Subject: HRI/MRI IP TV4 Flash report Date: Sat, 08 Mar 2003 22:12:46 -0500 From: Dennis Wellnitz Hi all, This is the flash report for Friday, March 7, 2003, for the HRI and MRI (IP) thermal-vac performance and calibration testing, which is calibration thermal vac 4. Marty and Ken started the testing day at 8 am with the usual 8 frames of darks for all modes for the HRI IR spectrometer. Other testing people arrived later in the day because they had stayed later the previous day to finish that day's work. Our emphasis today will be HRI IR spectrometer tests. The first test was IR spectrometer darks with variable delays since the last previous IR image, to study the higher offset of the first IR image after a period of non-readout of the detector. This effect had been discovered in analysis of the previous HRI-SIM thermal vacs but we did not have sufficient data from those thermal vacs to be able to characterize the effect adequately for sequence planning, either for same mode delays or for changing mode delays. These darks with variable delays were interspersed throughout the morning and early afternoon with gas cell absorption measurements using the SIRTF black body source viewed through the ZnSe window and the gas cell. The gas cell was successively filled with CO, CH4, and N2. Because the CO measurement was made at a SIRTF black body setting of 300 and the CH4 measurement was made at a setting of 350, the N2 measurement was made at both settings: 350 and 300. The quick looks at this data indicated that we had seen the absorptions (avoiding both too little signal and saturation), but we have not yet ratioed the spectra to permit us to quantify the exact spectral positions of the CO and CH4 absorptions. When the above tasks were finished, we moved the HRI system to view test station 2 through the fused silica chamber window. We viewed first the SIRTF black body through the fused silica chamber window and then the calibrated tungsten lamp with sapphire window, also through the fused silica chamber window, to permit comparisons of the spectra through the two different chamber windows. We also viewed the calibrated tungsten lamp reflected from each of our two gold diffusers, and with an ND1 filter. We then moved the HRI system back to viewing the ZnSe window, and then masked off that window with thick aluminum foil to reduce the input intensity to a minimum. In this mode of operation, the HRI aperture field of view is nearly filled by the liquid-nitrogen-cooled shroud (very cold surface), with a small fraction looking at the ZnSe window through a bending mirror. We also see part of the bending mirror mount, which may be considerably warmer than other things in the chamber, due to heat conducted from the translation mount drive, which is heated so that it will keep working. In this configuration we commanded the IR stimulator DAC to hex B3 (maximum permitted intensity) and took 64 IR frames in mode 1. Careful analysis of these 64 frames dark-subtracted and co-added showed no indication whatsoever of the IR stimulator illumination. We plan to look at the IR stimulator electrically at the end of this thermal vac, to see whether it still shows appropriate resistance or has opened. We expect to have one last chance to test the IR stimulator pre-flight, during the spacecraft thermal vac. After removing the foil from the ZnSe window, we took spectra of the calibrated tungsten lamp with sapphire window through the ZnSe window as reflected from the gold diffuser. However, we saw too much signal from other objects within the aperture of the HRI. Reducing the aperture of the HRI with an aluminum foil stop outside the chamber, adjusted so that only the illuminated gold diffuser was visible, permitted a good spectrum of the tungsten lamp without contamination from other reflecting materials. For our next test we masked both windows of the chamber with thick aluminum foil to provide darkness and then ran all three detectors (HRI-VIS, HRI-IR, and MRI-VIS), as well as both shutter wheels and both shutters, simultaneously, with varying phasing, as an "encounter-like sequence". This was designed to be both a thermal test to look at the heat generated by everything running at once, and a cross-talk test to look at instrument to instrument interference. A quick look for interference in the visible showed a few DN of noise; we will be interested in correlating the additional noise we saw in the detectors during this test with the times of operation of other detectors or mechanisms. While running some of the above tests, we also looked at yesterday's IR spectrometer data to review the spatial registration of the spectrum on the IR-FPA. It appears that the top end of the IR spectrometer slit has moved from about 3 pixels from the top of the IR-FPA (seen at TV2, after adjustment from the TV1 position) to less 1 pixel from the top of the IR-FPA. Thus we have seen a spatial displacement of the slit position on the IR-FPA of about 2 physical pixels upwards (1 binned pixel upwards), and a displacement of the spectrum of about 4 physical pixels (2 binned pixels) towards the long-wavelength end of the IR-FPA. At this point I presume that the motions are due to settling caused by the vibration testing of the instruments, but am open to other suggestions. These small motions do not require any re-adjustment of the IR spectrometer. The next test of the IR spectrometer was a detector test, looking at linearity at this operating temperature of the IR-FPA by changing the integration time of the IR-FPA while looking at dark images (chamber shroud and masked ZnSe window). This data will be very useful for correctly interpreting and using the flat fields we have gathered in this thermal vac. During this test we discovered that the read-out ADC (Analog to Digital Converter) of the B side of the IR-FPA was saturating before the detector was saturating. [The left, short-wavelength part of the detector is denoted the A side and the right, long-wavelength part of the detector the B side. These two parts of the detector are separate quadrants of the four-quadrant device. We use only two of the four quadrants.] We adjusted the offset bias for the B side until we could see the saturation of the detector rather than the saturation of the read-out ADC. Had we discovered and corrected this earlier in our testing, we would have had a larger range of illumination without saturation on the B side of the detector, which would have made test setup easier and faster. However, this ADC saturation should not affect our ability to reduce and interpret our results. The last test of the day was a measurement of the IR spectrometer boresight with respect to the HRI CCD detector. This concluded all required performance and calibration tests at this temperature, except for final cold soak and thermal balance, which we plan to do for all of Saturday and most of Sunday. We are currently planning to run another "encounter-like sequence" Sunday evening to look carefully at the thermal effects. Then we plan to start warming the system. Upon careful review of the data taken on the MRI at the ITS operating temperature as we were cooling the systems, there remain some inconsistencies that merit further investigation. Therefore we are planning to stop the warm-up of the instruments at the ITS operating temperature and make some additional measurements. If we can resolve the inconsistencies and thereby understand the focus variation of the MRI with temperature, we may be able to avoid having to do another thermal vac to check ITS focus at its operating temperature. As a result, we may forego the HRI measurements at 10 degrees warmer than cold soak temperatures, previously scheduled for Monday, so that we can more quickly warm the instruments to ITS operating temperature. Because we had essentially completed the intensive part of this performance and calibration thermal vac, we retired shortly after 7:30 pm to the Wilderness Pub for a celebration. I apologize for not preparing this flash report until now; taking part in the celebration and getting some rest had higher priority for me. I hope no one was seriously inconvenienced by the delay in receiving this report. While preparing this report, I have copied all of the data taken recently on the ITOC computers to the RAID drive on the workstation "arm" and also to the hard drive of my laptop computer, which will be moved off-site. As a result all data taken during this thermal vac has now been copied to arm and also to at least one other hard drive, so that we have an original copy and a backup. Much of the data has also been burned onto DVD+R's, thanks to Bill Smythe. Please let me know if you have any questions or comments. Also please let me know if you would prefer not to be included on this Flash report distribution list, or if there is someone else who should be included on this distribution list. Dennis