Data Set Information
DATA_SET_NAME STARDUST NAVCAM RAW PREFLIGHT CALIBRATION IMAGES V2.0
DATA_SET_ID STARDUST-CAL-NC-2-PREFLIGHT-V2.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Dataset Overview : This dataset contains the raw, preflight, thermal-vacuum calibration images collected by the Navigation Camera (NAVCAM) on 8-10 April 1998 for the Stardust mission. This is version 2.0 of the dataset, in which the original image data were converted from the standard PDS IMG format to the FITS format; no corrections were applied. This dataset supersedes version 1.0 which was safed by PDS because the data were not considered to be scientifically useful for the Stardust mission, due to the problems encountered during the flight (stuck filter wheel, contamination on the instrument window, etc.) that changed the instrument characteristics. During the Stardust-NExT mission (New Exploration of Tempel) to comet 9P/Tempel 1, additional data were obtained to improve the calibrations. During these recalibrations, some of these preflight data were used to check the exposure time offsets due to shutter reversal and to determine dark current rates. Images in this dataset were taken during calibration sequences that were executed with the Focal plane array at temperatures of -30, -40, and -50 degrees celsius (to cover the range of potential operating temperatures), using an integrating sphere as the observation target. (The preflight calibration temperature of -30 deg C was closest to the operating temperature of the CCD during flight.) The DOCUMENT/NCLOG subdirectory contains the calibration log sheets and additional files about the individual images. Documents in the DOCUMENT/CALRPT directory describe the data and how they were originally used to perform the tasks needed to characterize the instrument. Information about how the data were used in the updated calibration performed during the Stardust-NExT mission, see Klassen et al. (2011) [KLASSENETAL2011]. For complete list of the images in this dataset and their parameters, refer the PDS index table, INDEX/INDEX.TAB. The preflight images have been divided into four groups in the DATA directory. The 'MINUS30C', 'MINUS40C', and 'MINUS50C' directories contain calibration images taken at -30, -40, and -50 degrees celsius, respectively. The 'UNUSABLE' directory contains calibration images that were determined to be unusable. See UNUSABLE.ASC in the DOCUMENT directory for a list of the problematic images and a description of why they are considered to be unusable. Data : The images in this dataset have been converted by the PDS Small Bodies Node from the standard PDS IMG format to the FITS format with detached PDS labels. Relevant information in the PDS label has been placed into the FITS header, though due to differing conventions, the keywords may have changed. The description field in the FITS header should make it clear what the keyword represents. Camera Description ------------------ The STARDUST camera has an angular resolution of 59 microrad/pixel (12 arcsec/pixel) and a focal length of 202 mm at an f-ratio of about f/3.5. Early in the flight the filter wheel failed, possibly due to a failed power supply. Fortunately it failed on the filter with the largest throughput, but the broad bandpass of that filter caused images taken through it to have significant chromatic aberration, which resulted in an image resolution of about 2.5 pixels at FWHM (full width at half maximum) when observing a point source such as a star. (The high resolution filter, intended to be used for near encounter imaging, would have resulted in resolution exceeding a half pixel.) Without any image processing, the 2.5 pixel resolution resulted in a best linear resolution at closest approach of about 20 m/pixel. The camera has a 1024x1024 array as the active portion of the CCD. The images that are stored on this volume, however, contain more than just the active portion of the CCD. Each line contains a sync pattern, a line counter, 12 baseline stabilization pixels, the 1024 pixels from the active portion of the CCD, and finally 8 over-clock pixels used to measure the quantum efficiency. The number of rows for each image is always 1024, no matter what compression mode is used, but the number of columns for each image depends on the compression mode used. Compression Modes ----------------- The NAVCAM images can be either 8-bit or 12-bit data. The 12-bit data is commonly referred to as 'uncompressed data', while the 8-bit is referred to as 'compressed data'. This compression is accomplished by a 12-bit to 8-bit square-root look-up-table compression method, which is implemented in the hardware of the camera electronics. This compression is lossy and the estimate of the 12-bit image can be recovered using the look-up table mentioned in Appendix 3 of the Stardust NAVCAM Calibration Document located in the DOCUMENT directory. In uncompressed mode with 12-bit data, the pixels are expressed in two bytes, as 16 bits per pixel. Image Orientation ----------------- During the conversion to FITS format, the camera's mirror image has been removed by flipping the images from top to bottom. This is the same convention used in other Stardust and Stardust-NExT datasets. Images of the calibration lamp filament can be used to confirm the orientation relative to other data sets. Exposure Durations ------------------ The double-bladed shutter utilized by the camera has a delay in its slide mechanism that introduces an offset in the actual exposure time, compared to the commanded exposure time. During the recalibration of the NAVCAM as part of the Stardust NExT mission, it was determined that the original information about the exposure time offsets and the forward/reverse shutter parity were incorrect. However the images in this dataset have not been corrected to account for the updated information. See the file SHUTTER_CORRECTION.ASC in the DOCUMENT directory for more information. Author ------ The descriptions in this file were copied from version 1.0 of this dataset and modified by the PDS Small Bodies Node to include relevant information about conversion process and the NExT mission.
DATA_SET_RELEASE_DATE 2011-11-15T00:00:00.000Z
START_TIME 1998-04-08T12:00:00.000Z
STOP_TIME 1998-04-10T12:00:00.000Z
MISSION_NAME STARDUST
MISSION_START_DATE 1999-02-07T12:00:00.000Z
MISSION_STOP_DATE 2006-01-16T12:00:00.000Z
TARGET_NAME CALIBRATION
81P/WILD 2 (1978 A2)
TARGET_TYPE CALIBRATION
COMET
INSTRUMENT_HOST_ID SDU
INSTRUMENT_NAME NAVIGATION CAMERA
INSTRUMENT_ID NAVCAM
INSTRUMENT_TYPE IMAGING CAMERA
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The Stardust NExT mission used select pieces of these preflight data to help recalibrate the NAVCAM instrument for the comet 9P/Tempel1 encounter in February 2011. In particular some of the images were used to determine exposure time offsets and dark current rates. For more information see the NExT NAVCAM Calibration Overview report and the Shutter Polarity report located in the DOCUMENT directory. Also see Newburn, et al., 2003a [NEWBURNETAL2003] and Klaasen, et al., 2011 [KLAASENETAL2011B]. Data Quality : As noted above in the Dataset Overview section, the DATA/UNUSABLE directory contains preflight calibration images that were determined to be unusable. See UNUSABLE.ASC in the DOCUMENT directory for a description and list of the problematic images. Review : The data were peer review in December 2011.
CITATION_DESCRIPTION Newburn, R.L, T.L. Farnham, K.P. Klaasen, and S.A. McLaughlin, STARDUST-CAL-NC-2-PREFLIGHT-V2.0, STARDUST NAVCAM RAW PREFLIGHT CALIBRATION IMAGES V2.0, NASA Planetary Data System, 2011.
ABSTRACT_TEXT This dataset contains the raw, preflight, thermal-vacuum calibration images collected by the Navigation Camera (NAVCAM) on 8-10 April 1998 for the Stardust mission. This is version 2.0 of the dataset, in which the original image data were converted from the standard PDS IMG format to the FITS format; no corrections were applied. The NExT mission to comet 9P/Tempel 1 used some of these preflight data to check the exposure time offsets due to shutter reversal and to determine dark current rates. This dataset supersedes version 1.0 which was safed by PDS because the data were not considered to be scientifically useful for the Stardust mission, due to problems encountered during the flight (stuck filter wheel, contamination on the instrument window, etc.) that changed the instrument characteristics.
PRODUCER_FULL_NAME TONY FARNHAM
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