| CONFIDENCE_LEVEL_NOTE |
This data set contains SPICE kernel files created during mission
operations and after mission data reconstruction and analysis.
Some general information about this collection follows here,
but the prospective user is also referred to extensive
descriptions about each file that are stored inside each kernel
file. These metadata provide detailed information regarding
the information source from which the data were derived, the
type of processing applied to the source data, applicability
of the data, etc. Metadata are located in the ``comment area''
for binary kernel types (SPK, CK, ESQ), accessible using either
the COMMNT or SPACIT utility program found in the NAIF Toolkit.
Metadata are located after ``\begintext'' markers within the
text kernel types (PCK, IK, FK, LSK, SCLK), accessible by
using any available text file display tool such as a word
processor, text editor, or the UNIX ``more'' or ``cat''
commands.
In some cases data accuracy information does not exist because
it could not be estimated even after mission completion.
Where there are questions about data accuracy or ``confidence''
not addressed herein the reader is invited to examine subsequent
SPICE archive releases associated with this data set (if such
exist), or to contact the NAIF node of the Planetary Data System
for possible further information.
SPK Files
=========
The SP-Kernel files included in this data set provide reconstructed
trajectory of the Deep Impact Flyby (DIF) spacecraft and ephemeris
data for the mission target comet Hartley 2, Solar System planets,
and the Sun.
Additional information about SPK files provided in this data set
is available in the file ``data/spk/spkinfo.txt''.
CK Files
========
C-kernel files included in this data set provide the orientation
of the DIF spacecraft bus and the DIF high gain antenna (HGA).
Some of these CK files were produced from engineering telemetry
downlinked from the spacecraft; others, containing predicted
data, were produced by attitude simulation tools based on the
planned attitude profiles. As is often the case with spacecraft
engineering telemetry-based measurements, considerable
uncertainty exists as to the accuracy of such measurements, and,
data quality (accuracy and completeness) can vary significantly.
DIF Spacecraft Bus CK files
---------------------------
Three kinds of the DIF spacecraft bus orientation CK files are
included in this data set.
The first kind are reconstructed attitude kernels based on the
low rate telemetry (1/8 Hz). The coverage provided by these files
is full of gaps, which due to the attitude data downlink strategy
frequently happen at the times of transitions between different
attitude modes, making interpolation over these gaps produce
grossly incorrect attitude. For this reason the interpolation
intervals in these reconstructed files should not be altered
using CKSPANIT or a similar tool.
The second kind is the reconstructed attitude kernel based on the
high rate telemetry (up to 5 Hz) providing coverage only for
about 8 hour period around closest approach to Hartley 2. The
version 1 of this CK had internal time tags truncated by up to 2
milliseconds, introducing attitude errors of almost 30
microradians during the fastest spacecraft turn rates in the
~200 second interval around the closest approach to Hartley 2
(at other times attitude errors due to this truncation were
negligible). This problem was fixed in the version 2 of this CK.
The accuracy of the DIF spacecraft bus orientation determined
on-board and stored in the low- and high- CK files varied
significantly, from 50 micro-radians (~5 MRI pixels) at the times
when the attitude was determined based on the star tracker
measurements to a few hundreds of micro-radians (tens of MRI
pixels) for the periods when the attitude was determined by
propagating ACS gyro data without any star tracker updates for
extended periods of time.
The third kind are predicted kernels providing nominal attitude
for the whole or a part of the mission or just for the periods of
target star observations during the EPOCh part of the mission.
The predicted files were generated using prediCkt tool and are
included in the data set with the sole purpose of providing some
attitude for the periods when the reconstructed files have gaps.
Although a comparison of reconstructed and predicted CK files for
the periods when both provided coverage showed that in many cases
the predicted CK data matched the actual attitude to a fraction
of degree, the accuracy of the predicted CK files in general is
suspect because of the idealistic attitude modeling rules,
incorrect timing of attitude mode transitions, and lack of
modeling of some spacecraft activities altogether. Any users of
the predicted CKs are encouraged to compare them against the
reconstructed CKs during the period(s) of interest using the
FRMDIFF tool provided in the SPICE toolkit to assess the
differences.
All three types of files need to be loaded at the same time to
provide the most complete coverage with the predicted CKs loaded
first so that data from them is accessed last (lowest priority),
the low rate CKs with corrected times tags (v2) loaded second
(medium priority), and the high rate CK for the encounter loaded
last (highest priority).
DIF HGA CK Files
----------------
Two kinds of the DIF HGA orientation CK files are included in
this data set. The first kind is based on the measured HGA gimbal
angles provided in telemetry (``V-channels'') while the second
kind is based on the commanded HGA gimbal angles provided in
telemetry (``B-channels''). These files should be loaded together
to provide the most complete coverage with the file based on
measured angles loaded last (to be accessed first.) Even when
loaded together, the combined coverage provided by the files is
full of gaps, which can be alleviated by modifying the
interpolation interval information by using the CKSPANIT program.
Additional information about CK files provided in this data set
is available in the file ``data/ck/ckinfo.txt''.
PCK Files
=========
PCK files provide size, shape and orientation data for ``target''
bodies such as planets, satellites, comets and asteroids. A
description of these data items and reference to their source is
provided inside the PCK file, which is a simple text file that
can be viewed using any word processor, text editor or text
display utility.
This data set contains generic PCK file based on the official
IAU/IAG/COSPAR values accepted in 2000 and PCK file for EPOXI
mission target -- Hartley 2 -- providing constants determined
after the encounter. The PCK file for Hartley 2 contains both
rotation and shape/size data derived by the EPOXI science team
during post encounter data analysis.
Additional information about PCK files provided in this data set
is available in the file ``data/pck/pckinfo.txt''.
FK Files
========
Frames kernel files provide specifications for how one reference
frame is defined relative to another frame. The DI FK provided in
this data set contains a complete set of frame definitions for
the both spacecraft, their structures such as antennas, and all
of their science instruments. Comments in the FK file provide
the frame definitions, a description of the frame relationships,
the source of and accuracy of the mounting alignment information,
etc. The instrument frame definitions provided in the file
incorporate the latest mounting alignment data available at the
end of the mission.
Additional information about FK files provided in this data set
is available in the file ``data/fk/fkinfo.txt''.
IK Files
========
Instrument kernel files provide specifications for the optical
and physical instrument parameters and -- where applicable --
field-of-view size, shape and orientation for the named
instrument. Metadata describing these estimates are provided in
each IK file included in this archive. While a majority of the of
parameters included in the IK files archived in this data set
are based on the nominal instrument data, the files incorporate
the latest version of optical distortion model derived by the DI
optical navigation team.
Additional information about IK files provided in this data set
is available in the file ``data/ik/ikinfo.txt''.
SCLK Files
==========
Spacecraft Clock kernel files provide a tabulation of data needed
to convert time measurements between ephemeris time (ET) and
spacecraft clock time (SCLK). A SPICE SCLK file is made from a
similar file -- SCLK/SCET or SCLKvSCET file -- produced by
another mission entity. Each newly made SCLK file fully replaces
the previous SCLK file.
This data set includes SCLK kernels providing the correlations
for the DIF spacecraft primary (SCU-A) and secondary (SCU-B)
on-board clocks. Two SCLK kernels -- the ``official'' version and
``science'' version -- are available for the DIF primary clock
while only one SCLK kernel -- ``official'' version -- is
available for the DIF secondary clock.
The main difference between the ``official'' version of the
primary clock SCLK kernel and the ``science'' version is that the
``official'' version is based on the latest time correlation that
were used by the project during mission operations while the
``science'' version contain updated correlation that were used to
process science data for archiving in PDS.
The correlation update for the DIF primary clock SCLK kernel
was done to eliminate ``artificial'' data points introduced by
the tool-set that created source SCLKvSCET file and to adjust
clock rates in order to connect actual data points in a
continuous fashion. Such ``artificial'' data points were
eliminated only during two periods -- 2009-01-06 to 2010-10-27
and 2010-11-17 to 2011-03-01 -- because the ``official''
correlation prior to 2009-01-06 and around Hartley 2 encounter
did not need such adjustments.
Unfortunately, the absolute accuracy of both ``official'' and
``science'' correlations for all periods EXCEPT for the period
around Hartley 2 encounter (2010-10-27 to 2010-11-17) is no
better than 0.5 seconds due to poor quality of the source clock
correlations data. For the encounter period the correlation has
much better accuracy, down to .01 seconds for evaluating SCLK ->
UTC around closest approach, thanks to efforts by Steve Wissler
and Amy Walsh of EPOXI Spacecraft Team in correcting and
re-fitting the source correlation data
Note that the clock format defined by both ``official'' and
``science'' SCLK kernels (seconds with fractional seconds given
as a count of 1/256 second ticks) does not match the format of
on-board time tags in mission telemetry (seconds with fractional
seconds given as top 8 or 16 or full 20 bits of a count of
micro-seconds). For details on this discrepancy and the algorithm
to fix it see ``sclk140.txt'' provided in Deep Impact and EPOXI
documentation set (DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V3.0).
While all science images sent to the ground contained SCLK time
in the headers (spacecraft primary, SCU-A, SCLK for DIF),
optical- and auto-navigation image headers contain a different
time. This time was a so called on-board Ephemeris Time (ET) that
optical/auto navigation on-board software used internally to
perform autonomous trajectory and attitude solutions. This
on-board ET was computed from on-board clock by adding a constant
delta to it to make it synchronous with the actual ET to the
extent possible. Since the on-board clock was drifting throughout
the mission, the delta had to be changed many times. The table
below shows the delta, in seconds, that must be subtracted from
the on-board ET to get corresponding SCLK (spacecraft primary,
SCU-A, SCLK for DIF) and the time when a particular delta had
been uplinked and took effect in the on-board software (shown as
UTC):
Applicability Start UTC Delta
----------------------- --------
2007-351T17:35:02.1287 512.325
2007-363T17:25:04.4477 525.293
2008-078T16:12:19.5120 665.717
2008-105T23:24:20.9104 732.653
2008-137T03:57:41.1835 821.037
2008-142T10:13:15.6053 857.544
2008-151T19:54:10.8499 875.314
2008-165T17:57:03.9399 897.396
2008-184T11:28:57.2223 806.231
2008-212T17:28:54.5972 839.715
2008-240T04:28:57.5992 864.011
2008-268T02:58:58.9329 890.432
2008-319T23:59:00.3904 943.327
2008-349T23:59:08.6112 969.590
2009-005T21:59:15.8754 989.965
2009-046T00:14:05.8648 1056.877
2009-074T00:14:07.1411 1095.119
2009-083T22:13:28.6435 1121.229
2009-105T00:13:59.7459 1146.244
2009-135T00:13:59.6404 1187.763
2009-147T08:03:22.1973 1213.564
2009-153T06:34:59.1203 1223.314
2009-166T00:13:58.7132 1230.997
2009-182T11:59:00.0174 1252.004
2009-196T00:13:59.7825 1270.692
2009-227T00:14:00.0946 1311.956
2009-258T00:14:00.1187 1354.722
2009-268T15:30:09.3380 1371.659
2009-275T18:51:55.1384 1382.729
2009-288T00:14:01.1509 1396.132
2009-316T17:19:33.1640 1449.351
2009-319T00:14:05.5821 1435.769
2009-337T11:32:02.5265 1471.203
2009-344T19:02:28.8364 1481.542
2009-349T00:14:02.2259 1483.738
2009-351T15:28:11.1679 1490.387
2009-358T21:14:01.2625 1499.945
2010-001T02:14:01.7135 1510.532
2010-015T00:14:02.6994 1530.969
2010-046T00:13:58.9541 1581.193
2010-071T17:35:08.3947 1623.057
2010-074T00:13:58.9368 1622.033
2010-105T00:13:58.3922 1666.541
2010-135T00:13:59.2603 1708.935
2010-166T00:13:59.4915 1750.700
2010-183T20:58:59.3697 1775.852
2010-190T20:39:27.8465 1789.371
2010-196T00:13:59.4687 1792.938
2010-227T00:14:02.0552 1835.460
2010-246T18:50:23.1339 1866.382
2010-258T00:13:53.1890 1878.792
2010-272T20:47:43.1103 1906.565
2010-288T10:54:55.5247 1927.342
2010-289T08:49:17.9432 1924.467
2010-300T19:05:35.6008 1939.803
2010-307T19:16:24.8070 1949.819
2010-319T00:13:56.3420 1973.249
2010-349T00:14:00.1550 1999.840
2011-015T00:13:52.2455 2037.864
2011-046T00:13:44.2797 2076.248
2011-074T00:13:54.5237 2087.404
2011-105T00:14:01.1949 2105.201
2011-135T00:14:10.3797 2127.709
2011-166T00:13:42.7977 2176.681
Additional information about SCLK files provided in this data set
is available in the file ``data/sclk/sclkinfo.txt''.
LSK Files
=========
Leapseconds kernel files provide a tabulation of ``leapseconds''
and some other terms used in converting time measurements between
ephemeris time (ET) and Universal Time (UTC). ``Spacecraft Event
Time'' (SCET) is the commonly used name for UTC events measured
at the spacecraft.
Metadata describing how the LSK data are obtained or computed is
contained inside the LSK text file. The time conversion provided
by SPICE LSK files is accurate to approximately 0.000030 seconds.
Additional information about LSK files provided in this data set
is available in the file ``data/lsk/lskinfo.txt''.
EK Files
========
No Events kernel (EK) files are included in this archive.
Kernel Files Not Included In This Data Set
===========================================
A number of kernel files used to process image data archived in
PDS and mentioned in the image labels were not included in this
data set because they either were superseded by the files
provided in this archive, or were known to contain incorrect or
out-of-date information, or could be easily re-created from the
data provided in this archive using utility program(s) available
from NAIF. Among such files are:
- regular OPS SPK files:
spk_od218_full.bsp
spk_od219_full.bsp
spk_od221_full.bsp
spk_od222_full.bsp
spk_mars_drm232.bsp
were superseded by the SPK files ``dif_epoch_nav_v1.bsp'' and
``dif_dixi_nav_v1.bsp'' included in this data set.
- Jovian system SPK file
jup164_20year.bsp
is not included because no observations of Jupiter or its
satellites were made during the mission.
- SPK file containing an earlier version of Hartley 2 ephemeris
hartley_2_2005_2020.bsp
was superseded by the SPK file ``dif_dixi_nav_v1.bsp''
included in this data set.
- predicted CK files:
dif_epoxi_predict_v20081206.bc
dif_pred_earthobs4_1.bc
were superseded by the predicted CK files
``dif_sc_071103_090127_p.bc'' and
``dif_sc_071103_090127_p_to.bc'' included in this data set.
- star position SPK and PCK files:
starnames_2008253_074135.tpc
starnames_2009338_165219.tpc
stars_2008253_074135.bsp
stars_2010078_071625.bsp
were used in the Science Data Center image processing
pipeline to provide access via SPICE interfaces to positions
of the mission target stars. While these kernels successfully
served their purpose, they were not fully compliant with
official NAIF practices. For this reason they were not included
into this data set. On the other hand, recognizing the
importance of this data, it was decided to include the star
positions stored in these files and the NAIF names and ID codes
assigned to these stars into this data set's documentation
for the reference. The table below provides these positions.
Each line contains J2000 RA (hours, minutes, seconds), J2000
DEC (degrees, arcminutes, arcseconds) and name.
10,24,23.71,-74,1,53.8,PRETEND I CAR HD 90589
0,25,45.07,-77,15,15.3,BET HYI HD 2151
10,2,42,-60,7,0,NGC3114
6,23,57.11,-52,41,44.4,CANOPUS HD 45348
1,37,42.85,-57,14,12.3,ACHERNAR HD 10144
21,7,6,42,14,0,NGC7027
19,41,48.95,50,31,30.2,16 CYG A HD 186408
7,33,27.32,-50,35,3.3,HD 60753
18,36,56.34,38,47,1.3,VEGA HD 172167
0,24,5.22,-72,4,57.9,47 TUC NGC104
6,45,08.92,-16,42,58.0,SIRIUS HD 48915
9,11,16.72,-62,19,1.1,I CAR HD 79447
11,5,33,-58,43,48,NGC3532
18,51,6,-6,16,0,M11
10,36,16.079,-58,16,38.20,HD 92044
8,40,36,-53,2,0,OMI VEL CLUSTER IC2391
11,42,11.5968,26,42,16.812,GJ436
22,57,46.8,38,40,27.84,HAT-P-1
16,20,36,41,2,52.8,HAT-P-2
13,44,22.56,48,1,44.4,HAT-P-3
15,19,57.92712,36,13,46.7904,HAT-P-4
19,4,9.84,36,37,58.8,TRES-1
19,7,14.0304,49,18,59.2992,TRES-2
17,52,7.032,37,32,46.1004,TRES-3
17,53,12.96,37,12,43.2,TRES-4
0,20,40.08,31,59,24,WASP-1
20,30,54.24,6,25,48,WASP-2
16,2,11.76,28,10,12,XO-1
7,48,6.4704,50,13,32.988,XO-2
4,21,53.5104,57,49,0.5988,XO-3
9,22,39.7267,50,36,13.927,HD 80607
21,50,54.7530,25,19,07.495,TYC 2206-1748-1
18,34,31.6249,35,39,41.546,WASP-3
19,28,59.3616,47,58,10.264,HAT-P-7
17,48,1.95,-35,00,19.48,MOA-2009-BLG-266
The following NAIF name/ID mappings were assigned to these
stars:
NAIF_BODY_NAME += ( 'PRETEND I CAR HD 90589' )
NAIF_BODY_CODE += ( 9999000 )
NAIF_BODY_NAME += ( 'BET HYI HD 2151' )
NAIF_BODY_CODE += ( 9999001 )
NAIF_BODY_NAME += ( 'NGC3114' )
NAIF_BODY_CODE += ( 9999002 )
NAIF_BODY_NAME += ( 'CANOPUS HD 45348' )
NAIF_BODY_CODE += ( 9999003 )
NAIF_BODY_NAME += ( 'ACHERNAR HD 10144' )
NAIF_BODY_CODE += ( 9999004 )
NAIF_BODY_NAME += ( 'NGC7027' )
NAIF_BODY_CODE += ( 9999005 )
NAIF_BODY_NAME += ( '16 CYG A HD 186408' )
NAIF_BODY_CODE += ( 9999006 )
NAIF_BODY_NAME += ( 'HD 60753' )
NAIF_BODY_CODE += ( 9999007 )
NAIF_BODY_NAME += ( 'VEGA HD 172167' )
NAIF_BODY_CODE += ( 9999008 )
NAIF_BODY_NAME += ( '47 TUC NGC104' )
NAIF_BODY_CODE += ( 9999009 )
NAIF_BODY_NAME += ( 'SIRIUS HD 48915' )
NAIF_BODY_CODE += ( 9999010 )
NAIF_BODY_NAME += ( 'I CAR HD 79447' )
NAIF_BODY_CODE += ( 9999011 )
NAIF_BODY_NAME += ( 'NGC3532' )
NAIF_BODY_CODE += ( 9999012 )
NAIF_BODY_NAME += ( 'M11' )
NAIF_BODY_CODE += ( 9999013 )
NAIF_BODY_NAME += ( 'HD 92044' )
NAIF_BODY_CODE += ( 9999014 )
NAIF_BODY_NAME += ( 'OMI VEL CLUSTER IC2391' )
NAIF_BODY_CODE += ( 9999015 )
NAIF_BODY_NAME += ( 'GJ436' )
NAIF_BODY_CODE += ( 9999016 )
NAIF_BODY_NAME += ( 'HAT-P-1' )
NAIF_BODY_CODE += ( 9999017 )
NAIF_BODY_NAME += ( 'HAT-P-2' )
NAIF_BODY_CODE += ( 9999018 )
NAIF_BODY_NAME += ( 'HAT-P-3' )
NAIF_BODY_CODE += ( 9999019 )
NAIF_BODY_NAME += ( 'HAT-P-4' )
NAIF_BODY_CODE += ( 9999020 )
NAIF_BODY_NAME += ( 'TRES-1' )
NAIF_BODY_CODE += ( 9999021 )
NAIF_BODY_NAME += ( 'TRES-2' )
NAIF_BODY_CODE += ( 9999022 )
NAIF_BODY_NAME += ( 'TRES-3' )
NAIF_BODY_CODE += ( 9999023 )
NAIF_BODY_NAME += ( 'TRES-4' )
NAIF_BODY_CODE += ( 9999024 )
NAIF_BODY_NAME += ( 'WASP-1' )
NAIF_BODY_CODE += ( 9999025 )
NAIF_BODY_NAME += ( 'WASP-2' )
NAIF_BODY_CODE += ( 9999026 )
NAIF_BODY_NAME += ( 'XO-1' )
NAIF_BODY_CODE += ( 9999027 )
NAIF_BODY_NAME += ( 'XO-2' )
NAIF_BODY_CODE += ( 9999028 )
NAIF_BODY_NAME += ( 'XO-3' )
NAIF_BODY_CODE += ( 9999029 )
NAIF_BODY_NAME += ( 'HD 80607' )
NAIF_BODY_CODE += ( 9999030 )
NAIF_BODY_NAME += ( 'TYC 2206-1748-1' )
NAIF_BODY_CODE += ( 9999031 )
NAIF_BODY_NAME += ( 'WASP-3' )
NAIF_BODY_CODE += ( 9999032 )
NAIF_BODY_NAME += ( 'HAT-P-7' )
NAIF_BODY_CODE += ( 9999033 )
NAIF_BODY_NAME += ( 'MOA-2009-BLG-266' )
NAIF_BODY_CODE += ( 9999034 )
- text kernel providing times of encounter for the SDC pipeline
impacttoi_0007h2.tpc
This text kernel had the following contents:
Deep Impact/EPOXI at Hartley 2
Local times of DI TCA Hartley 2 as a leapsecond-corrected UTC
EOB_TOI: local time that photons from Hartley 2 reach the
Earth
DIF_TOI: local time that photons from Hartley 2 reach the
Deep Impact Flyby S/C
DII_TOI: local time that the Deep Impact Impactor S/C hits
Tempel 1
\begindata
EOB_TOI = ( '2010-308T14:01:05.242' )
DIF_TOI = ( '2010-308T13:59:47.310' )
DII_TOI = ( '2005-185T05:44:34.200' )
\begintext
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