PDS_VERSION_ID  = PDS3                                                        
RECORD_TYPE     = FIXED_LENGTH                                                
RECORD_BYTES    = 80                                                          
OBJECT          = TEXT                                                        
  PUBLICATION_DATE = 2014-07-01                                               
  NOTE             = "Data set overview from data set                         
                        SDU-A-NAVCAM-2-EDR-ANNEFRANK-V1.0                     
                     provided with this newer version of those data.          
                     "                                                        
END_OBJECT      = TEXT                                                        
END                                                                           
                                                                              
Preface                                                                       
=======                                                                       
                                                                              
The Stardust prime mission Wild 2 NAVCAM data have been re-delivered using    
the improved calibration developed as part of the Stardust-NExT mission.      
                                                                              
The data set description in the data set catalog for the new data sets        
  SDU-C-NAVCAM-2-EDR-WILD2-V3.0                                               
  SDU-C-NAVCAM-3-RDR-WILD2-V3.0                                               
  SDU-A-NAVCAM-2-EDR-ANNEFRANK-V3.0                                           
  SDU-A-NAVCAM-3-RDR-ANNEFRANK-V1.0                                           
has been re-written and mostly shortened.                                     
                                                                              
This document contains the data set overview from the old data set            
description; it has more detail of the imaging sequences.                     
                                                                              
Note that the old description has been copied verbatim, and has not been      
corrected for typos or grammar.                                               
                                                                              
Note also that the old document describes more imaging (e.g. calibrations;    
sequences where the target was not in the downlinked data) than the new data  
set, which only contains data that capture, or nearly so, asteroid Annefrank  
                                                                              
Refer to the original data set for that additional imaging.                   
                                                                              
The old data set overview follows the next two lines.                         
========================================================================      
                                                                              
    Data Set Overview                                                         
    =================                                                         
                                                                              
      This data set contains raw pre-encounter and encounter images           
      taken by the Stardust Navigation Camera during the encounter            
      with asteroid Annefrank.                                                
                                                                              
      Every image provided in this data set was taken as a part of a          
      particular imaging sequence, each of which is described in this         
      section by the NAVCAM Science Lead, Dr. Raymond L. Newburn, Jr.         
      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 NAVCAM Flight Images'', DOCUMENT/PIIMGLOG.PDF,              
      provided with this data set.                                            
                                                                              
      2002-09-03: Image Sequence #32 (Images 301-324)                         
      -----------------------------------------------                         
        In preparation for engineering readiness tests utilizing the          
        asteroid #5535 Annefrank, as STARDUST once more approached the        
        Sun and Earth sufficiently to begin limited imaging, a first          
        test was made of the new pattern matching and windowing               
        software. Coincident with this, a series of geometric                 
        calibrations was attempted, since those of June 2001 were not         
        totally successful. In addition a calibration lamp image and          
        four full frame fields were acquired at zero and thirty               
        degrees, one of the latter compressed. These were intended as a       
        modestly comprehensive check for contamination, for scattered         
        light, and for compression. It was found that there had been a        
        small amount of recontamination in the 10 months since the            
        previous image. This was most obvious in the calibration lamp         
        image. Star images remained sharp, with the same point spread         
        as earlier, but with a very shallow skirt of scattered light.         
        The pattern matching and windowing failed at 14 of the 19             
        angles. At larger scan mirror angles there was a problem with         
        increasing scattered light. The windows used were only 21x21          
        pixels, and it became clear that somewhat larger windows were         
        necessary and that there were still geometric calibration             
        problems. The contamination on the periscope was found to be          
        significantly reduced compared to that of two years earlier,          
        perhaps due to some evaporation of the condensate into the            
        vacuum of space.                                                      
                                                                              
      2002-10-09: Image Sequence #33 (Images 325-345)                         
      -----------------------------------------------                         
        This series of images again was intended as a test of pattern         
        matching and windowing and to supply some geometric calibration       
        of the system. The camera was brought above freezing for 60           
        hours and then allowed to cool back to normal operating               
        temperatures in an effort to remove contamination before              
        initiating these exposures. The series consisted of 20 pattern        
        matching and windowing tests, ten each at 47.8 and 64.0 degree        
        scan mirror settings, each image consisting of four 41x41 pixel       
        windows, and one full frame image at a scan mirror setting of         
        15 degrees to check on the effect of a split field (partially         
        on and partially off the periscope). Half of the 47.8 degree          
        and all of the 64.0 degree tests were successful in locking up        
        on the desired pattern of stars, but the target stars still           
        were not well centered. These were engineering tests and led to       
        significant improvement in the software and to a better               
        understanding of spacecraft behavior and capabilities, but the        
        images provided little useful data for any sort of photometric        
        calibration following the fourth heating cycle that preceded          
        this series. The split image indicated that it should be              
        possible to use the periscope on Wild 2 approach as always            
        intended. Good geometric calibration of the periscope still           
        remains to be carried out, and the periscope was not used for         
        the Annefrank encounter. In the absence of any dust hazard, it        
        was not necessary to keep the spacecraft oriented along the           
        velocity vector, so Annefrank tracking utilized mirror angles         
        from 17.7 to 111.3 degrees.                                           
                                                                              
      2002-10-31: Image Sequence #34 (Images 346-350)                         
      -----------------------------------------------                         
        One of the goals of the engineering readiness tests on                
        Annefrank was to exercise the optical navigation team and to          
        attempt to improve flyby accuracy using optical data. The             
        approach to Annefrank was from a phase angle of 150 degrees,          
        unfortunately, which meant the asteroid would be poorly               
        illuminated and be very faint. There were no asteroid data            
        available for phase angles larger than 100 degrees. It was            
        assumed that Annefrank would be about 1.5 magnitudes fainter          
        than the nearly linear decrease of about 0.03 mag/deg that is         
        common to asteroids at smaller phase angles. It seemed that we        
        would have a fair chance of detection 38 hours before                 
        encounter, which time was used for this first attempt. Five           
        images were obtained using three 151x151 pixel windows and            
        exposures of 1, 1, 2, 5, and 5 seconds. As we later found out,        
        the asteroid was much fainter than expected and the spacecraft        
        drift during the exposures (smear rate) much larger than we had       
        previously experienced. Further the camera pointing was not as        
        accurate as we had expected (the geometric calibration was not        
        yet solid). The use of new controller software, inadequate            
        settle times after attitude changes, and a larger moment of           
        inertia with the aerogel grid open were all suggested as              
        reasons for the drift and pointing problems. The cause is still       
        being investigated. This is why these tests were run, to make         
        sure something like this doesn't happen to us on Wild 2. The          
        bottom line is that the asteroid was not found in these five          
        E-38 hour images.                                                     
                                                                              
      2002-10-31: Image Sequence #35 (Images 351-355)                         
      -----------------------------------------------                         
        A second set of approach images was acquired at E-32 hours. The       
        same windows and exposure times were used as for the previous         
        set at E-38 hours. The problems were much the same, as were the       
        results. Annefrank was not found.                                     
                                                                              
      2002-10-31: Image Sequence #36 (Images 356-360)                         
      -----------------------------------------------                         
        A third set of images was acquired at E-26 hours. The same            
        windows and exposure times were used as for the previous sets         
        taken at E-38 and E-32 hours. The problems were much the same,        
        as were the results. Annefrank was not found.                         
                                                                              
      2002-11-01: Image Sequence #37 (Images 361-365)                         
      -----------------------------------------------                         
        Given the experience of the first three sets of approach              
        images, the navigators decided to increase the window size to         
        181x181 pixels and make all of the exposures 5 seconds for this       
        set at E-18 hours. The image smear can only be described as           
        horrendous. This doesn't matter for measurement purposes, IF          
        the target can be found. The asteroid was still several               
        magnitudes too faint for detection when smeared over some 20          
        pixels, and it was not located.                                       
                                                                              
      2002-11-01: Image Sequence #38 (Images 366-370)                         
      -----------------------------------------------                         
        A final set of approach images was attempted at E-12 hours.           
        This time all of the available communication bandwidth was            
        given to one window in one image (#368), making it 701x701            
        pixels. The other four images were given 3x3 pixel windows and        
        were retained only to avoid having to reprogram and transmit          
        too much last minute new command software. The smear was still        
        large (21.7 pixels) and the asteroid still was not located.           
                                                                              
      2002-11-01: Image Sequence #39 (Images 371-407)                         
      -----------------------------------------------                         
        Twenty-five minutes before the closest approach, images were          
        acquired to attempt autotracking. Pointing was based upon radio       
        navigation of the spacecraft and the best ephemeris for the           
        asteroid supplied by JPL's celestial mechanics specialists. By        
        this time the phase angle was down to 130 degrees and the range       
        was only 11,415 km. Annefrank appeared in the first image,            
        though far from centered. The navigators chose an exposure of         
        65 ms to make sure they were going ``deep enough,'' so the            
        images were well exposed. After the first few images, only            
        every third image was transmitted to the ground, the others           
        being used only to initiate autotrack. After 15 minutes, at a         
        range of 5434 km, exposure was reduced to 25 ms. In all, 15 of        
        37 images taken with 65 ms exposure were received on Earth. Of        
        these, the first two or three were partially on the periscope,        
        and three show a large amount of smear, but several are of            
        scientific use. Autotracking was initiated shortly before             
        reducing the exposure, and image 410 and all subsequent               
        Annefrank images are well centered in their frames.                   
                                                                              
      2002-11-01: Image Sequence #40 (Images 410-445)                         
      -----------------------------------------------                         
        Exposure times on Annefrank were reduced to 25 ms beginning           
        with image 410 at a range of 5088 km and a phase angle of 113         
        degrees. Images beginning with #420 started to show saturation.       
        This was predicted, but these images were being taken to test         
        the autotracking rather than for scientific purposes, and             
        autotrack works perfectly well with saturated images. The             
        images soon reached 80% saturation, so images 420 through 445         
        are of limited scientific use. Every image was transmitted to         
        the ground beginning with #426, a total of 26 images with 25 ms       
        exposure. Twenty-two of these have some to nearly total               
        saturation.                                                           
                                                                              
      2002-11-01: Image Sequence #41 (Images 446-476)                         
      -----------------------------------------------                         
        Beginning with image #446, exposure time was reduced to 5 ms.         
        In fact the characteristics of the shutter are such that              
        alternate images are given exposures shorter by 1.5 ms than the       
        set value, so in fact all even numbered images have an exposure       
        of 3.5 ms and odd numbered ones 5 ms. It was intended that            
        these images be of scientific as well as engineering use. If          
        Annefrank had not been acquired by this time, there was little        
        hope of acquiring it, so there was no need to saturate the            
        images. The subsequent images (through image 476) taken at            
        phase angles from 71.0 to 47.2 degrees constitute the best            
        images for scientific use. During this period the range fell          
        from 3133 km to 3078.5 km and increased back to 3162 km, so           
        there is minimal change to scale.