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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Studies of single-mode injection lasers and of quaternary materials. Volume 1: Single-mode constricted double-heterojunction AlGaAs diode lasers

Constricted double-heterojunction (CDH) lasers are presented as the class of single-mode nonplanar-substrate devices for which the lasing cavity is on the least resistive electrical path between the contact and the substrate. Various types of CDH structures are considered under three general topics: liquid-phase epitaxy over channeled substrates, lateral mode control, and current control in nonplanar-substrate devices. Ridge-guide CDH lasers have positive-index lateral-mode confinement and provide: single-mode CW operation to 7 mW/facet at room temperature and to 3 mW/facet at 150 C; light-current characteristics with second-harmonic distortion as low as -57 dB below the fundamental level; threshold-current temperature coefficients, as high as 375 C (pulsed) and 310 C (CW); constant external differential quantum efficiency to 100 C; and lasing operation to 170 C CW and 280 C pulsed. Semileakyguide CDH lasers have an asymmetric leaky cavity for lateral-mode confinement and provide single-mode operation to 15 to 20 mW/facet CW and to 50 mW/facet at 50% duty cycle. Modulation characteristics and preliminary reliability data are discussed.

Botez, D.↗
NASA NTRS1988

Optical Backplane Interconnect Technology (OBIT)

We describe and analyze a novel approach to implementing an Optical Backplane Interconnect Technology (OBIT) that is capable of optically connecting any row of a 32x32 backplane array to any row of a second 32x32 array. Each backplane array is formed monolithically on a wafer. The technology is based on the use of Grating Surface Emitting (GSE) waveguides formed on a wafer containing quantum-well and separate confinement waveguide layers. These layers are used for transverse guiding, gain, modulation, detection, and for the formation of wavelength tunable distributed-Bragg reflector lasers. The required surface structures are formed photolithographically. The GSE waveguides act as efficient antennae that radiate light at angles selected by tuning the wavelength of the lasers. The same waveguides may be used as the receiving antennae when the array is used in the receiving mode. Thus, wavelength tuning is used to direct each row of the transmitting array to the desired row of the receiving array. In summary: The optical backplane array will have the following characteristics: Any row of a 32x32 GSE array may be optically connected to any row of a second 32x32 array. Only one switch decision is required to switch 32 parallel connections to any one of 32 positions. Each monolithic array can be used as both transmitter and receiver by switching the bias on the quantum-well switch-detectors. Separate transmitting and receiving structures could be provided for duplex operation. For a bit error rate of 10 sup 9 at 100-MHz data rate, a required laser power of 12 mW is calculated based on an estimated total optical loss of 40 dB.

Hammer, J. M.↗
NASA NTRS2000

Loads Produced During the Ingression and Egression of the Portable Foot Restraint on the Hubble Space Telescope

The Hubble Space Telescope (HST) was deployed from the Space Shuttle Discovery on April 25, 1990. It is capable of performing observations in the visible, near-ultraviolet, and near-infrared (1150 A to 1 mm). The HST weighs 12 tons, and collects light with an 8-ft-diameter mirror. The attitude control and maneuvering is performed by four of six gyroscopes, or reaction wheels. The HST contains fine guidance sensors that lock onto guide stars to reduce the spacecraft drift and increase the pointing accuracy. The HST was designed to last 15 years, with crewed service missions approximately every three years. The first service mission, STS-61, took place in 1993. The second service mission took place in 1997. In 1999, the STS-103 crew performed the third service mission to the HST. This mission's purpose was to replace the right sensor units and make improvements on the fine guidance sensors. To perform these tasks on the HST, the STS-103 crewmembers used a portable foot restraint to anchor themselves to the HST in the zero-gravity environment. The solar arrays currently used on the telescope are second-generation, and therefore susceptible to loads placed on the telescope. The crew and Mission Operations Directorate worried about the damage that the crew could possibly cause during ingress and egress of the PFR and by transferring loads to the solar arrays. The purpose of this study is to inform the crewmembers of the loads they are imparting on the HST, and train them to decrease these loads to a safer level. Minimizing these loads will significantly decrease the chance of crewmembers causing damage to the solar arrays while repairing the HST.

Ramsey, Susan↗
NASA NTRS2004

Alignment and Performance of the Infrared Multi-Object Spectrometer

The Infrared Multi-Object Spectrometer (IRMOS) is a principle investigator class instrument for the Kitt Peak National Observatory 4 and 2.1 meter telescopes. IRMOS is a near-IR (0.8 - 2.5 micron) spectrometer with low-to mid-resolving power (R = 300 - 3000). IRMOS produces simultaneous spectra of approximately 100 objects in its 2.8 x 2.0 arc-min field of view (4 m telescope) using a commercial Micro Electro-Mechanical Systems (MEMS) micro-mirror array (MMA) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the MMA field stop, and the spectrograph images the MMA onto the detector. We describe ambient breadboard subsystem alignment and imaging performance of each stage independently, and ambient imaging performance of the fully assembled instrument. Interferometric measurements of subsystem wavefront error serve as a qualitative alignment guide, and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing provides verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Image testing is performed at multiple field points. A mercury-argon pencil lamp provides a spectral line at 546.1 nanometers, a blackbody source provides a line at 1550 nanometers, and a CCD camera and IR camera are used as detectors. We use commercial optical modeling software to predict the point-spread function and its effect on instrument slit transmission and resolution. Our breadboard and instrument level test results validate this prediction. We conclude with an instrument performance prediction for cryogenic operation and first light in late 2003.

Connelly, Joseph A.↗
NASA NTRS2001

A Daytime Aspect Camera for Balloon Altitudes

We have designed, built, and flight-tested a new star camera for daytime guiding of pointed balloon-borne experiments at altitudes around 40km. The camera and lens are commercially available, off-the-shelf components, but require a custom-built baffle to reduce stray light, especially near the sunlit limb of the balloon. This new camera, which operates in the 600-1000 nm region of the spectrum, successfully provided daytime aspect information of approximately 10 arcsecond resolution for two distinct star fields near the galactic plane. The detected scattered-light backgrounds show good agreement with the Air Force MODTRAN models, but the daytime stellar magnitude limit was lower than expected due to dispersion of red light by the lens. Replacing the commercial lens with a custom-built lens should allow the system to track stars in any arbitrary area of the sky during the daytime.

Dietz, Kurt L.↗
NASA NTRS2002

Daytime Aspect Camera for Balloon Altitudes

We have designed, built, and flight-tested a new star camera for daytime guiding of pointed balloon-borne experiments at altitudes around 40 km. The camera and lens are commercially available, off-the-shelf components, but require a custom-built baffle to reduce stray light, especially near the sunlit limb of the balloon. This new camera, which operates in the 600- to 1000-nm region of the spectrum, successfully provides daytime aspect information of approx. 10 arcsec resolution for two distinct star fields near the galactic plane. The detected scattered-light backgrounds show good agreement with the Air Force MODTRAN models used to design the camera, but the daytime stellar magnitude limit was lower than expected due to longitudinal chromatic aberration in the lens. Replacing the commercial lens with a custom-built lens should allow the system to track stars in any arbitrary area of the sky during the daytime.

Dietz, Kurt L.↗
NASA NTRS1973

Optical filtering for star trackers

The optimization of optical filtering was investigated for tracking faint stars, down to the fifth magnitude. The effective wavelength and bandwidth for tracking pre-selected guide stars are discussed along with the results of an all-electronic tracker with a star tracking photomultiplier, which was tested with a simulated second magnitude star. Tables which give the sum of zodiacal light and galactic background light over the entire sky for intervals of five degrees in declination, and twenty minutes in right ascension are included.

Wilson, R. E.↗
NASA NTRS1990

Possibilities for LWIR detectors using MBE-grown Si(/Si(1-x)Ge(x) structures

Traditionally, long wavelength infrared (LWIR) detection in Si-based structures has involved either extrinsic Si or Si/metal Schottky barrier devices. Molecular beam epitaxially (MBE) grown Si and Si/Si(1-x)Ge(x) heterostructures offer new possibilities for LWIR detection, including sensors based on intersubband transitions as well as improved conventional devices. The improvement in doping profile control of MBE in comparison with conventional chemical vapor deposited (CVD) Si films has resulted in the successful growth of extrinsic Si:Ga, blocked impurity-band conduction detectors. These structures exhibit a highly abrupt step change in dopant profile between detecting and blocking layers which is extremely difficult or impossible to achieve through conventional epitaxial growth techniques. Through alloying Si with Ge, Schottky barrier infrared detectors are possible, with barrier height values between those involving pure Si or Ge semiconducting materials alone. For both n-type and p-type structures, strain effects can split the band edges, thereby splitting the Schottky threshold and altering the spectral response. Measurements of photoresponse of n-type Au/Si(1-x)Ge(x) Schottky barriers demonstrate this effect. For intersubband multiquntum well (MQW) LWIR detection, Si(1-x)Ge(x)/Si detectors grown on Si substrates promise comparable absorption coefficients to that of the Ga(Al)As system while in addition offering the fundamental advantage of response to normally incident light as well as the practical advantage of Si-compatibility. Researchers grew Si(1-x)Ge(x)/Si MQW structures aimed at sensitivity to IR in the 8 to 12 micron region and longer, guided by recent theoretical work. Preliminary measurements of n- and p-type Si(1-x)Ge(x)/Si MQW structures are given.

Hauenstein, Robert J.↗
NASA NTRS1984

The Explorer's Guide to the Universe: A Reading List for Planetary and Space Science

During the last decade, both scientists and the public have been engulfed by a flood of discoveries and information from outer space. Distant worlds have become familiar landscapes. Instruments in space have shown us a different Sun by the "light" of ultraviolet radiation and X-rays. Beyond the solar system, we have detected a strange universe of unsuspected violence, unexplained objects, and unimaginable energies. We are completely remarking our picture of the universe around us, and scientists and the general public alike are curious and excited about what we see. The public has participated in this period of exploration and discovery to an extent never possible before. In real time, TV screens show moonwalks, the sands of Mars, the volcanoes of Io, and the rings of Saturn. But after the initial excitement, it is hard for the curious non-scientist to learn more details or even to stay in touch with what is going on. Each space mission or new discovery is quickly skimmed over by newspapers and TV and then preserved in technical journals that are neither accessible nor easily read by the average reader. This reading list is an attempt to bridge the gap between the people who make discoveries in space and the people who would like to read about them. The aim has been to provide to many different people--teachers, students, scientists, other professionals, and curious citizens of all kinds--a list of readings where they can find out what the universe is like and what we have learned about it. We have included sections on the objects that seem to be of general interest--the Moon, the planets, the Sun, comets, and the universe beyond. We have also included material on related subjects that people are interested in--the history of space exploration, space habitats, extraterrestrial life, and U F O ' s . The list is intended to be self-contained; it includes both general references to supply background and more specific sources for new discoveries. Although the list can be used by a wide range of people, it has been compiled with the non-scientist specifically in mind. A s a general rule, we have not included technical symposia or the special issues of

French, Bevan M.↗
NASA NTRS1979

High-acceleration mass drivers

High-acceleration mass drivers are discussed including the MD2 model of axial geometry, with individually powered drive coils of 13.1 cm diameter. Timing is derived through the interruption of light beams by the moving armature (bucket). Electric power is provided by the resonant discharge of sector capacitor banks through silicon-controlled rectifiers in a two-phase, quadrature circuit. The bucket flies in vacuum, guided by passive dynamic eddy-current magnetic forces, those currents flowing in strip conductors lining the inside of a nonconducting vacuum pipe. Quantitative measurements are obtained with a solid bucket carrying two superconducting coils with a current density of 25 kA/sq cm. A cryogenic station for cooling the bucket to liquid helium temperature is connected to the vacuum pipe.

Oneill, G. K.↗
NASA NTRS2005

Terrestrial Planet Finder Coronagraph Observatory summary

Creating an optical space telescope observatory capable of detecting and characterizing light from extra-solar terrestrial planets poses technical challenges related to extreme wavefront stability. The Terrestrial Planet Finder Coronagraph design team has been developing an observatory based on trade studies, modeling and analysis that has guided us towards design choices to enable this challenging mission. This paper will describe the current flight baseline design of the observatory and the trade studies that have been performed. The modeling and analysis of this design will be described including predicted performance and the tasks yet to be done.

space↗
NASA NTRS2016

The Staring OBservations of the Atmosphere (SOBA) Mission Concept

The Staring OBservations of the Atmosphere (SOBA) Mission is a concept that was developed and matured under the guidance of the NASA Ames Project EXellence (APEX) program. If funded, it will provide an unprecedented opportunity to improve ash transport forecasts and climate model simulations associated with volcanic eruptions. NASA and National science objectives require a better understanding of volcanic aerosol and trace gas emissions, transport, chemical transformation, and deposition, since they impact Earth's climate and atmospheric composition, human health, and aviation safety. Natural hazards such as the 2010 eruption of the Eyjafjallajökull volcano in Iceland demonstrated how existing remote-sensing assets were inadequate for individual volcanic event monitoring. During this eruption, available instruments were unable to provide data necessary to initialize volcanic plume transport models so that they could accurately predict the quantity and location of volcanic ash. As a result, thousands of flights around the world were grounded unnecessarily, at great expense. Volcanoes can also play a large role in regulation of the Earth's climate, so SOBA observations will also be used to evaluate and improve volcanic aerosol and trace gas simulation in chemical transport models (CTMs) and global climate models (GCMs). We propose the development of an airborne remote sensing concept and field campaign that will respond to an eruption and provide near real time observations of a volcanic plume, specifically ash injection height, transport, aerosol microphysical physical properties, and the location and concentration of sulfur dioxide (SO2) (sulfate (SO42-) aerosol precursor). This airborne system will utilize a depolarization sensitive, downward looking Light Detection And Ranging (lidar) instrument and an ultraviolet (UV) imaging spectrometer, and will provide data to be ingested by volcanic ash advisory models. Furthermore, the lessons learned in the development of this system could eventually guide regular deployment of similar systems by NASA or other government agencies.

Aerosols↗
NASA NTRS1992

XRONOS: A timing analysis software package. User's guide, version 3.00

XRONOS is a general purpose timing analysis package. Although it was designed mainly for x-ray astronomy, XRONOS is basically detector and wavelength independent. It has been used to analyze data from the Einstein Observatory, Exosat and Ginga, as well as optical photometry and helioseismology data. It includes programs for: light curve(s), hardness ratio and color-color plotting, epoch folding, power spectrum, autocorrelation, cross correlation, time skewness, and statistical analysis. An overview of XRONOS and walkthrough of a XRONOS session are presented. The QDP/PLT plotting and function fitting program used by XRONOS is outlined and the algorithm and features of XRONOS are detailed.

Stella, L.↗
NASA NTRS2004

Control of gravitropic orientation. II. Dual receptor model for gravitropism

Gravitropism of vascular plants has been assumed to require a single gravity receptor mechanism. However, based on the evidence in Part I of this study, we propose that maize roots require two. The first mechanism is without a directional effect and, by itself, cannot give rise to tropism. Its role is quantitative facilitation of the second mechanism, which is directional like the gravitational force itself and provides the impetus for tropic curvature. How closely coupled the two mechanisms may be is, as yet, unclear. The evidence for dual receptors supports a general model for roots. When readiness for gravifacilitation, or gravifacilitation itself, is constitutive, orthogravitropic curvature can go to completion. If not constitutively enabled, gravifacilitation can be weak in the absence of light and water deficit or strong in the presence of light and water deficit. In either case, it can decay and permit roots to assume reproducible non-vertical orientations (plagiogravitropic or plagiotropic orientations) without using non-vertical setpoints. In this way roots are deployed in a large volume of soil. Gravitropic behaviours in shoots are more diverse than in roots, utilising oblique and horizontal as well as vertical setpoints. As a guide to future experiments, we assess how constitutive v. non-constitutive modes of gravifacilitation might contribute to behaviours based on each kind of setpoint.

NASA Discipline Plant Biology↗
NASA NTRS1991

Operation of the University of Hawaii 2.2M telescope on Mauna Kea

NASA's planetary astronomy program provides part of the funding for the 2.2 meter telescope. The parameters for time on the telescope are laid out. A major instrumental highlight has been the commissioning of a 256 x 256 near infrared camera which uses a Rockwell NICMOS-3 array. At the f/10 focus, image scales of 0.37 and 0.75 arcsec/pixel are available. A new, high quantum efficiency Tektronix 1024 x 1024 CCD saw first light on the telescope in 1991, and was available regularly from April 1991. Data from both of these detectors are transmitted directly to the Sun workstation for immediate analysis by the observers. The autoguider software was enhanced to permit guided tracking on objects have nonsideral motions (i.e., solar system objects).

Hall, Donald N. B.↗
NASA NTRS2005

Enhanced Lighting Techniques and Augmented Reality to Improve Human Task Performance

One of the most versatile tools designed for use on the International Space Station (ISS) is the Special Purpose Dexterous Manipulator (SPDM) robot. Operators for this system are trained at NASA Johnson Space Center (JSC) using a robotic simulator, the Dexterous Manipulator Trainer (DMT), which performs most SPDM functions under normal static Earth gravitational forces. The SPDM is controlled from a standard Robotic Workstation. A key feature of the SPDM and DMT is the Force/Moment Accommodation (FMA) system, which limits the contact forces and moments acting on the robot components, on its payload, an Orbital Replaceable Unit (ORU), and on the receptacle for the ORU. The FMA system helps to automatically alleviate any binding of the ORU as it is inserted or withdrawn from a receptacle, but it is limited in its correction capability. A successful ORU insertion generally requires that the reference axes of the ORU and receptacle be aligned to within approximately 0.25 inch and 0.5 degree of nominal values. The only guides available for the operator to achieve these alignment tolerances are views from any available video cameras. No special registration markings are provided on the ORU or receptacle, so the operator must use their intrinsic features in the video display to perform the pre-insertion alignment task. Since optimum camera views may not be available, and dynamic orbital lighting conditions may limit viewing periods, long times are anticipated for performing some ORU insertion or extraction operations. This study explored the feasibility of using augmented reality (AR) to assist with SPDM operations. Geometric graphical symbols were overlaid on the end effector (EE) camera view to afford cues to assist the operator in attaining adequate pre-insertion ORU alignment.

Maida, James C.↗
NASA NTRS1988

Public-Facilities Locator For The Blind

Proposed optoelectronic system guides blind people to important locations in public buildings, With system, sightless person easily determines directions and distances of restrooms, water fountains, stairways, emergency exits, and elevators. Circuitry uncomplicated and inexpensive, in both transmitter and receiver. Readily-available light-emitting diodes, photodiodes, and integrated-circuit chips used to build locator aid for the blind.

Moore, Kevin D.↗
NASA NTRS1988

High performance composites research at NASA-Langley

Barriers to the more extensive use of advanced composites in heavily loaded structures on commercial transports are discussed from a materials viewpoint. NASA-Langley matrix development activities designed to overcome these barriers are presented. These include the synthesis of processible, tough, durable matrices, the development of resin property/composite property relationships which help guide the synthesis program, and the exploitation of new processing technology to effectively combine reinforcement filament with polymer matrices. Examples of five classes of polymers being investigated as matrix resins at NASA Langley are presented, including amorphous and semicrystalline thermoplastics, lightly crosslinked thermoplastics, semi-interpenetrating networks and toughened thermosets. Relationships between neat resin modulus, resin fracture energy, interlaminar fracture energy, composite compression strength, and post-impact compression strength are shown. Powder and slurry processing techniques are discussed.

Stclair, Terry L.↗