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NASA NTRS1981

CCD sensors for interplanetary spacecraft navigation and pointing control

The applications of practical optical image sensing CCDs to interplanetary spacecraft precision science payload delivery are discussed. The increasing demand for precision and flexibility in spacecraft for proposed new missions is forcing a transition to autonomous onboard navigation and pointing control. Onboard processing of video data is a crucial element in this transition and is made possible by CCD imagers and microprocessors. The pending Halley's comet close flyby is used as an example to examine details of the sensor design and the data processing which will meet the requirements. Target body centerfinding for optical navigation, target body tracking signal processing, and CCD sensor heads are examined, and flow charts and block diagrams are given for each.

Eisenman, A. R.↗

NASA NTRS1982

Differential imaging using charge-coupled device (CCD) imagers with on-chip charge storage

A CCD technique is described which allows long integration periods between readouts together with moderate chopping rates. During each phase of a differential chopping cycle, one set of charge images is shifted to the center of the chip, which is light sensitive. At the same time, the other set of charge images is shifted under one of two masked areas which serve as charge-storage sites. Since the vertical shifting between phases can be accomplished in much less time than the typical exposure per phase, there is negligible image smearing. For a given light level and chopping rate the performance of this technique is limited primarily by the readout noise and the vertical charge transfer inefficiency. If many transfer cycles are required between readouts, the charge transfer inefficiency will diffuse the accumulated charge images along the vertical columns. Laboratory and astronomical data obtained with this technique using a CCD camera and the 2.3 m telescope on Kitt Peak are presented.

Stockman, H. S.↗

NASA NTRS1985

CCD observations of comet Tuttle 1980 XIII - The H2O(+) ionosphere

A CCD spectrum of comet Tuttle 1980h has been analyzed with emphasis on the emission of H2O(+) ions. The fine angular resolution (1.5 arcsec) and the capability of absolute brightness calibration of the CCD instrument made it possible to determine the spatial concentration of the H2O(+) ions of this faint comet and the total number of these ions confined within a spherical region. Solar photoionization of the H2O atmosphere can account for the production of the H2O(+) ions observed in the confined region. The dimension of the H2O(+) ionosphere at the time of observation was found to be comparatively small, implying the possible existence of an ionopause sharply delineating the extension of the cometary ionosphere.

Ip, W.-H.↗

NASA NTRS1987

CCD Luminescence Camera

New diagnostic tool used to understand performance and failures of microelectronic devices. Microscope integrated to low-noise charge-coupled-device (CCD) camera to produce new instrument for analyzing performance and failures of microelectronics devices that emit infrared light during operation. CCD camera also used to indentify very clearly parts that have failed where luminescence typically found.

Janesick, James R.↗

NASA NTRS1986

Spectroscopy and CCD-photography of extended red emission in reflection nebulae

Recent spectrographic studies of extended red emission (ERE) seen in the 0.6 to 0.9 micron spectral region in many reflection nebulae have shown fluorescence by amorphous hydrogenated carbon to be the most probable cause of the ERE. Spectrographic observations were performed on the nebulae NGC 2023 and NGC 7023, using the intensified Reticon scanner (IRS) of Kitt Peak National Observatory on the N0-2 0.9 mm telescope. Charge coupled device (CCD) images of NGC2023 and NGC 7023 were obtained with the CfA CCD detector on the 0.6 mm telescope of the Whipple Observatory. Results are discussed.

Witt, A. N.↗

NASA NTRS1986

Optical manifestations of mass outflows from young stars - At atlas of CCD images of Herbig-Haro objects

An attempt is made to provide deep CCD images suitable for tracing the shock-excited and scattered-light components characterizing extended Herbig-Haro complexes. Tabular data include astrometric positions for all stars, shock-excited emission knots, prominent scattered-light patches, as well as an identification for all H-alpha emission objects within the CCD images. It is concluded that: (1) optical outflows are not always accompanied by molecular flows, (2) optical outflows show a higher degree of collimation than their molecular counterparts, and (3) the Herbig-Haro phenomenon is not restricted to low-mass young stellar objects.

Strom, K. M.↗

NASA NTRS1986

The AXAF CCD imaging spectrometer

The AXAF CCD Imaging Spectrometer (ACIS) is currently being defined as a possible focal plane instrument to be flown on the Advanced X-ray Astrophysics Facility (AXAF). The imaging spectrometer consists of an array of charge coupled devices (CCD's) to be placed at the focus of the AXAF mirrors. The array will provide high angular resolution (0.5 arc seconds), moderate spectral resolution (150 eV) over the energy range 0.1 to 10 keV, temporal resolution down to 60 microseconds, and single photon quantum detection efficiencies of up to 90 percent. X-ray sensitivity for a point source exceeds 10 to the -15th ergs/sq cm sec for a 10 to the 5th sec exposure. When used in conjunction with the objective gratings, the array will yield wavelength resolution of up to 200.

Garmire, G. P.↗

NASA NTRS1986

Thinning and mounting a Texas Instruments 3-phase CCD

Thin CCDs with precise control of thickness and surface quality allow astronomers to optimize chips for specific applications. A means of mechanically thinning a TI 800 x 800 CCD with an abrasive slurry of aluminum oxide is presented. Using the same techniques, the abrasives can be replaced with a chemical solution to eliminate subsurface damage. A technique of mounting the CCD which retains the high quality surface generated during thinning is also demonstrated. This requires the backside of the chip to be bonded to a glass window which closely matches silicon's thermal expansion properties. Thinned CCDs require backside treatment to enhance blue and UV quantum efficiency. Two methods are discussed which may be effective with this mounting system.

Lesser, M. P.↗

NASA NTRS1986

The CCD flash gate

Preliminary findings are presented for a new approach that significantly improves the quantum efficiency of the current generation of high-performance, thinned, backside illuminated silicon CCDs. Experiments have shown that the application of a less than 4-micron thick layer of metal with high work function to the backside of the CCD can yield 100-percent internal quantum efficiency in the visible, UV, XUV and soft X-ray regions of the spectrum. Theory and solid state models describing the new technique (the 'CCD flash gate'), and a considerable amount of experimental data, are discussed. Specific recommendations for use of the flash gate in present and future CCDs are also reviewed.

Janesick, James↗

NASA NTRS1987

Differential CCD photometry of faint asteroids in crowded star fields and nonphotometric sky conditions

It is demonstrated that the use of an imaging CCD detector array allows photometric observations of comparatively faint asteroids moving rapidly through a complex background of star images. The shortage of observing time is alleviated by taking advantage of the presence of comparison stars that are observed simultaneously on the CCD imaging area and at small angular separations from the asteroid. These reference stars allow the effects of thin cirrus clouds or haze to be compensated to a degree adequate for the acquisition of scientifically original data.

Wisniewski, W. Z.↗

NASA NTRS1987

Matching a curved focal plane with CCD's - Wide field imaging of glancing incidence X-ray telescopes

The design of a wide field imaging camera suitable for use with a glancing incidence X-ray telescope is complicated by the sharply concave nature of the optimum focal surface of such a telescope. Such a camera made up of a mosaic of CCDs is being designed which is intended for flight aboard the Advanced X-ray Astrophysics Facility (AXAF). The design rationale and tradeoffs are discussed, and the layout for the imaging CCD array is presented. The related issue of optimizing performance of transmission objective gratings is also discussed, and the array of CCD orientations suitable for this problem is presented.

Nousek, J. A.↗

NASA NTRS1989

Photographic, near-infrared, and CCD photometry of the distant globular cluster AM-1

New photographic, CCD, and near-infrared photometry of stars in the distant globular cluster AM-1 are presented. Based on the photographic and CCD photometry down to the horizontal branch, a distance modulus (m-M)v = 20.4 mag is derived, with E(B-V) = 0.0 mag, corresponding to a distance of 120 kpc from the sun. Using the (V-K) colors of two giants in AM-1, a metallicity of Fe/H = -2.0 + or - 0.2 is deduced, in good agreement with earlier determinations. Using complete photometry and star counts, a core radius of 10 arcsec (6 pc) and a tidal radius of 100 arcsec (58 pc) are derived. Despite the low intrinsic luminosity (Mv = -5.0 mag) and the large galactocentric distance of this globular cluster, the apparent magnitude distribution of the giant branch stars of AM-1 is not found to be unusual.

Madore, Barry F.↗

NASA NTRS1990

Rotation of Comet P/Tempel 2 from CCD and photoelectric photometry

Two lightcurves have been obtained of the periodic comet Tempel 2 during May and June 1988, using a CCD camera, as well as five photoelastic photometer lightcurves. On each observational occasion, two uneven maxima were observed which suggest that the lightcurves in question are not products of an active spot on the comet, but rather are true reflections from an elongated rotating nucleus that are being observed through a transparent coma. A comparison of CCD and photoelectric photometry leads to an encouragement of users of the latter to sustain their efforts with such instruments.

Wisniewski, W. Z.↗

NASA NTRS1990

An analysis of CCD images of the coma of Comet Halley

The analysis of selected CCD images of the coma of comet P/Halley is presented. The images were taken using specially designed filters that isolate regions of a comet's spectrum such that only sunlight which has been scattered by the dust in the coma is recorded. The modeling analysis objective is to make use of the skills developed in the development of Monte Carlo particle trajectory models for the distributions of gas species in cometary comae and to use those models as a basis for a new dust coma model. This model will include a self-consistant picture of the time-dependent dusty-gas dynamics of the inner coma and the three-dimensional time-dependent trajectories of the dust particles under the influence of solar gravity and solar radiation pressure in the outer coma. The model is intended to be used as a tool to analyze selected images from the two sets of CCD images with the hope that it will help the understanding of the effects of a number of important processes on the spatial morphology of the observed dust coma. The processes of importance to the observed dust coma include: (1) the dust particle size distribution function; (2) the terminal velocities of various sized dust particles in the inner coma; (3) the radiation scattering properties of dust particles, which are important both in terms of the observe scattered radiation and the radiation pressure acceleration on dust particles; (4) the fragmentation and/or vaporization of dust particles; and (5) the relative importance of CHON and silicate dust particles as they contribute both to the dusty-gasdynamics in the inner coma (that produce the dust particle terminal velocities) and to the observed spatial morphology on the outer dust coma.

Combi, Michael↗

NASA NTRS1990

Photometric narrowband CCD imaging of comets P/Brorsen-Metcalf and Austin (1989c1)

Simultaneous wide-field CCD images and conventional aperture photometry were obtained of Comets P/Brorsen/Metcalf (1989o) and Austin (1989c1). These data allow direct testing of absolute calibration of the CCD images and the ability to generate full-come, continuum-subtracted emission band images. Preliminary photometric calibration for a portion of the Brorsen-Metcalf observations yields reduced emission band and continuum fluxes which agree to within about 10 percent with those from the photoelectric observations. Conventional photometry of Comet Austin shows unusual variations among the production rates of the different species as a function of heliocentric distance.

Schleicher, David G.↗

NASA NTRS1991

New Cepheid distances to nearby galaxies based on BVRI CCD photometry. II - The local group galaxy M33

A true distance modulus to the nearby spiral galaxy M33 has been determined based on CCD photometry obtained at BVRI wavelengths. M33 is presently one of five nearby galaxies used in the calibration of the IR Tully-Fisher relation, and thereby in the determination of the Hubble constant. Using period-luminosity relations at several wavelengths offers the advantage that the distance moduli derived can be corrected for the effects of interstellar extinction. These data indicate that there is internal reddening affecting the Cepheid photometry in M33 which must be accounted for if a true distance modulus is to be obtained for this galaxy. Adopting a true distance modulus to the LMC of 18.5 mag, the new CCD data yield a true distance to M33 of 24.64 + or - 0.09 mag, corresponding to a linear distance of 840 kpc. A mean value of the total color excess (foreground and internal) for the Cepheids in M33 is estimated to be E(B - V) = 0.10 + or - 0.09 mag, assuming a value for the total mean LMC Cepheid color excess of 0.10 mag.

Freedman, Wendy L.↗

NASA NTRS1990

Charge transfer efficiency measurements at low signal levels on STIS/SOHO TK1024 CCD's

Charge transfer efficiency (CTE) test methods are reviewed, and the results and conclusions of the tests are given. The test methods have been utilized to describe the CTE characteristics of the Tektronix 1024 by 1024 CCD to optimize low dark current, low readout noise, and high CTE at low signal levels. CTE modelling is described, and three test methods are set forth and compared. The Fe-55 X-ray response method utilizes the response of a CCD to X-ray photons from the radioactive source Fe-55. The extended pixel edge response method employs the measurement of the charge lost to successive pixels by a known initial signal as it is shifted through the array. The charge injection method consists of charge injection through the output amplifier reset transistor. These measurements were performed on several devices with known CTEs. The CTEs are found to be in agreement for the three methods, making application and test requirements the principal criteria for their use.

Orbock, J. D.↗

NASA NTRS1991

Using image area to control CCD systematic errors in spaceborne photometric and astrometric time-series measurements

The effect of some systematic errors for high-precision time-series spaceborne photometry and astrometry has been investigated with a CCD as the detector. The 'pixelization' of the images causes systematic error in astrometric measurements. It is shown that this pixelization noise scales as image radius r exp -3/2. Subpixel response gradients, not correctable by the 'flat field', and in conjunction with telescope pointing jitter, introduce further photometric and astrometric errors. Subpixel gradients are modeled using observed properties of real flat fields. These errors can be controlled by having an image span enough pixels. Large images are also favored by CCD dynamic range considerations. However, magnified stellar images can overlap, thus introducing another source of systematic error. An optimum image size is therefore a compromise between these competing factors.

Buffington, Andrew↗