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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Comparing and Contrasting Detectors: JWST NIR vs HST WFC3

In many ways, WFC3s IR channel is a good indicator for what to expect with JWST. There are some differences, most of which should be beneficial in JWST- JWSTs lower operating temperature will freeze out charge traps that would affect WFC3. Benefits should include lower dark current, lower persistence, and better reciprocity- JWSTs more recent HgCdTe process has lower defect density. The benefits are as described above- JWST uses better indium barriers. The benefits should include fewer RC type pixels. One area where more study might be beneficial is stability. The detector electronics play a significant role in determining how stable a detector system is(v.s. bias drifts and photometry). JWSTs SIDECARs are completely WFC3s Ball electronics- Studies comparing the bias and photometric stability of WFC3 and JWST might be useful to informing data acquisition and calibration strategies for JWST.

NIR↗
NASA NTRS1988

Simulations of HST observations of globular clusters

Simulations of Hubble Space Telescope observations to study galactic globular clusters are examined. Studies of the cores of nearby globular clusters to determine the stellar density distributions and luminosity functions in the innermost regions of the clusters are presented. Pictures of M 13 are included to demonstrate the usefulness of these studies. Stellar population studies of a relatively unobscured globular cluster to detect white dwarfs and the faint red end of the cluster luminosity function are discussed and illustrated with pictures of NGC 6397.

Bahcall, John N.↗
NASA NTRS1989

Particle background effects for Hubble Space Telescope (HST) and the Lyman Far Ultraviolet Spectroscopic Explorer

Requirements on orbital background counting rates are described for the UV and visible detectors on the planned second generation instrument Space Telescope Imaging Spectrograph (STIS) and for the proposed Lyman Far Ultraviolet Spectroscopic Explorer. Expected background rates and shielding requirements are analyzed for detector types in both instruments for low earth orbits, and for high orbits in the case of Lyman.

Woodgate, B. E.↗
NASA NTRS1989

HST battery test expert systems

During the testing of nickel-cadmium and nickel-hydrogen batteries for the Hubble Space Telescope, an urgent need for data management was recognized. Testing of these batteries generates much needed data that is used for vital decision making, such as when to recondition, change the charging scheme, or adjust the workload of the batteries. To solve this problem, an expert system called NICBES was developed. NICBES can recognize a testbed anomaly, identify the malfunctioning component, recommend a course of action, evaluate battery status, and provide decision support. A description of NICBES and some of its enhancements are given.

Johnson, Yvette B.↗
NASA NTRS1991

Using HST: From proposal to science

The following subject areas are covered: a short history; uses of network STSCII (general communication, science collaboration, functional activities, internal data management, and external data access); proposal/observation handling; DMF access; and future uses and requirements.

Shames, P.↗
NASA NTRS1991

Photometric calibration of the HST wide-field/planetary camera. I - Ground-based observations of standard stars

This paper describes the observation and analysis of field stars, undertaken as a step toward understanding the photometric properties of the filters and CCDs aboard the Wide-Field/Planetary Camera of the Hubble Space Telescope. Ground-based CCD observations have been made simulating 15 of the most important WF/PC passbands. Data are presented here for an equatorial network of stars including many UBVRI standards and some spectrophotometric standards. They serve to establish a photometric system that will be used in the calibration of in-flight data and that is useful for the calibration of other ground-based data. Transformations between WF/PC and other photometric systems are discussed, as well as the effects of interstellar absorption and atmospheric extinction on data in the WF/PC system. Synthetic photometry has been used as an aid in the data analysis and is described.

Harris, Hugh C.↗
NASA NTRS1991

The current ability of HST to reveal morphological structure in medium-redshift galaxies

The capabilities of the Faint Object Camera (FOC) and the Wide Field Camera (WFC) are assessed on the basis of a brief program of single-orbit images of medium-faint galaxies. The FOC yielded a good resolved image of a compact galaxy at a blue magnitude J of 20.5 in a single-orbit exposure. WFC images have a survey capability that can include many galaxies per field, with sufficient resolving power to distinguish clearly between galaxies and stars down to the level of 0.2 arcsec, depending on the signal-to-noise ratio, and a reasonable capacity for morphology. Although some morphological detail can be discerned in even the aberrated images, deconvolutions are found to greatly enhance the ability to see structural detail. Even at the low S/N that is provided by single-orbit exposures, the more sophisticated restoration methods offer some advantage over simple Fourier or Lucy techniques.

King, Ivan R.↗
NASA NTRS1992

Capacity loss on storage and possible capacity recovery for HST nickel-hydrogen cells

Negatively precharged nickel hydrogen cells will experience a useable capacity loss during extended open circuit storage periods. Some of the lost capacity can be recovered through cycling. Capacity recovery through cycling can be enhanced by cycling at high depths of discharge (DOD). The most timely procedure for recovering the faded capacity is to charge the cell fully and allow the cell to sit open-circuit at room temperature. This procedure seems to be effective in part because of the enlarged structure of the active materials. The compounds that formed during storage at the low electrode potentials can more easily dissolve and redistribute. All of the original capacity cannot be recovered because the lattice structure of the active material is irreversibly altered during storage. The recommendation is to use positively precharged cells activated with 26 percent KOH if possible. In aerospace applications, the benefits of negative precharge are offset by the possibility of delays and storage periods.

Lowery, John E.↗
NASA NTRS1992

Comparing restored HST and VLA imagery of R Aquarii

The maximum entropy method is applied to Hubble Space Telescope data taken of the R Aquarii binary system and its jet with the Faint Object Camera in order to restore an image in forbidden O III at 5007 A plagued by spherical aberration and detector saturation. These results are compared with 2-cm radio continuum imagery taken with the Very Large Array at the same limiting resolution of about 0.1 arcsec. The comparison suggests that shock excitation of the inner jet accounts for a spatial difference between the forbidden O III and radio continuum emission regions.

Hollis, J. M.↗
NASA NTRS1991

The Next Generation Space Telescope - A large UV-IR successor to HST

Attention is given to the science goals of the Next Generation Space Telescope (NGST), namely, detection and spectroscopy of gas giant planets to earthlike planets around nearby stars, study of nearby star-forming complexes with resolutions of 5-50 AU in the visible and IR, measurement of stellar populations in a variety of environments, spatial resolution and mapping of complex structures in the inner narrow line regions for AGN and QSOs, and investigation of the structure and evolution of galaxies at redshifts greater than 1. The NGST characteristics, milestones, long-term strategy, and launch capability are also discussed.

Illingworth, Garth↗
NASA NTRS1992

A Zero-Gyro safemode controller for HST

The purpose of this paper is to document the Zero-Gyro Sunpoint mode for Hubble Space Telescope, a safemode designed to ensure a power positive state without the use of rate gyros. This paper presents an overview of the Zero-Gyro Sunpoint algorithm, followed by details of the algorithm, control system design, and simulation results. A new, related safemode test, the System Momentum Test, is also discussed.

Markley, F. L.↗
NASA NTRS1992

Ultraviolet observations of stellar coronae - Early results from HST

The first GHRS spectra of two very different late-type giant stars - Capella and Gamma Dra are reported. Capella is a 104 day period binary system consisting of two stars (G9 III and GO III) each of which shows bright emission lines formed in solar-like transition region and coronae. By contrast, Gamma Dra is a hybrid-chromosphere star with very weak emission lines from high-temperature plasma. Low-dispersion spectra of these stars covering the 1160 to 1717 A spectral range show unresolved emission lines from neutral species through N V. The very different surface fluxes detected in the spectra of these stars suggest different types of heating mechanisms.

Linsky, Jeffrey L.↗
NASA NTRS1993

Photometric calibration of the HST wide-field/planetary camera. II - Ground-based observations of calibration fields

Ground-based CCD observations have been made simulating the photometric properties of the Wide Field/Planetary Camera (WF/PC) of the Hubble Space Telescope. This paper gives results in 15 of the most important WF/PC passbands for two fields chosen to provide efficient in-flight calibration of the WF/PC. These calibration fields are located in the outskirts of the globular clusters Omega Cen and NGC 6752.

Harris, Hugh C.↗
NASA NTRS1993

HST observations of NGC 4395, the least luminous Seyfert 1 nucleus - Evidence against the starburst hypothesis for broad-lined active galactic nuclei

The starburst hypothesis for broad-line AGN is examined here using ultraviolet spectra and optical images of NGC 4395, the least luminous Seyfert 1 nucleus. From the evidence it is concluded that the apparent activity in the Seyfert 1 nucleus of NGC 4395 probably cannot be explained in the context of the starburst hypothesis of Terlevich et al. (1992). The strongest piece of evidence is the absence of stellar absorption lines, especially in the UV and NIR spectra. Other relevant characteristics are the UV spectral index of roughly -1, small physical size, low luminosity, and lack of obvious variability.

Filippenko, Alexei V.↗
NASA NTRS1993

On-orbit test of the HST Zero-Gyro safemode controller

The purpose of this paper is to document the on-orbit testing of the Zero-Gyro Sunpoint mode for Hubble Space Telescope, a safemode designed to ensure a power positive state without the use of rate gyros. This paper presents an overview of the test planning and test results.

Markley, F. L.↗