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:S.McLaughlin Resolved liens from Apr 2006 peer review 2006-10-05 DI:S.McLaughlin Revised impact time based on Jan 2006 analysis " OBJECT = INSTRUMENT_HOST INSTRUMENT_HOST_ID = "DIF" OBJECT = INSTRUMENT_HOST_INFORMATION INSTRUMENT_HOST_NAME = "DEEP IMPACT FLYBY SPACECRAFT" INSTRUMENT_HOST_TYPE = "SPACECRAFT" INSTRUMENT_HOST_DESC = " Instrument Host Overview ======================== The Deep Impact Flyby vehicle was a 3-axis stabilized spacecraft that carried three scientific instruments and was joined to the impactor spacecraft from launch until one day before impact. On July 3, 2005, the flyby craft successfully delivered the impactor into the path of comet 9P/Tempel 1. About 24 hours later, the spacecraft recorded the resulting 19 gigajoule impact beginning about 05:44:34 UT on July 4, 2005 (Earth-received time 05:52:00 UT). The encounter occurred at distances of 1.5 AU from the Sun and 0.9 AU from the Earth. About 14 minutes after impact, the flyby craft was at closest approach of 500 km from the nucleus. The instruments, an integrated set of four hemispherical resonator gyros, and two star-trackers were all mounted on a rigid platform attached to the spacecraft in the X-Z plane, parallel to the solar panel. The instrument pointing direction was in the X-Z plane, at approximately 45 degrees to the -X and +Z axes, where +Y was perpendicular to the solar panels on the sunward side. Because the instruments was body-mounted, pointing was accomplished by slewing the spacecraft with reaction wheels and hydrazine thrusters. The spacecraft was equipped with a once-deployed solar panel and and one NiH2 battery for its power subsystem. The 7.2-meter^2 solar panel had a maximum off-sun pointing constraint of 30 degrees to avoid problems caused by overheating of the subsystems. The flyby craft had redundant RAD750 computers with 309 megabytes (MB) of memory for scientific data. All critical data were stored redundantly on both computers and a subset was transmitted in near- real time to Earth. Communications were achieved via either a gimballed high-gain antenna (HGA) or a fixed low-gain antenna (LGA). During the mission, Deep Space Network (DSN) support was provided primarily with 34-m antennas with 70-m support used during the comet encounter phase. The HGA antenna had the capability to transmit 20 to 200 kilobits per second (kbps). At the maximum downlink rate, it took 4.5 hours to empty the 309-MB memory. Pointing range of the HGA was limited to the +x hemisphere of the flyby craft. The flyby craft used X-band to communicate with Earth and S-band for bi-directional communication with the impactor spacecraft after separation. Attitude control and propulsive maneuvers were performed using a blowdown hydrazine propulsion subsystem designed to provide 190 m/s of delta-velocity. The normal spacecraft attitude during the mission pointed the +y- axis of the spacecraft to within 30 degrees of the sun. Pointing outside this range was limited to 15 minutes every 4 hours to avoid overheating of subsystems. This constraint limited calibrations during cruise and observations of the comet during closest approach and prior to 10 days before impact. Debris shields were placed on the spacecraft to protect it from high velocity dust impacts during the encounter with Tempel 1. The shielding was designed for a velocity vector of the spacecraft in the +X direction (dust relative motion toward -X). Science objectives are met using three instrument subsystems: the High Resolution Imager IR Spectrometer (HRII), the High Resolution Imager Visual CCD (HRIV), and the Medium Resolution Imager Visual CCD (MRI). The system requirement specifications for the flyby spacecraft were: Payload Power : 92 watts, average during engagement Payload Mass : 370-kg impactor, 90-kg instruments Payload Total Data Volume : 309 MB Payload Data Downlinked : 309 MB Pointing Accuracy : 200 microradian Pointing Knowledge : 65 microradian, 3 axes 3-sigma Telecom Band to Earth : X-band Uplink/Downlink Rates : 125 bps/200 kbps Telecom Band to Impactor : S-band Data Rate to Impactor : 64 kbps Propulsion : 190 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 for the true impact time. The timing discrepancy is discussed in the 'Deep Impact Spacecraft Clock Correlation' report included on the Deep Impact documentation volume, DIDOC_0001. To help account for the discrepancy, the project generated self-consistent SPICE CK kernels and adjusted the estimated impact time from 05:44:36 UTC on 4 July 2005, as reported by A'Hearn, et al. (2005) [AHEARNETAL2005A], to 05:44:34 UTC. The improved kernels were included in the Deep Impact SPICE data set archived in the PDS. Recommended Reading =================== For a detailed descriptions of the flyby 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]. 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 END_OBJECT = INSTRUMENT_HOST END