are needed. If common names are not needed, the query directly against "tle_current" should be faster, especially since it does not need to be broken up into smaller queries.

geosynchronous - Geosynchronous bodies

This is case (1) above, though some fiddling is needed. The problem is that the version 1 definition of a geosynchronous satellite requires mean motion between 0.99 and 1.01 revolutions per day, and eccentricity less than 0.01. We kind of have to hit class "satcat" to find out what is in orbit, but neither mean motion nor eccentricity are in that class.

The trick is that period in minutes is in "satcat", and the required mean motion corresponds to a period between 1425.6 and 1454.4 (compared to the specimen query on the version 2 web site, which puts the period between 1430 and 1450). We do not require the object type to be 'PAYLOAD', because the version 1 bulk download contains both rocket bodies and debris.

We can then query the "tle" or "tle_current" classes for the OIDs we have found, but restrict the query by requiring eccentricity less than 0.01.

The result of this combination of queries has 813 bodies in it, the same as the bulk data for geosynchronous satellites. They are slightly different lists, though. The following OIDs appear only in the bulk data:

     OID  Common Name             Period  Object Type
    20315 INTELSAT 602            1454.43 PAYLOAD
    20401 SKYNET 4A               1454.49 PAYLOAD
    23598 DIRECTV 3 (DBS/NIMIQ 3) 1454.56 PAYLOAD

On the other hand, the following OIDs appear only in the results of the above-described query:

     OID  Common Name             Period  Object Type
    11890 EKRAN 5                 1436.55 PAYLOAD
    12851 SL-12 R/B(2)            1425.65 ROCKET BODY
    29233 SL-12 R/B(2)            1425.69 ROCKET BODY

In theory this query could be satisfied from class "tle_current" if no names were needed.

navigation - Navigation satellites.

This appears not to be case (1) above. One could look for 'NAVSTAR' and 'GLONASS', but though this would catch the bulk of them, others are listed, and some of them are simply identified as 'COSMOS' and a number.

This is probably not case (2) either, since Celestrak does not have a simple 'navigation' list, but a number of them. Except for Celestrak's 'glonass' list, there does not seem to be much overlap between Space Track's and Celestrak's idea of what is a navigational satellite.

So this appears to be case (3) above.

weather - Weather satellites

There appears not to be case (1) above. You could query for "/SATNAME/~~GOES" and "/SATNAME/~~METEOSAT", but some of the list entries are simply identified as 'COSMOS' and a number.

Furthermore, case (2) is of limited usefulness, since there is not much overlap between Celestrak's and Space Track's idea of what a weather satellite is. Space Track lists 57 weather satellites, whereas Celestrak lists 34. Moreover, only 12 satellites appear on both lists.

So this appears to be case (3) above.

iridium - Iridium satellites

This is case (1) above. The query that implements the Space Track version 1 definition of an Iridium satellite is "/SATNAME/~~IRIDIUM". The Celestrak list includes two dummy masses launched by the Chinese while trying to qualify for an Iridium launch contract. The dummy masses are not in the Space Track list, but I doubt that this is significant.

orbcomm - OrbComm satellites

This is case (1) above, though it takes two queries: "/SATNAME/~~ORBCOMM" and "/SATNAME/~~VESSELSAT". The corresponding Celestrak list omits the two Vesselsats.

globalstar - Globalstar satellites

This is case (1) above, with query "/SATNAME/~~GLOBALSTAR". The corresponding Celestrak list is identical.

intelsat - Intelsat satellites

This is case (1) above, with query "/SATNAME/~~INTELSAT".

The corresponding Celestrak list is substantially different, missing many satellites named 'Intelsat', and adding others (notably, but not limited to, the 'Galaxy' satellites). Space Track has 89 satellites in this list, Celestrak has 64, and 44 appear in both lists.

inmarsat - Inmarsat satellites

This is case (1) above, with query "/SATNAME/~~INMARSAT". There is no corresponding Celestrak list.

amateur - Amateur Radio satellites

This appears not to be case (1) above. There are a bunch of Oscars and Radios, but 'Oscar' appears in several other lists, and besides there are the ubiquitous 'Cosmos' satellites.

There is a Celestrak amateur list, but there is not much overlap between the two, with 51 satellites in the Space Track list, 37 in the Celestrak list, but only 18 in both lists.

This appears to be case (3) above.

visible - Visible satellites

This appears not to be case (1) above. I had hoped that something could be done with "RCSVALUE", but this turns out not to be the case. The minimum "RCSVALUE" found among the 212 objects in the Space Track 'visible' data set is 1.4205 (as of September 1 2012). But there are 7027 objects in the "satcat" table having a Radar Cross Section of at least that value. Now, none of the 212 'visible' objects are debris, but screening out debris only gets us down to 6328 objects.

The corresponding Celestrak list is called 'visual', but there are substantial differences between the two lists. The Space Track list contains 212 satellites, the Celestrak list contains 148, but only 91 satellites are in both lists.

special - Special satellites

This appears to be case (3) above. The list appears to be a miscellany with no obvious selection criteria, and there is no corresponding Celestrak list.

AUTHOR

Thomas R. Wyant, III (wyant at cpan dot org)

COPYRIGHT AND LICENSE

LICENSE

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