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STARDUST NAVCAM RAW PREFLIGHT CALIBRATION IMAGES V2.0 (PDS)

NSSDCA ID: PSSB-00542

Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1998-04-08 to 1998-04-10

Description

This description was generated automatically using input from the Planetary Data System.

Data Set 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.

These data are available on-line from the Planetary Data System (PDS) at:

http://pdssbn.astro.umd.edu/holdings/stardust-cal-nc-2-preflight-v2.0/

Alternate Names

  • STARDUST-CAL-NC-2-PREFLIGHT-V2.0

Discipline

  • Planetary Science: Small Bodies

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Ray L. Newburn, Jr.Data ProviderNASA Jet Propulsion Laboratorynewburn@scn1.jpl.nasa.gov
Dr. Tony FarnhamGeneral ContactUniversity of Marylandfarnham@astro.umd.edu
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