PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "2004-09-01 S.McLaughlin Created 2005-02-03 S.McLaughlin Resolved liens from Oct 2004 thermal-vac review 2005-11-03 S.McLaughlin Updated time of impact 2006-05-22 DI:McLaughlin Resolved liens from Apr 2006 peer review 2006-10-05 DI:S.McLaughlin Revised impact time based on Jan 2006 analysis 2006-12-04 DI:S.McLaughlin Resolved liens from Nov 2006 peer review 2007-05-07 DI:McLaughlin Added RECORD_TYPE 2013-03-08 EPOXI:McLaughlin Resolved liens from Mar 2013 peer review: Replaced reference to the old DI doc set with the newer DI/EPOXI doc set DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0; Added expected completion date of 2013 for s/c clock correlation corrections. " OBJECT = INSTRUMENT_HOST INSTRUMENT_HOST_ID = "DII" OBJECT = INSTRUMENT_HOST_INFORMATION INSTRUMENT_HOST_NAME = "DEEP IMPACT IMPACTOR SPACECRAFT" INSTRUMENT_HOST_TYPE = "SPACECRAFT" INSTRUMENT_HOST_DESC = " Instrument Host Overview ======================== The Deep Impact Impactor vehicle was a complete spacecraft with a CCD-based camera and telescope called the Impactor Targeting Sensor (ITS) for both scientific imaging and auto-navigation; a complete attitude control subsystem using hemispherical resonator gyros; a star tracker; and a complete, hydrazine-based propulsion system. Electrical power was supplied by an internal battery since the expected operating lifetime was very short (24 hours). The impactor was mechanically and electrically attached to the flyby spacecraft and both launched together. They flew together until one day before the impact event. On July 3, 2005, the impactor was released and gently pushed away from the flyby craft at a distance of about 864,000 km from comet Tempel 1. The auto-navigation system took control and maneuvered the impactor to ensure an impact on an illuminated portion of the cometary nucleus. On July 4, 2005, the impactor hit the nucleus at a relative speed of 10.3 km/s. The 360-kg Impactor released 19 gigajoules of kinetic energy to excavate a crater on the surface of the nucleus. The best estimate of the time of the impact was 05:44:34.200 UT (at the impactor spacecraft, Earth-received time 05:52:00 UT). About half of the mass of the impactor was copper, a noble metal, which minimized chemical reactions that could lead to species that might contaminate the spectrum with bright lines. About half this copper was in a spherical cap at the 'front' of the impactor. This cap was made of chambered discs that were internally hollowed, much like a lightweight telescope mirror, to reduce the density by a factor two or so from the bulk density of copper. Data taken by the ITS were white-light images and were used by the on-board software for auto-navigation and transmitted to the flyby craft over an S-band link at 64 kilobits per seconds (kbps). Attitude control and minor trajectory corrections were performed using a small hydrazine propulsion subsystem. Some of the last ITS frames taken before impact were blurred due to dust hits. Analysis of ITS data show a slight degradation of the amount of light received by the CCD, apparently caused by the sandblasting of the optics by small particles. The last ITS image was taken a few seconds before impact. The system requirement specifications for the impactor were: Image Data Volume : Approximately 17 megabytes Pointing Accuracy : 2 milliradian 3-sigma Pointing Knowledge : 150 microradian, 3 axes, 3-sigma Targeting Accuracy : 300 m 3-sigma with respect to the center of brightness of the nucleus Telecom Band : S-Band Data Rate to Flyby : 64 kbps Command Rate : 16 kbps Energy Storage : 2.8 kilowatt-hr for 24 hr mission Propulsion : 25 m/s delta-velocity Flight Performance ================== Clock Correlation ----------------- During the Deep Impact mission, clock correlation packets indicated large drifts in the clocks on-board the flyby and impactor spacecraft due to thermal changes induced by trajectory correction maneuvers near encounter. The drifts resulted in a difference of several seconds between impact times based on data from the flyby and impactor spacecraft and ground-based data. During January 2006 the project used available spacecraft data and advice from engineering personnel to correlate the flyby clock and Dynamical Barycentric Time (TDB) to within one or two seconds and the flyby and impactor clocks to one-half of a second. The project moved the estimated impact time forward by two seconds, from 05:44:36 UTC on 4 July 2005 as reported by A'Hearn, et al. (2005) [AHEARNETAL2005A] to 05:44:34.265 UTC at the flyby spacecraft and 05:44:34.200 UTC at the impactor spacecraft. The project also generated self-consistent SPICE CK kernels based on this analysis. The improved kernels were included in the Deep Impact SPICE data set archived in the PDS. The timing discrepancy is discussed in the Deep Impact Spacecraft Clock Correlation report included in the Deep Impact and EPOXI documentation data set, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0. As of early 2009, the best spacecraft clock correlation data still had known inaccuracies of up to 0.5 seconds. The mission operations team has since figured out how to correct raw clock correlation data for the flyby spacecraft to allow timing fits that are accurate to at least the sub-second level. The project plans to generate, most likely in 2013, a complete corrected set of correlations since launch. This will ultimately result in a future version of a spacecraft clock SPICE kernel that will retroactively change correlation for **all** Deep Impact and EPOXI data. When this kernel is available, it will be added to the SPICE data sets for the two missions and posted on the NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/. Recommended Reading =================== For a detailed descriptions of the impactor spacecraft and auto-navigation, see A'Hearn, et al. (2005) [AHEARNETAL2005B], Blume (2005) [BLUME2005], Hampton, et al. (2005) [HAMPTONETAL2005], and Mastrodemos, et al. (2005) [MASTRODEMOSETAL2005]. For information about the anticipated flight data and the cratering experiment, see Klaasen, et al. (2005) [KLAASENETAL2005], Richardson, et al. (2005) [RICHARDSONETAL2005], and Schultz and Ernst (2005) [SCHULTZ&ERNST2005]. Initial results from the mission were presented by A'Hearn, et al. (2005) [AHEARNETAL2005A]. This instrument host description was provided by Dr. Michael A'Hearn, the principal investigator for the Deep Impact mission. " END_OBJECT = INSTRUMENT_HOST_INFORMATION OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "AHEARNETAL2005A" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "AHEARNETAL2005B" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "BLUME2005" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "HAMPTONETAL2005" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "KLAASENETAL2005" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "MASTRODEMOSETAL2005" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "RICHARDSONETAL2005" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "SCHULTZ&ERNST2005" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO END_OBJECT = INSTRUMENT_HOST END