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Delamere, W. A.

Publications and source records attributed to Delamere, W. A..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

MRO's High Resolution Imaging Science Experiment (HiRISE): Polar Science Expectations

The Mars Reconnaissance Orbiter (MRO) is expected to launch in August 2005, arrive at Mars in March 2006, and begin the primary science phase in November 2006. MRO will carry a suite of remote-sensing instruments and is designed to routinely point off-nadir to precisely target locations on Mars for high-resolution observations. The mission will have a much higher data return than any previous planetary mission, with 34 Tbits of returned data expected in the first Mars year in the mapping orbit (255 x 320 km). The HiRISE camera features a 0.5 m telescope, 12 m focal length, and 14 CCDs. We expect to acquire approximately 10,000 observations in the primary science phase (approximately 1 Mars year), including approximately 2,000 images for 1,000 stereo targets. Each observation will be accompanied by a approximately 6 m/pixel image over a 30 x 45 km region acquired by MRO s context imager. Many HiRISE images will be full resolution in the center portion of the swath width and binned (typically 4x4) on the sides. This provides two levels of context, so we step out from 0.3 m/pixel to 1.2 m/pixel to 6 m/pixel (at 300 km altitude). We expect to cover approximately 1% of Mars at better than 1.2 m/pixel, approximately 0.1% at 0.3 m/pixel, approximately 0.1% in 3 colors, and approximately 0.05% in stereo. Our major challenge is to find the dey contacts, exposures and type morphologies to observe.

McEwen, A.↗
NASA NTRS2002

HiRISE: The High Resolution Imaging Science Experiment for Mars Reconnaissance Orbiter

HiRISE, an experiment on the 2005 MRO mission, will provide an unprecedented combination of ground sampling dimension (25-50 cm/pixel), signal-to-noise ratio (greater than 100:1 at all latitudes), swath width (5-10 km), partial 3-color coverage, greater than 2% coverage of Mars at 1 m/pixel or better, and stereo imaging. Additional information is contained in the original extended abstract.

McEwen, A. S.↗
NASA NTRS1992

CCDs and photon counting devices: Applications in space and from the ground

The development of the 2048 by 2048 CCD (Charge Coupled Device) for a second generation space telescope instrument has resulted in devices with very few defects, dark currents of less than 12 electrons/pixel/hour at -80 deg, readout noise levels of less than 4 electrons rms, and excellent charge transfer efficiency at signal levels of less than 10 electrons. A second generation of devices that capitalize on these characteristics have been produced and are currently in test. Faster frame transfer devices that preserve these characteristics have been designed that include tridirectional taps in the serial register. The state of the art in CCD's as photon counting detectors is reviewed.

Delamere, W. A.↗
NASA NTRS1991

The Space Telescope imaging spectrograph 2048 CCD and its characteristics

Development of a 2048-squared CCD for a second-generation Space Telescope instrument has produced some very encouraging devices. The first experimental lot of 10 devices have very few defects, dark currents of less than 40 electrons/pixel/hour at -80 C, readout noise levels of less than 4 electrons rms and excellent charge transfer efficiency at signal levels of less than 10 electrons.

Delamere, W. A.↗
NASA NTRS1990

Proton radiation effects on multi-pinned-phased CCDs

Three Tektronix 1024 x 1024 multi-pinned-phased (MPP) charge coupled devices were irradiated with protons to obtain data on CCD performance degradation in a proton radiation environment. The devices were irradiated with a spectrum of energies up to 120 MeV, simulating the total radiation dose of a long-term space experiment. Basic parameters such as charge transfer efficiency, dark current, noise, and full well were measured before and after irradiation. A test was also performed to determine the effectiveness of various thicknesses of tantalum shielding in protecting the CCD from damage. Dark current increase and CTE degradation were the most noticeable effects of proton radiation. This paper will present the objectives, test data, and conclusions of the proton testing, and will identify future testing to be performed.

Murata-Seawalt, D.↗
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 NTRS1989

Dust distribution in the inner coma of Comet Halley - Comparison with models

Giotto observations of the inner coma of Comet Halley are analyzed, focusing on the dust distribution and the gas-dust interaction. Differences between the azimuthal and radial dust distributions are discussed. The profiles of dust jets suggest that gas emission is localized in the same source areas that give rise to dust. The observational results are compared with models of cometary dust and suggestions are made for improving the models to give better agreement with observations.

Reitsema, H. J.↗
NASA NTRS1989

Active polar region on the nucleus of Comet Halley

The images of the nucleus of Comet Halley returned by the Giotto spacecraft reveal a number of active regions on the surface, one of which is near the expected location of the rotation pole. This feature is larger and brighter than other source regions, suggesting that the mechanism that drives this source is also different. At this active region near the rotation pole, the sun was circumpolar for a significant portion of the solar encounter. Continuous insolation heated the nucleus to greater depths than in other areas, producing the broad, active polar region.

Reitsema, H. J.↗
NASA NTRS1988

A model for intensity profiles of dust jets near the nucleus of Comet Halley

The Giotto spacecraft's Halley Multicolor Camera images have been used to derive intensity profiles of the jetlike dust features that are associated with active regions of the Comet Halley nucleus. An intensity profile's asymptotic behavior at a radius greater than 100 km from the nucleus can be seen as arising from a source located at a hypothetical point below the active source region. Several source distributions are investigated. The extended source model considers divergent dust flow from an active area of arbitrary shape. It is concluded that the surface is neither smooth nor homogeneous, but must instead be characterized by varying curvature and roughness in order to reflect the observed conical dust flow.

Huebner, W. F.↗
NASA NTRS1987

Comparison of active regions on the nucleus of Comet Halley

The images of the nucleus of Comet Halley returned by the Giotto spacecraft reveal a number of active regions on the surface, one of which is near the expected location of the rotation axis. This feature is larger and brighter than other source regions, suggesting that the mechanism which drives this source is also different. At this active region near the rotation pole the Sun is circumpolar for a significant portion of the solar encounter. Continuous solar insolation causes heating of the nucleus to greater depths and results in the unique properties of this source region. For example, the dust scattering in the antisolar regions around the nucleus is less from the polar region than from the region at the sunward end of the nucleus, consistent with spotty ejection of dusty mantle from the sunward tip and widespread activity in the polar region.

Reitsema, H. J.↗
NASA NTRS1986

Observations by the Halley multicolor camera

The first image of comet Halley was taken by the multicolor camera (HMC) on 9 March from a distance of 23.6 million km. During the encounter HMC was switched on at 4:12 hr before closest approach CA. It took its first image at 3:06 h before CA. Overall 2043 images were taken in single sensor mode. The inner coma was observed using all 11 filters and polarizers. The transmission curves of the filters (except polarizers) are shown together with the sensitivity of the camera. At 6 min before CA HMC switched to multiple sensor mode taking 4 images almost simultaneously through the clear, blue, and red wideband filters. Only 2% of all data taken could be transmitted in 69 image sets. The last image showing details of the nuclear surface was taken from a slant distance of 1740 km and has a nominal resolution of 39 m per pixel.

Keller, H. U.↗
NASA NTRS1986

Nucleus morphology of Comet Halley

Images obtained by the Halley multicolor camera were used to determine the projected size and shape of the nucleus. The location of the terminator and numerous surface features were determined. There is good correlation between the brightest surface features and the dust jets; however, many bright features are seen which are not associated with jets. Most of the observed features are circular and appear to be related to surface elevation. The angularity of the terminator gives an indication of the three-dimensional structure of the face which was observed.

Reitsema, H. J.↗
NASA NTRS1986

Radiometric observations of the nucleus of Comet Halley

Images obtained by the Halley multicolor camera (HMC) were used to determine the surface brightness of the nucleus. Radiometric values of jet-free areas of the surface are presented and a range of possible surface brightness values are derived. These direct measures are compared with brightnesses derived from the size of the nucleus, as determined from HMC images, and ground-based observations obtained before the onset of coma activity.

Delamere, W. A.↗
NASA NTRS1986

Dust activity of Comet Halley's nucleus

Images obtained by the Halley multicolor camera using the clear filter with a pass band from 300 to 1000 nm were used to study dust activity in the comet nucleus. Comparisons with ground based observations confirm that dust production towards the Sun increases in activity relative to the southern background source while the Giotto spacecraft was approaching. This is in agreement with the assumption that the sunward activity becomes stronger when the source rotates towards the Sun. Estimated dust column density is 90 billion/sqm, with optical thickness less than or = 0.3. Surface reflectivity is less than 1%, indicating a very rough surface with large fractions of shadowed areas.

Keller, H. U.↗
NASA NTRS1986

Dust-gas interaction deduced from Halley multicolor camera observations

The dust and gas productions of comet Halley were measured by the dust counter and the mass spectrometers on the Giotto spacecraft. These instruments give only little information about the spatial asymmetry of the activity. The asymmetry in the dust production is clearly evident from the dust jets seen in the Halley Multicolor Camera images. Since the dust is entrained by the gas, gas production must be similarly asymmetric. The intensity profiles along and across several dust jets are related to their source regions on the nucleus. Properties of the dust jets are investigated. A few compact, but highly active source regions on the nucleus produce most of the visible dust and can account for most of the gas produced by the comet.

Huebner, W. F.↗
NASA NTRS1986

A three-dimensional model of the nucleus of Comet Halley

The nucleus of comet Halley was observed by the Halley Multicolor Camera (HMC) during the last minutes of the flyby sequence before reaching the point of closest approach. The phase angle change during the observational period was less than 17 deg, so HMC data can only define a two-dimensional contour of the nucleus at a certain time. The overall geometry during the HMC observations is outlined and the findings are related to information available from other sources at different times. The nucleus of the comet is described as a triaxial ellipsoid with major axes of 16, 10, and 9 km. The rotation axis is directed towards delta 1950 = -(40 + or - 5) deg and alpha 1950 = (50 + or - 10) deg. The rotation with a period of P = (54 + or - 1) is in a prograde sense with respect to the orbital motion.

Wilhelm, K.↗