Search NASA⌕ Search

SEARCH · Search NASA

Results for “Performance Indicators”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

MIL-C-38999 electrical connector applicability tests for on-orbit EVA satellite servicing

MIL-C-38999 electrical connectors were tested for their applicability to the on-orbit EVA satellite servicing environment. The investigation provided a methodical approach to the evaluation of the human-machine interface of these connectors. The physical characteristics of thirty-five MIL-C-38999 connectors were tested in two simulated space environments, the NASA Johnson Space Center Weightless Environment Training Facility and an evacuated glovebox which incorporated the Extravehicular Maneuvering Unit series 3000 gloves. Physical characteristics of the connectors were documented, including operating torque and work profiles. STS crewmembers tested a select group of connectors in two WETF test and subjectively ranked the G&H PMM Wing-Tab connectors as most applicable to the on-orbit servicing environment. WETF performance times indicated that the G&H PMM Wing-Tab connector had the fastest operating time. The evacuated glovebox participants ranked the G&H 64600 Wing-Tab and the G&H PMM Wing-Tab connectors as those most applicable to the on-orbit servicing environment. During the evacuated glovebox tests, the G&H 64600 Wing-Tab connector had the fastest operating time.

Griffin, Thomas J.↗
NASA NTRS1989

Analysis of creep and relaxation in composite laminates with holes

The time-dependent behavior of composite laminates subjected to mechanical loads is studied using linear viscoelastic theory. Three-dimensional finite elements are formulated to solve the integral equilibrium equations. Analyses of creep and stress relaxation in composites with holes are performed. Results indicate that the relaxation of interlaminar stresses depends on temperature and layups, and that the creep response of strains is affected by stress redistribution between plies.

Lin, Kuen Y.↗
NASA NTRS1988

The effects of format in computer-based procedure displays

Two experiments were conducted to investigate display variables likely to influence the effectiveness of computer-based procedure displays. In experiment 1, procedures were presented in three formats, text, extended-text, and flowchart. Text and extended-text are structured prose formats which differ in the spatial density of presentation. The flowchart format differs from the text format in both syntax and spatial representation. Subjects were required to use the procedures to diagnose a hypothetical system anomaly. The results indicate that performance was most accurate with the flowchart format. In experiment 2, procedure window size was varied (6-line, 12-line, and 24-line) in addition to procedure format. In the six line window condition, experiment 2 replicated the findings of experiment 1. As predicted, completion times for flowchart procedures decreased with increasing window size; however, accuracy of performance decreased substantially. Implications for the design of computer-based procedure displays are discussed.

Desaulniers, David R.↗
NASA NTRS1989

Closed loop navigation and guidance for gravity probe B orbit insertion

This paper addresses the problem of guiding the Gravity Probe B (GP-B) spacecraft from its location after initial insertion to a very precise low earth orbit. Specifically, the satellite orbit is required to be circular to within 0.001 eccentricity, polar to within 0.001 deg inclination, and aligned with the direction of the star Rigel to within 0.001 deg. Navigation data supplied by an on-board GPS receiver is used as feedback to a control algorithm designed to minimize the time to achieve the desired orbit. Translational control is provided by the proportional helium thrusters, which are used for drag-free and attitude control during the remainder of the science mission. Simulations of the guidance system are presented which give an indication of performance characteristics for several types of orbit injection errors. This research is the first reported effort to use GPS as a sensor for a closed loop space guidance system.

Axelrad, P.↗
NASA NTRS1989

Optimal aeroassisted guidance using Loh's term approximations

This paper presents three guidance algorithms for aerocapture and/or aeroassisted orbital transfer with plane change. All three algorithms are based on the approximate solution of an optimal control problem at each guidance update. The chief assumption is that Loh's term may be modeled as a function of the independent variable only. The first two algorithms maximize exit speed for fixed exit altitude, flight path angle and heading angle. The third minimizes, in one sense, the control effort for fixed exit altitude, flight path angle, heading angle and speed. Results are presented which indicate the near optimality of the solutions generated by the first two algorithms. Results are also presented which indicate the performance of the third algorithm in a simulation with unmodeled atmospheric density disturbances.

Mceneaney, W. M.↗
NASA NTRS1989

Space Shuttle 2 Advanced Space Transportation System. Volume 1: Executive Summary

An investigation into the feasibility of establishing a second generation space transportation system is summarized. Incorporating successful systems from the Space Shuttle and technological advances made since its conception, the second generation shuttle was designed to be a lower-cost, reliable system which would guarantee access to space well into the next century. A fully reusable, all-liquid propellant booster/orbiter combination using parallel burn was selected as the base configuration. Vehicle characteristics were determined from NASA ground rules and optimization evaluations. The launch profile was constructed from particulars of the vehicle design and known orbital requirements. A stability and control analysis was performed for the landing phase of the orbiter's flight. Finally, a preliminary safety analysis was performed to indicate possible failure modes and consequences.

Adinaro, James N.↗
NASA NTRS1990

Fabrication and optimization of a whiskerless Schottky barrier diode for submillimeter wave applications

The following accomplishments were made towards the goal of an optimized whiskerless diode chip for submillimeter wavelength applications. (1) Surface channel whiskerless diode structure was developed which offers excellent DC and RF characteristics, reduced shunt capacitance and simplified fabrication compared to mesa and proton isolated structures. (2) Reliable fabrication technology was developed for the surface channel structure. The new anode plating technology is a major improvement. (3) DC and RF characterization of the surface channel diode was compared with whisker contacted diodes. This data indicates electrical performance as good as the best reported for similar whisker contacted devices. (4) Additional batches of surface channel diodes were fabricated with excellent I-V and reduced shunt capacitance. (5) Large scale capacitance modelinng was done for the planar diode structure. This work revealed the importance of removing the substrate gallium arsenide for absolute minimum pad capacitance. (6) A surface channel diode was developed on quartz substrate and this substrate was completely removed after diode mounting for minimum parasitic capacitance. This work continues with the goal of producing excellent quality submillimeter wavelength planar diodes which satisfy the requirements of easy handling and robustness. These devices will allow the routine implementation of Schottky receivers into space-based applications at frequencies as high as 1 THz, and, in the future, beyond.

Bishop, W.↗
NASA NTRS1990

Factors affecting pressure in Li-SOCl2 cells

A model was developed to describe internal pressure in a Li-SOCl2 cell as a function of state of charge and temperature. The model was used to generate sets of predicted pressure variations in a hypothetical 250-Ah cell with assumed ranges of cell design variables including initial void volume and inert gas pressure. Results were assessed to establish values of the cell design parameters that would yield a vent pressure within a temperature range that was deemed safe and also adequate for cell performance. Results indicate that a suitable design for this cell would require an initial void volume near 112 cu cm and inert gas pressure near 40 psi.

Frank, H.↗
NASA NTRS1990

Photovoltaic superiority for Space Station Freedom power in the 21st century

Complete power systems capable of delivering 75 kW of continuous power in low earth orbit have been compared. Performance, liabilities, and advantages are discussed for a shielded nuclear system, a solar dynamic system, and photovoltaic systems, both current Freedom Si design and near-term GaAs/Ge with NaS storage. System components include power generation, storage (if required), heat rejection, power conversion and distribution, structural support, and shielding (if required). Performance parameters indicate the substantial advantage of the GaAs/Ge photovoltaic system, which does not require altering the support structure of the current Freedom design.

Bailey, Sheila G.↗
NASA NTRS1991

The use of carboranes as oxidation inhibitors for carbon-carbon composites

Carbon-carbon composites have many beneficial properties for use in aerospace applications, including their high specific strength and modulus at elevated temperatures. However, they share with all carbon based substances a strong tendency to burn when heated in air. In order to exploit their good qualities, it is necessary to slow or prevent their oxidation during use. Molecular inhibiters offer protection with the advantage of being able to form a homogeneous solution with the resin. Since boron oxides are known to provide the desired kind of protection, molecular compounds based on boron seem reasonable candidates to test as inhibitors. Performance tests indicated that carboranes are excellent materials for obtaining high uniform loadings of boron inhibitors in glassy carbon materials and thus reducing their rates of oxidation. Further, there is evidence that the use of substituted derivatives could provide more complete and thorough forms of protection.

Petty, John T.↗
NASA NTRS1992

The ultimate quantum limits on the accuracy of measurements

A quantum generalization of rate-distortion theory from standard communication and information theory is developed for application to determining the ultimate performance limit of measurement systems in physics. For the estimation of a real or a phase parameter, it is shown that the root-mean-square error obtained in a measurement with a single-mode photon level N cannot do better than approximately N exp -1, while approximately exp(-N) may be obtained for multi-mode fields with the same photon level N. Possible ways to achieve the remarkable exponential performance are indicated.

Yuen, Horace P.↗
NASA NTRS1992

Coherent summation of spatially distorted Doppler lidar signals using a two-dimensional heterodyne detector array

We have investigated the improvement in the signal-to-noise ratio for a coherent Doppler lidar through the use of a multi-element heterodyne detector array. Such an array enables the spatial summation of atmospheric refractive turbulence induced speckles, and time varying target speckles. Our recent experiments have shown that the non-coherent summation of the lidar signals from a heterodyne detector array can enhance the heterodyne mixing efficiency and thus the signal-to-noise ratio. In this paper, we expand this work to include the coherent summation of array signals. The digitized heterodyne signals were stored in a personal computer. Fast Fourier transforms were performed on both the non-coherent and coherent summations of the detector array signals. It was found that the coherent summation greatly enhanced the accuracy in the Doppler frequency estimate. A theoretical analysis was performed and indicated good agreement with experimental results. We have also applied these results to the more general lidar applications including atmospheric wind sensing, and have found that in most lidar applications the Doppler frequency estimate is increased through the use of the heterodyne detector array.

Chan, Kin Pui↗
NASA NTRS1992

A hydrodynamic approach to cosmology - Methodology

The present study describes an accurate and efficient hydrodynamic code for evolving self-gravitating cosmological systems. The hydrodynamic code is a flux-based mesh code originally designed for engineering hydrodynamical applications. A variety of checks were performed which indicate that the resolution of the code is a few cells, providing accuracy for integral energy quantities in the present simulations of 1-3 percent over the whole runs. Six species (H I, H II, He I, He II, He III) are tracked separately, and relevant ionization and recombination processes, as well as line and continuum heating and cooling, are computed. The background radiation field is simultaneously determined in the range 1 eV to 100 keV, allowing for absorption, emission, and cosmological effects. It is shown how the inevitable numerical inaccuracies can be estimated and to some extent overcome.

Cen, Renyue↗
NASA NTRS1992

Development of magnetostrictive active members for control of space structures

The goal of this Phase 2 Small Business Innovative Research (SBIR) project was to determine the technical feasibility of developing magnetostrictive active members for use as truss elements in space structures. Active members control elastic vibrations of truss-based space structures and integrate the functions of truss structure element, actively controlled actuator, and sensor. The active members must control structural motion to the sub-micron level and, for many proposed space applications, work at cryogenic temperatures. Under this program both room temperature and cryogenic temperature magnetostrictive active members were designed, fabricated, and tested. The results of these performance tests indicated that room temperature magnetostrictive actuators feature higher strain, stiffness, and force capability with lower amplifier requirements than similarly sized piezoelectric or electrostrictive active members, at the cost of higher mass. Two different cryogenic temperature magnetostrictive materials were tested at liquid nitrogen temperatures, both with larger strain capability than the room temperature magnetostrictive materials. The cryogenic active member development included the design and fabrication of a cryostat that allows operation of the cryogenic active member in a space structure testbed.

Johnson, Bruce G.↗
NASA NTRS1993

Compiler-assisted multiple instruction rollback recovery using a read buffer

Multiple instruction rollback (MIR) is a technique that has been implemented in mainframe computers to provide rapid recovery from transient processor failures. Hardware-based MIR designs eliminate rollback data hazards by providing data redundancy implemented in hardware. Compiler-based MIR designs have also been developed which remove rollback data hazards directly with data-flow transformations. This paper focuses on compiler-assisted techniques to achieve multiple instruction rollback recovery. We observe that some data hazards resulting from instruction rollback can be resolved efficiently by providing an operand read buffer while others are resolved more efficiently with compiler transformations. A compiler-assisted multiple instruction rollback scheme is developed which combines hardware-implemented data redundancy with compiler-driven hazard removal transformations. Experimental performance evaluations indicate improved efficiency over previous hardware-based and compiler-based schemes.

Alewine, N. J.↗
NASA NTRS1993

External induced contamination environment assessment for Space Station Freedom

An assessment of the Space Station Freedom performance as affected by the external induced contamination environment is in progress. The assessment procedure involves comparing the Space Station Freedom external contamination requirements, SSP 30426, Revision B (1991), with calculated molecular deposition, molecular column density, and other effects from potential sources of contamination. The current assessment comprises discussions of Space Shuttle proximity operations, Space Shuttle waste-water dumps (while docked to the Space Station), Space Station fluid and waste-gas venting, system gas leakage, external material outgassing, and a combined contamination assessment. This performance assessment indicates that Space Station Freedom contamination requirements are realistic and can be satisfied when all contamination sources are included.

Leger, Lubert↗
NASA NTRS1993

Hubble Space Telescope characterized by using phase-retrieval algorithms

We describe several results characterizing the Hubble Space Telescope from measured point spread functions by using phase-retrieval algorithms. The Cramer-Rao lower bounds show that point spread functions taken well out of focus result in smaller errors when aberrations are estimated and that, for those images, photon noise is not a limiting factor. Reconstruction experiments with both simulated and real data show that the calculation of wave-front propagation by the retrieval algorithms must be performed with a multiple-plane propagation rather than a simple fast Fourier transform to ensure the high accuracy required. Pupil reconstruction was performed and indicates a misalignment of the optical axis of a camera relay telescope relative to the main telescope. After we accounted for measured spherical aberration in the relay telescope, our estimate of the conic constant of the primary mirror of the HST was - 1.0144.

Fienup, J. R.↗