Multianode microchannel arrays (MAMAs) are a family of digital photon-counting imaging arrays designed specifically for use in space. Two MAMAs with formats of 1024×1024 pixels were included in the Space Telescope Imaging Spectrograph (STIS) to cover the far-ultraviolet (FUV) from 115 to 170 nm and the near-ultraviolet (NUV) from 165 to 310 nm. STIS was installed on orbit in the Hubble Space Telescope in February 1997. The flight-spare FUV MAMA was installed on orbit in the Advanced Camera for Surveys in March 2002, and the flight-spare NUV MAMA was installed on orbit in the Cosmic Origins Spectrograph in May 2009. This paper describes the construction, modes of operation, and on-orbit performances of the MAMAs and the resulting lessons for future space astrophysics missions.
The Hubble Space Telescope 1st Servicing Mission carried with it a total of 14 corrective mirrors, four in wide field (WF) 2 and the planetary (PC) 2 (three WF and one PC), two each for the three axial SIs (FOS red and blue), faint object camera (f48 and f/96), and Goddard high resolution spectrograph, which were packaged in a single module, corrective optics space telescope axial replacement (COSTAR). This paper presents the fabrication and validation of these mirrors that were the cornerstone of strategy to recover the telescope performance. The COSTAR optics were particularly challenging and represented one of the earliest examples of anamorphic aspheric mirrors fabricated to <0.005 waves RMS of surface figure residual. Other firsts included one of the earliest applications of phase stepping interferometry, now an industry standard. Insights into the corrective designs, the mirror figure shapes, and the technology used in the validation of the mirrors are presented.
Radiation testing results for a Geiger-mode avalanche photodiode (GM-APD) array-based imager are reviewed. Radiation testing is a crucial step in technology development that assesses the readiness of a specific device or instrument for space-based missions or other missions in high-radiation environments. Pre- and postradiation values for breakdown voltage, dark count rate (DCR), after pulsing probability, photon detection efficiency (PDE), crosstalk probability, and intrapixel sensitivity are presented. Details of the radiation testing setup and experiment are provided. The devices were exposed to a total dose of 50 krad(Si) at the Massachusetts General Hospital’s Francis H. Burr Proton Therapy Center, using monoenergetic 60 MeV protons as the radiation source. This radiation dose is equivalent to radiation absorbed over 10 solar cycles at an L2 orbit with 1-cm aluminum shielding. The DCR increased by 2.3 e−/s/pix/krad(Si) at 160 K, the afterpulsing probability increased at all temperatures and settings by a factor of ∼2, and the effective breakdown voltage shifted by +1.5 V. PDE, crosstalk probability, and intrapixel sensitivity were unchanged by radiation damage. The performance of the GM-APD imaging array is compared to the performance of the CCD on board the ASCA satellite with a similar radiation shield and radiation environment.
HgCdTe detector arrays with a cutoff wavelength of ∼10 μm intended for the Near-Earth Object Camera (NEOCam) space mission were subjected to proton-beam irradiation at the University of California Davis Crocker Nuclear Laboratory. Three arrays were tested—one with 800-μm substrate intact, one with 30-μm substrate, and one completely substrate-removed. The CdZnTe substrate, on which the HgCdTe detector is grown, has been shown to produce luminescence in shorter wave HgCdTe arrays that causes an elevated signal in nonhit pixels when subjected to proton irradiation. This testing was conducted to ascertain whether or not full substrate removal is necessary. At the dark level of the dewar, we detect no luminescence in nonhit pixels during proton testing for both the substrate-removed detector array and the array with 30-μm substrate. The detector array with full 800-μm substrate exhibited substantial photocurrent for a flux of 103 protons/cm2 s at a beam energy of 18.1 MeV (∼750 e−/s) and 34.4 MeV (∼65 e−/s). For the integrated space-like ambient proton flux level measured by the Spitzer Space Telescope, the luminescence would be well below the NEOCam dark current requirement of <200 e−/s, but the pattern of luminescence could be problematic, possibly complicating calibration.
We report on multilayer high efficiency antireflection coating (ARC) design and development for use at UV wavelengths on CCDs and other Si-based detectors. We have previously demonstrated a set of single-layer coatings, which achieve >50% quantum efficiency (QE) in four bands from 130 to 300 nm. We now present multilayer coating designs that significantly outperform our previous work between 195 and 215 nm. Using up to 11 layers, we present several model designs to reach QE above 80%. We also demonstrate the successful performance of 5 and 11 layer ARCs on silicon and fused silica substrates. Finally, we present a five-layer coating deposited onto a thinned, delta-doped CCD and demonstrate external QE greater than 60% between 202 and 208 nm, with a peak of 67.6% at 206 nm.
The 2.1-m Otto Struve Telescope, world’s second largest in 1939, today has modern motion control and superb tracking, yet the 19-m-diameter Art Deco dome has resisted many attempts to record its azimuth electronically. Demonstrated in January 2016, a small tactical-grade fiber-optic gyro located anywhere on the rotating structure, aided by a few fiducial points to zero gyro drift, adequately locates the azimuth. The cost of a gyro is practically independent of dome size, offering an economical solution for large domes that cannot be easily encoded with conventional systems. The 100-Hz sampling is capable of revealing anomalies in the rotation rate, valuable for preventive maintenance on any dome. I describe software methods and time series analysis to integrate angular velocity to dome azimuth; transformation of telescope hour angle and declination into required dome azimuth, using a formula that accounts for a cross-axis mount inside an offset dome; and test results.