The next generation of astronomical photocathode / microchannel plate based UV photon counting detectors will overcome existing count rate limitations by replacing the anode arrays and external cabled electronics with anode arrays integrated into imaging Read Out Integrated Circuits (ROICs). We have fabricated a High Event Rate ROIC (HEROIC) consisting of a 32 by 32 array of 55 μm square pixels on a 60 μm pitch. The pixel sensitivity (threshold) has been designed to be globally programmable between 1 × 10<sup>3</sup> and 1 × 10<sup>6</sup> electrons. To achieve the sensitivity of 1 × 10<sup>3</sup> electrons, parasitic capacitances had to be minimized and this was achieved by fabricating the ROIC in a 65 nm CMOS process. The ROIC has been designed to support pixel counts up to 4096 events per integration period at rates up to 1 MHz per pixel. Integration time periods can be controlled via an external signal with a time resolution of less than 1 microsecond enabling temporally resolved imaging and spectroscopy of astronomical sources. An electrical injection port is provided to verify functionality and performance of each ROIC prior to vacuum integration with a photocathode and microchannel plate amplifier. Test results on the first ROICs using the electrical injection port demonstrate sensitivities between 3 × 10<sup>3</sup> and 4 × 10<sup>5</sup> electrons are achieved. A number of fixes are identified for a re-spin of this ROIC.
A small fraction of Kepler telescope exposures are rejected because of transient, excess background in the field. The
patterns of illumination vary from broad streaks to diffuse patches, sometimes filling the focal plane. Examination of
such images and their temporal variation shows that they can be attributed to nearby particles crossing the field-of-view
of the telescope. Most of the particles appear to be receding. The visual appearance and frequency are consistent with the
"debris storms" reported by STEREO SECCHI observers and which they found to be coincident with meteoroid impacts.
In addition, a few events, lasting several hours each, appear to be caused by more distant extended sources, possibly the
remains of comet dust trails. The tracking cameras, located at the opposite end from the telescope's entrance, and pointed
at roughly right angles to its line-of-sight, also detected moving light sources. Their behavior was consistent with the
main telescope sightings. Future missions requiring precise, uninterrupted photometry and pointing may benefit from
understanding this phenomenon and mitigating it by design and data analysis.
Kepler is NASA's first space mission dedicated to the study of exoplanets. The primary scientific goal is statistical - to
estimate the frequency of planetary systems associated with sun-like stars. Kepler was launched into an Earth-trailing
heliocentric "drift-away" orbit in March 2009, and is monitoring 150,000 stars. The instrument detects the faint
photometric signals of transits of those systems whose orbital planes are oriented in our line-of-sight. An Earth-Sun
analog will produce a transit depth of 80 parts per million (ppm), lasting for at most a few tens of hours, and repeating
once per "year". The instrumentation was designed to provide photometric data with a precision of 20 parts per million
in 6.5 hours for 12<sup>th</sup> magnitude stars, resulting in a signal-to-noise ratio of 4 for an Earth-Sun transit. The stability of the
flight system enables the precision of the data that reveal subtle instrumental and astrophysical effects that in turn allow a
deeper understanding of the performance of the hardware, to enhanced operational procedures, and to novel post-processing
of the data. The data are approaching the sensitivity needed to detect transits of terrestrial planets. Intrinsic
stellar variability is now the most significant component of the photometric error budget.
The Kepler Mission is designed to detect the 80 parts per million (ppm) signal from an Earth-Sun equivalent
transit. Such precision requires superb instrument stability on time scales up to 2 days and systematic error
removal to better than 20 ppm. The sole scientific instrument is the Photometer, a 0.95 m aperture Schmidt
telescope that feeds the 94.6 million pixel CCD detector array, which contains both Science and Fine Guidance
Sensor (FGS) CCDs. Since Kepler's launch in March 2009, we have been using the commissioning and science
operations data to characterize the instrument and monitor its performance. We find that the in-flight detector
properties of the focal plane, including bias levels, read noise, gain, linearity, saturation, FGS to Science crosstalk,
and video crosstalk between Science CCDs, are essentially unchanged from their pre-launch values. Kepler's
unprecedented sensitivity and stability in space have allowed us to measure both short- and long- term effects from
cosmic rays, see interactions of previously known image artifacts with starlight, and uncover several unexpected
systematics that affect photometric precision. Based on these results, we expect to attain Kepler's planned
photometric precision over 90% of the field of view.
In order for Kepler to achieve its required <20 PPM photometric precision for magnitude 12 and brighter stars,
instrument-induced variations in the CCD readout bias pattern (our "2D black image"), which are either fixed or slowly
varying in time, must be identified and the corresponding pixels either corrected or removed from further data
processing. The two principle sources of these readout bias variations are crosstalk between the 84 science CCDs and the
4 fine guidance sensor (FGS) CCDs and a high frequency amplifier oscillation on <40% of the CCD readout channels.
The crosstalk produces a synchronous pattern in the 2D black image with time-variation observed in <10% of individual
pixel bias histories. We will describe a method of removing the crosstalk signal using continuously-collected data from
masked and over-clocked image regions (our "collateral data"), and occasionally-collected full-frame images and
reverse-clocked readout signals. We use this same set to detect regions affected by the oscillating amplifiers. The
oscillations manifest as time-varying moiré pattern and rolling bands in the affected channels. Because this effect
reduces the performance in only a small fraction of the array at any given time, we have developed an approach for
flagging suspect data. The flags will provide the necessary means to resolve any potential ambiguity between
instrument-induced variations and real photometric variations in a target time series. We will also evaluate the
effectiveness of these techniques using flight data from background and selected target pixels.
The Kepler instrument is designed to detect Earth size planets in the "habitable zone" orbiting 9<mv<16, F through M
type stars. A 0.95 m aperture Schmidt telescope feeds the 96 million pixel Kepler focal plane array resulting in ~13°
diameter FOV, so that greater than 100,000 suitable stars in the FOV are continuously monitored over a three and a
half year mission. Detection of planetary transits is made possible through 20 ppm differential photometry using pixel
data from a focal plane array specifically developed for Kepler. The Kepler focal plane array is suspended above the
primary mirror and consists of twenty one 2K x 2K Science CCD modules mounted on a curved Invar substrate with
four output taps per module. Four fine guidance sensor (FGS) CCD modules are mounted to the corners of the Invar
substrate to gather additional pointing information for the Attitude Control System in order to attain the required <2.5
milli-pixel pointing accuracy. A space staring radiator and a closed loop thermal control system maintains the CCD
module temperatures at -85°C with <10mK thermal stability. Low noise electronics reads out both the Science and
FGS CCD modules at a 3 MHz pixel rate. In order to achieve a 4-sigma detection of an Earth-sized planet orbiting a
12th magnitude Sun-like star, the overall noise budget allocates 150 e- to the read noise of each Science CCD module
output. This paper discusses key elements of the Kepler focal plane array design, development, characterization and
We present an overview of the Advanced Camera for Surveys (ACS) CCD detectors performance based on the ground testing and the calibration observations taken during the first four months of ACS operation. ACS has been installed into the Hubble Space Telescope in March 2002 and consists of three different cameras. Two of them employ CCD detectors: the Wide Field Camera a mosaic of two 4096 x 2048 CCDs and the High Resolution Camera a single 1024 x 1024 chip. A review of the on-orbit performance is presented here and also comparison is made with the instrument specifications, published performance expectation and ground test results.
The ACS solar blind channel (SBC) is a photon-counting MAMA detector capable of producing two-dimensional imaging in the UV at wavelengths 1150-1700 Angstroms, with a field of view (FOV) of 31" × 35". We describe the on-orbit performance of the ACS/SBC from an analysis of data obtained from the service mission observatory verification (SMOV) programs. Our summary includes assessment of the point-source image quality and point spread function (PSF) over the SBC FOV, the dark current measurements, the characteristics of the flat fields, fold analysis, throughput, and the UV sensitivity monitor to check for contamination. Where appropriate, a comparison with pre-launch calibration data will also be made.
The Advanced Camera for Surveys (ACS) is a third generation science instrument scheduled for installation into the Hubble Space Telescope (HST) during the servicing mission 3B scheduled for late February 2002. The instrument has three cameras, each of which is optimized for a specific set of science goals. The first, the Wide Field Camera, is a high throughput (43% at 700 nm, including the HST OTA), wide field (200' X 204'), optical and I-band optimized camera. The second, the High Resolution Channel (HRC) has a 26' X 29' field of view, it is optimized for the near-UV (a peak throughput of 24% at 500 nm) and is critically sampled at approximately 630 nm. The third camera, the Solar-Blind Camera is a far-UV, photon counting array that has a relatively high throughput over a 26' X 29' field of view. Two of the three cameras employ CCD detectors: the WFC a mosaic of two SITe 2048 X 4096 pixel CCDs and the HRC a 1024 X 1024 CCD based on the Space Telescope Imaging Spectrograph 21 micrometers pixel CCD. In this paper we review the performance of the flight detectors selected for ACS.
The Space Telescope Imaging Spectrograph (STIS) is a versatile HST instrument covering the 115 - 1000 nm wavelength range in a variety of spectroscopic and imaging modes. Coverage of the ultraviolet range (115 - 310 nm) is provided by two Multi- Anode Microchannel Array (MAMA) detectors built by Ball Aerospace. The FUV MAMA covers the 115 - 170 nm range using an opaque CsI photocathode on the microchannel plate; the NUV MAMA covers the 165 - 310 nm range using a semi-transparent Cs<SUB>2</SUB>Te photocathode on the detector window. Both MAMAS utilize a 1024 X 1024 anode format, but detected photon events are positioned to half the spacing of the anode lines, leading to a 2048 X 2048 format for the final readout. The active area of each detector is 25.6 X 25.6 mm. Since the installation of STIS onto the Hubble Space Telescope (HST) in February 1997, the MAMAs have carried out a varied program of astronomical observing and in-flight calibration. The detectors have performed extremely well. In this report, we briefly describe the design of the STIS MAMA detectors, provide illustrative examples of their scientific use on HST, and summarize their technical performance in orbit, in such areas as sensitivity, resolution, flat-field uniformity and stability, signal-to-noise capability, dynamic range, and background.
BATC was contracted by Langley Research Center (LaRC) to design and fabricate a gallium arsenide photomultiplier tube (GaAs PMT) for LIDAR applications. This particular GaAs PMT uses a high strip current ceramic channel electron multiplier (CEM), manufactured by K&M electronics, capable of operating at a gain of 10<SUP>4</SUP> to 10<SUP>7</SUP>. The GaAs photocathode, processed by Litton Electro-Optical Systems, is used in reflection mode so that light passes through a faceplate, strikes the photocathode and generates photoelectrons, which are collected and multiplied by the CEM. Key issues during the development of this device were; (1) increasing the CEM strip current, (2) improvements in the CEM collection efficiency, (3) processing of an opaque extended blue GaAs photocathode, (4) CEM and photocathode lifetime and (5) electron optic modeling. This paper will discuss the test results from the three functional GaAs PMTs fabricated during this effort as well as development and fabrications issues.
The Space Telescope Imaging Spectrograph (STIS) is a second- generation instrument for the Hubble Space Telescope (HST), designed to cover the 115-1000 nm wavelength range in a versatile array of spectroscopic and imaging modes that take advantage of the angular resolution, unobstructed wavelength coverage, and dark sky offered by the HST. STIS was successfully installed into HST in 1997 February and has since completed a year of orbital checkout, capabilities that it brings to HST, illustrate those capabilities with examples drawn from the first year of STIS observing, and describe at a top level the on-orbit performance of the STIS hardware. We also point the reader to related papers that describe particular aspects of the STIS design, performance, or scientific usage in more detail.
Two multi-anode microchannel array (MAMA) detectors were fabricated at Ball Aerospace Technology Corporation for the Space Telescope Imaging Spectrograph (STIS) which was installed into the Hubble Space Telescope in February 1997. The photometric stability of the opaque CsI and semi- transparent Cs<SUB>2</SUB>Te sealed MAMA tubes has been characterized as a function of operating voltage and illumination conditions. A total exposure of 5 by 10<SUP>7</SUP> counts per pixel results in < 1 percent change in the detection quantum efficiency (DQE), which is attributed to conditioning of the microchannel plate (MCP) during tube processing. Employing good engineering practices to power supply design mitigates the effects of these components in long term detector stability. Other factors contributing to the photometric stability include the use of a curved channel MCP, photocathode processing, hydrocarbon free ultra high vacuum processing and sealed tube processing techniques. Contributions to the low resolution mode DQE stability are discussed along with empirical results on high resolution mode stability.
The space telescope imaging spectrograph (STIS) was designed as a versatile spectrograph capable of maintaining or exceeding the spectroscopic capabilities of both the Goddard High Resolution Spectrograph and the Faint Object Spectrograph (FOS) over the broad bandpass extending from the UV through the visible. STIS achieves performance gains over the aforementioned first generation Hubble Space Telescope instruments primarily through the use of large a real detectors in both the UV and visible regions of the spectrum. Simultaneous spatial and spectral coverage is provided through long slit or slitless spectroscopy. This paper will review the detector design and in-flight performance. Attention will be focussed on the key issue of S/N performance. Spectra obtained during the first few months of operation, illustrate that high signal-to-noise spectra can be obtained while exploiting STIS's multiplexing advantage. From analysis of a single spectrum of GD153, with counting statistics of approximately 165, a S/N of approximately 130 is achieved per spectral resolution element in the FUV. In the NUV a single spectrum of GRW + 70D5824, with counting statistics of approximately 200, yields a S/N of approximately 150 per spectral resolution element. An even higher S/N capability is illustrated through the use of the fixed pattern split slits in the medium resolution echelle modes where observations of BD28D42 yield a signal-to-noise of approximately 250 and approximately 350 per spectral resolution element in the FUV and NUV respectively.
The STIS instrument was installed into HST in February 1997 during the Servicing Mission 2. It has almost completed checkout and is beginning its science program, and is working well. Several scientific demonstration observations were taken to illustrate some of the range of scientific uses and modes of observation of STIS.
The Space Telescope Imaging Spectrograph (STIS), a next-generation instrument for the Hubble Space Telescope, has begun the fabrication of the flight units (plus spares) of the multi-anode microchannel array (MAMA) detectors. STIS will fly two MAMA detectors, one with a CsI photocathode covering the short-wavelength (1150-1750 angstrom) band and a second with Cs<SUB>2</SUB>Te covering the 1650-3100 angstrom band. Good tube yields continue to be realized with many of the MAMAs exceeding flight specifications by substantial amounts in key parameters. Evnironmental testing on the earlier engineering model units (EMUs) demonstrate the ruggedness of the tube design. We present performance results of the STIS flight MAMAs which have been fabricated to date. Life and other engineering tests on EMU detectors will be presented as well.
The space telescope imaging spectrograph (STIS), a next-generation instrument for the Hubble Space Telescope, has fabricated several engineering model units (EMUs) of the multi-anode microchannel array (MAMA) detectors. Good tube yields have been realized in producing these EMUs and some have performances suitable for flight. One of these EMU MAMAs has been operated for substantial periods of time after having undergone both shake and thermal environmental testing. A second will undergo similar environmental tests later this year. An earlier demonstration tube has been used extensively for over a year to evaluate STIS gratings in the Goddard Diffraction Grating Evaluation Facility. The STIS MAMA detectors have now matured to the point where half of the total test and evaluation effort is concerned with the characterization of subtle processes, a level of characterization needed to achieve data with a signal-to-noise ratio in excess of 100. We present test results from these EMUs including detailed analysis of data collected with vacuum chambers specifically designed for the evaluation of these detectors.