PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " 2004-09-01 S.McLaughlin Created 2005-02-03 S.McLaughlin Resolved liens " 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 = " This description was provided by Dr. Michael A'Hearn, the principal investigator for the Deep Impact mission. The Deep Impact Flyby vehicle is a 3-axis stabilized spacecraft that carries three scientific instruments and is joined to the Impactor spacecraft from launch until one day before impact. The Flyby is designed to deliver the Impactor into the path comet Tempel 1, then record the impact event scheduled for 06:08 +/- 00:25 UTC on July 4, 2005. The encounter will occur at 1.5 AU from the Sun and 0.9 AU from the Earth. At closest approach, minutes after impact, the Flyby is only 500 km from the nucleus. The instruments, an integrated set of four hemispherical resonator gyros, and two star-trackers are all mounted on a rigid platform that is attached to the spacecraft in the X-Z plane, that is parallel to the solar panel. The instrument pointing direction is in the X-Z plane, at approximately 45 degrees to the -X and +Z axes, where +Y is perpendicular to the solar panels on the sunward side. Because the instruments are body-mounted, pointing is accomplished by slewing the spacecraft with reaction wheels and hydrazine thrusters. The spacecraft is equipped with a once-deployed solar panel and and one NiH2 battery for its power subsystem. The 7.2-meter^2 solar panel has a maximum off-sun pointing constraint of 30 degrees to avoid problems caused by overheating of the subsystems. The Flyby has redundant RAD750 computers with 309 megabytes (MB) of memory for scientific data. All critical data are stored redundantly on both computers and a subset is transmitted in near-real time to Earth. Communications are achieved via either a gimbaled high-gain antenna (HGA) or a fixed low-gain antenna (LGA). During the mission, Deep Space Network (DSN) support will be provided primarily with 34-m antennas with 70-m support being used during the comet encounter phase. These antennas provide the capability for transmitting 20 to 200 kilobits per second (kbps). At the maximum downlink rate, it takes 4.5 hours to empty the 309-MB memory. Pointing range of the HGA is limited to the +x hemisphere of the Flyby. The Flyby uses X-band to communicate with Earth and S-band for bi-directional communication with the impactor spacecraft after separation. Attitude control and propulsive maneuvers are performed using a blowdown hydrazine propulsion subsystem designed to provide 190 m/s of delta-velocity. The normal spacecraft attitude during the mission points the +y-axis of the spacecraft to within 30 degrees of the sun. Pointing outside this range is limited to 15 minutes every 4 hours to avoid overheating of subsystems. This constraint limits calibrations during cruise and observations of the comet during closest approach and prior to 10 days before impact. Debris shields are placed on the spacecraft to protect it from high velocity dust impacts during the encounter with Tempel 1. The shielding is 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). System Requirement Specifications for the Flyby are: 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 For detailed descriptions of the flyby spacecraft, including the anticipated flight data, see A'Hearn, et al. (2005) [AHEARNETAL2005], Blume (2005) [BLUME2005], Hampton, et al. (2005) [HAMPTONETAL2005], and Klaasen, et al. (2005) [KLAASENETAL2005]. " END_OBJECT = INSTRUMENT_HOST_INFORMATION OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "AHEARNETAL2005" 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