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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Processing lunar soils for oxygen and other materials

Two types of lunar materials are excellent candidates for lunar oxygen production: ilmenite and silicates such as anorthite. Both are lunar surface minable, occurring in soils, breccias, and basalts. Because silicates are considerably more abundant than ilmenite, they may be preferred as source materials. Depending on the processing method chosen for oxygen production and the feedstock material, various useful metals and bulk materials can be produced as byproducts. Available processing techniques include hydrogen reduction of ilmenite and electrochemical and chemical reductions of silicates. Processes in these categories are generally in preliminary development stages and need significant research and development support to carry them to practical deployment, particularly as a lunar-based operation. The goal of beginning lunar processing operations by 2010 requires that planning and research and development emphasize the simplest processing schemes. However, more complex schemes that now appear to present difficult technical challenges may offer more valuable metal byproducts later. While they require more time and effort to perfect, the more complex or difficult schemes may provide important processing and product improvements with which to extend and elaborate the initial lunar processing facilities. A balanced R&D program should take this into account. The following topics are discussed: (1) ilmenite--semi-continuous process; (2) ilmenite--continuous fluid-bed reduction; (3) utilization of spent ilmenite to produce bulk materials; (4) silicates--electrochemical reduction; and (5) silicates--chemical reduction.

Knudsen, Christian W.↗
NASA NTRS1992

COMPAS: Compositional mineralogy with a photoacoustic spectrometer

There is an important need for an in situ method of mineral and rock identification and quantification that provides true absorption spectra for a wide spectral range for lunar lander/rover missions. Many common minerals such as feldspars, magnetite, ilmenite, and amorphous fine solids or glasses, can exhibit flat spectral reflectances in the 400-2500 nm spectral region that render inaccurate or difficult their spectral detection and quantitative analysis. Ideal rock and mineral spectra are, of course, pure absorption spectra that are independent of the spectral effects of scattering, particle size, and distribution that can result in a suppression or distortion of their spectral features. This ideal seldom pertains to real samples. Since sample preparation is difficult and may fundamentally alter the observed diffuse spectral reflectance, an in situ spectral measurement method for rocks and minerals on the Moon, insensitive to the sample morphology, would be invaluable. Photoacoustic spectroscopy is a well-established technique appropriate for this task that has been widely applied in condensed-phase spectral studies of complex, highly light scattering, unprepared samples of everything from coal to whole blood, including rock and mineral characterization. A Compositional Mineralogy Photoacoustic Spectrometer, or COMPAS, can enable in situ spectral measurement of rocks and minerals, bypassing the major limitations of diffuse reflectance spectroscopy. COMPAS spectral capabilities for rock and mineral samples will be incorporated into an instrument prototype specifically for lunar measurements, compatible with rover capabilities.

Smith, W. Hayden↗
NASA NTRS1992

A process for prototyping onboard payload displays for Space Station Freedom

Significant advances have been made in the area of Human-Computer Interface design. However, there is no well-defined process for going from user interface requirements to user interface design. Developing and designing a clear and consistent user interface for medium to large scale systems is a very challenging and complex task. The task becomes increasingly difficult when there is very little guidance and procedures on how the development process should flow from one stage to the next. Without a specific sequence of development steps each design becomes difficult to repeat, to evaluate, to improve, and to articulate to others. This research contributes a process which identifies the phases of development and products produced as a result of each phase for a rapid prototyping process to be used to develop requirements for the onboard payload displays for Space Station Freedom. The functional components of a dynamic prototyping environment in which this process can be carried out is also discussed. Some of the central questions which are answered here include: How does one go from specifications to an actual prototype? How is a prototype evaluated? How is usability defined and thus measured? How do we use the information from evaluation in redesign of an interface? and Are there techniques which allow for convergence on a design?

Moore, Loretta A.↗
NASA NTRS1991

Hybrid neural network and fuzzy logic approaches for rendezvous and capture in space

The nonlinear behavior of many practical systems and unavailability of quantitative data regarding the input-output relations makes the analytical modeling of these systems very difficult. On the other hand, approximate reasoning-based controllers which do not require analytical models have demonstrated a number of successful applications such as the subway system in the city of Sendai. These applications have mainly concentrated on emulating the performance of a skilled human operator in the form of linguistic rules. However, the process of learning and tuning the control rules to achieve the desired performance remains a difficult task. Fuzzy Logic Control is based on fuzzy set theory. A fuzzy set is an extension of a crisp set. Crisp sets only allow full membership or no membership at all, whereas fuzzy sets allow partial membership. In other words, an element may partially belong to a set.

Berenji, Hamid R.↗
NASA NTRS1992

An on-orbit viewpoint of life sciences research

As a Payload Specialist and a life science researcher, I want to present several issues that impact life science research in space. During early space station operations, life science and other experiments will be conducted in a time-critical manner and there will be the added duties of both space shuttle and space station systems operation (and the concomittent training overhead). Life sciences research is different from other science research done in space because the crew is involved both as an operator and as a subject. There is a need for pre- and post-flight data collection as well as in flight data collection. It is imperative that the life science researcher incorporate the crew members into their team early enough in the training cycle to fully explain the science and to make the crew aware of the importance and sensitivities of the experiment. During the pre-flight phase, the crew is incredibly busy with a myriad of duties. Therefore, it is difficult to get 'pristine' subjects for the baseline data collection. There are also circadian shifts, travel, and late nights to confound the data. During this time it is imperative that the researcher develop, along with the crew, a realistic estimate of crew-time required for their experiment. In flight issues that affect the researcher are the additional activities of the crew, the stresses inherent in space flight, and the difficulty of getting early in-flight data. During SSF activities, the first day or two will be taken up with rendezvous and docking. Other issues are the small number of subjects on any given flight, the importance of complete and concise procedures, and the vagaries of on-board data collection. Post flight, the crew is tired and experiences a 'relaxation.' This along with circadian shifts and rapid re-adaptation to 1-g make immediate post-flight data collection difficult. Finally, the blending of operational medicine and research can result in either competition for resources (crew time, etc.) or influence on the physiological state of the crew. However, the unique opportunity to conduct research in an environment that cannot be duplicated on Earth outweighs the 'challenges' that exist for space life researchers.

Lichtenberg, Byron K.↗
NASA NTRS1992

Planar GaAs diodes for THz frequency mixing applications

Schottky barrier diodes for terahertz applications are typically fabricated as a micron to sub-micron circular anode metallization on GaAs which is contacted with a sharp wire (whisker). This structure has the benefits of the simplicity of the fabrication of the diode chip, the minimal shunt capacitance of the whisker contact and the ability of the whisker wire to couple energy to the diode. However, whisker-contacted diodes are costly to assembly and difficult to qualify for space applications. Also, complex receiver systems which require many diodes are difficult to assemble. The objective of this paper is to discuss the advantages of planar Schottky diodes for high frequency receiver applications and to summarize the problems of advancing the planar technology to the terahertz frequency range. Section 2 will discuss the structure, fabrication and performance of state-of-the-art planar Schottky diodes. In Section 3 the problems of designing and fabricating planar diodes for terahertz frequency operation are discussed along with a number of viable solutions. Section 4 summarizes the need for further research and cooperation between diode designers and RF engineers.

Bishop, William L.↗
NASA NTRS1992

Quantification of human responses

Human perception is a complex phenomenon which is difficult to quantify with instruments. For this reason, large panels of people are often used to elicit and aggregate subjective judgments. Print quality, taste, smell, sound quality of a stereo system, softness, and grading Olympic divers and skaters are some examples of situations where subjective measurements or judgments are paramount. We usually express what is in our mind through language as a medium but languages are limited in available choices of vocabularies, and as a result, our verbalizations are only approximate expressions of what we really have in mind. For lack of better methods to quantify subjective judgments, it is customary to set up a numerical scale such as 1, 2, 3, 4, 5 or 1, 2, 3, ..., 9, 10 for characterizing human responses and subjective judgments with no valid justification except that these scales are easy to understand and convenient to use. But these numerical scales are arbitrary simplifications of the complex human mind; the human mind is not restricted to such simple numerical variations. In fact, human responses and subjective judgments are psychophysical phenomena that are fuzzy entities and therefore difficult to handle by conventional mathematics and probability theory. The fuzzy mathematical approach provides a more realistic insight into understanding and quantifying human responses. This paper presents a method for quantifying human responses and subjective judgments without assuming a pattern of linear or numerical variation for human responses. In particular, quantification and evaluation of linguistic judgments was investigated.

Steinlage, R. C.↗
NASA NTRS1992

Flight Testing and Simulation of an F-15 Airplane Using Throttles for Flight Control

Flight tests and simulation studies using the throttles of an F-15 airplane for emergency flight control have been conducted at the NASA Dryden Flight Research Facility. The airplane and the simulation are capable of extended up-and-away flight, using only throttles for flightpath control. Initial simulation results showed that runway landings using manual throttles only control were difficult, but possible with practice. Manual approaches flown in the airplane were much more difficult, indicating a significant discrepancy between flight and simulation. Analysis of flight data and development of improved simulation models that resolve the discrepancy are discussed. An augmented throttles-only control system that controls bank angle and flightpath with appropriate feedback parameters has also been developed, evaluated in simulations, and is planned for flight in the F-15.

Flight Testing↗
NASA NTRS1992

On the scaling of small-scale jet noise to large scale

An examination was made of several published jet noise studies for the purpose of evaluating scale effects important to the simulation of jet aeroacoustics. Several studies confirmed that small conical jets, one as small as 59 mm diameter, could be used to correctly simulate the overall or PNL noise of large jets dominated by mixing noise. However, the detailed acoustic spectra of large jets are more difficult to simulate because of the lack of broad-band turbulence spectra in small jets. One study indicated that a jet Reynolds number of 5 x 10 exp 6 based on exhaust diameter enabled the generation of broad-band noise representative of large jet mixing noise. Jet suppressor aeroacoustics is even more difficult to simulate at small scale because of the small mixer nozzles with flows sensitive to Reynolds number. Likewise, one study showed incorrect ejector mixing and entrainment using small-scale, short ejector that led to poor acoustic scaling. Conversely, fairly good results were found with a longer ejector and, in a different study, with a 32-chute suppressor nozzle. Finally, it was found that small-scale aeroacoustic resonance produced by jets impacting ground boards does not reproduce at large scale.

Soderman, Paul T.↗
NASA NTRS1993

Sensitivity based coupling strengths in complex engineering systems

The iterative design scheme necessary for complex engineering systems is generally time consuming and difficult to implement. Although a decomposition approach results in a more tractable problem, the inherent couplings make establishing the interdependencies of the various subsystems difficult. Another difficulty lies in identifying the most efficient order of execution for the subsystem analyses. The paper describes an approach for determining the dependencies that could be suspended during the system analysis with minimal accuracy losses, thereby reducing the system complexity. A new multidisciplinary testbed is presented, involving the interaction of structures, aerodynamics, and performance disciplines. Results are presented to demonstrate the effectiveness of the system reduction scheme.

Bloebaum, C. L.↗
NASA NTRS1993

Evaluation of medical treatments to increase survival of ebullism in guinea pigs

Spaceflight carriers run a constant risk of exposure to vacuum. Above 63,000 ft (47 mmHg), the ambient pressure falls below the vapor pressure of water at 37 C, and tissue vaporization (ebullism) begins. Little is know about appropriate resuscitative protocols after such an ebullism exposure. This study identified injury patterns and mortality rates associated with ebullism while verifying effectiveness of traditional pulmonary resuscitative techniques. Male Hartley guinea pigs were exposed to 87,000 ft for periods of 40 to 115 sec. After descent, those animals that did not breathe spontaneously were given artificial ventilation by bag and mask for up to 15 minutes. Those animals surviving were randomly assigned to one of three treatment groups--hyperbaric oxygen (HBO), ground-level oxygen (GLO2), and ground-level air (GLAIR). The HBO group was treated on a standard treatment table 6A while the GLO2 animals received O2 for an equivalent length of time. Those animals in the GLAIR group were observed only. All surviving animals were humanely sacrified at 48 hours. Inflation of the animal's lungs after the exposure was found to be difficult and, at times, impossible. This may be due to surfactant disruption at the alveolar lining. Electron microscopy identified a disruption of the surfactant layer in animals that did not survive initial exposure. Mortality was found to increase with exposure time: 40 sec--0 percent; 60 sec--6 percent; 70 sec--40 percent; 80 sec--13 percent; 100 sec--38 percent; 110 sec--40 percent; and 115 sec--100 percent. There was no difference in the delayed mortality among the treatment groups (HBO--15 percent, GLO2--11 percent, GLAIR--11 percent). However, since resuscitation was ineffective, the effectiveness of any post-exposure treatment was severely limited. Preliminary results indicate that reuscitation of guinea pigs following ebullism exposure is difficult, and that current techniques (such as traditional CPR) may not be appropriate.

Stegmann, Barbara J.↗
NASA NTRS1993

Access to Japanese aerospace-related scientific and technical information: The NASA Aerospace Database

With Japan's growing R&D strength in aerospace-related fields, it is increasingly important for U.S. researchers to be aware of Japanese advances. However, several factors make it difficult to do so. After reviewing the diffusion of aerospace STI in Japan, four factors which make it difficult for U.S. researchers to gather this information are discussed: language, the human network, information scatter, and document acquisition. NASA activities to alleviate these difficulties are described, beginning with a general overview of the NASA STI Program. The effects of the new National Level Agreement between NASA and NASDA are discussed.

Hoetker, Glenn P.↗
NASA NTRS1993

Design and control of a macro-micro robot for precise force applications

Creating a robot which can delicately interact with its environment has been the goal of much research. Primarily two difficulties have made this goal hard to attain. The execution of control strategies which enable precise force manipulations are difficult to implement in real time because such algorithms have been too computationally complex for available controllers. Also, a robot mechanism which can quickly and precisely execute a force command is difficult to design. Actuation joints must be sufficiently stiff, frictionless, and lightweight so that desired torques can be accurately applied. This paper describes a robotic system which is capable of delicate manipulations. A modular high-performance multiprocessor control system was designed to provide sufficient compute power for executing advanced control methods. An 8 degree of freedom macro-micro mechanism was constructed to enable accurate tip forces. Control algorithms based on the impedance control method were derived, coded, and load balanced for maximum execution speed on the multiprocessor system. Delicate force tasks such as polishing, finishing, cleaning, and deburring, are the target applications of the robot.

Wang, Yulun↗
NASA NTRS1992

Temporal variation in spectral detection thresholds of substrate and vegetation in AVIRIS images

The ability to map changes over large surface areas over time is one of the advantages in using remote sensing as a monitoring tool. Temporal changes in the surface may be gradual, making them difficult to detect in the short-term, and because they commonly occur at the subpixel scale, they may be difficult to detect in the long-term as well. Also, subtle changes may be real or merely an artifact of image noise. It is, therefore, necessary to understand the factors that limit the detection of surface materials in evaluating temporal data. The spectral detectability of vegetation and soil in the 1990 July and October Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data of Jasper Ridge, CA was evaluated and compared.

Sabol, Donald E., Jr.↗
NASA NTRS1993

Explicit solution techniques for impact with contact constraints

Modern military aircraft transparency systems, windshields and canopies, are complex systems which must meet a large and rapidly growing number of requirements. Many of these transparency system requirements are conflicting, presenting difficult balances which must be achieved. One example of a challenging requirements balance or trade is shaping for stealth versus aircrew vision. The large number of requirements involved may be grouped in a variety of areas including man-machine interface; structural integration with the airframe; combat hazards; environmental exposures; and supportability. Some individual requirements by themselves pose very difficult, severely nonlinear analysis problems. One such complex problem is that associated with the dynamic structural response resulting from high energy bird impact. An improved analytical capability for soft-body impact simulation was developed.

Mccarty, Robert E.↗
NASA NTRS1993

Petrogenesis of Apollo 12 mare basalts. Part 2: An open system model to explain the pigeonite basalt compositions

Original petrogenetic models suggested that the pigeonite basalts were the evolved equivalents of the olivine basalts. Rhodes et al. concluded that the olivine and pigeonite basalts were co-magmatic, but Neal et al. have demonstrated that these two basaltic groups are distinct and unrelated. The pigeonite suite is comprised of porphyritic basalts with a fine-grained ground mass and range continuously to coarse-grained microgabbros with ophitic to graphic textures. Although it was generally recognized that the pigeonite basalts were derived from the olivine basalts by olivine + minor Cr-spinel fractionation, the compositional gap between these groups is difficult to reconcile with such a model. Indeed, Baldridge et al. concluded that these two basaltic groups could not have been co-magmatic. In this paper, we suggest an open system AFC model for pigeonite basalt petrogenesis. The assimilant is lunar anorthositic crust and the r value used is 0.6. While the choice of assimilant composition is difficult to constrain, the modeling demonstrates the feasibility of this model.

Neal, Clive R.↗
NASA NTRS1993

Exposure ages of carbonaceous chondrites, 1

The recent exposure histories of carbonaceous chondrites have been investigated using cosmogenic radionuclides. Our results may indicate a clustering of exposure ages of C1 and C2 chondrites into two peaks, 0.2 My and 0.6 My, perhaps implying two collisional events of Earth-crossing parent bodies. Among carbonaceous chondrites are some having short exposure ages which Mazor et al. hypothesized cluster into a small number of families. This hypothesis is based on spallogenic Ne-21 exposure ages, which in some instances are difficult to determine owing to the large amounts of trapped noble gases in carbonaceous chondrites. Also, since Ne-21 is stable, it integrates a sample's entire exposure history, so meteorites with complex exposure histories are difficult to understand using exclusively Ne-21. Cosmogenic radionuclides provide an alternative means of determining the recent cosmic ray exposure duration. To test the hypothesis of Mazor et al. we have begun a systematic investigation of exposure histories of Antarctic and non-Antarctic carbonaceous chondrites especially C2s.

Nishiizumi, K.↗
NASA NTRS1993

Formation and evolution of radial fracture systems on Venus

A survey of approximately 90 percent of the surface of Venus using Magellan data has been carried out to locate all radial fracture systems and to assess their association with other features such as volcanic edifices and coronae. Squyres et al. and Stofan et al. have discussed the association of radial fracture features in relation to coronae features, our approach was to assess the associations of all of the fracture systems. These fracture systems have two broad types of form - some fracture systems are associated with updomed topography, radiate from a point and have relatively uniform fracture lengths while others have a wider range of fracture lengths and radiate from the outer edge of a central caldera. Squyres et al. and Stofan et al. have interpreted both types of feature as reflecting tectonic fracturing resulting from uplift of the surface as a mantle plume impinges upon the crust. While it is true that a number of features are related to uplift and that such uplift will induce stresses consistent with radial fracturing, we explore the possibility that these fractures are not exclusively of tectonic origin. Purely tectonic fracturing will tend to generate a few main fractures/faults along which most of the stresses due to uplift will be accommodated leading to the triple-junction form common for terrestrial updoming. Though this type of feature is observed on Venus (e.g., feature located at 34S86), the majority of radial fracture systems display much more intensive fracturing than this through a full 360 degrees; this is difficult to explain by purely tectonic processes. The association of many of the fractures with radial lava flows leads us to interpret these fractures as reflecting dike emplacement: the form of the fractures being consistent with primarily vertical propagation from the head of a mantle plume. In the case of the second type of fracture system (those radiating from a central caldera), an even stronger case can be made that the fractures are not of tectonic origin. These features are not as commonly associated with updoming of the surface and where they are, the fractures extend out well beyond the edge of the topographic rise - an observation which is not consistent with the fractures being of tectonic uplift origin. Furthermore the fractures have a distribution of lengths (many short, fewer long) which is characteristic of dike swarms, and show direct associations with calderas and lava flows consistent with a volcanic origin. In addition, the longest fractures have a radial pattern only close to the center of the system but bend with distance to align themselves with the regional stress field - this behavior is very difficult to explain on purely tectonic grounds but is a pattern commonly seen for terrestrial dikes. For these reasons, we argue that many, if not the majority, of radial fracture systems found on Venus are the surface reflection of dike swarms, those associated with positive topography reflecting vertical emplacement and those radiating from calderas reflecting lateral propagation.

Parfitt, E. A.↗