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NASA NTRS1980

Spin prediction techniques

The NASA Langley Research Center has the responsibility to advance the state-of-the-art in the area of stall/spin technology. This includes the development and validation of experimental and analytical techniques for the prediction of stall/spin characteristics. As a part of this effort, a rotary balance facility located in the Langley spin tunnel was developed two and a half years ago to rapidly identify an airplane's aerodynamic characteristics in a rotational flow environment. On-line rotary balance data plots and on-line predicted steady spin modes permit the designer to develop, on site, a configuration highly resistant to spins, or one which has good spin characteristics, i.e., no spin equilibrium conditions possible with lateral-directional controls neutral, if the airplane is to be used for acrobatic maneuvers or training. The rotary balance data are also used to compute time histories of a spin's incipient, developed, and recovery phases. These spin analysis techniques and their correlation with spin tunnel model and full-scale flight results are discussed herein.

Bihrle, W., Jr.↗

NASA NTRS1994

Dynamics of a split torque helicopter transmission

Split torque designs, proposed as alternatives to traditional planetary designs for helicopter main rotor transmissions, can save weight and be more reliable than traditional designs. This report presents the results of an analytical study of the system dynamics and performance of a split torque gearbox that uses a balance beam mechanism for load sharing. The Lagrange method was applied to develop a system of equations of motion. The mathematical model includes time-varying gear mesh stiffness, friction, and manufacturing errors. Cornell's method for calculating the stiffness of spur gear teeth was extended and applied to helical gears. The phenomenon of sidebands spaced at shaft frequencies about gear mesh fundamental frequencies was simulated by modeling total composite gear errors as sinusoid functions. Although the gearbox has symmetric geometry, the loads and motions of the two power paths differ. Friction must be considered to properly evaluate the balance beam mechanism. For the design studied, the balance beam is not an effective device for load sharing unless the coefficient of friction is less than 0.003. The complete system stiffness as represented by the stiffness matrix used in this analysis must be considered to precisely determine the optimal tooth indexing position.

Krantz, Timothy L.↗

NASA NTRS1994

Simulations of phase space distributions of storm time proton ring current

We use results of guiding-center simulations of ion transport to map phase space densities of the stormtime proton ring current. We model a storm as a sequence of substorm-associated enhancements in the convection electric field. Our pre-storm phase space distribution is an analytical solution to a steady-state transport model in which quiet-time radial diffusion balances charge exchange. This pre-storm phase space spectra at L approximately 2 to 4 reproduce many of the features found in observed quiet-time spectra. Using results from simulations of ion transport during model storms having main phases of 3, 6, and 12 hr, we map phase space distributions from the pre-storm distribution in accordance with Liouville's theorem. We find stormtime enhancements in the phase space densities at energies E approximately 30-160 keV for L approximately 2.5 to 4. These enhancements agree well with the observed stormtime ring current. For storms with shorter main phases (approximately 3 hr), the enhancements are caused mainly by the trapping of ions injected from open night side trajectories, and diffusive transport of higher-energy (greater than or approximately 160 keV) ions contributes little to the stormtime ring current. However, the stormtime ring current is augmented also by the diffusive transport of higher-energy ions (E greater than or approximately 160 keV) durinng stroms having longer main phases (greater than or approximately 6 hr). In order to account for the increase in Dst associated with the formation of the stormtime ring current, we estimate the enhancement in particle-energy content that results from stormtime ion transport in the equatorial magnetosphere. We find that transport alone cannot account for the entire increase in absolute value of Dst typical of a major storm. However, we can account for the entire increase in absolute value of Dst by realistically increasing the stormtime outer boundary value of the phase space density relative to the quiet-time value. We compute the magnetic field produced by the ring current itself and find that radial profiles of the magnetic field depression resemble those obtained from observational data.

Chen, Margaret W.↗

NASA NTRS1996

On the Relationship Between Schottky Barrier Capacitance and Mixer Performance at Cryogenic Temperatures

The flat-band voltage is the Schottky junction voltage required to shrink the depletion width to zero. At cryogenic temperatures, mixer diodes are generally biased and/or pumped beyond the flat-band condition to minimize conversion loss and noise figure. This occurs despite the presumed sharp increase in junction capacitance near flat-band, which should instead limit mixer performance. Past moderate forward bias, the diode C-V relationship is difficult to measure. A simple analytic expression for C(V) is usually used to model and predict mixer performance. This letter provides experimental data on C(V) at 77 K based on a microwave measurement and modeling technique. Data is also provided on the conversion loss of a singly balanced mixer optimized for 77 K operation. The connection between junction capacitance, flat-band potential, and conversion loss is examined. It is shown that the analytic expression greatly overestimates the junction capacitance that occurs as flat-band is approached.

Romanofsky, Robert R.↗

NASA NTRS1981

Rotative balance of the I.M.F. Lille and associated experimental techniques

The study of aerodynamic effects at high incidence associated with motions of wide amplitude incorporating continuous rotations requires the consideration of coupled effects, which are generally nonlinear, in a formulation of equations of motion. A rotative balance designed to simulate such maneuvers in a windtunnel was created to form a test medium for analytical studies. A general description of the assembly is provided by considering two main ranges of application. The capacities and performance of the assembly are discussed.

Verbrugge, R.↗

NASA NTRS1985

Current sheets in solar flares

Numerical simulations of current sheets in solar flares are described, including new features such as the presence of a shock in Petschek's mechanism and impulsive burst-like reconnection due to secondary tearing and coalescence. The general properties of magnetic reconnection are discussed in connection with the basic requirements of numerical current sheet models. Emphasis is given to the need for realistic criteria for energy balance, the Lundquist number, and line tying in calculations of tearing and reconnection modes. The need for analytical models of current sheet processes to compare with the numerical simulations is also stressed.

Priest, E. R.↗

NASA NTRS1993

Using parallel banded linear system solvers in generalized eigenvalue problems

Subspace iteration is a reliable and cost effective method for solving positive definite banded symmetric generalized eigenproblems, especially in the case of large scale problems. This paper discusses an algorithm that makes use of two parallel banded solvers in subspace iteration. A shift is introduced to decompose the banded linear systems into relatively independent subsystems and to accelerate the iterations. With this shift, an eigenproblem is mapped efficiently into the memories of a multiprocessor and a high speed-up is obtained for parallel implementations. An optimal shift is a shift that balances total computation and communication costs. Under certain conditions, we show how to estimate an optimal shift analytically using the decay rate for the inverse of a banded matrix, and how to improve this estimate. Computational results on iPSC/2 and iPSC/860 multiprocessors are presented.

Zhang, Hong↗

NASA NTRS1994

Using parallel banded linear system solvers in generalized eigenvalue problems

Subspace iteration is a reliable and cost effective method for solving positive definite banded symmetric generalized eigenproblems, especially in the case of large scale problems. This paper discusses an algorithm that makes use of two parallel banded solvers in subspace iteration. A shift is introduced to decompose the banded linear systems into relatively independent subsystems and to accelerate the iterations. With this shift, an eigenproblem is mapped efficiently into the memories of a multiprocessor and a high speedup is obtained for parallel implementations. An optimal shift is a shift that balances total computation and communication costs. Under certain conditions, we show how to estimate an optimal shift analytically using the decay rate for the inverse of a banded matrix, and how to improve this estimate. Computational results on iPSC/2 and iPSC/860 multiprocessors are presented.

DISTRIBUTED MEMORY MULTIPROCES↗

NASA NTRS1995

A Simulated Geochemical Rover Mission to the Taurus-Littrow Valley of the Moon

We test the effectiveness of using an alpha backscatter, alpha-proton, X ray spectrometer on a remotely operated rover to analyze soils and provide geologically useful information about the Moon during a simulated mission to a hypothetical site resembling the Apollo 17 landing site. On the mission, 100 soil samples are "analyzed" for major elements at moderate analytical precision (e.g., typical relative sample standard deviation from counting statistics: Si[11%], Al[18%], Fe[6%], Mg[20%], Ca[5%]). Simulated compositions of soils are generated by combining compositions of components representing the major lithologies occurring at the site in known proportions. Simulated analyses are generated by degrading the simulated compositions according to the expected analytical precision of the analyzer. Compositions obtained from the simulated analyses are modeled by least squares mass balance as mixtures of the components, and the relative proportions of those components as predicted by the model are compared with the actual proportions used to generate the simulated composition. Boundary conditions of the modeling exercise are that all important lithologic components of the regolith are known and are represented by model components, and that the compositions of these components are well known. The effect of having the capability of determining one incompatible element at moderate precision (25%) is compared with the effect of the lack of this capability. We discuss likely limitations and ambiguities that would be encountered, but conclude that much of our knowledge about the Apollo 17 site (based on the return samples) regarding the distribution and relative abundances of lithologies in the regolith could be obtained. This success requires, however, that at least one incompatible element be determined.

Korotev, Randy L.↗

NASA NTRS1999

The Submillimeter-Wave Astronomy Satellite: On-Orbit Thermal Performance and Design Retrospective

A large telescope aperture, stringent thermal stability and temperature range requirements, and a passively-cooled 1500K module presented major challenges in thermal design and hardware fabrication of this Small Explorer satellite. This paper reviews briefly the thermal design of the SWAS science instrument, and examines the first three months of on-orbit thermal history. Measured temperatures for both the science payload and the spacecraft module and solar arrays are compared with those predicted by the correlated analytical model. Similarities and differences are interpreted in terms of the major uncertainties remaining after thermal-balance testing, especially those of MLI performance and telescope aperture properties. Review of the thermal model adequacy and thermal design verification are included to suggest improvements in the thermal design process for future missions.

Boyd, David A.↗

NASA NTRS1999

The Submillimeter-Wave Astronomy Satellite: On-Orbit Thermal Performance and Design Retrospective

A large telescope aperture, stringent thermal stability and temperature range requirements, and a passively-cooled 150 K module presented major challenges in thermal design and hardware fabrication of this Small Explorer satellite. This paper reviews briefly the thermal design of the SWAS science instrument, and examines the first three months of on-orbit thermal history. Measured temperatures for both the science payload and the spacecraft module and solar arrays are compared with those predicted by the correlated analytical model. Similarities and differences are interpreted in terms of the major uncertainties remaining after thermal-balance testing, especially those of MLI performance and telescope aperture properties. Review of the thermal model adequacy and thermal design verification are included to suggest improvements in the thermal design process for future missions.

Boyd, David A.↗

NASA NTRS2001

Precipitation Efficiency in the Tropical Deep Convective Regime

Precipitation efficiency in the tropical deep convective regime is analyzed based on a 2-D cloud resolving simulation. The cloud resolving model is forced by the large-scale vertical velocity and zonal wind and large-scale horizontal advections derived from TOGA COARE for a 20-day period. Precipitation efficiency may be defined as a ratio of surface rain rate to sum of surface evaporation and moisture convergence (LSPE) or a ratio of surface rain rate to sum of condensation and deposition rates of supersaturated vapor (CMPE). Moisture budget shows that the atmosphere is moistened (dryed) when the LSPE is less (more) than 100 %. The LSPE could be larger than 100 % for strong convection. This indicates that the drying processes should be included in cumulus parameterization to avoid moisture bias. Statistical analysis shows that the sum of the condensation and deposition rates is bout 80 % of the sum of the surface evaporation rate and moisture convergence, which ads to proportional relation between the two efficiencies when both efficiencies are less han 100 %. The CMPE increases with increasing mass-weighted mean temperature and creasing surface rain rate. This suggests that precipitation is more efficient for warm environment and strong convection. Approximate balance of rates among the condensation, deposition, rain, and the raindrop evaporation is used to derive an analytical solution of the CMPE.

Li, Xiaofan↗

NASA NTRSDate not supplied

Scaling Methodology for Buckling of Composite Conical Shells in Axial Compression

Conical shells are commonly used as structural components for launch vehicles. The axial compression experienced during launch is one of the sizing load cases, because it can lead to loss of stability. As Because experimentally testing these large full-scale structures is cumbersome and expensive, it is studied how reduced-scale shells can be designed such that their buckling behavior is representative of the full-scale scale shell behavior. An analytical, sequential scaling procedure methodology is developed based on the nondimensional governing equations for composite conical shells with a symmetric, balanced layup and negligible flexural anisotropy. The buckling behavior of the shells of different size is compared using linear and nonlinear finite element analyses, and good comparisons . Accurate results are obtained for the considered shells in terms of buckling load, displacement, and mode. The inclusion of a geometric imperfections affects reduces the prediction accuracy, but it does not to the extent that the methodology is no longer valid cause the methodology to fail.

Buckling↗

NASA NTRS1979

Computer-assisted high-speed balancing of T53 and T55 power turbines

Standard overhaul procedures for U.S. Army helicopter engines require operational vibration acceptance testing after rebuild. Engines frequently experience vibrations which exceed allowable overhaul work requirement limits. The rework/retest cycle for these engines constitute a significant cost penalty to the overhaul center. This paper reviews both analytical and test data which indicate bending critical speeds within the operating speed range of the low-speed power turbine rotor as the cause of most test cell rejections. High-speed balancing techniques are applicable and are capable of significantly reducing this reject rate. A complete prototype computer-assisted high-speed balancing system for assembled T53 and T55 power turbine rotors is described.

Pojeta, T. J.↗

NASA NTRS1989

CSI sensing and control: Analytical and experimental results

Recent work on structural identification and large-angle maneuvers with vibration suppression was presented. The recent work has sought to balance structural and controls analysis activities by involving the analysts directly in the validation and experimental aspects of the research. Some new sensing, actuation, system identification, and control concepts were successfully implemented. An overview of these results is given.

Junkins, J. L.↗

NASA NTRS1994

Concept verification of three dimensional free motion simulator for space robot

In the development of automatic assembling technologies for space structures, it is an indispensable matter to investigate and simulate the movements of robot satellites concerned with mission operation. The movement investigation and simulation on the ground will be effectively realized by a free motion simulator. Various types of ground systems for simulating free motion have been proposed and utilized. Some of these methods are a neutral buoyancy system, an air or magnetic suspension system, a passive suspension balance system, and a free flying aircraft or drop tower system. In addition, systems can be simulated by computers using an analytical model. Each free motion simulation method has limitations and well known problems, specifically, disturbance by water viscosity, limited number of degrees-of-freedom, complex dynamics induced by the attachment of the simulation system, short experiment time, and the lack of high speed super-computer simulation systems, respectively. The basic idea presented here is to realize 3-dimensional free motion. This is achieved by combining a spherical air bearing, a cylindrical air bearing, and a flat air bearing. A conventional air bearing system has difficulty realizing free vertical motion suspension. The idea of free vertical suspension is that a cylindrical air bearing and counter balance weight realize vertical free motion. This paper presents a design concept, configuration, and basic performance characteristics of an innovative free motion simulator. A prototype simulator verifies the feasibility of 3-dimensional free motion simulation.

Okamoto, Osamu↗

NASA NTRS1999

Zarya Energy Balance Analysis: The Effect of Spacecraft Shadowing on Solar Array Performance

The first element of the International Space Station (ISS). Zarya, was funded by NASA and built by the Russian aerospace company Khrunichev State Research and Production Space Center (KhSC). NASA Glenn Research Center (GRC) and KhSC collaborated in performing analytical predictions of the on-orbit electrical performance of Zarya's solar arrays. GRC assessed the pointing characteristics of and shadow patterns on Zarya's solar arrays to determine the average solar energy incident on the arrays. KHSC used the incident energy results to determine Zarya's electrical power generation capability and orbit-average power balance. The power balance analysis was performed over a range of solar beta angles and vehicle operational conditions. This analysis enabled identification of problems that could impact the power balance for specific flights during ISS assembly and was also used as the primary means of verifying that Zarya complied with electrical power requirements. Analytical results are presented for select stages in the ISS assembly sequence along with a discussion of the impact of shadowing on the electrical performance of Zarya's solar arrays.

Hoffman, David J.↗

NASA NTRS1973

Extravehicular mobility unit thermal simulator

The analytical methods, thermal model, and user's instructions for the SIM bay extravehicular mobility unit (EMU) routine are presented. This digital computer program was developed for detailed thermal performance predictions of the crewman performing a command module extravehicular activity during transearth coast. It accounts for conductive, convective, and radiative heat transfer as well as fluid flow and associated flow control components. The program is a derivative of the Apollo lunar surface EMU digital simulator. It has the operational flexibility to accept card or magnetic tape for both the input data and program logic. Output can be tabular and/or plotted and the mission simulation can be stopped and restarted at the discretion of the user. The program was developed for the NASA-JSC Univac 1108 computer system and several of the capabilities represent utilization of unique features of that system. Analytical methods used in the computer routine are based on finite difference approximations to differential heat and mass balance equations which account for temperature or time dependent thermo-physical properties.

Hixon, C. W.↗