PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "2004-04-24 A.C.Raugh Minor editing to conform with current standards" OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "GIO" INSTRUMENT_ID = "HMC" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "HALLEY MULTICOLOUR CAMERA" INSTRUMENT_TYPE = "LINEAR ARRAY CAMERA" INSTRUMENT_DESC = " Instrument Overview =================== The HMC utilizes a 16-cm modified Ritchey-Chretien telescope with a 1.00-m focal length to image the sky onto a set of linear-array detectors. The telescope is mounted with its axis perpendicular to the rotational axis of the spacecraft. A 45- degree mirror in front of the telescope, which rotates together with the entire telescope assembly, allows the telescope to view any direction from parallel to the spacecraft's axis of spin to perpendicular to that axis. Thus, depending on the rotational orientation of the telescope, the spin of the spacecraft causes the linear field of view of the camera to sweep out a circle on the sky (when pointed nearly parallel to the axis of spin), or an annulus on the sky (when pointed at intermediate directions), or a rectangular strip (when pointed perpendicular to the axis of spin). A reticon detector with two rows of 936 pixels (30 by 375 microns each) has a linear field of view of 1.6 degrees and was used primarily to search for the comet before the encounter. Two CCDs (22.35 micron square pixels; 584 lines of 390 pixels) were masked to provide two linear detectors on each CCD. Each linear detector was several pixels high and the readouts were clocked to move the charge from line to line synchronized with the effective motion of the image across the detector. Three detectors were fitted with fixed filters (red, blue, and clear) and the third was fitted with a filter wheel containing a variety of narrow-band filters. In some modes, on-chip binning was used to improve the signal-to-noise ratio at the expense of reduced spatial resolution. On-board electronics located the brightest portion of each image and transmitted a region centered on that point, discarding the periphery of each image. Science Objectives ================== The technical goals of the experiment were first to obtain high- quality images of the cometary nucleus in four colors with two polarizations and secondarily to obtain images of the cometary coma in a variety of narrow bandpasses. The primary scientific goal to be addressed with these images was to determine the basic properties of the nucleus including the size and shape, the morphology and topography of the surface, the photometric properties of the surface, the rotational state, the degree of heterogeneity in the outgassing, and the energy balance at the surface. The secondary scientific goal was to study the properties of the inner coma including the production and evolution of gas and dust, the scales of the relevant physical processes, the size distribution of the dust, the chemistry of the inner coma, and the temporal variability in the inner coma. Calibration Description ======================= Flat-fielding, or determining the responsivity matrix for each pixel, was carried out using pre-flight exposures on the ground. These were all taken without on-chip binning (i.e. in SPF-0, Super Pixel Format 0). Because the detectors are one- dimensional, defects in the responsivity matrix show up as vertical lines in an image. For detector C, the most frequently used detector, the encounter data in both SDM and MDM were used, by integrating parallel to the tracking, to locate vertical lines in the images and the responsivity matrix was adjusted to make these integrated brightnesses vary smoothly along the window. Detectors B and D were strongly affected by blooming of the charge in the pre-flight calibration exposures so only faint exposures could be used and these required fitting of a polynomial to the illumination. The gain switch, used to reduce the gain by a nominal factor 4 during non SPF-0 SDM observations, was calibrated by comparing images of Jupiter taken in SDM at both gains. The ratio was 4.115, in good agreement with ground-based tests prior to launch. The absolute calibration was carried out by observing bright stars, Jupiter, and Venus while enroute to the comet. The absolute fluxes from the stars were obtained from published sources and, when not available from these sources, by fitting black-body curves to the known fluxes. Observations of Venus and Jupiter were also used together with published fluxes, taking into account the variation with phase. The final overall calibration is thought to be accurate to about 5%. See Thomas and Keller, 1990, Applied Optics, 29, 1503-1519 fur further details. Operational Considerations ========================== The instrument operated at a much higher temperature than planned, resulting in a much higher dark current than expected. Because the clocking of the CCD was synchronized with the rotation of the spacecraft as projected on the sky, the effective exposure time varies with the orientation of the telescope and its periscopic 45-degree mirror with the shortest effective exposure times occurring at closest approach (viewing perpendicular to the axis of spin). Because of the periscopic approach to scanning, the shape of the field of view is a function of the rotation of the telescope and its 45-degree periscopic mirror. Geometric rectification was carried out after the image was transmitted back to Earth. Instrument Manufacturer : MAX-PLANCK-INSTITUT-FUER-AERONOMIE Detectors ========= Detector A ---------- Detector type : RETICON Nominal Operating Temperature : 253. Model CP 1001 Reticon with two rows of 936 pixels each with no dead area between pixels. Individual pixels are 30 by 375 microns. Coincidence between the two rows was used to discriminate against cosmic rays. Two clocking speeds were used to allow for different brightness levels of the target. Detector B ---------- Detector type : CCD Minimum Wavelength : 0.30 Maximum Wavelength : 1.05 Nominal Operating Temperature : 253. This detector is one of two windows in the mask on CCD number 1. The CCD is a virtual-phase device by Texas Instruments with two independent sections of 390 by 292 pixels and the two windows are at the 'leading' edge of each section. Pixel size is 22.35 microns square. The window in the mask is the full width of 390 pixels by several pixels and the clocking is varied to synchronize with the apparent motion of the image across the detector window. The output is thus a line of 390 pixels for each of many different positions in the image. This window is always viewing through a red filter and is the first of the four imaging detectors to 'see' an object as the field of view of the telescope sweeps across the sky. Sensitivity Description: See response curve for CCD given in Schmidt et al. (1986), Figure 9 and the reflectivity of the mirror given in Figure 7 of the same reference. See also the characteristics of Filter B in the appropriate template or in Table I of the same reference. Detector C ---------- Detector type : CCD Minimum Wavelength : 0.30 Maximum Wavelength : 1.05 Nominal Operating Temperature : 253. This detector is one of two windows in the mask on CCD number 1. The CCD is a virtual-phase device by Texas Instruments with two independent sections of 390 by 292 pixels and the two windows are at the 'leading' edge of each section. Pixel size is 22.35 microns square. The window in the mask is the full width of 390 pixels by several pixels and the clocking is varied to synchronize with the apparent motion of the image across the detector window. The output is thus a line of 390 pixels for each of many different positions in the image. This window views through the filter wheel containing a series of polarizers and narrow-band filters. It is the second of the four imaging detectors to 'see' an object as the field of view of the telescope sweeps across the sky. Sensitivity Description: See response curve for CCD given in Schmidt et al. (1986), Figure 9 and the reflectivity of the mirror given in Figure 7 of the same reference. See also the characteristics of Filters Cn in the appropriate templates or in Table I of the same reference. Detector D ---------- Detector type : CCD Minimum Wavelength : 0.30 Maximum Wavelength : 1.05 Nominal Operating Temperature : 253. This detector is one of two windows in the mask on CCD number 2. The CCD is a virtual-phase device by Texas Instruments with two independent sections of 390 by 292 pixels and the two windows are at the 'leading' edge of each section. Pixel size is 22.35 microns square. The window in the mask is the full width of 390 pixels by several pixels and the clocking is varied to synchronize with the apparent motion of the image across the detector window. The output is thus a line of 390 pixels for each of many different positions in the image. This window is always viewing through a blue filter and is the third of the four imaging detectors to 'see' an object as the field of view of the telescope sweeps across the sky. Sensitivity Description: See response curve for CCD given in Schmidt et al. (1986), Figure 9 and the reflectivity of the mirror given in Figure 7 of the same reference. See also the characteristics of Filter D in the appropriate template or in Table I of the same reference. Detector E ---------- Detector type : CCD Minimum Wavelength : 0.30 Maximum Wavelength : 1.05 Nominal Operating Temperature : 253. This detector is one of two windows in the mask on CCD number 2. The CCD is a virtual-phase device by Texas Instruments with two independent sections of 390 by 292 pixels and the two windows are at the 'leading' edge of each section. Pixel size is 22.35 microns square. The window in the mask is the full width of 390 pixels by several pixels and the clocking is varied to synchronize with the apparent motion of the image across the detector window. The output is thus a line of 390 pixels for each of many different positions in the image. This window is always open to white light without a filter and is the last of the four imaging detectors to 'see' an object as the field of view of the telescope sweeps across the sky. Sensitivity Description: See response curve for CCD given in Schmidt et al. (1986), Figure 9 and the reflectivity of the mirror given in Figure 7 of the same reference. See also the characteristics of Filter E in the appropriate template or in Table I of the same reference. Electronics =========== The CCDs are read out using a Correlated Double Sampling technique to minimize noise and are then digitized with a 12-bit ADC. A 4-to-1 gain switch in front of the ADC effectively provides a 14-bit ADC. Super-pixels are created in various formats by binning the charge from multiple pixels on the charge-sensing node of the output gate of the CCD. Formats for binning are: SPF-0 = 1 x 1; SPF-1 = 2 x 2; SPF-2 = 4 x 4; SPF-3 = 8 x 8; SPF-4 = 16 x 16; and SPF-5 = 4 x 3. Noise of 75 electrons (rms) has been achieved in flight but there appears to have been some interference from other experiments or other parts of this experiment. The two CCDs are read out in parallel in MDM. The two lines of the reticon are each read out on two video lines alternately. There are two readout speeds, a slow speed using both lines of pixels for acquiring the comet initially, and a high speed used with a single line of pixels to evaluate the position of the comet prior to the arrival of that part of the image at the first CCD detector. An acquisition preprocessor converts the reticon signals into the minimum number of bytes needed to specify the passage of a bright object across the field of view of the reticon. A tracking preprocessor determines the actual location of the bright object relative to the spacecraft for use in acquisition and in controlling the clocking of the CCD readout. A mass memory unit can store the full readout from all four detectors during a single spin of the spacecraft. The digital processing unit uses an algorithm to select portions of the images for telemetry since the maximum data rate can not accommodate transmission of the full images. Filters ======= Filter 1 -------- Filter Name : C1 Filter Type : OPAQUE SHUTTER Filter 2 -------- Filter Name : C2 Filter Type : CLEAR Filter 2A --------- Filter Name : E Filter Type : CLEAR Filter 3 -------- Filter Name : C3 Filter Type : WIDE-BAND RED Minimum Wavelength : 0.700 Minimum wavelength is for 500f peak transmission and has a tolerance of 0.005 microns. Filter transmits to wavelengths longer than the response of the CCD. Filter 3A --------- Filter Name : B Filter Type : WIDE-BAND RED Minimum Wavelength : 0.700 Minimum wavelength is for 500f peak transmission and has a tolerance of 0.005 microns. Filter transmits to wavelengths longer than the response of the CCD. Filter 4 -------- Filter Name : C4 Filter Type : WIDE-BAND ORANGE Minimum Wavelength : 0.580 Center Filter 0.700 Maximum and minimum wavelengths refer to points with 500f peak transmission. Both have tolerances of 0.005 microns. Filter 5 -------- Maximum Wavelength : 0.490 Maximum wavelength refers to point with 500f peak transmission and has a tolerance of 0.005 microns. Filter extends with transmission greater than 900f peak to wavelengths less than 0.360 microns. Filter 5A --------- Maximum Wavelength : 0.490 Maximum wavelength refers to point with 500f peak transmission and has a tolerance of 0.005 microns. Filter extends with transmission greater than 900f peak to wavelengths less than 0.360 microns. Filter 6 -------- Filter Name : C6 Filter Type : PARALLEL POLARIZER Polarizer is oriented to transmit electric vector parallel to line of image in sky. Polarizer transmits with >900f peak transmission at all wavelengths at which the CCD responds, from <0.300 to >1.100 microns. Filter 7 -------- POLARIZER Polarizer is oriented to transmit electric vector parallel to line of image in sky. Polarizer transmits with >900f peak transmission at all wavelengths at which the CCD responds, from <0.300 to >1.100 microns. Filter 8 -------- Filter Name : C8 Filter Type : NARROW-BAND FOR VIOLET CONT Minimum Wavelength : 0.440 Wavelength : 0.456 Maximum and minimum wavelengths refer to points with 500f peak transmission. Both have tolerances of 0.002 microns. Filter 9 -------- Filter Name : C9 Filter Type : NARROW-BAND RED CONTINUUM Minimum Wavelength : 0.716 Center Filter Wavelength : 0.729 Maximum Wavelength : 0.742 Maximum and minimum wavelengths refer to points with 500f peak transmission. Both have tolerances of 0.002 microns. Filter 10 --------- Filter Name : C10 Filter Type : NARROW-BAND FOR OH RADICAL Minimum Wavelength : 0.302 Center Filter Wavelength : 0.311 Maximum Wavelength : 0.320 Maximum and minimum wavelengths refer to points with 500f peak transmission. Both have tolerances of 0.002 microns. Filter 11 --------- Filter Name : C11 Filter Type : NARROW-BAND FOR C3 RADICAL Minimum Wavelength : 0.398 Center Filter Wavelength : 0.407 Maximum Wavelength : 0.416 Maximum and minimum wavelengths refer to points with 500f peak transmission. Both have tolerances of 0.002 microns. Filter 12 --------- Filter Name : C12 Filter Type : NARROW BAND FOR C2 RADICAL Minimum Wavelength : 0.500 Center Filter Wavelength : 0.510 Maximum Wavelength : 0.520 Maximum and minimum wavelengths refer to points with 500f peak transmission and they have tolerances of 0.002 microns. Optics ====== The basic telescope is a modified Ritchey-Chretien with a correcting field lens at the focal plane. The primary has a clear aperture of 166 mm. The primary and secondary are separated by 246 mm. The unvignetted field of view has a diameter of 1.4 located near the entrance pupil of the telescope. Telescope ID : HMC Telescope Focal Length : 0.998 Telescope Diameter : 0.160 Telescope F Number : 6.24 Telescope Resolution : 0.000044 Telescope T Number : 7.7 Instrument Mounting Description =============================== The HMC is mounted inside the body of the Giotto spacecraft, looking out the side, perpendicular to the axis of spin of the spacecraft. The 45-degree diagonal mirror at the entrance pupil of the telescope extends beyond the body of the spacecraft to enable viewing in all directions. Instrument Section/Operating Mode Descriptions ============================================== Data Rate : 20058 bit/sec Sample Bits : 8 FOV Shape : RECTANGULAR Instrument Parameter Name : PIXEL Sampling Parameter Name : PIXEL ACQ Mode -------- ACQ, or Acquisition Mode, was used prior to encounter to search a 4.4- by 4.6-degree field centered on the spacecraft's axis of spin. The searching is accomplished by a combination of the spin and tilting the 45-degree, periscopic mirror. The reticon was used in a coincidence mode to locate the brightest object in the field of view. After a sufficient number of detections, the instrument's DPU calculated the position of the comet relative to the spacecraft and predicted the pointing of the camera for the transmitted to Earth. Data Path Type: INTERNAL TO INSTRUMENT ONLY SDM Mode -------- Single Detector Mode, or Coma Mode, was used for most observations far from the time of closest approach when the annular field of view swept out by the detectors had such a small radius of curvature that the motion of the field could be orthogonal to only one of the linear detectors. Detector C was used to locate the center of brightness which was then fed back, once every second spin of the spacecraft, to the controlling electronics. These then adjusted the periscopic mirror to make the motion orthogonal to detector C and adjusted the clocking rate of the detector to match the motion of the field of view. A sub-mode of this mode, known as 'Photometer Mode', involved stopping the clocking of the CCD so that it integrated across the entire coma. MDM Mode -------- Multi Detector Mode, or Nucleus Mode, was used for imaging near the time of closest approach (when the radius of the annular field swept out was greater than 1.6 degrees), starting roughly 5 minutes before closest approach. In this mode, the spacecraft and all four detectors were used. Data Path Type: REAL-TIME TELEMETRY OF SUBSET OF PIXELS OBS Mode -------- Observatory Mode was intended for observations of stars during cruise phase, primarily for calibration of the camera. The camera did not track in this mode and fast sequences of filters were used." END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KELLERETAL1987" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "NATURE321" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "SCHMIDTETAL1986" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "THOMAS&KELLER1990" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END