\header ENTRY_TIME = 2000 MAY 04 21:01:35 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JET PROPULSION LABORATORY START_TIME = 2000 FEB 22 21:22:28 STOP_TIME = NULL TARGET = CAL DAY = NULL \text As planned, following analysis of the October images, two images of the calibration lamp were obtained through the OpNav filter as image sequence 3 and given numbers 110 and 111. With the spacecraft at 2.5 AU from Earth, the downlink rate was only some 2kbps into a 70 m antenna, so extensive imaging was not practical. I asked for exposures of 200ms, although the calibration lab images of the cal lamp were only 20 ms. I had intended to make these exposures identical, but I didn't actually look up the number before hand, and I remembered it incorrectly. (Good lesson learned. Memory is fallible. Look up everything!) Given the weak images we had been obtaining, 200 ms sounded right. When the two images came down, they were saturated! Even these saturated images told us two things. There was nothing wrong with the exposure times, and the light was probably being more diffused than absorbed. The hardware and software people at both JPL and LMA had already concluded that they could find nothing wrong with the exposures, but this was experimental confirmation of their conclusions. The next step needed was to repeat these exposures at the correct 20 ms duration. \header ENTRY_TIME = 2000 MAY 04 21:53:49 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JET PROPULSION LABORATORY START_TIME = 2000 FEB 29 19:02:52 STOP_TIME = NULL TARGET = CAL DAY = NULL \text Image sequence 4 repeated the cal lamp exposures through the OpNav filter, this time at the correct 20 ms duration. The images so obtained were numbered 112 and 113. These exposures were excellent. They had to be returned via 34 m antennas, so it took several weeks to get everything down, but the first 100 or so lines showed that the image appeared somewhat brighter than for the same exposure in the calibration lab! Analysis of the complete images showed that the summed dn level of all pixels on the CCD was in fact slightly higher that the calibration lab value. Unlike the calibration work, the CCD had taken only a few zero level exposures before taking the transmitted images, so it was a bit colder and the bias level therefore higher, which accounts for most of the difference. We did not have an actual bias frame for subtraction and therefore had to estimate the bias level from the BLS pixels, introducing some uncertaintly in the exact values. This clearly says there is no absorption caused by contamination on the STARDUST lens or CCD, however. In calibration laboratory images through filters that include red light, a magnified ghost image of the cal lamp filament is clearly visible. In frames 112 and 113 the filament image is replaced by a diffuse glow. Shyam Bhaskaran estimates that each pixel would have to be diffused over an area of some 10 x 10 pixels to reproduce the result obtained. In addition a general background of points and striations cover the entire images. It is like looking at a bright light through a frost covered windshield. Clearly some glass surfaces in the optical train have been contaminated by some form of residue that seriously scatters light but does not absorb it. Ray trace analyses of the lens indicate that the most probably contaminated surfaces are the front surface of the first lens element and/or the outer surface of the CCD cover window. The results to date indicate that there has been contamination of the optical system from internal sources, external sources, or both, with the first now seeming the more likely. I say this because all observations to date can apparently be explained by diffusing contamination on optical surfaces, probably from within a degasing spacecraft bus. The next series of images must confirm whether there is possibly an external source of contamination as well, such as rocket fuel residue from the second or third stage burns of the launch vehicle or from our own attitude control jets. \header ENTRY_TIME = 2000 MAY 05 20:44:31 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JET PROPULSION LABORATORY START_TIME = 2000 MAY 25 00:00:00 STOP_TIME = NULL TARGET = STAR DAY = NULL \text Rationale for the May 25, 2000 STARDUST Imaging Series Five separate goals will be met or aided by the series of 30 windowed images proposed for the May 25 session. These are as followes: 1.) We urgently need to know whether the source of contamination of the camera optics was internal or external (or both?). This will help us list what the contaminants may be. If the source was external, most probably rocket motor residue from the second and or third stages of the launch vehicle, then the periscope should be heavily contaminated, and images taken through the periscope should be much dimmer and/or more diffuse than those taken just via the scan mirror. If the source was internal, degassing from electronics boards, space frame epoxy, etc, then there should be little or no contamination of the periscope, but there could be direct deposits on the CCD itself or perhaps on optical surfaces immediately "upstream" from the CCD. The range of bright star images (of Vega) proposed should give us adequate exposures even if the periscope is heavily contaminated. 2.) We need to know whether the contamination is just diffusing (scattering) light or both absorbing and diffusing light. Using a very bright source should allow us to measure the diffusion well above the bias background, even if the image is spread over 50 or 100 pixels instead of the single pixel expected for the HiRes filter. This also will tell us something about the type of contamination we are dealing with. 3.) We need to be sure the compression chip is working properly. It has never been tested. If we had to attempt the encounter without compression, we could take only half as many images, and all of the encounter software would have to be rewritten. The compressed frame and associated bias frame taken adjacent to an identical uncompressed frame will give us the answer. 4.) These frames will be taken three months after the previous cal lamp frames. Taken under identical conditions, the 20ms OpNav frame will tell us whether the contamination has improved, gotten worse, or stayed the same. Can we help with our problem by doing nothing? 5.) Finally, the two narrowband frames C2 (blue) and Red will tell us whether the contamination is causing more or less absorption in the blue or red part of the spectrum. Thought not too likely, this could help determine the composition of the contaminant. The images we plan to take are listed in the following table. Each is of Vega (Alpha Lyra) except when the "mirror angle" column notes "off Vega." At those times we can point anywhere there isn't a bright star. Exp.# Filter Exposure (ms) Cal. Lamp Compression Mirror Angle 1 HiRes (7) 0 (bias) off off 30 deg. 2 HiRes (7) 10 off off 30 deg. 3 HiRes (7) 35 off off 30 deg. 4 HiRes (7) 100 off off 30 deg. 5 HiRes (7) 350 off off 30 deg. 6 HiRes (7) 1000 off off 30 deg. 7 OpNav (0) 0 (bias) off off 30 deg. 8 OpNav (0) 10 off off 30 deg. 9 OpNav (0) 50 off off 30 deg. 10 OpNav (0) 200 off off 30 deg. 11 OpNav (0) 1000 off off 30 deg. 12 OpNav (0) 0 (bias) off off 0 deg. 13 OpNav (0) 10 off off 0 deg. 14 OpNav (0) 50 off off 0 deg. 15 OpNav (0) 200 off off 0 deg. 16 OpNav (0) 1000 off off 0 deg. 17 HiRes (7) 0 (bias) off off 0 deg. 18 HiRes (7) 10 off off 0 deg. 19 HiRes (7) 35 off off 0 deg. 20 HiRes (7) 100 off off 0 deg. 21 HiRes (7) 350 off off 0 deg. 22 HiRes (7) 1000 off off 0 deg. 23 HiRes (7) 0 (bias) off off 0 deg. 24 HiRes (7) 30 on off off Vega 25 C2 (3) 20000 on off off Vega 26 Red (5) 2000 on off off Vega 27 OpNav (0) 20 on off off Vega 28 OpNav (0) 20 on on off Vega 29 OpNav (0) 0 (bias) off on off Vega 30 OpNav (0) 0 (bias) off off off Vega All 30 of the images listed are planned to be 350 x 350 pixel windows in order to get the results down in a reasonable time. \header ENTRY_TIME = 2000 SEP 12 18:44:18 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JET PROPULSION LABORATORY START_TIME = 2000 MAY 30 00:00:00 STOP_TIME = NULL TARGET = STAR DAY = NULL \text The sequence proposed for May 25 was not taken until May 30 because of concerns about problems when the sequence was tested in the STL at LMA. Exposures 28 & 29 using the compression chip were not taken in the actual imaging sequence, again because of concerns about doing too much that was new and not STL tested. \header ENTRY_TIME = 2001 JUN 07 00:43:01 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JPL (CHIPTON-ROSS) START_TIME = 2000 MAY 30 00:00:00 STOP_TIME = NULL TARGET = STAR DAY = NULL \text The "Vega series" was taken primarily to determine the state of the periscope optics by comparing images of Vega through the periscope and off the periscope. In fact Vega was not seen through the periscope. There was an enormous amount of scattered light in all of the periscope images, but in my opinion the Vega images were in fact just outside of the windowed frames because of motion within the spacecraft deadband. Vega was seen near the edge of the off periscope images as a huge diffuse object. Calibration lamp images showed no improvement over those taken three months earlier, appearing only as a diffuse source of illumination. Clearly there was little absorption in the optical path but a great deal of scattering. \header ENTRY_TIME = 2001 JUN 07 01:08:11 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JPL (CHIPTON-ROSS) START_TIME = 2000 AUG 16 00:00:00 STOP_TIME = NULL TARGET = CAL DAY = NULL \text Beginning with a pair of pre-heating images at 14:45 UT on August 16, a heating cycle was begun with the CCD heater, which raised the CCD temperature from -35 deg C to +8 deg C in about six hours. Heating was continued for 143 1/2 hours, with images taken after 1,2,4,8,16,32,56,100, and 143 1/2 hours. A further pair was taken two weeks later after the CCD had cooled back down to its normal operating temperature. Every image of the cal lamp showed changes, especially during the first few hours. Large cracks appeared in the images, as if ice floes were breaking up. The "granularity" changed in size. However, the cal lamp filament did not reappear, the image remaining very diffuse. \header ENTRY_TIME = 2001 JUN 07 17:14:33 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JPL (CHIPTON-ROSS) START_TIME = 2000 SEP 26 00:00:00 STOP_TIME = NULL TARGET = STAR DAY = NULL \text Five images were taken on September 12, 2000, but one axis was not properly clamped and the drift rates were very high (~19 pixels/s). These images were therefore repeated on September 26. Their purpose was to evaluate more quanti- tatively the effect of the heating cycle. In fact there was very little effect. The images were still extremely broad, with the point spread near 10 pixels at the half amplitude point and a huge "skirt." The limiting magnitude was still near 7. \header ENTRY_TIME = 2001 JUN 07 17:30:50 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JPL (CHIPTON-ROSS) START_TIME = 2000 OCT 17 00:00:00 STOP_TIME = NULL TARGET = STAR DAY = NULL \text As a further check of the state of the camera, images were taken of the open cluster M45, the Pleiades. These would give an indication of the uniformity of the contamination on the optics. It was also intended that a comparison be made of the OpNav and HiRes filters to see if the smaller point spread of the latter would give better images. The images showed no more than a half magnitude variation across the field. Unfortunately the three images taken through the High Resolution filter all suffered from high drift rates (2.4 to 6.4 pixels/s). No firm conclusions could be drawn about any advantage of one filter over the other, but the huge scattered light halo caused by the contamination clearly dominated both. \header ENTRY_TIME = 2001 JUN 07 17:56:13 SYSTEM_NAME = NAVCAM AUTHOR = RAY L. NEWBURN, JR. INSTITUTION = JPL (CHIPTON-ROSS) START_TIME = 2000 NOV 27 00:00:00 STOP_TIME = NULL TARGET = CAL DAY = NULL \text A calibration lamp image was taken on November 27 to furnish a baseline for a new heating cycle that would include heating the CCD radiator with direct sunlight. The entire spacecraft was now approaching perihelion and EGA, so the CCD heater alone brought the CCD up to +12 C where it stayed for a week before the spacecraft was rotated to put sunlight on the radiator. This maneuver brought the CCD temperature up to +24 C on December 5, and it stayed there for about 30 minutes, roughly the time the spacecraft could be operated solely on the battery without draining it below the 50% level. The CCD then cooled back down to +12 C over the next few hours and then to +10 C during the next two weeks due to spacecraft reorientation. The CCD heater was turned off on December 18 and the CCD cooled back down to -33 C over the next eight hours. The period during December and early January was devoted to navigation studies, preparing for Earth Gravity Assist and studying to see just how accurately the spacecraft could be guided in preparation for Earth return in 2006. No further images were taken until January 5, a fact which led to later uncertainties.