APOLLO 16 Subsatellite Trajectory SPK file, JPL SSD Solution
===========================================================================
Created by Alex Konopliv, Solar System Dynamics group, JPL, July 3,
2007. Comments added by Boris Semenov, NAIF/JPL, July 5, 2007.
Objects in the Ephemeris
--------------------------------------------------------
This file contains ephemeris data for the APOLLO 16 Subsatellite (NAIF
ID -916300) with respect to the Moon in the J2000 inertial reference
frame.
Approximate Time Coverage
--------------------------------------------------------
This file covers the following time period:
Start of Interval (ET) End of Interval (ET)
------------------------ ------------------------
1972 APR 27 23:45:42.185 1972 MAY 29 04:10:42.184
Status
--------------------------------------------------------
This file contains the APOLLO 16 Subsatellite trajectory determined
by the Solar System Dynamics group, JPL. Contact the data producer if
you are unsure whether this file is applicable for your application.
Pedigree
--------------------------------------------------------
This file contains APOLLO 16 Subsatellite trajectory determined using
the lunar gravity field LP150Q. This spherical harmonic 150th degree
gravity solution includes Apollo, Lunar Orbiter, Clementine and all
Lunar Prospector tracking data. The Apollo 16 subsatellite impacted
the lunar surface about 35 days after release from the Apollo 16 CSM.
It was a simple spin stabilized spacecraft with out a propulsive
system (unable to raise its altitude).
Segment Boundary Discontinuities
--------------------------------------------------------
This SPK file contains a number of SPK segments that came from
original individual SPK files. Although, each segment provides
continuous trajectory within the interval that it covers, in general a
position and velocity discontinuity exists at the boundary of the
segment and the segments whose coverage immediately precede and follow
it. The times and magnitudes of these discontinuities are provided in
the Appendix 1 of these comments.
Contacts
--------------------------------------------------------
If you have questions regarding this data contact
Alex Konopliv
818 354-6105
Alexander.S.Konopliv@jpl.nasa.gov
or
Boris V. Semenov
(818)-354-8136,
Boris.Semenov@jpl.nasa.gov
Appendix 1: Segment Boundary Discontinuity Summary
--------------------------------------------------------
This SPK file contains a number of SPK segments that came from
original individual SPK files. Although, each segment provides
continuous trajectory within the interval that it covers, in general a
position and velocity discontinuity exists at the boundary of the
segment and the segments whose coverage immediately precede and follow
it. The times and magnitudes of these discontinuities are provided in
the table included in this Appendix.
The top portion of the table contains the name of this SPK file. All
descriptive lines in the top portion of the file start with the ``#''
character to allow direct plotting of the data in the freeware
``gnuplot'' application.
The table consists of 4 columns. The first column contains the UTC
time of that segment boundary. The last three columns (2..4) contain
view coordinate frame components -- ``down track'' (this direction is
parallel to the velocity vector), ``normal to plane'' (this direction
is computed as cross product of position vector by velocity vector)
and ``in plane'' (this direction is computed as a cross product of
``down track'' by ``normal to plane'') -- of the difference between
the state vectors computed at that UTC time defining segment boundary
at which a discontinuity exists.
The pairs of segments and discontinuity times are determined using an
algorithm that emulates the standard SPK loading priority -- ``last
loaded segment takes precedence''. Therefore, the discontinuities
summarized in the file are those which a user reading file would
actually see.
The difference components in the view coordinate frame were computed
for each discontinuity using the following algorithm:
-- A single state was computed from each pair of segment the
J2000 frame at the time of discontinuity.
-- For this pair of states, a position difference vector was
computed by subtracting the state computed from the segment
with higher priority from the state computed from segment
with lower priority. Then, a frame transformation matrix
rotating these difference vectors from J2000 to the view
coordinate frame defined by the state obtained from the
higher priority segment was computed, and the position
difference vector was rotated to the view frame coordinates
using this matrix.
The segment boundary discontinuities for this file are:
#
# Summary of discontinuities at segment boundaries for
# SPK file a16_subsat_ssd_lp150q.bsp:
#
# BOUNDARY TIME (UTC) DOWNTRK INPLANE NORMAL
#----------------------- ------- ------- -------
1972-05-03T22:00:00.000 0.013 -0.014 -0.190
1972-05-09T20:10:00.000 -0.020 -0.018 -0.021
1972-05-12T19:10:00.000 -0.067 -0.013 0.126
1972-05-15T18:10:00.000 -0.003 -0.001 0.003
1972-05-18T21:15:00.000 -0.015 0.002 -0.085
1972-05-23T17:50:00.000 -0.150 0.024 -0.156