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At least 1,009 records · Page 56

Orion: Design of a system for assured low-cost human access to space

In recent years, Congress and the American people have begun to seriously question the role and importance of future manned spaceflight. This is mainly due to two factors: a decline in technical competition caused by the collapse of communism, and the high costs associated with the Space Shuttle transportation system. With these factors in mind, the ORION system was designed to enable manned spaceflight at a low cost, while maintaining the ability to carry out diverse missions, each with a high degree of flexibility. It is capable of performing satellite servicing missions, supporting a space station via crew rotation and resupply, and delivering satellites into geosynchronous orbit. The components of the system are a primary launch module, an upper stage, and a manned spacecraft capable of dynamic reentry. For satellite servicing and space station resupply missions, the ORION system utilizes three primary modules, an upper stage, and the spacecraft, which is delivered to low earth orbit and used to rendezvous, transfer materials, and make repairs. For launching a geosynchronous satellite, one primary module and an upper stage are used to deliver the satellite, along with an apogee kick motor, into orbit. The system is designed with reusability and modularity in mind in an attempt to lower cost.

Elvander, Josh↗

FIFE data analysis: Testing BIOME-BGC predictions for grasslands

The First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) was conducted in a 15 km by 15 km research area located 8 km south of Manhattan, Kansas. The site consists primarily of native tallgrass prairie mixed with gallery oak forests and croplands. The objectives of FIFE are to better understand the role of biology in controlling the interactions between the land and the atmosphere, and to determine the value of remotely sensed data for estimating climatological parameters. The goals of FIFE are twofold: the upscale integration of models, and algorithm development for satellite remote sensing. The specific objectives of the field campaigns carried out in 1987 and 1989 were the simultaneous acquisition of satellite, atmospheric, and surface data; and the understanding of the processes controlling surface energy and mass exchange. Collected data were used to study the dynamics of various ecosystem processes (photosynthesis, evaporation and transpiration, autotrophic and heterotrophic respiration, etc.). Modelling terrestrial ecosystems at scales larger than that of a homogeneous plot led to the development of simple, generalized models of biogeochemical cycles that can be accurately applied to different biomes through the use of remotely sensed data. A model was developed called BIOME-BGC (for BioGeochemical Cycles) from a coniferous forest ecosystem model, FOREST-BGC, where a biome is considered a combination of a life forms in a specified climate. A predominately C4-photosynthetic grassland is probably the most different from a coniferous forest possible, hence the FIFE site was an excellent study area for testing BIOME-BGC. The transition from an essentially one-dimensional calculation to three-dimensional, landscape scale simulations requires the introduction of such factors as meteorology, climatology, and geomorphology. By using remotely sensed geographic information data for important model inputs, process-based ecosystem simulations at a variety of scales are possible. The second objective of this study is concerned with determining the accuracy of the estimated fluxes from BIOME-BGC, when extrapolated spatially over the entire 15-km by 15-km FIFE site. To accomplish this objective, a topographically distributed map of soil depth at the FIFE site was developed. These spatially-distributed fluxes were then tested with data from aircraft by eddy-flux correlation obtained during the FIFE experiment.

Hunt, E. Raymond, Jr.↗

Nonlinear system guidance in the presence of transmission zero dynamics

An iterative procedure is proposed for computing the commanded state trajectories and controls that guide a possibly multiaxis, time-varying, nonlinear system with transmission zero dynamics through a given arbitrary sequence of control points. The procedure is initialized by the system inverse with the transmission zero effects nulled out. Then the 'steady state' solution of the perturbation model with the transmission zero dynamics intact is computed and used to correct the initial zero-free solution. Both time domain and frequency domain methods are presented for computing the steady state solutions of the possibly nonminimum phase transmission zero dynamics. The procedure is illustrated by means of linear and nonlinear examples.

Meyer, G.↗

Resource recovery and epidemiology of anaerobic wastewater treatment process in a controlled ecological life support system

The results of work accomplished under two different areas: (1) Resource Recovery of an Anaerobic Wastewater Treatment process, and (2) Epidemiological Study of an Anaerobic Wastewater Treatment Process are documented. The first part of the work was to set up and test three anaerobic digesters and then run these three digesters with a NASA-simulated wastewater. The second part of the work was to use a multi-drug resistant strain of Salmonella choleraesuis as the indicator bacteria for the epidemiological study. Details of these two parts can be found in two master's theses and are described in Sections 3 and 4 of this report. Several important results condensed from these two parts are summarized in Section 2.

Li, Ku-Yen↗

Atomic Oxygen Textured Polymers

Atomic oxygen can be used to microscopically alter the surface morphology of polymeric materials in space or in ground laboratory facilities. For polymeric materials whose sole oxidation products are volatile species, directed atomic oxygen reactions produce surfaces of microscopic cones. However, isotropic atomic oxygen exposure results in polymer surfaces covered with lower aspect ratio sharp-edged craters. Isotropic atomic oxygen plasma exposure of polymers typically causes a significant decrease in water contact angle as well as altered coefficient of static friction. Such surface alterations may be of benefit for industrial and biomedical applications. The results of atomic oxygen plasma exposure of thirty-three (33) different polymers are presented, including typical morphology changes, effects on water contact angle, and coefficient of static friction.

Banks, Bruce A.↗

An acoustic charge transport imager for high definition television applications

The primary goal of this research is to develop a solid-state high definition television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels per frame. This imager offers an order of magnitude improvement in speed over CCD designs and will allow for monolithic imagers operating from the IR to the UV. The technical approach of the project focuses on the development of the three basic components of the imager and their integration. The imager chip can be divided into three distinct components: (1) image capture via an array of avalanche photodiodes (APD's), (2) charge collection, storage and overflow control via a charge transfer transistor device (CTD), and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the development of manufacturable designs for each of these component devices. In addition to the development of each of the three distinct components, work towards their integration is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail in Sections 2-4.

Hunt, W. D.↗

Velocity surface measurements for ZnO films over /001/-cut GaAs

A potential application for a piezoelectic film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs /001/-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the group of zone axes (110) propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the group of zone axes (100) direction. The passivation layer of SiO2 or Si3N4 (less than 0.2 micrometer thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/microseconds at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theorectical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 micrometer thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

Kim, Yoonkee↗

Tunnel-Junction Mixers Perform Well At 205 GHz

Superconductor-Insulator Superconductor (SIS) tunnel junctions made of NbN/MgO/NbN and Nb/AlOx/Nb, with cross-sectional areas of about 0.30 and 0.25 micrometer(Sup2) respectively, fabricated and tested for use as mixers at frequencies near 205 GHz. Cross sections must be small to make capacitances of devices acceptably small for operation at this frequency. NbN and Nb good materials choices as superconductors because of high energy gap, and mechanically and electrically rugged and chemically stable.

Javadi, Hamid H. S.↗

Probes For Measuring Changing Internal Temperatures

Improved thermocouple probes devised for measuring rapidly changing temperatures within layers of solid materials. In original application, layers in question are carbon-cloth phenolic liners in solid-rocket motor nozzles, and probes inserted in layers to various depths of order of 0.5 in. measure changing temperatures in layers during hot-fire tests. Probe concept adapted to measurements of temperatures inside various other layers, materials, and components, including material test specimens.

Hunt, S. B.↗

Microbolometers Based On Epitaxial YBa(2)Cu(3)O(7-x) Thin Films

Improved microbolometers of superconducting-transition type developed with view toward eventual fabrication of staring, infrared-imaging planar arrays of such microbolometers integrated with addressing electronic circuitry. Superconducting thin films in microbolometers epitaxial. These devices exhibit high sensitivity and low noise.

Foote, Marc C.↗

Fabrication Of SNS Weak Links On SOS Substrates

High-quality superconductor/normal-conductor/superconductor (SNS) devices ("weak links") containing epitaxial films of YBa(2)Cu(3)O(7-x) and SrTiO(3) fabricated on silicon-on-sapphire (SOS) substrates with help of improved multilayer buffer system. Process for fabrication of edge-defined SNS weak links described in "Edge-Geometry SNS Devices Made of Y/Ba/Cu" (NPO-18552).

Hunt, Brian D.↗

Reactively Deposited Aluminum Oxide and Fluoropolymer Filled Aluminum Oxide Protective Coatings for Polymers

Reactive ion beam sputter deposition of aluminum simultaneous with low energy arrival of oxygen ions at the deposition surface enables the formation of highly transparent aluminum oxide films. Thick (12 200 A), adherent, low stress, reactively deposited aluminum oxide films were found to provide some abrasion resistance to polycarbonate substrates. The reactively deposited aluminum oxide films are also slightly more hydrophobic and more transmitting in the UV than aluminum oxide deposited from an aluminum oxide target. Simultaneous reactive sputter deposition of aluminum along with polytetrafluoroethylene (PTFE Teflon) produces fluoropolymer-filled aluminum oxide films which are lower in stress, about the same in transmittance, but more wetting than reactively deposited aluminum oxide films. Deposition properties, processes and potential applications for these coatings will be discussed.

Rutledge, Sharon K.↗

SSME propellant path leak detection

Initial research established that the occurrence of a leak in the powerhead of the Space Shuttle Main Engine (SSME) is accompanied by a sudden, but sustained, change in intensity in a given region of an image. Based upon this, temporal processing of video images on a frame-by-frame basis has been used to detect leaks within a given field of view. The leak detection algorithm developed in this study consists of a digital highpass filter cascaded with a moving average filter applied at each point in the image field. The absolute value of the output is then averaged over the full frame to produce a single time-varying mean value estimate that is indicative of the intensity and extent of a leak. Recent work has included the processing of an extensive amount of data obtained from NASA MSFC to verify the performance of the leak detection system. Further research is being conducted on applying the leak detection algorithm to anomaly detection in the SSME exhaust by means of three channel color processing as opposed to single channel monochrome processing in the case of the leak detection system.

Smith, L. M.↗

Metal clad aramid fibers for aerospace wire and cable

High strength light weight metal clad aramid fibers can provide significant weight savings when used to replace conventional metal wire in aerospace cable. An overview of metal clad aramid fiber materials and information on performance and use in braided electrical shielding and signal conductors is provided.

Tokarsky, Edward W.↗

Cross correlation and length scales in turbulent flows near surfaces

Two kinds of length scales are used in turbulent flows; 'functional length scales' such as mixing length, dissipation length L(sub epsilon), etc., and 'flow-field length scales' derived from cross correlations of velocity, pressure, etc. in the flow. Some connection between these scales are derived here. We first consider the cross correlation R(sub vv)(y,y(sub 1)) of the normal components u at two heights y, y(sub 1) above a rigid surface, normalized by the velocity y(sub 1) (greater than y). For shear-free boundary layers it is found theoretically, and in field and numerical experiments that R(sub vv) approximately equals y/y(sub 1). For shear layers it is also found that R(sub vv) approximately equals f(y/y(sub 1)) less than or equal to y,y(sub 1). This function f differs slightly between low Reynolds number numerical simulations and field experiments. The lateral structure defined by R(sub vv)(y,r(sub 3); y(sub 1),0) is also self similar and shows that the eddies centered at about y(sub 1) appear to have constant lateral width a(sub 3) above and below y(sub 1), where a(sub 3, sup +) approximately equals 7+1/(1.4dU(sup +)/dy(sup +)), when normalized on u(sub *) and v, where U is the mean velocity. Results for L(sub epsilon, sup -1) from direct numerical simulation are found to compare well with the formula L(sub epsilon, sup -1) = A(sub B)/y + A(sub S)dU/dy/v, for unidirectional and reversing turbulent boundary layers and channel flow, except near where dU/dy approximately equals 0. The conclusion is that the large-scale eddy structure and length scales in these flows are determined by a combination of shear and blocking, and that the vertical component of turbulence has a self-similar structure in both kinds of boundary layer.

Hunt, J. C. R.↗

Airbreathing hypersonic vehicle design and analysis methods

The design, analysis, and optimization of airbreathing hypersonic vehicles requires analyses involving many highly coupled disciplines at levels of accuracy exceeding those traditionally considered in a conceptual or preliminary-level design. Discipline analysis methods including propulsion, structures, thermal management, geometry, aerodynamics, performance, synthesis, sizing, closure, and cost are discussed. Also, the on-going integration of these methods into a working environment, known as HOLIST, is described.

Lockwood, Mary Kae↗

SNS Devices With Pinhole-Defined Active Regions

Superconductor/normal conductor/superconductor (SNS) microbridge devices with pinhole-defined active regions undergoing development. Device includes thin, electrically insulating layer deposited epitaxially, with controlled formation of pinholes, on one of two superconducting layers. Normally conducting metal deposited epitaxially in pinholes and on insulating layer, forming electrical contact between two superconducting layers. Junction resistances and maximum junction voltages expected to be increased.

Hunt, Brian D.↗

Hypersonic Airbreathing Vehicles/Technologies

Hypersonic airbreathing horizontal takeoff and landing (HTOL) vehicles are highly integrated systems involving many advanced technologies. The design environment is variable rich, intricately networked, and sensitivity intensive; as such, it represents a tremendous challenge. Creating a viable design requires addressing three main elements: (1) an understanding of the 'figures of merit' and their relationship, (2) the development of sophisticated configuration discipline prediction methods and a synthesis procedure, and (3) the synergistic integration of advanced technologies across the discipline spectrum. This paper will focus on the vision for hypersonic airbreathing vehicles and the advanced technologies that forge the designs. Airbreathing hypersonics encompass endoatmospheric (airplanes...missiles are a part of the matrix but will not be included in this paper since they are an air force focus) and space access vehicles with speed from Mach 4 up to Mach 25 (orbital). These vehicles can be divided into two classes...cruisers and accelerators. The cruiser designs reflect high lift-to-drag whereas the accelerators reflect low drag per unit inlet capture; thus, the cross section of the accelerator attributes a much larger percentage to propulsion. One of the more design influencing items is fuel. The hydrogen fueled vehicles must be very volumetric efficient to contain the low density fuel and thus tend to be a bit bulgy (more conducive to lifting bodies or wing bodies) whereas with hydrocarbon fueled vehicles, the concern is loading because of the high density fuel; thus, they may tend to be more towards waveriders which are not usually very volumetric efficient. Hydrocarbon fuels (endothermic) are limited in their engine cooling capacity to below Mach 8.

Hunt, James L.↗