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At least 739 records · Page 41

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NASA NTRS1972

Dynamical characteristics of Phobos and Deimos.

The orbital properties of the two small Martian satellites, Phobos and Deimos, are discussed, as well as those dynamical constants of Mars that can be determined from the satellite orbits. The secular acceleration of the mean motion of Phobos is shown to be very small. Of mechanisms that could cause any such acceleration, only tidal friction appears to be important. From the orbital evolution of the Martian satellites under tidal forces, Phobos and Deimos seem to have originated in nearly circular orbits of low inclination fairly close to the distance at which a satellite's orbital period is the planet's rotation period. It is proposed that the Martian satellites were born at the same time as Mars from equatorial dust clouds. The satellites are predicted to be locked in synchronous rotation, with their axes of minimum moment of inertia pointing on the average toward Mars, whereas their maximum axes are approximately normal to their orbit planes.

Burns, J. A.↗

NASA NTRS1971

Damping characteristics of a liquid squeeze film.

Consideration of the damping characteristics of a liquid film located between two nearly parallel plane surfaces in relative normal motion which are always closely spaced compared to the dimensions describing the area of the two like surfaces. It was found that if the motion is slow enough (about 3 centipoise or less), the fluid inertia can be neglected and the resulting fluid flow conforms to Reynold's lubrication theory. Experiments were also carried out to determine how the damping factor of a liquid squeeze film varies with film viscosity, film thickness, amplitude, and frequency under free vibration of a single-degree-of-freedom system. The data are compared to computer solutions of the nonlinear differential equation of motion. With other variables held constant, the damping factor was found to decrease as the plate spacing is increased, decrease as the viscosity is decreased, and increase as the initial spacing is decreased.

Yabe, T.↗

NASA NTRS1971

Forced axisymmetric response of fluid filled spherical shells.

A general solution for the forced, linear axisymmetric response of a fluid filled spherical shell is derived with the effects of shell transverse shear and rotational inertia included. The fluid is assumed to be inviscid and compressible. Expressions for the shell radial displacement are computed for the problem of a uniform radial Heaviside load on a cap of the shell surface. In addition, the time history of the shell inner fiber stresses at the impact pole is obtained. Some comparisons with the in vacuo shell theory are also given.

Lee, Y. C.↗

NASA NTRS1972

Moon model - An offset core.

The lunar model proposed helps to account for the offset of the center of gravity from the center of the optical figure, the moments of inertia of the Moon, the 'mascons,' the localization of the maria basins on the near side of the Moon, the igneous nature of rocks, and the remanent magnetism. In the proposed model the Moon has a core whose center is offset from the center of the outside spheroid towards the earth. Such a core will be formed if the Moon were entirely molten at some time in its past, and on solidification was synchronous with the earth.

Ransford, G.↗

NASA NTRS1972

The composition of the Martian atmosphere - Minor constituents.

The Mariner 6 and 7 infrared spectrometers provided data which, in principle, determine upper limits on the possible atmospheric abundance of every gaseous substance that was undetected but which has recognized absorptions in the accessible spectral region, 1.9 to 14.4 microns. Through supporting laboratory determinations of curves of growth under pressure-broadening conditions appropriate to Mars, upper limits can be specified (expressed first in cm-atm, STP, for a vertical column and then in parts per million) for NO2, NH3, C3O2, SO2, OCS, NO, O3, CH4, N2O, HCL, HBr, and H2S. In addition, considerations of band contours, moments of inertia, and experimental absorption coefficients make it possible to place useful upper limits on 27 additional substances that were not detected and for which curves of growth have not been measured.

Horn, D.↗

NASA NTRS1972

Determination of parameters related to the interior of Mercury.

Discussion of the determination possibilities and requirements for certain crucial inertia-moment and radial-mass-distribution parameters of Mercury. It is shown that the high precision of 1 min of arc, which reasonable bounds on some of these parameters demand, cannot be obtained by either earth-based observations or the television imagery of the Mariner 73 flyby. Some methods are proposed for both landers and orbiters that could determine unambiguously most of these parameters.

Peale, S. J.↗

NASA NTRS1972

Aircraft handling qualities data

Available information on weight and inertia, aerodynamic derivatives, control characteristics, and stability augmentation systems is documented for 10 representative contemporary airplanes. Data sources are given for each airplane. Flight envelopes are presented and dimensional derivatives, transfer functions for control inputs, and several selected handling qualities parameters have been computed and are tabulated for 10 different flight conditions including the power approach configuration. The airplanes documented are the NT-33A, F-104A, F-4C, X-15, HL-10, Jetstar, CV-880M, B-747, C-5A, and XB-70A.

Heffley, R. K.↗

NASA NTRS1972

Dynamic Nonlinear Elastic Stability of Helicopter Rotor Blades in Hover and in Forward Flight

Equations for large coupled flap-lag motion of hingeless elastic helicopter blades are consistently derived. Only torsionally-rigid blades excited by quasi-steady aerodynamic loads are considered. The nonlinear equations of motion in the time and space variables are reduced to a system of coupled nonlinear ordinary differential equations with periodic coefficients, using Galerkin's method for the space variables. The nonlinearities present in the equations are those arising from the inclusion of moderately large deflections in the inertia and aerodynamic loading terms. The resulting system of nonlinear equations has been solved, using an asymptotic expansion procedure in multiple time scales. The stability boundaries, amplitudes of nonlinear response, and conditions for existence of limit cycles are obtained analytically. Thus, the different roles played by the forcing function, parametric excitation, and nonlinear coupling in affecting the solution can be easily identified, and the basic physical mechanism of coupled flap-lag response becomes clear. The effect of forward flight is obtained with the requirement of trimmed flight at fixed values of the thrust coefficient.

Friedmann, P.↗

NASA NTRS1971

Expendable second stage reusable space shuttle booster. Volume 4: Detail mass properties data

Mass properties data are presented to describe the characteristics of an expendable second stage with a reusable space shuttle booster. The final mass characteristics of the vehicle configurations for three specified payloads are presented in terms of weight, center of gravity, and mass moments of inertia. Three basic subjects are the integrated vehicle system, the expendable second stage, and the booster modifications.

Source record↗

NASA NTRS1972

Mathematical characterization of mechanical behavior of porous frictional granular media

A new definition of loading and unloading along the yield surface of Roscoe and Burland is introduced. This is achieved by noting that the strain-hardening parameter in the plastic potential function is deduced from the yield locus equation of Roscoe and Burland. The analytical results are compared with the experimental results for plate-bearing and cone-penetrometer problems and close agreements are demonstrated. The wheel-soil interaction is studied under dynamic loading. The rate-dependent plasticity or viscoelastoplastic behavior is considered. This is accomplished by the internal (hidden) variables associated with time-dependent viscous properties directly superimposed with inelastic behavior governed by the yield criteria of Roscoe and Burland. Effects of inertia and energy dissipation are properly accounted for. Example problems are presented.

Chung, T. J.↗

NASA NTRS1971

Geophysical aspects of remote sensing

Results obtained through the NASA Earth Resources Aircraft Program at Mill Creek, Oklahoma, provide a case history example of the application of remote sensing to the identification of geologic rock units. Thermal infrared images are interpreted by means of a sequence of models of increasing complexity. The roles of various parameters are examined: rock properties (thermal inertia, albedo, emissivity), site location (latitude), season (sun's declination), atmospheric effects (cloud cover, transmission, air temperature), and topographic orientation (slope, azimuth). The results obtained at this site also illustrate the development of an important application of remote sensing in geologic identification. Relatively pure limestones and dolomites of the Mill Creek test area can be differentiated in nighttime infrared images, and facies changes between them can be detected along and across strike. The predominance on the earth's surface of sedimentary rocks, of which limestone and dolomite are major members, indicates the importance of this discrimination.

Watson, K.↗

NASA NTRS1973

Spin reorientation of a nonsymmetric body with energy dissipation

Stable rotating semi-rigid bodies were demonstrated analytically, and verified in flights such as Explorer 1 and ATS-5 satellites. The problem arises from the two potential orientations which the final spin vector can take after large angle reorientation from minor to major axis, i.e., along the positive or negative axis of the maximum inertia. Reorientation of a satellite initially spinning about the minor axis using an energy dissipation device may require that the final spin orientation be controlled. Examples of possible applications are the Apogee Motor Assembly with Paired Satellites (AMAPS) configuration, where proper orientation of the thruster is required; and reorientation of ATS-5, where the spin sensitive nature of the despin device (yo-yo mechanism) requires that the final spin vector point is a specified direction.

Cenker, R. J.↗

NASA NTRS1972

Study of the dynamics of orbital assemblies including interactions with geometrical appendages

The complete equations for the Unified Flexible Spacecraft Simulation (UFSS) program developed for the NASA/MSFC are presented. This general purpose simulation program is based on an algorithm which utilizes the digital computer to synthesize the dynamic and kinematic equations for a topological tree configuration of N interconnected bodies (the interconnected system of bodies forms no closed loops), the terminal members of which may be flexible. Necessary input quantities to the dynamic subroutine include the mass and inertia properties of each body and the flexible characteristics of each terminal member in addition to the specification, for each body, of those bodies to which it connects. This latter description involves the specification of the number of rotational degrees of freedom at each interconnection along with the associated position vectors defining these connections relative to the mass centers of the bodies involved. These position vectors can be input as time-varying functions if desired, thus affording the capability of studying the effects of time-varying hinge locations. Springs and dampers are assumed to act at each interconnection and structural damping in the flexible terminal members is included in the form of equivalent viscous damping.

Ness, D. J.↗

NASA NTRS1973

A movable mass control system to detumble a disabled space vehicle

An internal autonomous control system to either completely detumble a spacecraft or lessen the tumbling motions until the rescue craft arrives is discussed. Such a device would become active upon loss of control. The development of a movable mass control system to convert the tumbling motions of a disabled vehicle into simple spin is presented. A simple spin state would greatly facilitate crew evacuation and final despinning by an external means. The system moves a control mass, according to a selected control law, in the acceleration environment created by the tumbling motion. By moving the mass properly, the rotational kinetic energy of the system may be increased or decreased creating simple spin states about the minimum or maximum moment of inertia axis, respectively. The control system is designed for the latter case due to its associated stability in the presence of perturbing forces.

Edwards, T. L.↗

NASA NTRS1972

Vibration computer programs E13101, E13102, E13104, and E13112 and application to the NERVA program. Project 187: Methodology documentation

Programs for the analyses of the free or forced, undamped vibrations of one or two elastically-coupled lumped parameter teams are presented. Bearing nonlinearities, casing and rotor distributed mass and elasticity, rotor imbalance, forcing functions, gyroscopic moments, rotary inertia, and shear and flexural deformations are all included in the system dynamics analysis. All bearings have nonlinear load displacement characteristics, the solution is achieved by iteration. Rotor imbalances allowed by such considerations as pilot tolerances and runouts as well as bearing clearances (allowing concail or cylindrical whirl) determine the forcing function magnitudes. The computer programs first obtain a solution wherein the bearings are treated as linear springs of given spring rates. Then, based upon the computed bearing reactions, new spring rates are predicted and another solution of the modified system is made. The iteration is continued until the changes to bearing spring rates and bearing reactions become negligibly small.

Mironenko, G.↗

NASA NTRS1972

Some effects of elasticity on lunar rotation

A general Hamiltonian function for a rotating moon in the field of the earth is expanded in terms of parameters orienting the spin angular momentum relative to the principal axes of the moon and relative to coordinate axes fixed in the orbit plane. The effects of elastic distortion are included as modifications of the moment of inertia tensor, where the magnitude of the distortion is parameterized by the Love number k sub 2.

Peale, S. J.↗

NASA NTRS1973

Nonlinear Equations for Bending of Rotating Beams with Application to Linear Flap-Lag Stability of Hingeless Rotors

The nonlinear partial differential equations for the flapping and lead-lag degrees of freedom of a torisonally rigid, rotating cantilevered beam are derived. These equations are linearized about an equilibrium condition to study the flap-lag stability characteristics of hingeless helicopter rotor blades with zero twist and uniform mass and stiffness in the hovering flight condition. The results indicate that these configurations are stable because the effect of elastic coupling more than compensates for the destabilizing flap-lag Coriolis and aerodynamic coupling. The effect of higher bending modes on the lead-lag damping was found to be small and the common, centrally hinged, spring restrained, rigid blade approximation for elastic rotor blades was shown to be resonably satisfactory for determining flap-lag stability. The effect of pre-cone was generally stabilizing and the effects of rotary inertia were negligible.

Hodges, D. H.↗

NASA NTRS1973

Proposed gravity-gradient dynamics experiments in lunar orbit using the RAE-B spacecraft

A series of seven gravity-gradient dynamics experiments is proposed utilizing the Radio Astronomy Explorer (RAE-B) spacecraft in lunar orbit. It is believed that none of the experiments will impair the spacecraft structure or adversely affect the continuation of the scientific mission of the satellite. The first experiment is designed to investigate the spacecraft dynamical behavior in the absence of libration damper action and inertia. It requires stable gravity-gradient capture of the spacecraft in lunar orbit with small amplitude attitude librations as a prerequisite. Four subsequent experiments involve partial retraction, ultimately followed by full redeployment, of one or two of the 230-meter booms forming the lunar-directed Vee-antenna. These boom length change operations will induce moderate amplitude angular librations of the spacecraft.

Blanchard, D. L.↗