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The paper examines the feasibility of using the H2 rotational Raman spectrum to study the physical structure of the atmospheres of the outer planets. Computations of the strengths of the S(0) and S(1) lines are made for a wide range of physical conditions on the basis of a semi-infinite homogeneous pure H2 atmospheric model. Initial applications of the Raman probe technique to Jupiter and Uranus are reported.
The mechanisms by which orbital resonance locks are maintained among Io, Europa and Ganymede are analyzed, and the effects of the dissipative tides in Jupiter and Io on their establishment and evolution are considered. According to the proposed model, initially all three satellites are in orbits far from the 2:1 commensurabilities or the three body lock. The tide raised on Io damps down the free eccentricity; only modest tidal heating occurs. Subsequently the dissipative tide raised on Jupiter by Io causes Io's orbit to spiral outwards; Io approaches the 2:1 commensurability with Europa. Io's forced eccentricity increases rapidly to a critical value, and thereafter the resonant interaction causes Europa's orbit to expand at half that of Io's orbit. A fluid core is probably formed as the result of tidal heating. Finally Europa approaches the 2:1 commensurability, angular momentum is transferred from Europa's orbit to Ganymede's, and a steady state is attained. On the basis of the observed three-body resonance amplitude (0.066 deg), it is concluded that three-body resonance may have formed less than 500 million years ago; a measurement of the rate of tidal heating in Io may determine the Q value of both Io and Jupiter. Upper and lower limits for the Jovian Q value of 2 million and 20,000 are suggested.
The requirements and preliminary design of a general purpose, real-time executive computers program for flight computers are provided. A description and the requirements are included for the major elements of the executive: an initialization model, a task scheduler, and an interrupt handler. Task priorities and various process interrupts are discussed. System parameters and variables are identified which make the design adaptable to various flight computer and applicaton specifications.
Employment as a means of transportation in the civilian construction trades represents one of the many applications of the helicopter. However, a major limitation to its use in heavy construction has been that the mass which can be effectively and safely transported is severely restricted. The construction of the so-called 'heavy lift' helicopter provided one solution to this problem. But it has been found that there are physical and economic limitations to the payload which can be transported. The proposal has been made to overcome these limitations by making use of multiple helicopters to move a single mass. A study of the feasibility of this proposal showed that automatic control would be needed to make the concept successful. The present investigation is concerned with some initial models in regard to the twinlift problem, taking into account the control theoretic problems.
It is estimated that 30 to 200 large impact basins could have been formed on the early Earth. These large impacts may have resulted in extensive volcanism and enhanced endogenic geologic activity over large areas. Initial modelling of the thermal and subsidence history of large terrestrial basins indicates that they created geologic and thermal anomalies which lasted for geologically significant times. The role of large-scale impact in the biological evolution of the Earth has been highlighted by the discovery of siderophile anomalies at the Cretaceous-Tertiary boundary and associated with North American microtektites. Although in neither case has an associated crater been identified, the observations are consistent with the deposition of projectile-contaminated high-speed ejecta from major impact events. Consideration of impact processes reveals a number of mechanisms by which large-scale impact may induce extinctions.
A planetary model is described which requires fractional vapor/liquid condensation, planet accumulation during condensation, a late start for accumulation of the Moon, and volatile accretion to the surfaces of each planet only near the end of the accumulation process. In the model, initial accumulation of small objects is helped if the agglomerating particles are somewhat sticky. Assuming that growth proceeds through this range, agglomeration continues. If the reservoir of vapor is being preferentially depleted in iron by fractional condensation, an iron-rich planetary core forms. As the temperature decreases, condensing material becomes progressively richer in silicates and poorer in iron, forming the silicate-rich mantle of an already differentiated Earth. A second center of agglomeration successfully forms near the growing Earth after most of the iron in the reservoir has been used up. The bulk composition of the Moon then is similar to the outer mantle of the accumulating Earth.
LANDSAT visible imagery and a one-dimensional Lagrangian boundary layer model were used to hypothesize the nature and the development of the marine boundary layer during a winter episode of strong seaward cold air advection. Over-water heating and moistening of the cold, dry continental air is estimable from linear relations involving horizontal gradients of the near-surface air temperature and humidity. A line of enhanced convection paralleling the Atlantic U.S. coast from south of New York Bay to the vicinity of Virginia Beach, VA was attributed to stronger convergence at low levels. This feature was characterized as a mesoscale front. With the assistance of a three-dimensional mesoscale boundary layer model, initialized with data obtained from the MASEX, the marine boundary layer can be mapped over the entire Atlantic coastal domain and the evolution of the boundary layer can be studied as a function of different characteristics of important surface level forcings. The effects on boundary layer growth due to the magnitude and pattern of sea surface temperature, to the shape of the coastline, and to atmospheric conditions, such as the orientation of the prevailing wind are examined.
A system of seven tables, which cover analysis archiving, observation types, quality control, data assimilation cycles, assimilating models, initialization, and analysis techniques was adopted. The set of prepared tables allows side-by-side comparison of the characteristics of the six data assimilation systems (European Center for Medium Range Weather Forecasts, Geophysical Fluid Dynamics Laboratory, Goddard Laboratory for Atmospheric Science, National Meteorological Center, Florida State University, and Naval Environmental Prediction Research Facility) used to produce FGGE IIIb analyses.
Data from three NCAR radars are used in both single and dual Doppler analyses to trace the evolution of a June 30, 1982 Colorado convective storm containing downburst-type winds and strong vortices 1-2 km in diameter. The analyses show that a series of small circulations formed along a persistent cyclonic shear boundary; at times as many as three misocyclones were present with vertical vorticity values as large as 0.1/s using a 0.25 km grid interval. The strength of the circulations suggests the possibility of accompanying tornadoes or funnels, although none were observed. Dual-Doppler analyses show that strong, small-scale downdrafts develop in close proximity to the misocyclones. A midlevel mesocyclone formed in the same general region of the storm where the misocylones later developed. The observations are compared with numerical simulations from a three-dimensional cloud model initialized with sounding data from the same day.
A three-dimensional simulation model was developed to study magnetosphere-ionosphere coupling in the auroral region. One-fluid MHD equations are adopted to model the magnetosphere, and current density continuity equations were solved consistently to model the ionosphere. In the preliminary simulation runs described here, the electrodynamics of region 1 field-aligned currents were modeled. Initially, the electric field is taken to be in the magnetospheric equatorial plane. Alfven waves then propagate down to the ionosphere, accompanying a field-aligned current and exciting the electrostatic potential in the ionosphere by electrodynamic coupling. The results of the preliminary runs directly correspond with the fundamental characteristics of global magnetosphere-ionosphere coupling. These characteristics include an ionospheric electrostatic potential which varies in its development in time, depending upon the ratio of ionospheric resistance to magnetospheric impedance, the flowing of field-aligned currents into the ionosphere on the dawnside and out on the duskside, and the distribution along the geomagnetic field of the amplitude of the field-aligned current density in proportion to the field intensity.
High-temperature thin-shell leading-edge buckling test data are analyzed using NASA structural analysis (NASTRAN) as a finite element tool for predicting thermal buckling characteristics. Buckling points are predicted for several combinations of edge boundary conditions. The problem of relating the appropriate plate area to the edge stress distribution and the stress gradient is addressed in terms of analysis assumptions. Local plasticity was found to occur on the specimen analyzed, and this tended to simplify the basic problem since it effectively equalized the stress gradient from loaded edge to loaded edge. The initial loading was found to be difficult to select for the buckling analysis because of the transient nature of thermal stress. Multiple initial model loadings are likely required for complicated thermal stress time histories before a pertinent finite element buckling analysis can be achieved. The basic mode shapes determined from experimentation were correctly identified from computation.
Under a rotorcraft structural dynamics program sponsored by the NASA Langley Research Center, Sikorsky Aircraft, together with the other major helicopter airframe manufacturers, is engaged in a study to improve the use of finite element analysis to predict the dynamic behavior of helicopter airframes. This program, which was designated DAMVIBS (Design Analysis Methods for VIBrationS), includes activities in the areas of: planning, creating, and documenting finite element models of helicopter airframes; the performance of ground vibration tests; and the correlation of test and analysis. The work performed at Sikorsky Aircraft for planning, creating, and documenting a finite element model of the UH-60A BLACK HAWK helicopter airframe is summarized. A complete description of the components of the helicopter which are to be represented in the model is presented and includes: the structural arrangement, the identification of primary and secondary structure, the components of the drive and power trains, and the attachment of large weight items to the structure. Also presented are the techniques which were used to formulate the structural finite element model for static analysis, for forming the mass and vibration models for dynamic analysis, and the procedures which were used to check out and verify the integrity of the model. Initial predictions for the vibration modes for the helicopter are included.
A convective event over the Gulf of Mexico is used to address the question of how well nonhydrostratic convectively explicit models initialized by imposing a 'bubble', typically a temperature perturbation, on a horizontally homogeneous stratification background field, respond to usually subtle variations on meso-beta scale thermodynamic structure. Whether a meso-beta scale convective precipitation pattern can be produced numerically by performing a group of convectively explicit simulations is studied. Storm-scale low-level forcing is found to be important for producing desired convective precipitation patterns. The additional numerical approaches that must be incorporated to understand and forecast meso-beta scale weather events are considered.
A comprehensive study is presented of the postexplosion hydrodynamics of the ejecta of SN 1987A encompassing the Rayleigh-Taylor instabilities at the shell interfaces and the dynamical effects of the energy input due to the radioactive decay of Ni-56 and Co-56. The dependence of the hydrodynamical behavior on progenitor structure, initial perturbations, explosion energy, and dimensionality of the numerical simulation is investigated in order to explain the observed high-velocity wings of the iron line of SN 1987A. It is shown that none of these factors leads to the required high-velocity tail of iron. When nickel is artificially premixed in the initial model, it is found that this early mixing has to affect the inner 1.5 solar mass of the ejecta to reproduce the high-velocity wings at a time of 90 d. It is argued that the high-entropy bubble associated with the delayed mechanism is responsible for this premixing by driving convective motions early in the explosion.
A team of Space Station Freedom (SSF) system engineers are in the process of extensive analysis of the SSF requirements, particularly those pertaining to the electrical power system (EPS). The objective of this analysis is the development of a comprehensive, computer-based requirements model, using an enhanced modern structured analysis methodology (EMSA). Such a model provides a detailed and consistent representation of the system's requirements. The process outlined in the EMSA methodology is unique in that it allows the graphical modeling of real-time system state transitions, as well as functional requirements and data relationships, to be implemented using modern computer-based tools. These tools permit flexible updating and continuous maintenance of the models. Initial findings resulting from the application of EMSA to the EPS have benefited the space station program by linking requirements to design, providing traceability of requirements, identifying discrepancies, and fostering an understanding of the EPS.
The Office of Safety and Mission Quality initiated a Pyrotechnically Actuated Systems (PAS) Program in FY-92 to address problems experienced with pyrotechnically actuated systems and devices used both on the ground and in flight. The PAS Program will provide the technical basis for NASA's projects to incorporate new technological developments in operational systems. The program will accomplish that objective by developing/testing current and new hardware designs for flight applications and by providing a pyrotechnic data base. This marks the first applied pyrotechnic technology program funded by NASA to address pyrotechnic issues. The PAS Program has been structured to address the results of a survey of pyrotechnic device and system problems with the goal of alleviating or minimizing their risks. Major program initiatives include the development of a Laser Initiated Ordnance System, a pyrotechnic systems data base, NASA Standard Initiator model, a NASA Standard Linear Separation System and a NASA Standard Gas Generator. The PAS Program sponsors annual aerospace pyrotechnic systems workshops.
Using the Langley Research Center galactic cosmic-ray transport computer code and the Computerized Anatomical Man model, initial estimates of interplanetary exposure of astronauts to galactic cosmic rays, during periods of solar minimum activity, are made for a realistic human geometry shielded by various thicknesses of spacecraft aluminum shielding. Conventional dose assessment in terms of total absorbed dose and dose equivalent is made for the skin, ocular lens, and bone marrow. Included in the analyses are separate evaluations of the contributions from the incident primary ions, from subsequent-generation fragmentation products, and from target fragments. In all cases considered, the equivalent sphere approximation yielded conservative overestimates for the actual organ exposures.
The Vibroacoustic Payload Environment Prediction System (VAPEPS) was used to predict the stationary on-orbit environments in one of the Space Station Freedom modules. The model of the module included the outer structure, equipment and payload racks, avionics, and cabin air and duct systems. Acoustic and vibratory outputs of various source classes were derived and input to the model. Initial results of analyses, performed in one-third octave frequency bands from 10 to 10,000 Hz, show that both the microgravity and acoustic environments will be exceeded in some one-third octave bands with the current SSF design. Further analyses indicate that interior acoustic level requirements will be exceeded even if the microgravity requirements are met.