Instrument Host Information |
|
IDENTIFIER | urn:nasa:pds:context:instrument_host:spacecraft.dif::1.2 |
NAME |
DEEP IMPACT FLYBY SPACECRAFT |
TYPE |
Spacecraft |
DESCRIPTION |
Instrument Host Overview ======================== The Deep Impact flyby spacecraft was used for the NASA Deep Impact mission in 2005 and for the extended mission EPOXI from October 2007 through end of mission on 20 September 2013. The flyby vehicle carries three scientific instruments: a high-resolution infrared imaging spectrometer (HRII), a high-resolution multi-spectral visible CCD (HRIV), and a medium-resolution multi-spectral visible CCD (MRI). It was launched on 12 January 2005 with an attached impactor spacecraft. On 3 July 2005, the flyby craft released the impactor, successfully delivering it into the path of comet 9P/Tempel 1. About 24 hours later, the flyby spacecraft recorded the resulting 19-gigajoule impact beginning about 05:44:34.265 UT on July 4, 2005 (at the flyby spacecraft, 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 vehicle was at closest approach of 500 km from the nucleus. Because the flyby spacecraft and its instruments survived the encounter with Tempel 1, NASA executed a trajectory correction maneuver on 20 July 2005 which put the spacecraft on a new orbit to fly past Earth in late December 2007 and solicited proposals for an extended mission. The spacecraft was put into sleep mode on 9 August 2005. It was woken up on 25 September 2007 in preparation for the selected EPOXI mission. From mid-January through August 2008, the HRIV instrument successfully observed transits of eight known extrasolar planets for the EPOXI mission. Also during this period, the HRII and HRIV instruments continuously observed the Earth at equatorial latitudes for 24 hours at three different times. In 2009 the same instruments observed Earth again but at northern and southern latitudes. Also Mars was observed for 24 hours and the exoplanet microlensing event, MOA-2009-BLG-266 was imaged over several days. From mid-October to mid-November 2008, the first deep space communications network, also known as the Interplanetary Internet, was successfully tested using the Deep Impact flyby spacecraft. Using software called Delay-Tolerant Networking (DTN) dozens of images were transmitted to and from the flyby spacecraft located more than 32 million kilometers from Earth. In late 2010 the flyby spacecraft wrapped up its EPOXI mission with an encounter of comet 103P/Hartley 2. After observing the comet for 60 days with the same suite of instruments used at 9P/Tempel 1, the flyby spacecraft had its closest approach of 103P/Hartley 2 at 13:59:47.31 UTC on 4 November 2010 at a distance of 694 km and a flyby speed of 12.3 km/s. The spacecraft flew under the comet on a slightly northward trajectory in an ecliptic reference frame, then rotated to keep the body-mounted instruments pointed at the comet for departure imaging that continued for 21 days. On 14 August 2013, the flyby spacecraft failed to phone home. The operations team eventually traced the issue to a problem with a time computation that put the spacecraft computer into an infinite reboot loop, thereby losing both attitude control and communications. After trying unsuccessfully for more than a month to regain contact, NASA announced the end of operations for the Deep Impact flyby spacecraft on 20 September 2013. Instrument Host Details ======================= The flyby vehicle is a 3-axis stabilized spacecraft that carries three scientific instruments as noted above: HRII, HRIV, and MRI. The instruments, an integrated set of four hemispherical resonator gyros, and two star-trackers are mounted on a rigid platform attached to the spacecraft in the X-Z plane, 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 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 spacecraft 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 can be transmitted in near-real time to Earth. Communications are achieved via either a gimballed high-gain antenna (HGA) or a fixed low-gain antenna (LGA). During the missions, Deep Space Network (DSN) support is provided primarily with 34-m antennas with 70-m support used during the comet encounter phases. The HGA antenna has the capability to transmit 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 vehicle. The flyby craft uses X-band to communicate with Earth. For Deep Impact, it used the 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 missions 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 comets during closest approach and prior to 10 days before encounter. 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 for the Deep Impact mission were met using three instrument subsystems: HRII, HRIV, and MRI. The EPOXI mission uses these same three instruments to achieve its scientific objectives. Additionally for the Deep Impact mission, data from the DSN radio subsystem were analyzed for deflections of the spacecraft caused by the mass of the comet and for slowdowns as a result of gas and dust drag (as expected, no effects were noted in the tracking data). For more information about the DSN and its use in radio science see the report by Asmar and Renzetti (1993) [ASMAR&RENZETTI1993]. 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 ----------------- 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/. Safe Mode and Telecom Anomaly ----------------------------- During the EPOCh phase of the EPOXI mission, the flyby spacecraft experienced a safe mode and a telecom anomaly that disrupted and delayed data acquisition for several weeks, which was very unusual. On 17 February 2008, the flyby spacecraft autonomously entered safe mode as it was turning to an optimal attitude to transmit EPOCh data to Earth. Mission controllers believed the safe mode was triggered when one of the reaction wheels, which helps maintain spacecraft attitude, experienced slightly higher temperatures than the on-board fault protection software would allow. After slowly downlinking some engineering data to Earth, controllers determined the spacecraft could be brought out of safe mode without triggering new problems. On 29 February the spacecraft successfully exited safe mode and began downlinking the EPOCh images taken before safe mode was entered. On 6 March 2008, the flyby spacecraft resumed observations of exoplanet transits. After the March 28th downlink of 5000 photometric HRIV frames of transiting planet system XO-2, a telecommunication anomaly occurred. This was the largest volume of data in a single downlink for EPOXI to date. Following this downlink, EPOCh observations were paused to investigate the cause of an 8-dB (33%) loss of downlink signal and some slightly elevated temperatures on the spacecraft as it passed through perihelion. As the spacecraft cooled over three weeks (a combination of moving further from the sun and all instruments being turned off), telemetry strength returned, and the project restarted EPOCh by first downlinking the images of XO-2 that had been stored on board the spacecraft since the end of March. Telecommunications functioned as expected and observations of exoplanet transit resumed. Pointing Stability ------------------ Rieber and Sharrow (2009) [RIEBER&SHARROW2009] discuss how the flight system was re-adapted to improve pointing stability of the flyby spacecraft to prevent EPOCh exoplanet targets from wandering outside the HRIV frame. 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 for the Deep Impact mission, see Klaasen, et al. (2005) [KLAASENETAL2005], Richardson, et al. (2005) [RICHARDSONETAL2005], and Schultz and Ernst (2005) [SCHULTZ&ERNST2005]. The submitted versions of these publications are included in the Deep Impact and EPOXI documentation data set, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0. Initial results from Deep Impact are presented by A'Hearn, et al. (2005) [AHEARNETAL2005A]. Rieber and Sharrow, (2009) [RIEBER&SHARROW2009] describe how the flight system and mission operations were re-adapted such that exoplanet transit imaging for EPOCh posed minimal risk to the Hartley 2 encounter for DIXI. The pointing stability of the flyby spacecraft is also discussed in this paper. This instrument host description was originally provided by Dr. Michael A'Hearn for the Deep Impact mission and will be updated as the EPOXI mission progresses. |
NAIF INSTRUMENT IDENTIFIER |
DIF |
SERIAL NUMBER | |
REFERENCES |
A'Hearn, M.F., M.J.S. Belton, W.A. Delamere, J. Kissel, K.P. Klaasen, L.A.
McFadden, K.J. Meech, H.J. Melosh, P.H. Schultz, J.M. Sunshine, P.C. Thomas, J.
Veverka, D.K. Yeomans, M.W. Baca, I. Busko, C.J. Crockett, S.M. Collins, M.
Desnoyer, C.A. Eberhardy, C.M. Ernst, T.L. Farnham, L. Feaga, O. Groussin, D.
Hampton, S.I. Ipatov, J.-Y. Li, D. Lindler, C.M. Lisse, N. Mastrodemos, W.M.
Owen, J.E. Richardson, D.D. Wellnitz, and R.L. White, Deep Impact: Excavating
Comet Tempel 1, Science, 310, 258-264, 2005, doi:10.1126/science.1118923. A'Hearn, M.F., M.J.S. Belton, A. Delamere, and W.H. Blume, Deep Impact: A Large-Scale Active Experiment on a Cometary Nucleus, Space Science Reviews, 117, 1-21, 2005, doi:10.1007/s11214-005-3387-3. Asmar, S. W., N. A. Renzetti, The Deep Space Network as an instrument for radio science research, NASA Technical Reports Server, 1993STIN...9521456A, 1993. Blume, W.H., Deep Impact Mission Design, Space Science Reviews, 117, 23-42, 2005, doi:10.1007/s11214-005-3386-4. Hampton, D.L., J.W. Baer, M.A. Huisjen, C.C. Varner, A. Delamere, D.D. Wellnitz, M.F. A'Hearn, and K.P. Klaasen, An Overview of the Instrument Suite for the Deep Impact Mission, Space Science Reviews, 117, 43-93, 2005, doi:10.1007/s11214-005-3390-8. Klaasen, K.P., B. Carcich, G. Carcich, E.J. Grayzeck, and S. McLaughlin, Deep Impact: The Anticipated Flight Data, Space Science Reviews, 117, 335-372, 2005, doi:10.1007/s11214-005-3385-5. Mastrodemos, N., D.G. Kubitschek, and S.P. Synnott, Autonomous Navigation for the Deep Impact Mission Encounter with with Comet Tempel 1. Space Science Reviews, 117, 95-121, 2005, doi:10.1007/s11214-005-3394-4. Richardson, J.E., H.J. Melosh, N.A. Artemeiva, and E. Pierazzo, Impact Cratering Theory and Modeling for the Deep Impact Mission: From Mission Planning to Data Analysis, Space Science Reviews, 117, 241-267, 2005, doi:10.1007/s11214-005-3393-5. Rieber, R.R., and R.F. Sharrow, The Contingency of Success: Operations for Deep Impact's Planet Hunt, Aerospace Conference, 2009 IEEE, pages 1-9, 7-14 March 2009, doi:10.1109/AERO.2009.4839704. Schultz, P.H., C.M. Ernst, and J.L.B. Anderson, Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision, Space Science Reviews, 117, 207-239, 2005, doi:10.1007/s11214-005-3383-7. |