PDS_VERSION_ID = PDS3 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 " 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 estimated time of impact was 05:44:36 UT (Earth-received time 05:52:02 UT), as reported by A'Hearn, et al. (2005) [AHEARNETAL2005A]. 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 chamfered 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 these 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 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. There is an uncertainty window of a few seconds in the true impact time. The timing discrepancy was discussed in the 'Deep Impact Spacecraft Clock Correlation' report included on the Deep Impact documentation volume, DIDOC_1000. To help account for the discrepancy, the project generated self-consistent SPICE CK kernels. These kernels are included in the Deep Impact SPICE data set. Recommended Reading =================== For a detailed descriptions of the impactor spacecraft and auto-navigation, see A'Hearn, et al. (2005) [AHEARNETAL2005B], Hampton, et al. (2005) [HAMPTONETAL2005], and Mastrodemos, et al. (2005) [MASTRODEMOSETAL2005]. For information about the anticipated flight data and the cratering experiment, Klaasen, et al. (2005) [KLAASENETAL2005], Richardson, et al. (2005) [RICHARDSONETAL2005], and Schultz and Ernst (2005) [SCHULTZ&ERNST2005]. The estimated time of impact noted above was reported in Science 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 = "AHEARNETAL2005B" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "AHEARNETAL2005A" 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