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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

A Mobility Concept for Martian Exploration

Soil mechanics and geological investigations on Mars or on the Moon are described herein, using a novel mobility system, designated as the "Elastic Loop Mobility System (ELMS)". ELMS was developed as a spin-off of the U. S. Lunar Roving Vehicle (LRV) which operated on the Moon during the Apollo 15, 16, and 17 Missions. Extensive testing of the ELMS, both on soft soil and on rigid obstacles, has shown that the ELMS outperforms by far both the LRV and the two manned, self-propelled Soviet rovers, Lunokhod 1 and 2, which landed on the Moon in the western part of Mare Imbrium, aboard the spacecraft Luna 17 and 21. In this paper, examples of soil mechanics and geological investigations that can be conducted either by an unmanned, self-propelled ELMS rover, or by an ELMS attached to a Martian Lander are discussed, along with the associated instrumentation. Through such investigations, ascertaining the existence of some primitive forms of past or present life on Martian or Lunar geological formations may become possible, in addition to obtaining numerous data on the mechanical and physico-chemical properties of Martian or Lunar soils along long traverses.

Costes, Nicholas↗
NASA NTRS1986

Elastic robot control - Nonlinear inversion and linear stabilization

An approach to the control of elastic robot systems for space applications using inversion, servocompensation, and feedback stabilization is presented. For simplicity, a robot arm (PUMA type) with three rotational joints is considered. The third link is assumed to be elastic. Using an inversion algorithm, a nonlinear decoupling control law u(d) is derived such that in the closed-loop system independent control of joint angles by the three joint torquers is accomplished. For the stabilization of elastic oscillations, a linear feedback torquer control law u(s) is obtained applying linear quadratic optimization to the linearized arm model augmented with a servocompensator about the terminal state. Simulation results show that in spite of uncertainties in the payload and vehicle angular velocity, good joint angle control and damping of elastic oscillations are obtained with the torquer control law u = u(d) + u(s).

Singh, S. N.↗
NASA NTRS1985

Robust torque control of an elastic robotic arm based on invertibility and feedback stabilization

An approach to the control of elastic robotic systems for space applications using inversion, servocompensation, and feedback stabilization is presented. For simplicity, a robot arm (PUMA-type) with three rotational joints is considered. The third link is assumed to be elastic. Using an inversion algorithm, a nonlinear decoupling control law, u sub d, is derived such that in the closed loop system, independent control of joint angles by the three joint torquers is accomplished. For the stabilization of elastic oscillations, a linear feedback torquer control law, u sub s, is obtained applying linear quadratic optimization to the linearized arm model augmented with a servocompensator about the terminal state. Simulation results show that, in spite of uncertainties in the payload and vehicle angular velocity, good joint angle control and damping of elastic oscillations are obtained with the torquer control law u = u sub d + u sub s.

Singh, S. N.↗
NASA NTRS1978

Origin of multi-ring basin ridge systems - An upper limit to elastic deformation based on a finite-element model

A finite-element model of a 500-km diameter lunar basin flooded with 10 km of basalt was used to represent the central portion of a multi-ring basin undergoing elastic deformation as a result of basin subsidence. Gravitational forces due to the weight of the basalt were set as the initial forces in the model; elastic constants computed from seismic velocities of lunar samples provided strength specifications. In addition, the crust was constrained by permitting no displacements at a depth of 60 km. Because of the strength of the lithosphere, surface subsidence amounted to only 20 m. This magnitude of elastic deformation does not equal that found on the lunar surface, but the orientation of principal stress and the position of circumferential compressional stress are compatible with the evolution of inner-ring and radial ridge systems by gravitational-induced downdropping.

Maxwell, T. A.↗
NASA NTRS1979

Development and validation of a piloted simulation of a helicopter and external sling load

A generalized, real time, piloted, visual simulation of a single rotor helicopter, suspension system, and external load is described and validated for the full flight envelope of the U.S. Army CH-54 helicopter and cargo container as an example. The mathematical model described uses modified nonlinear classical rotor theory for both the main rotor and tail rotor, nonlinear fuselage aerodynamics, an elastic suspension system, nonlinear load aerodynamics, and a loadground contact model. The implementation of the mathematical model on a large digital computing system is described, and validation of the simulation is discussed. The mathematical model is validated by comparing measured flight data with simulated data, by comparing linearized system matrices, eigenvalues, and eigenvectors with manufacturers' data, and by the subjective comparison of handling characteristics by experienced pilots. A visual landing display system for use in simulation which generates the pilot's forward looking real world display was examined and a special head up, down looking load/landing zone display is described.

Shaughnessy, J. D.↗
NASA NTRS1976

Buckling of structures; Proceedings of the Symposium, Harvard University, Cambridge, Mass., June 17-21, 1974

The papers deal with such topics as the buckling and post-buckling behavior of plates and shells; methods of calculating critical buckling and collapse loads; finite element representations for thin-shell instability analysis; theory and experiment in the creep buckling of plates and shells; creep instability of thick shell structures; analytical and numerical studies of the influence of initial imperfections on the elastic buckling of columns; mode interaction in stiffened panels under compression; imperfection-sensitivity in the interactive buckling of stiffened plates; buckling of stochastically imperfect structures; and the Liapunov stability of elastic dynamic systems. A special chapter is devoted to design problems, including the design of a Mars entry 'aeroshell', and buckling design in vehicle structures. Individual items are announced in this issue.

Budiansky, B.↗
NASA NTRS1983

Structural optimization with dynamic behavior constraints

The minimum weight optimum design of damped linearly elastic structural systems subjected to periodic loading with behavior constraints on maximum deflections and side constraints on design variables is addressed. Attention is focused on the two major impediments to an optimal solution: (1) the time parametric nature of the behavior constraints; and (2) the severe nonconvexity of the design space. A solution method based on upper bound approximations for the behavior constraints and an innovative mathematical programming scheme for seeking the optimal frequency subspace is set forth. Numerical results for several test problems illustrate the effectiveness of the method reported.

Mills-Curran, W. C.↗
NASA NTRS1985

Ultra lightweight mirror performance at 8 degrees kelvin

Earlier work funded by DARPA, evaluating the optical stability of a 0.5-m ultra-lightweight, frit-bonded, fused silica mirror, is extended from the previous 100 deg K specification down to 8 deg K. The thermal stability is excellent and comparable to that for conventional fusion and solid mirrors. The total mirror change of 0.10 lambda rms (lambda = 0.6328 microns) meets the needs of most IR systems. Thermal elastic quilting is excellent (0.008 lambda). Ames Research Center and Kodak data evaluations, done independently, are in very good agreement.

Crowe, D. A.↗