This description was written by B. Carcich with support from the Stardust-NExT operations and science teams.   Data Set Overview :  This data set contains Level 3 (RDR) pre- and post-encounter and encounter images taken by the Stardust Navigation Camera during the encounter with comet 9P/Tempel 1 (1867 G1), plus calibration images taken throughout the Stardust-NExT mission.  Every image provided in this data set was taken as a part of a particular imaging sequence, each of which is described in the Data Collection Periods section below.   Data Collection Periods :  For the complete list of images and their parameters, refer to the data set's index table, INDEX/INDEX.TAB. For additional notes on individual images also consult with the document ``Log of Stardust-NExT NAVCAM Flight Images', DOCUMENT/NEXTIMAGELOG.LBL, provided with this data set.  N.B. The NAVCAM data collection periods listed here have gaps between the stop time of one period and the start of the next; this is intentional and consistent with the NAVCAM data set in that no NAVCAM image data were taken between these periods.  N.B. The NAVCAM data collection periods listed here overlap, but are defined differently than, the mission phases defined in the mission catalog (NEXT.CAT).  N.B. Each data collection period listed here corresponds to one or more two-letter codes in the NAVCAM image file names and PRODUCT_IDs, corresponding to NAVCAM subphases (see DATA/DATAINFO.TXT). The two-letter codes are listed here with their corresponding NAVCAM subphase periods and the mission catalog phases which they overlap:  Two- Letter Overlapping Mission Code NAVCAM Subphase Catalog Phase(s) : : : CO Checkout CRUISE C5 Cruise 5 CRUISE C6 Cruise 6 CRUISE TE Tempel 1 Encounter APPROACH, ENCOUNTER, DEPARTURE  For the NAVCAM, operational mission subphases were defined as CO (CHECKOUT), C5 and C6 (CRUISE 5 and 6), and TE (TEMPEL ENCOUNTER), and those two-letter acronyms were used in the NAVCAM PRODUCT_IDs and FILE_NAMEs. C6 was not intentional but was added when the NAVCAM image ID was reset during C5, temporarily causing duplicate FILE_NAMEs in the ground data system for NAVCAM images taken at different times. An earlier mission phase, C4 (CRUISE 4) was defined but no NAVCAM data were taken during that phase.   The following sections list the NAVCAM data collection periods:   2007-01-25 to 2010-08-23 -- Checkout, Cruise 5, Cruise 6 --------------------------------------------------------  This section covers the entire CRUISE phase described in the Mission Catalog.  The performance of the NAVCAM was monitored throughout the Stardust-NExT extended mission using a standard calibration sequence along with a few special calibrations. Calibrations involved imaging of a variety of stars, several of which are photometric standards, acquiring dark frames, and taking images illuminated by the NAVCAM internal calibration lamp.  All of these images were taken with NAVCAM in CRUISE mode which included the option to only store and downlink selected windows of pixels from the full CCD array, and many of these images used this windowing option.  The problem with recurring camera contamination (Hillier, et al., 2011; Newburn, et al., 2003a & b; Tsou, et al., 2004; Li, et al., 2009 [HILLIERETAL2011] [NEWBURNETAL2003] [NEWBURNETAL2003B] [TSOUETAL2004] [LIETAL2009]) was successfully controlled by periodic heating of the instrument using its internal electrical heaters and by placing direct Sunlight on the camera radiator.  The cruise calibrations allowed characterization of camera imaging performance in the areas of geometric fidelity, spatial resolution, and radiometry (including zero-exposure signals, shutter times, linearity, field flatness, noise, and radiometric response rate) more accurately than had been possible during the primary mission. Preliminary radiometric calibration results have been incorporated into the image processing pipeline. Special observations allowed determination of the NAVCAM periscope throughput as a function of scan mirror angle, scattered light levels from the spacecraft structure as functions of mirror angle and the Sun illumination direction on the spacecraft, and charge bleeding and residual image in the CCD detector.   2010-12-17 to 2011-02-25 -- 9P/Tempel 1 (1867 G1) Encounter -----------------------------------------------------------  This section covers the entire APPROACH, ENCOUNTER and DEPARTURE phases described in the Mission Catalog.  NAVCAM imaging of Tempel 1 was initiated 60 days before Encounter (E-60d) and was repeated twice per week. Exposures of 10s and 20s (the maximum commandable by the spacecraft) were used; however, the comet was not bright enough to be detected in the initial images even after summing all 8 images taken at each sampling time. Many frames had several pixels of smear using these long exposure times. At this time, the spacecraft was oriented with its dust shields pointed away from the comet (to avoid having to image it through the periscope) and with the high-gain communication antenna pointed at Earth to allow data downlinking. As the spacecraft range to the comet decreased, the mirror angle required to view the comet progressively increased. When it exceeded 168deg, increasing levels of scattered light began to raise the background signal and decrease the signal-to-noise ratio (SNR). Starting at E-27d, the mirror was moved back to 160deg, and the spacecraft was maneuvered off Earth point to view the comet. This reduced the scattered light and allowed the first detection of the comet in stacks of 8 summed images. Daily 8-frame image sets of 351x351-pixel subframes were typically acquired after this time. These images were usable for optical navigation, but the SNR was still too low for useful science. At E-7d, the spacecraft was flipped around to put the dust shields forward, and the scan mirror was set at 20deg for comet imaging. The comet SNR in 8-frame stacks became scientifically useful at about this time, and sets were taken every 2 hours from this point until E-2d when approach imaging was halted to prepare the spacecraft for the encounter. Evidence of the nucleus brightening the central pixel was first seen at about E-3d.  The close encounter image set was restricted by spacecraft memory and software to 72 full-frame compressed images, as had also been the case at Wild 2. These images were sequenced to occur within E+/-4m (minutes). Images were taken on 8s centers outside E+/-144s (seconds) and on 6s centers inside that period. Scan mirror pointing was controlled by the onboard autonomous navigation software, which worked flawlessly to keep the nucleus in the camera FOV. The pixel scale in the encounter image set ranged from 158 m/pixel down to 11 m/pixel at closest approach. Four of the 72 images (the first, last, and those at E+/-72s) were intentionally overexposed to allow better detection of any near-nucleus jets. Other than those frames, nearly all images were well exposed. Slight saturation of the bright limb occurred on two frames (E-33s and E-15s) due to the actual arrival time being 15s earlier than nominal. The first 24 images viewed the comet through the periscope; 6 of those frames showed evidence of double images, as expected for mirror angles between 8 and 15deg, where light reaches the camera both through the periscope and from just outside it. No evidence of any optical contamination was observed.  Departure imaging resumed at E+1d. With the dust shields forward, the scan mirror angle began at about 174deg. Significant scattered light was apparent, but the SNR was adequate for continued useful science. Single 351x351-pixel subframes were acquired every 5 minutes to support high-time-resolution monitoring of coma activity. Increased central pixel brightening due to the nucleus was no longer seen after about E+5d. At E+7d, the sampling rate was decreased to every 11 minutes due to decreasing Deep Space Network ground receiving station coverage, and the subframe size was reduced to 201x201 pixels one day later. The scattered light level gradually decreased with time, as did the comet signal. Useful science imaging was no longer achieved after E+10d, and comet imaging was then terminated. All approach and departure images were acquired uncompressed. No evidence of optical contamination was observed except for the residual contamination seen after the last heating procedure during cruise.  Calibration sequences similar to the standard cruise calibration were executed at E-18d and at E+10d. The NAVCAM performance remained essentially unchanged throughout the Stardust-NExT mission. A publication with more complete NAVCAM calibration results is available (Klaasen, et al., 2011 [KLAASENETAL2011B]).  All approach and departure imaging used CRUISE mode with the windowing option. The close encounter images used ENCOUNTER mode which does not have a windowing option, so all close encounter images are full-frame images.   Instrument and data calibrations :  This section is duplicated in both calibrated and raw data sets, even though it is not represented in the raw data, as calibration is an integral part of understanding and using the data.   Calibration sources -------------------  The calibration data for NAVCAM were derived from pre-launch and in-flight testing.  The NAVCAM was specified as an engineering instrument for the prime mission to Wild 2. Its main purpose was for navigation, calibration was done on a best-efforts basis, and late hardware deliveries severely hampered those efforts.  For Stardust-NExT, imaging was a key part of the science goals, and review of existing data plus extensive in-flight calibration was done to characterize NAVCAM performance [KLAASENETAL2011B].  This data set includes documents (see /DOCUMENT/DOCINFO.TXT), references to published papers, and calibration files (see /CALIB/CALINFO.TXT) detailing the calibration of the NAVCAM instrument.   Data calibration process ------------------------  The data calibration pipeline comprised several steps: masking pixels outside any windows; quality checks (saturation); decompression of compressed data; bias estimation and subtraction; dark-current estimation and subtraction; signal-to-noise ratio calculation; flat-fielding to remove stable pixel-to-pixel variations; calculation of DN rate; conversion to radiance.  The data calibration process does not remove coherent noise (CNoise) or Fixed-Pattern Noise (FPN) from the images. See below for a brief description of these effects.   N.B. Coherent Noise (CNoise) ----------------------------  Coherent Noise is usually only visible in underexposed, uncompressed images when viewed using extreme contrast enhancement, and appears as stripes of noisy dark and light pixels. The CNoise variation is about +/-5DN in the raw images [KLAASENETAL2011B].   N.B. Fixed-Pattern Noise (FPN) ------------------------------  Fixed-Pattern Noise (FPN) is usually only noticeable in images where the NAVCAM has been on for more than ten hours. The rise in FPN is accompanied by an associated rise in CCD temperature. It occurs independent of the contamination level of the camera. But a peculiar aspect of the FPN is that even after long power-on times with elevated CCD temperatures, the FPN does not show up in dark frames, only in those that have had the shutter open to admit some level of external photons (even if only a low-level scattered light background).  Investigation of the FPN during NExT showed that the FPN level also depends on the amount of background scattered light in an image. The Wild 2 approach images had scattered light levels of <100 DN and raw FPN amplitudes of 6-20 DN rms. But during the NExT approach to Tempel 1, much higher levels of scattered light were encountered, and the FPN amplitude increased to 25-45 DN rms even when the camera had been powered on for only a short time and the CCD temperature remained low.  The FPN can be largely eliminated by successive frame differencing when identical frame pairs are acquired. No evidence of FPN is found in the Tempel 1 close encounter images, which were acquired using data compression, at short power-on time, and with minimal scattered light. No attempts to correct for FPN are included in the NAVCAM processing pipeline [KLAASENETAL2011B].   Data Product Type and Format Overview :  NAVCAM data files provided in this archive are divided by target, 9P/TEMPEL 1 (1867 G1) and other (CALIBRATION or N/A).  The images in this data set are in FITS format with detached PDS labels.  The Primary Data Unit (PDU) of each image file in this data set is a two-dimensional array of brightnesses as measured by the array of pixels in the NAVCAM CCD, and as viewed through the NAVCAM optics.  The brightnesses in the PDU are the calibrated data values from the NAVCAM Analog-to-Digital Converter (ADC) as it read the voltages in the CCD pixels. The data calibration converts the raw Data Numbers (DNs) to radiance, typically, or to bias- and dark-subtracted DN for images with zero exposure duration.  Extension Data Units (EDUs) contain maps of parameters associated with each PDU image pixel: a quality map; an uncertainty map; a signal-to-noise ratio map.  The value of a quality map pixel indicates whether the corresponding pixel in the PDU could be calibrated or not, and if not, then why.  The value of an uncertainty map pixel gives the calculated uncertainty for the corresponding pixel in the PDU.  The value of a signal-to-noise ratio (SNR) map pixel gives the calculated SNR for the corresponding pixel in the PDU.  Refer to the data labels and the calibration documentation for more details about the EDUs.  Additional image-synoptic data such as CCD temperature, geometry and windowing parameters are stored in the image labels.  In cases where only windows of the detector were stored and downlinked, the program filled the pixels in the image corresponding to the areas for which data had not been downlinked with raw zeroes. In such images WINDOW OBJECTs define the areas containing non-null data.   Parameters :  The primary parameters in this data set are brightness images, two-dimensional arrays of brightnesses corresponding to the pixels in the NAVCAM CCD, and as viewed through the NAVCAM optics.  The brightnesses are the calibrated Data Number (DN) values from the NAVCAM Analog-to-Digital Converter (ADC), converted to engineering units: radiance or bias- and dark-subtracted DN.  Ancillary data include quality, uncertainty signal-to-noise ratio maps, and image-synoptic data such as CCD temperature and observational geometry.   Data Processing :  The images in this data set were initially assembled at the Jet Propulsion Laboratory (JPL) from raw telemetry packets sent down by the spacecraft; attached preliminary PDS labels were populated with housekeeping values and computed geometry parameters from SPICE kernels.  The JPL image files were then multiplexed to several Science Data Center (SDC) systems with identical processing pipelines operated by Cornell University, where they were converted to FITS format and where detached PDS labels for the FITS files were generated.  The data calibration portion of the pipeline comprised several steps, summarized in Data Calibration above.   Ancillary Data :  The geometry items included in the image PDS labels were computed using the SPICE kernels archived in the Stardust SPICE data set, SDU-C-SPICE-6-V1.0 [SEMENOVETAL2004B]; refer to that data set for details.  Lockheed Martin Astronautics (LMS) provided image command logs, which were needed to calibrate the data; see /CALIB/CALINFO.TXT for details.   Reference Frames :  The geometry items provided in the files are relative to the J2000 reference frame. Refer to the description of the geometry table columns in /INDEX/INDEX.TAB to see which parameters are defined in which frame.  The J2000 reference frame is defined as follows:  - +Z axis is along Earth Mean Equator North at the J2000 epoch (2000 JAN 01 12:00 ET);  - +X axis is along the vernal Equinox at the J2000 epoch;  - +Y completes the right hand frame.  The Stardust spacecraft reference frame is defined as follows:  - +X axis is along the longer side of the spacecraft bus and points from the aerogel capsule side towards the dust shield side;  - +Z is perpendicular to the deployed solar arrays surface and points along the HGA pointing direction;  - +Y completes the right hand frame.  This diagram, which is not to scale, illustrates the spacecraft reference frame:   ^+Z Solar Array .-. | Shield Solar Array | | | .-. :o:o:|:| | .-------------------| | | `-' | Periscope/| | | | --------> (former | _ | | | | | +X Nominal aerogel | NAVCAM / \ | | | | x-------> Comet- capsule)| and| | |/ | | +Y relative | Mirror \_/ | | (into Spacecraft '-------------------| | page) velocity | | during | `-' Encounter Direction to comet at | Whipple closest approach | Shield along spacecraft -Z | | V   As seen on the diagram, NAVCAM is located on the -Y side of the spacecraft bus. The NAVCAM boresight before the mirror points along the spacecraft -Y axis. The mirror redirects the boresight in the spacecraft XZ plane, pointing near spacecraft +X on approach, along spacecraft -Z at closest approach, and near spacecraft -Z on departure.   Epoch of Geometric Parameters -----------------------------  All geometric parameters provided in each image PDS label were computed at the epoch specified in the start time for that label.   Software :  The images in this data set conform to the FITS standard, and have standard PDS image labels. They can be viewed by a number of PDS-provided and/or open-source and/or commercial programs. For this reason no data-set-specific software is provided with this data set.   Contact Information :  For any questions regarding the data format of the archive, contact Stardust-NExT NAVCAM Science Lead:  Dr. Joseph F. Veverka [JVEVERKA]  or Science Data Center Manager  Brian Carcich [BCARCICH]

Confidence Level Overview :  All telemetry data produced by the NAVCAM contained checksums that were validated upon ground receipt.  During the processing of the data in preparation for delivery with this volume, the structure of the image data was verified. This verification included detection of both the sync word and the length of each packet, which ensured that all packets were complete and not damaged. The fundamental validity of the data has been inferred by the NAVCAM Science Lead and Science team members by display and subsequent review of the images.   Breaks in image sequences and missing data :  All NAVCAM image data for the Stardust-NExT mission, which were successfully downlinked without corrupted or lost packets during the data collection periods listed above, are included in this data set.  Images may appear to be missing because of breaks in the sequence of image numbers. This section gives possible reasons for breaks in the sequences, lists all breaks in the image number sequences, and states whether any data are actually missing for each break.  Due to the operational constraints on telemetry playback, some of the pre-encounter images taken by the camera could not have been reconstructed due to an incomplete set of packets and, therefore, are not present in this data set. Specifically an image could not have been reconstructed if its first packet was missing or if it was a windowed image and any packet was missing.  Some images were only intended for on-board auto-tracking (NAV) and never intended for playback. However, their existence still incremented the image number, so images taken from before and after NAV image(s) will show a break in their sequence.  Some breaks in the image number sequence occurred because the image number was intentionally reset.  A final break in the image number sequence occurred at the end of science imaging, as the spacecraft receded from the comet, when it was determined that the comet was too dim to be detected in any remaining images, which were at that time stored on the spacecraft and scheduled to be downlinked, nor would it be detected in future images. At that point the operations and science teams agreed to terminate science imaging operations, erase the remaining images from spacecraft memory without downlinking them, and prepare for the final NAVCAM calibration and end of mission activities.  The breaks in the sequence of image numbers are as follows:  Preceding Following Image Image Reason for Absence --------- --------- ------------------ N0005CO N0000C5 Reset sequence to zero; no missing data N0133C5 N0000C6 Reset sequence to zero; no missing data N0036C6 N10000TE Reset sequence to zero; no missing data N10004TE N10006TE Missing packets; missing N10005TE N10318TE N10320TE Missing packets; missing N10319TE N10344TE N10346TE Missing packets; missing N10345TE N10357TE N10359TE Missing packets; missing N10358TE N10366TE N10368TE Missing packets; missing N10367TE N10404TE N10409TE Missing packets; missing 4 from N10405TE N10414TE N10416TE Missing packets; missing N10415TE N10419TE N10421TE Missing packets; missing N10420TE N10638TE N10641TE Missing packets; missing 2 from N10639TE N10710TE N30004TE NAV, Reset sequence to 30000; no missing data N30100TE N30102TE Missing packets; missing N30101TE N30954TE N30956TE Missing packets; missing N30955TE N30956TE N30958TE Missing packets; missing N30957TE N30965TE N30969TE Missing packets; missing 3 from N30966TE N31135TE N31137TE Missing packets; missing N31136TE N31213TE N31215TE Missing packets; missing N31214TE N31574TE N31648TE Science imaging terminated; no missing data