The Environment For Application Software Integration and Execution (EASIE) is a methodology and a set of software utility programs developed at the NASA Langley Research Center for coordinating the use of engineering design and analysis computer programs. Under user direction, EASIE controls the execution of independently developed programs and manages the flow of data to and from a common relational data base in order to accomplish design or analysis objectives. The process is highly automated. For example, a utility program generates a DATA DICTIONARY, describing the contents of the data base and the various subsets of data used by the application programs. Other utilities automatically generate FORTRAN or C subroutines to link the application programs with the database or to pre- and post-process the data. EASIE is also “user friendly,” providing “windows” into the data base to view subsets of the data and the means to modify the data at any time A key feature is the degree of independence it provides to the programmer and user from the details of the operating system and Data Base Management System. EASIE has been used successfully in the integration of several design systems at Langley and within the aerospace industry. This paper discusses the application of EASIE to these specific systems, emphasizing the advantages it has provided to both programmers and users. Significant improvements made as a result of these experiences will also be discussed.

Many studies for the preliminary definition of a space teleoperated robotic devices are recently completed or under development. One example of such devices is the Flight Telerobotic Servicer (FTS) developed by NASA. These studies will assist astronauts in many ot the on- and off-board tasks of assembly, maintenance, servicing and inspection of the Space Station. This paper makes an assessment of the role that teleprogramming may have in furthering the automation capabilities of these devices by extending their capacity for growth and evolution. Relevant system engineering design issues are identified for its programming. An outline of teleprogramming environments is given which comprises of task planning and interpretation, simulation, specialized modules known as system agents and world model manager (influencing teleoperator decisions at a remote worksite). A Space Robotic Workcell (SRW) is a collection of robots, sensors, and other equipment grouped in a cooperative environment to perform various complex tasks in space. Due to their distributed nature, the control and programming of SRW s is often a difficult task, for which dedicated space environments have to be designed. There is clearly established need to perform intervention tasks remotely in hazardous environments by machines. Examples of this need that are highly relevant to our discussion are space safety applications, space exploration and underwater structure maintenance and repair. In this paper we focus on Space Robotics & Automation . We have discussed a detailed study of autonomy versus teleoperation for intervention robots making a case for task level teleprogramming as a new emerging field in Telerobotics. A rationale for teleprogramming and its techniques, Expert Systems, SRW Subsystem Agents, SRW Task Planner and SRW Plan (for growth and evolution) are also covered in this paper.

This work summarizes results for a three cylinder fuel injector that has been adopted as a model for investigating combustion phenomenon in the 8-Foot High Temperature Tunnel (HTT) at NASA Langley Research Center. The primary objective here is to understand the flame lift-off phenomenon in the three cylinder fuel injector geometry in two-dimensions. Three chemistry models, namely fast chemistry, one-step kinetics and two-step kinetics are employed in conjunction with a computational fluid dynamics code to analyze the flame structure and flame lift-off characteristics downstream of the fuel injector. Effects of fuel jet velocity and chemistry model on the flame lift-off phenomenon from the injector surface are analyzed by considering simultaneously the combined convection (outside the cylinders) and conduction (inside the cylinders). Results indicate that as the fuel jet velocity is increased, the flame is transformed from a wrap around configuration to a clearly lifted flame configuration. Of the three chemistry models considered in the present study, only the two-step chemistry model predicts a clearly lifted flame. The ability of the CFD code to predict lifted flame is important since a slightly lifted but stable flame is of paramount importance to the operation of the combustor.

Low-contact-ratio spur gears were tested in the NASA gear-noise rig to study the noise radiated from the top of the gearbox. Experimental results were compared with a NASA acoustics code to validate the code for predicting transmission noise. The analytical code is based on the boundary element method (BEM) which models the gearbox top as a plate in an infinite baffle. Narrow-band vibration spectra measured at 63 nodes on the gearbox top were used to produce input data for the BEM model. The BEM code predicted the total sound power based on this measured vibration. The measured sound power was obtained from an acoustic intensity scan taken near the surface of the gearbox at the same 63 nodes used for vibration measurements. Analytical and experimental results were compared at four different speeds for sound power at each of the narrow-band frequencies over the range of 400 to 3200 Hz. Results are also compared for the sound power level at meshing frequency plus three sideband pairs and at selected gearbox resonant frequencies. The difference between predicted and measured sound power is typically less than 3 dB with the predicted value generally less than the measured value.

Low-contact-ratio spur gears were tested in the NASA gear-noise rig to study the noise radiated from the top of the gearbox. The measured sound power from the gearbox top was obtained from a near-field acoustic intensity scan taken at 63 nodes just above the surface. The sound power was measured at a matrix of 45 operating speeds and torque levels. Results are presented in the form of a spectral speed map and as plots of sound power versus torque (at constant speed) and as sound power versus speed (at constant torque). Because of the presence of vibration modes, operating speed was found to have more impact on noise generation than torque level. A NASA gear dynamics code was used to compute the gear tooth dynamic overload at the same 45 operating conditions used for the experiment. Similar trends were found between the analytical results for dynamic tooth overload and experimental results for sound power. Dynamic analysis may be used to design high-quality gears with profile relief optimized for minimum dynamic load and noise.

A comparison was made between computer model predictions of gear dynamic behaviour and experimental results. The experimental data were derived from the NASA gear noise rig, which was used to record dynamic tooth loads and vibration. The experimental results were compared with predictions from the Australian Defence Science and Technology Organisation Aeronautical Research Laboratory’s gear dynamics code, for a matrix of 28 load-speed points. At high torque the peak dynamic load predictions agree with experimental results with an average error of 5 percent in the speed range 800 to 6000 rpm. Tooth separation (or bounce), which was observed in the experimental data for light-torque, high-speed conditions, was simulated by the computer model. The model was also successful in simulating the degree of load sharing between gear teeth in the multiple-tooth-contact region.

This paper presents a computer simulation showing how the gear contact ratio affects the dynamic load on a spur gear transmission. The contact ratio can be affected by the tooth addendum, the pressure angle, the tooth size (diametral pitch), and the center distance. The analysis presented in this paper was performed by using the NASA gear dynamics code DANST. In the analysis the contact ratio was varied over the range 1.20 to 2.40 by changing the length of the tooth addendum. In order to simplify the analysis, other parameters related to contact ratio were held constant. The contact ratio was found to have a significant influence on gear dynamics. Over a wide range of operating speeds a contact ratio close to 2.0 minimized dynamic load. For low-contact-ratio gears (contact ratio less than 2.0), increasing the contact ratio reduced the gear dynamic load. For high-contact-ratio gears (contact ratio equal to or greater than 2.0), the selection of contact ratio should take into consideration the intended operating speeds. In general, high-contact-ratio gears minimized dynamic load better than low-contact-ratio gears.

A computer program was developed for designing a low vibration gearbox. The code is based on a finite element shell analysis method, a modal analysis method, and a structural optimization method. In the finite element analysis, a triangular shell element with 18 degrees-of-freedom is used. In the optimization method, the overall vibration energy of the gearbox is used as the objective function and is minimized at the exciting frequency by varying the finite element thickness. Modal analysis is used to derive the sensitivity of the vibration energy with respect to the design variable. The sensitivity is representative of both eigenvalues and eigenvectors. The optimum value is computed by the gradient projection method and a unidimensional search procedure under the constraint condition of constant weight. The computer code is applied to a design problem derived from an experimental gearbox in use at the NASA Lewis Research Center. The top plate and two side plates of the gearbox are redesigned and the contribution of each surface to the total vibration is determined. Results show that optimization of the top plate alone is effective in reducing total gearbox vibration.

In 1987 work was initiated on the Automated Structural Assembly Laboratory (ASAL) at NASA/LaRC to demonstrate the feasibility of robotic construction in orbit. To move itself as the structure grows, the robot is mounted on a carriage that traverses a beam which moves longitudinally, similar to a gantry crane. Gantry motions will be operated by the self-sufficient robot with its wrist roll motion. Interfaces for the robot at each gantry motor shaft are provided for that purpose. Wrist roll is limited by the large and growing number of wires that must communicate thru the wrist joint to connect the end-effector to power, sensory devices, and computation services. Rotation-Rectifiers applied to robot mobility simplify the end-effector to motor shaft interface, reduce the number of interface operations that must be performed, and convert oscillating robot wrist roll motions to continuous rotation in either direction.

Experimental tests were performed on the OH-58A helicopter main-rotor transmission in the NASA Lewis 500-hp helicopter transmission test stand. The testing was part of a joint Navy/NASA/Army lubrication program. The objectives of the joint program are to develop and demonstrate a separate lubricant for gearboxes with improved performance in life and load-carrying capacity. The goal of these experiments was to develop a testing procedure to fail certain transmission components using a MIL-L-23699 based reference oil and then to run identical tests with improved lubricants and demonstrate improved performance. The tests were directed at components that failed due to marginal lubrication from Navy field experience. These failures included mast shaft bearing micropitting, sun gear and planet bearing fatigue, and spiral bevel gear scoring. A variety of tests were performed and over 900 hr of total run time accumulated for these tests. Some success was achieved in developing a testing procedure to produce sun gear and planet bearing fatigue failures. Only marginal success was achieved in producing mast shaft bearing micropitting and spiral bevel gear scoring.

Two versions of the planetary reduction stages from U.S. Army OH-58 helicopter main rotor transmissions were tested at the NASA Lewis Research Center. One sequential and one nonsequential planetary were tested. Sun gear and ring gear teeth strains were measured, and stresses were calculated from the strains. The alternating stress at the fillet of both the loaded and unloaded sides of the teeth and at the root of the sun gear teeth are reported. Typical stress variations as the gear tooth moves through the mesh are illustrated. At the tooth root location of the thin-rimmed sun gear, a significant stress was produced by a phenomenon other than the passing of a planet gear. The load variation among the planets was studied. Each planet produced its own distinctive load distribution on the ring and sun gears. The load variation was less for a three-planet, nonsequential design as compared to that of a four-planet, sequential design. The results reported enhance the data base for gear stress levels and provide data for the validation of analytical methods.

The framework of an engineering creep-fatigue durability model has been adapted for use in estimating the radial static burst pressure and cyclic low-cycle fatigue macro-crack initiation resistance of continuous fiber reinforced (CFR) metal matrix composite (MMC) rings for application at 800 °F. Rings of circumfrentially wrapped SCS6/Ti-15-3 were manufactured by Textron Specialty Metals and burst tested by Pratt & Whitney as a part of a cooperative program with the NASA Lewis Research Center. Fatigue tests have as yet to be performed. The engineering model is based on a 3-D elasto-plastic micromechanics analysis of the tensile-loaded composite architecture. Use is made of the rule of mixtures, strain compatibility, equilibrium, and the stress-strain relationships of the constituents. Knowledge is required of the mechanical and fatigue properties of the matrix and fibers and how the presence of each affects the sharing of imposed stresses and strains. The model addresses specific issues such as residual fabrication stresses, inelastic deformation within the ductile matrix, multiaxial constraint imposed on the matrix, cyclic relaxation of both residual and applied mean stresses in the matrix, fatigue micro-crack initiation and propagation in the matrix, and tensile fracture of both the ductile matrix and the brittle fibers. In the current application of the model, the specific issues were empirically calibrated through use of tensile and tension-tension fatigue coupons that had been subjected to essentially identical loading as the rings.

Pratt & Whitney Aircraft and NASA Lewis Research Center studied a silicon-carbide-fiber-reinforced, titanium-metal-matrix (MMC) composite designated SiC(SCS-6)/Ti-15V-3Cr-3Al-3Sn. Fracture tests of three nominal 15.24-cm (6-in.) diameter SCS–6/Ti-15-3 rings at 427 °C (800 °F) and room temperature resulted in failure at internal pressures of 0.172 GPa (25 ksi) (average) and 0.235 GPa (34.1 ksi), respectively. Predictions of internal pressure to failure varied from 0.140 to 0.276 GPa (20.3 to 40.1 ksi) at 427 °C (800 °F). Nondestructive evaluation revealed that the rings’ MMC cores had varying density and were not uniformly distributed inside the monolithic casing. Analytical predictions of ring cyclic life at 0.154-GPa (22.4-ksi) internal pressure varied from 1000 to 15 000 cycles. No fatigue life data were obtained with the MMC rings for comparison with theory.

A recent task to design a Rankine-cycle space-power turbine system employing eutectic alloys of alkali metals prompted the present authors to re-examine the NASA design procedure for axial-flow turbines, as outlined by Glassman and Futral (and based on works of Stewart) in 1963. After clarifying the role of the singular case of a single-stage turbine, and organizing the procedure in clear steps, a computer program AXITURB was written. The present paper reports essentially the success of AXITURB in performing parametric studies of NaK and CsK turbines (using 78.4% and 23.1%, respectively, of potassium by weight), after re-generating all the reported NASA designs for turbines employing pure Na, K and Cs. An outline of design steps is also given. AXITURB has been put in public domain. Its heavily commented source code in FORTRAN is available to designers for adaption or modification.

We present an explicit solution to a stochastic control problem generally referred to as the LQG ( L inear Q uadratic G aussian) or Stochastic Regulator problem for continuum models of flexible structures with collocated rate sensors, which holds a fortiori for FEM or truncated modal models. Robustness properties accruing from the positive realness of the optimal compensator transfer function are described, and convergence of modal approximations is proved. Preliminary experimental results on the NASA LaRC SCOLE testbed are included.

This paper gives an overview of Probabilistic Design Methodology (PDM) with emphasis on quantification of the effects of uncertainties for structural variables and the evaluation of failure probability. The application of Probabilistic Fault Tree Analysis (PFTA) to the design of a shaft carrying a spur gear is also presented. The PFTA includes the development of a fault tree to represent the system, construction of an approximation function for bottom events, computation of sensitivity factors of design variables, and the calculation of the system reliability. The computer code employed for the analyses is known as “Numerical Evaluation of Stochastic Structures Under Stress” (NESSUS). NESSUS is developed under NASA probabilistic structural analysis program.

An algorithm and a computer program are developed for spacecraft structural analysis to determine the maximum linear static response (stress, deformation, etc.) and the corresponding “worst direction” of the loading. Compared to the brute force approach of repeating the structural analysis to cover all the possible orientations of the load vector, the proposed approach is faster, more accurate, and computationally more efficient. Maximum structural response determination is illustrated through a case study of stress analysis conducted for the TRMM (Tropical Rainfall Measuring Mission) payload developed by NASA Goddard Space Flight Center and NASDA (National Space Development Agency of Japan). The paper includes part of the structural analysis conducted in sizing the Upper Instrument Support Platform, which provides support for two of TRMM’s major instruments.

The paper investigates computational efficiency of various finite element solvers, including the state-of-the-art iterative methods based on multigrid-like and Modified Incomplete Cholesky preconditioners, as well as sparse direct solver recently developed at NASA Langley. These methods are compared to the newly developed Finite Element Oriented Solver (FEOS), which combines the advantages of the iterative and direct solution techniques. Numerical tests are conducted for both well-conditioned three dimensional problems as well as poor-conditioned problems, such as thin shells. The proposed FEOS solver has been found to possess a remarkable robustness and computational efficiency, by far superior to its comprising ingredients.

The capability of the INS3D-UP code in the prediction of turbulent flow in a sharp bend of circular cross-section has been investigated. The code, developed by the NASA Ames Research Center, is being used by the NASA Marshal Space Flight Center to analyze turbulent flow of liquid propellant in vaned pipe bends designed for use in the Space Shuttle Main Engine. The FORTRAN code is based on finite difference method and uses the concept of pseudocompressibility to solve incompressible Navier-Stokes equation. The Baldwin-Barth turbulence model is embedded in the code for turbulence computation. The flow field, at a Reynolds number of 43,000, in a sharp 90° bend has been predicted and compared with measurement. It is found that the agreement between the predicted and measured velocities is very well. The predicted pressures at the bend wall also compares reasonably well with the measurement. It is concluded that the INS3D-UP code is a good computational tool to analyze similar flow problems.

This paper presents a follow-the-leader algorithm for control of the Payload Inspection and Processing System (PIPS) at NASA Kennedy Space Center. PIPS is an automated system, programmed off-line for inspection of Space Shuttle payloads after integration and prior to launch. PIPS features a hyper-redundant 18-dof serpentine truss manipulator capable of snake-like motions to avoid obstacles. Given an obstacle-free trajectory for the manipulator tip, the follow-the-leader algorithm ensures whole-arm collision avoidance by forcing ensuing links to follow the same trajectory. This paper summarizes modular development, implementation, testing, and graphical demonstration of the algorithm for prototype PIPS hardware.