[Spice_discussion] kernel data

cc cc at pw-wspx.org
Thu Aug 27 01:51:31 PDT 2015


I'm new to this so please forgive my ignorance.  I've tried to
understand the information as given on the SPICE site, but not being a
C/Fortran/Matlab programmer, I didn't quite grasp how to get what I
want from the bsp file I got (de432s.bsp) (SPK file).

What I'm trying to do is to get the ephemerides data from the
bsp file using Python.

Here's what I got:

1) I did manage to get a dump of the file record (that's the easy
2) I can retrieve the comment data (though I haven't yet figured
   how to determine how long the Comment data is though I have
   a sneak suspicion that it has something to do with FWARD and
   BWARD and ND and NI.

As I understand it, after the comment data block, there's the
Summary records, and then the Name records and then the element

Looking through the bsp file in a hexeditor, I'm getting confused
with what I see in the File Record and with the actual data.

For example, in the file record, I have FWARD=3, BWARD=3.
This means that the rec# of the initial summary record is at
the 3rd record and since BWARD == FWARD, there's only one
summary record.  Now looking through the bsp file, the
comment data starts and ends at the 2nd record.  So the next
record (3rd) should be the  name records.  But I don't see
any strings there.  The only strings I see are DE-0432LE-0432
and that's in the 4th Record.  Am I understanding that this
means that the # of records stated in FWARD and BWARD doesn't
include the File Record?  As in when FWARD = 3, it means
count the third record AFTER the file record?  (Or does
this mean that the record #s are zero based?)

If that's the case, in the Name records, what does the
DE-0432LE-0432 mean?  If that's the array name,
where would I find the Mercury eccentricity(for example)?

(Or did I get the wrong kernel?  The readme files on
the site seems to indicate that they are the files.)

Any clarifications appreciated.


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