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Several approaches were investigated to obtain a measure of the quality of the contact resistance between metal and a diffused or polysilicon layer. These approaches have included the use of both short and very long contact strings as well as arays of contacts with different sizes to determine the contact resistance process cliff. Results from these approaches are discussed.
The effort to determine the size and shape of the hollow cathode cloud emitted from an orbiting system was continued. In addition, the results obtained for the ionospheric wave impedance of a tethered system was applied to the experiments under consideration. The recent plasma chamber experimental results reported by Urrutia and Stenzel are still being considered. The problem is being studied as to how the ionospheric plasma's global response to the moving disturbance presented by the electrodynamic tethered satellite system affects the system's ability to function as a power generator or thruster.
Aircraft observations and high resolution Landsat MSS digital data are used to determine the sizes of spatial inhomogeneities ('holes') in cumulus clouds. The majority of holes are found near cloud edges, but the larger holes tend to be found in cloud interiors. Aircraft measurements show these cloud spatial inhomogeneities in the range of 100 to 500 m, while Landsat data show them in the range of 100 m to 3 km. The number of holes per cloud decreases exponentially with increasing hole diameter. Small clouds not only have smaller holes, but also fewer holes than large clouds. Large clouds have large holes in them, as well as large numbers of the smaller holes. The total cloud area occupied by holes increases with increasing cloud size.
Described are methods for reducing vibration in helicopter rotor blades by determining optimum sizes and locations of tuning masses through formal mathematical optimization techniques. An optimization procedure is developed which employs the tuning masses and corresponding locations as design variables which are systematically changed to achieve low values of shear without a large mass penalty. The finite-element structural analysis of the blade and the optimization formulation require development of discretized expressions for two performance parameters: modal shaping parameter and modal shear amplitude. Matrix expressions for both quantities and their sensitivity derivatives are developed. Three optimization strategies are developed and tested. The first is based on minimizing the modal shaping parameter which indirectly reduces the modal shear amplitudes corresponding to each harmonic of airload. The second strategy reduces these amplitudes directly, and the third strategy reduces the shear as a function of time during a revolution of the blade. The first strategy works well for reducing the shear for one mode responding to a single harmonic of the airload, but has been found in some cases to be ineffective for more than one mode. The second and third strategies give similar results and show excellent reduction of the shear with a low mass penalty.
Spaceflight, stellar pointing telescopes require baffle systems to define the field of view and protect this observational area from stray and scattered light. In the case of near normal incidence telescope systems, the problem consists in controlling the stray/scattered radiation reaching the image plane when circular plates, the primary and secondary mirrors, are the imaging elements. The case addressed in this paper is quite different in that it involves baffling two conical surfaces, i.e., the primary and secondary mirrors of a Wolter Type II telescope. A strategy is described for systematically moving through the telescope system and establishing criteria for placement of baffles. Calculations are given which determine the size and number of permitted baffles as a function of practical physical parameters. Clear options are given for the design of minimum baffle lengths to meet packaging constraints.
The accurate determination of dust levels on optical surfaces is necessary to assess sensor system performance. A comparison study was made on several particle measurement methods including those based on direct imaging and light scattering. The effectiveness of removing the particles from the surface prior to determining particle size distributions was also assessed. These studies revealed that some methods, especially those requiring particle removal before analysis, are subject to large systematic errors affecting particle size distributions. Thus, an understanding of the particle measurement methods employed is necessary before any surface cleanliness or obstruction value assignments are accepted as true representations of an optical surface contamination condition.
Models indicate that stratospheric aerosols play a major role in the destruction of ozone during the Austral winter. Although many in situ measurements of stratospheric aerosols were made during the Airborne Antarctic Ozone Experiment, changes of aerosol concentration and size distributions across the polar vortex are important to understanding changes of chemical species taking place during this time. Therefore comparing the in situ measurements with measurements made by satellites scanning wider areas will give a clearer picture of the possible role played by aerosols during this period. The wire impactor size distributions are compared to those from the aerosol spectrometers and a best fit size distribution determined. Aerosol extinctions are calculated from the in situ measurements and compared to the extinctions measured by the satellites. Five comparisons are made with SAGE 2 and four with SAM 2. Extinctions agree as close as a factor of two.
The ephemerides needed to acquire radar data at Arecibo from observations of various solar-system objects was developed. The resultant data to test fundamental laws of gravitation and to determine the size, shape, topography, and spin vectors of the targets were analyzed. The surface properties of these objects through their radar scattering and polarization characteristics were studied. The observing program also included Arecibo observations of Mercury, Venus, and the Galilean satellites of Jupiter. The Mercury observations at Arecibo were all within a week of the epoch of a closure point (same surface position as a previous observation), and one was matched by a near-simultaneous observation at Goldstone.
The results of a continuing investigation of the phenomena associated with the oblique hypervelocity impact of spherical projectiles onto multi-sheet aluminum structures are given. A series of equations that quantitatively describes these phenomena is obtained through a regression of experimental data. These equations characterize observed ricochet and penetration damage phenomena in a multi-sheet structure as functions of geometric parameters of the structure and the diameter, obliquity, and velocity of the impacting projectile. Crater damage observed on the ricochet witness plates is used to determine the sizes and speeds of the ricochet debris particles that caused the damage. It is observed that the diameter of the most damaging ricochet debris particle can be as large as 40 percent of the original particle diameter and can travel at speeds between 24 percent and 36 percent of the original projectile impact velocity. The equations necessary for the design of shielding panels that will protect external systems from such ricochet debris damage are also developed. The dimensions of these shielding panels are shown to be strongly dependent on their inclination and on their circumferential distribution around the spacecraft.
The results of a continuing investigation of the phenomena associated with the oblique hypervelocity impact of spherical projectiles onto multi-sheet aluminum structures are described. A series of equations that quantitatively describes these phenomena is obtained through a regression of experimental data. These equations characterize observed ricoshet and penetration damage phenomena in a multi-sheet structure as functions of the geometric parameters of the structure and the diameter, obliquity, and velocity of the impacting projectile. Crater damage observed on the ricochet witness plates is used to determine the sizes and speeds of the ricochet debris particles that caused the damage. It is shown that, in general, the most damaging ricochet debris particle is approximately 0.25 cm (0.10 in) in diameter and travels at the speed of approximately 2.1 km/sec (6,890 ft/sec). The equations necessary for the design of shielding panels that will protect external systems from such ricochet debris damage are also developed. The dimensions of these shielding panels are shown to be strongly dependent on their inclination and on their circumferential distribution around the spacecraft. It is concluded that obliquity effects of high-speed impacts must be considered in the design of any structure exposed to the meteoroid and space debris environment.
Time-domain control design for stability robustness of linear systems with structured uncertainty is addressed. Upper bounds on the linear perturbation of an asymptotically stable linear system are obtained, making it possible to maintain stability by using the structural information of the uncertainty. A quantitative measure called the stability robustness index is introduced and used to design controllers for robust stability. The proposed state feedback control design algorithm can be used, for a given set of perturbations, to select the range of control effort for which the system is stability-robust. Conversely it can be used, for a given control effort, to determine the size of the tolerable perturbation. The algorithm is illustrated with examples from aircraft control and large-space-structure control problems.
The relationship between volcanic eruptions on earth and the observed climatic changes is investigated. The results of the comparison and analyses of volcanologic and climatologic data sets for the years between 1880 and 1980 indicate that changes in temperature caused by even of the largest eruptions recorded during this time were about the same as normal variations in temperature. However, when temperature records for several months or years preceding and following a given eruption were analyzed, a statistically significant temperature decrease of 0.2-0.5 C was found for the periods of one to two years immediately following some of the 19th and 20th century explosive events that prodiced large aerosol clouds (e.g., Krakatau and Agung eruptions). It is suggested that the content of sulfur in the erupted magma determines the size of aerosol cloud producing the cooling effect.
To investigate the role of Siberian Shelf polynyas in water mass formation, and that of Whalers Bay in the cooling of the West Spitsbergen Current, satellite observations from the Nimbus 7 scanning multichannel microwave radiometer are used to determine the size and location of polynyas for November-March, 1978-1982. If salt contributes only to the Arctic Intermediate Water, the results show that the continental shelves can produce 20-60 percent of this water. Alternatively, if the salt contributes only to the deep water of the Eurasian Basin, then without consideration of the mixing of the bottom water with the Greenland and Norwegian Sea water, the contribution from the shelves yields a renewal time of about 100 years. These results imply that there is insufficient water produced in the shelf polynyas to perform all of the roles that have historically been assigned to it.
The Simulation Computer System (SCS) is the computer hardware, software, and workstations that will support the Payload Training Complex (PTC) at Marshall Space Flight Center (MSFC). The PTC will train the space station payload scientists, station scientists, and ground controllers to operate the wide variety of experiments that will be onboard the Space Station Freedom. In the first step of this task, a methodology was developed to ensure that all relevant design dimensions were addressed, and that all feasible designs could be considered. The development effort yielded the following method for generating and comparing designs in task 4: (1) Extract SCS system requirements (functions) from the system specification; (2) Develop design evaluation criteria; (3) Identify system architectural dimensions relevant to SCS system designs; (4) Develop conceptual designs based on the system requirements and architectural dimensions identified in step 1 and step 3 above; (5) Evaluate the designs with respect to the design evaluation criteria developed in step 2 above. The results of the method detailed in the above 5 steps are discussed. The results of the task 4 work provide the set of designs which two or three candidate designs are to be selected by MSFC as input to task 5-refine SCS conceptual designs. The designs selected for refinement will be developed to a lower level of detail, and further analyses will be done to begin to determine the size and speed of the components required to implement these designs.
This project addresses the problem of cutting lunar stones into blocks to be used to construct shelters to protect personnel and equipment from harmful solar radiation. This plant will manufacture 6 in x 1 ft x 2 ft blocks and will be located near the south pole to allow it to be in the shade at all times. This design uses a computer controlled robot, a boulder handler that uses hydraulics for movement, a computer system that used 3-D vision to determine the size of boulders, a polycrystalline diamond tipped saw blade that utilizes radiation for cooling, and a solar tower to collect solar energy. Only two electric motors are used in this plant because of the heavy weight of electric motors and the problem of cooling them. These two motors will be cooled by thermoelectric cooling. All other motors and actuators are to be hydraulic. The architectural design for the building as well as the conceptual design of the machines for cutting the blocks are described.
The lifting machine will assist in lifting cargo off of landers sent to the Moon and in the construction of a lunar base. Three possible designs were considered for the overall configuration of the lifting machine: the variable angle crane, the tower crane, and the gantry crane. Alternate designs were developed for the major components of the lifting machine. A teleoperable, variable angle crane was chosen as its final design. The design consists of a telescoping boom mounted to a chassis that is supported by two conical wheels for towing and four outriggers for stability. Attached to the end of the boom is a seven degree of freedom robot arm for light, dexterous, lifting operations. A cable and hook suspends from the end of the boom for heavy, gross, lifting operations. Approximate structural sizes were determined for the lifter and its components. However, further analysis is needed to determine the optimum design dimensions. The design team also constructed a model of the design which demonstrates its features and operating principals.
A systematic experimental evaluation of whisker and particulate reinforced aluminum matrix composites was conducted to assess the variation in tensile properties with reinforcement type, volume fraction, and specimen thickness. Each material was evaluated in three thicknesses, 1.8, 3.18, and 6.35 mm, to determine the size, distribution, and orientation of the reinforcements. This information was used to evaluate several micromechanical models that predict composite moduli. The longitudinal and transverse moduli were predicted for reinforced aluminum. The Paul model, the Cox model and the Halpin-Tsai model were evaluated. The Paul model gave a good upper bound prediction for the particulate reinforced composites but under predicted whisker reinforced composite moduli. The Cox model gave good moduli predictions for the whisker reinforcement, but was too low for the particulate. The Halpin-Tsai model gave good results for both whisker and particulate reinforced composites. An approach using a trigonometric projection of whisker length to predict the fiber contribution to the modulus in the longitudinal and transverse directions was compared to the more conventional lamination theory approach.
The strong far-infrared continuum source associated with the OH maser-ultracompact H II region W3(OH) was observed from the Kuiper Airborne Observatory in order to determine its size at 50 and 100 microns. Maximum entropy deconvolutions of the slit scans made in orthogonal directions across the source show it to be approximately circular with FWHM sizes of 8 arcsec and 13 arcsec at 50 and 100 microns, respectively. For these sizes, W3(OH) is optically thick in the far-infrared. A spherically symmetric, dusty molecular cloud model is developed to fit the data.