Data set overview  :  This dataset contains raw Framing Camera 1 (FC1) images sometimes  called level-1a or EDR data. It includes images from the Dawn Ceres  eXtended Mission 1 Orbit 3 (XMO3, aka Ceres Extended GRaND - CXG) phase  on 2017-02-19 and the Ceres eXtended Mission Orbit 4 (XMO4, aka Ceres  Extended Opposition - CXO) phase on 2017-04-29. In addition, there are  images from eXtended Mission 2 (XM2), orbits XMO6 (C2I - intermediate),  and XMO7 (C2E - elliptical) as well as some checkout and end-of-mission  star calibration images.FC1 is one of two identical units flying  on the Dawn spacecraft. It was designated as the backup system to be  used only in the event of a failure of the primary system, FC2. Prior to the Ceres extended mission, FC1 had only been used for in-flight  calibration and to periodically exercise its various mechanisms (door,  filter wheel, etc.). This is the only science dataset generated by FC1.   As in the FC2 raw data sets, in addition to the imagery, ancillary  information is stored within the image headers, as well as a detailed  account of all the reference files used for the calibration. Calibration files needed for further processing are archived as a separate data set. The images in this dataset have been radiometrically calibrated by means of fully reversible procedures, transforming the value of the pixels  from digital units to applicable engineering units without modification  of the geometry.   For more information on the contents and organization of the volume  set refer to the aareadme.txt file located in the root directory of  the data volumes.   Parameters  :   Compression: FC images may optionally be compressed by wavelet  transformation.   Wavelet compression: Images may be integer or floating point wavelet  transform-compressed in the DPU. The integer approach produces lossless  compression, while the floating point can induce distortions of +/-1 DN. The encoding of the wavelets ensures that any length of the data  starting at the beginning can be decoded, thus allowing to compress  further by discarding the trailing part.   Windowing: In order to manage downlink resources, up to 10 portions  of the image can be selected in the DPU and downlinked as subframes.  The subframes are allowed to overlap. During EDR construction each  subframe is stored separately and also mosaicked into the original  image.   Exposure Control: The exposure time of FC images is set  by command for each image.   Pointing: The Framing Cameras are fix mounted onto the Dawn Instrument  deck, with the nominal alignment of the optical axis with the +Z axis of the spacecraft. Deviations from the nominal are documented in the  calibration data.   Filter selection: The FC has 8 filters at its disposal, numbered from F1 to F8. F1 is a broadband (clear) filter, sensitive in the wavelength  interval from 400 to 1100 nm peaking at 700 nm. The narrow-band color  filters are of the interference type, and have wavelengths ranging from  430 to 980 nm.   Processing  :  An FC image downlinked by the spacecraft unpacks into a succession of  one or more compressed image subframes with an attached PDS headers  containing housekeeping items that include full status of the instrument hardware, software configuration, temperature, voltage and current  readings.   The data in one EDR consists of one or more reconstructed image frames,  with the accompanying header translated into text format in the label.  The dimensions and location (pixel coordinates) of each frame are  included for proper further processing. Each frame is formatted into  one file (suffix *.IMG), with an attached label.   Subframes are retained as separate entities and also are reassembled  into their original coordinates in the 'summary' image. Parts of the  reconstructed image not included in the subframes are given a value  of zero.   Darks are acquired in a different mode than normal images, leading to  different cropping and therefore different image file structure.  Darks are acquired as full 1092x1056 pixel images, which are cropped  due to operational considerations to include 1088x1056 (Frame 0) and  4x1056 (Frame 6) allowing the complete reconstruction of the original  full frame. In contrast, normal images are cropped into several  smaller sections (the most prominent of which is the 1024x1024 active  area), and therefore have several smaller frames.   For further details on the layout of the data and the possible  combinations of frames, please refer to the Software Interface  Specification.   The label contains all relevant housekeeping information in calibrated  form (e.g. degrees Celsius, volts, or amperes).   For further details on the layout of the data and the possible  combinations of frames, please refer to the Software Interface  Specification.   For information on the calibration process, please refer  to [SCHROEDER&GUTIER2011]. For a discussion of which calibration  images to use for a given activity, please refer to the data set catalog file for DAWN-CAL-FC1-2-EDR-CALIB-IMAGES-V1.0.   Coordinate System  :  The geometry items SC_SUN_POSITION_VECTOR,  SC_TARGET_POSITION_VECTOR and SC_TARGET_VELOCITY_VECTOR  provided in the label of the data product are relative to the  Earth Mean Equator frame of J2000.   SUB_SPACECRAFT_LATITUDE, SUB_SPACECRAFT_LONGITUDE are  given in the IAU PLANETOCENTRIC coordinate system. These parameters  are corrected for planetary and stellar aberrations.  Distances are given in km, angles in degrees.

Exposure times  :  Due to an idiosyncrasy of the proximity electronics, that takes  approximately 193 milliseconds from the commanding of the image  acquisition to the actual start of the exposure, the images report the  commanding time and the end of exposure. This results in a difference of 193 milliseconds between the usual calculation of exposure time  (STOP_TIME - START_TIME) and the reported EXPOSURE_DURATION, which is  always shorter than the difference of the other two.   Calibration files  :  Since FC1 had not been previously used for science, new flats and  composite darks were generated specifically to be used with these  data (see calibration volume).   Data Coverage  :  -------------------------------------------------------------------------- Dawn Ceres Extended Mission 1 Science Observations with FC1  : Start Mission Activity Activity  Date Phase Name Description  -------------------------------------------------------------------------- 16-12-14 CXG XMO3 Ceres Extended GRaND Phase (range ~8000-9500 km)  -------------------------------------------------------------------------- 17-02-19 CXG CYCLE3 307 FC2~nadir clear+color (1 orbit)  107 FC1~nadir clear+color   -------------------------------------------------------------------------- 17-04-28 CXO XMO4 Ceres Extended Opposition Phase (range 14-55E3 km) -------------------------------------------------------------------------- 17-04-29 CX0 Opposition 205 FC2~nadir clear+color (range ~20,000 km) 199* FC1~nadir clear+color  : Extended Mission 2 Science Observations with FC1  -------------------------------------------------------------------------- 17-07-01 CX2 XMO5 Ceres Extended Mission 2 Phase (range ~15000 km)  -------------------------------------------------------------------------- 18-01-13 Checkout 65 of 65 non-pointed clear and color  -------------------------------------------------------------------------- 18-04-15 CTI TRANSFER_ Ceres Transfer to Intermediate Orbit  TO_INTERMEDIATE  -------------------------------------------------------------------------- No FC science observations in this phase  -------------------------------------------------------------------------- 18-05-15 C2I XMO6 Ceres Extended 2 Intermediate (range ~1950 km)  -------------------------------------------------------------------------- 18-05-15 C2I XMO6 512 of 1349 nadir clear+color (3 of 10 orbits)   ------------------------------------------------------------------------  18-05-31 CTE TRANSFER_ Ceres Transfer to Elliptical Phase  TO_ELLIPTICAL  ------------------------------------------------------------------------  No FC science observations in this phase  ------------------------------------------------------------------------  18-06-09 C2E XMO7** Ceres Extended 2 Elliptical (peri range ~35 km)  ------------------------------------------------------------------------  18-06-09 C2E da942 498 of 913 nadir clear only (5 orbits)  18-06-15 C2E da942 629 of 906 nadir clear only (5 orbits)  18-06-21 C2E da942 553 of 553 nadir Cerelia at Periapsis (3 orbits)  18-09-29 C2E Star Cal 128 of 128 images  ------------------------------------------------------------------------- -------------------------------------------------------------------------- * FC1 clear images were interleaved with the FC2 clear images by acquiring them at the same cadence (5 minutes) but offset in time 2.5 minutes  later. FC1 color images were acquired inbound to minimum phase and FC2  images were acquired on the outbound leg providing functional redundancy while maximizing science return.  ** FC1 images were interleaved with the FC2 images by images by acquiring  them at the same cadence (5 minutes) but offset in time by 3 seconds.  The image cadence at periapsis is 7 seconds.