Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “vulnerabilities”

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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Robot Gripper With Signal Processing

Single-chip computer and sensor-circuit chips preprocess sensor data. Self-contained circuitry combines sensor signals for serial digital transmission. Gripping surfaces crossed with grooves for grasping differently shaped objects. Gripper cavities house sensors and preprocessing circuitry. Sensors and preprocessing circuitry in robot gripper reduce amount of data being transmitted between robot controller and gripper. Placement in gripper reduces signal delays and vulnerability to electromagnetic interference.

Killion, Richard R.↗
NASA NTRS1988

Measuring Critical Charges For Single-Event Upsets

Concept for determining susceptibility of integrated circuits to single-event upsets (SEU's) based on direct measurement of critical charge causing upset. Test circuit is modified version of standard complementary metal-oxide/semiconductor static cell. Contains six transistors, connected to form latch that retains state of cell set by input pulses. Makes possible to evaluate vulnerability to SEU during design and development of digital equipment.

Buehler, Martin G.↗
NASA NTRS1987

Improved oil-off survivability of tapered roller bearings

The aim of this program is to improve the oil-off survivability of a tapered roller bearing when applied to a helicopter transmission, since the tapered bearing has shown a performance advantage in this application. However, the critical roller end-rib conjunction is vulnerable to damage in an oil-off condition. Three powdered metal materials were selected to use as the rib material for oil-off evaluation. These were: M2 steel to a 65% density, CBS 1000M 65% density, and CBS 1000M 75% density. The bearing styles tested were ribbed cone (inner race) and ribbed cup (outer race). Carburized solid CBS 600 was also used as a ribbed material for comparison of oil-off results. The tests were conducted at six speeds from 4000 rpm (0.26 million DN) through 37000 rpm (2.4 million DN).The ribbed cup style bearing achieved longer lives than the ribbed cone style. A standard bearing lasted only 10 minutes at 4000 rpm; however, the 30-min oil-off goal was achieved through 11000 rpm using the survivable ribbed cup bearing. The oil-off lives at 37000 rpm were less than 10 seconds. The grinding of the powder metal materials and surface preparation to achieve an open porosity is extremely critical to the oil-off performance of the powder metal component.

Kreider, Gary E.↗
NASA NTRS1987

Techniques for fire detection

An overview is given of the basis for an analysis of combustable materials and potential ignition sources in a spacecraft. First, the burning process is discussed in terms of the production of the fire signatures normally associated with detection devices. These include convected and radiated thermal energy, particulates, and gases. Second, the transport processes associated with the movement of these from the fire to the detector, along with the important phenomena which cause the level of these signatures to be reduced, are described. Third, the operating characteristics of the individual types of detectors which influence their response to signals, are presented. Finally, vulnerability analysis using predictive fire modeling techniques is discussed as a means to establish the necessary response of the detection system to provide the level of protection required in the application.

Bukowski, Richard W.↗
NASA NTRS1988

Experience with duplex bearings in narrow angle oscillating applications

Duplex ball bearings are matched pairs on which the abutting faces of the rings have been accurately ground so that when the rings are clamped together, a controlled amount of interference (preload) exists across the balls. These bearings are vulnerable to radial temperature gradients, blocking in oscillation and increased sensitivity to contamination. These conditions decrease the service life of these bearings. It was decided that an accelerated thermal vacuum life test should be conducted. The test apparatus and results are described and the rationale is presented for reducing a multiyear life test on oil lubricated bearings to less than a year.

Phinney, D. D.↗
NASA NTRS1988

General-aviation's view of progress in the aviation weather system

For all its activity statistics, general-aviation is the most vulnerable to hazardous weather. Of concern to the general aviation industry are: (1) the slow pace of getting units of the Automated Weather Observation System (AWOS) to the field; (2) the efforts of the National Weather Service to withdraw from both the observation and dissemination roles of the aviation weather system; (3) the need for more observation points to improve the accuracy of terminal and area forecasts; (4) the need for improvements in all area forecasts, terminal forecasts, and winds aloft forecasts; (5) slow progress in cockpit weather displays; (6) the erosion of transcribed weather broadcasts (TWEB) and other deficiencies in weather information dissemination; (7) the need to push to make the Direct User Access Terminal (DUAT) a reality; and (7) the need to improve severe weather (thunderstorm) warning systems.

Lundgren, Douglas J.↗
NASA NTRS1988

Effects of meteoroids and space debris on the particulate environment for space station

A large orbiting platform such as Space Station will be subjected to numerous impacts by meteoroids and space debris fragments. These hypervelocity impacts will produce clouds of ejected structural material in the vicinity of the Station. The development of a preliminary model for impact-generated ejecta production which combines the fluxes of meteoroids and space debris fragments with a description of the number of ejecta particles produced by hypervelocity impacts is reported. Modeling results give mean ejecta densities from 30 to 100 percent of the present particulate background limitation of 1 particle 5 microns and larger per orbit per 1 x 10(-5) sr field-of-view as seen by a 1-m-diameter aperture telescope in the 1990's time frame. Projected increases in the space debris flux raise this density to 300 percent of this limitation after 2010. The model is also applied to estimate the vulnerability of metallic claddings on composite structural members to penetration by hypervelocity projectiles, thereby exposing the substrate to atomic oxygen. The estimated annual number of penetrations is from 4 to 8 per square meter of cross-sectional area in the mid 1990's, increasing to more than 40 penetrations per square meter after 2010.

Seebaugh, W. R.↗
NASA NTRS1987

Quantification of the memory imprint effect for a charged particle environment

The effects of total accumulated dose on the single-event vulnerability of NMOS resistive-load SRAMs are investigated. The bias-dependent shifts in device parameters can imprint the memory state present during exposure or erase the imprinted state. Analysis of these effects is presented along with an analytic model developed for the quantification of these effects. The results indicate that the imprint effect is dominated by the difference in the threshold voltage of the n-channel devices.

Bhuva, B. L.↗
NASA NTRS1988

Space Station pressure wall repair techniques

Space Station components are susceptible to hypervelocity impact damage from orbital debris and meteoroids. An especially vulnerable and critical space station component is the module pressure wall. Even with shielding, sufficiently large impacting particles can create penetrations ranging from pinholes to large jagged holes. This paper describes pressure wall damage repair patches along with procedures and tools for performing the repair. One patch incorporates an aluminum foil protected from the jagged hole edge with a Kevlar or foam pad. An adhesive holds the patch in place. Another patch uses a stiff plate held away from the damaged area by a low durrometer rubber ring which also seals the plate edge. An adhesive will also secure this patch in place. Procedures were developed to prepare the punctured wall surface and apply the patch under weightless and unpressurized conditions. The procedures were tested in a laboratory and in the MSFC Neutral Buoyancy Simulator with models of the patches and tools.

Gibbins, Martin N.↗
NASA NTRS1987

Selection for optimal crew performance - Relative impact of selection and training

An empirical study supporting Helmreich's (1986) theoretical work on the distinct manner in which training and selection impact crew coordination is presented. Training is capable of changing attitudes, while selection screens for stable personality characteristics. Training appears least effective for leadership, an area strongly influenced by personality. Selection is least effective for influencing attitudes about personal vulnerability to stress, which appear to be trained in resource management programs. Because personality correlates with attitudes before and after training, it is felt that selection may be necessary even with a leadership-oriented training cirriculum.

Chidester, Thomas R.↗
NASA NTRS1989

Protection Against Brief Interruptions Of Power

Rotating standby power system compensates for brief interruptions in commercial power supply. System furnishes few cycles of alternating current from its stored rotational energy. Protects equipment vulnerable to brief losses of power; for example, prevents computers from erroneously suppressing or adding bits to data being handled at moment of power failure.

Casad, Theodore A.↗
NASA NTRS1989

Hollow-Cathode Source Generates Plasma

Device generates argon, krypton, or xenon plasma via thermionic emission and electrical discharge within hollow cathode and ejects plasma into surrounding vacuum. Goes from cold start up to full operation in less than 5 s after initial application of power. Exposed to moist air between operations without significant degradation of starting and running characteristics. Plasma generated by electrical discharge in cathode barrel sustained and aided by thermionic emission from emitter tube. Emitter tube does not depend on rare-earth oxides, making it vulnerable to contamination by exposure to atmosphere. Device modified for use as source of plasma in laboratory experiments or industrial processes.

Deininger, W. D.↗
NASA NTRS1989

Polymeric Electrolytic Hygrometer For Harsh Environments

Design of polymeric electrolytic hygrometer improved to meet need for reliable measurements of relative humidity in harsh environments of pulpmills and papermills. Redesigned sensor head features shorter, more-rigidly-held sensing element, less vulnerable than previous version to swell and loss of electrical contact. Useful for control of batch dryers in food and pharmaceutical industries.

Lawson, Daniel D.↗
NASA NTRS1986

Distributed Ada: Methodology, notation and tools

The task of creating software to run on a distributed system brings with it many problems not encountered in a uni-processor environment. The designer, in addition to creating a solution to meet the functional requirements of the applicaiton, must determine how to distribute that functionality in order to meet the nonfunctional requirements such as performance and fault tolerance. In the traditional approach to building distributed software systems, decisions of how to partition the software must be made early in the design process so that a separate program can be written for each of the processors in the system. This design paradigm is extremely vulnerable to changes in the target hardware environment, as well as being sensitive to poor initial guesses about what distribution of functionality will satisfy the nonfunctional requirements. The paradigm is also weak in that no compiler has a complete view of the system. Many of the advantages of using a powerful language system are lost in a one-program-per-processor environment. Another approach to the development of distributed software systems, Honeywell's Distributed Ada program, is presented.

Eisenhauer, Greg↗
NASA NTRS1989

Cryogenic reactant storage for lunar base regenerative fuel cells

There are major advantages to be gained by integrating a cryogenic reactant storage system with a hydrogen-oxygen regenerative fuel cell (RFC) to provide on-site electrical power during the lunar night. Although applicable to any power system using hydrogen-oxygen RFC's for energy storage, cryogenic reactant storage offers a significant benefit whenever the sun/shade cycle and energy storage period approach hundreds of hours. For solar power installations on the moon, cryogenic reactant storage reduces overall specific mass and meteoroid vulnerability of the system. In addition, it offers synergistic benefits to on-site users, such as availability of primary fuel cell reactants for surface rover vehicles and cryogenic propellants for OTV's. The integration involves processing and storing the RFC reactant streams as cryogenic liquids rather than pressurized gases, so that reactant containment (tankage per unit mass of reactants) can be greatly reduced. Hydrogen-oxygen alkaline RFC's, GaAs photovoltaic (PV) arrays, and space cryogenic processing/refrigeration technologies are assumed to be available for the conceptual system design. Advantages are demonstrated by comparing the characteristics of two power system concepts: a conventional lunar surface PV/RFC power system using pressurized gas storage in SOA filament wound pressure vessels and, that same system with gas liquefaction and storage replacing the pressurized storage. Comparisons are made at 20 and 250 kWe. Although cryogenic storage adds a processing plant (drying and liquefaction) to the system plus 30 percent more solar array to provide processing power, the approximate order of magnitude reduction in tankage mass, confirmed by this analysis, results in a reduction in overall total system mass of approximately 50 percent.

Kohout, Lisa L.↗
NASA NTRS1988

Radiation effect on rocket engine performance

The effects of radiation on the performance of modern rocket propulsion systems operating at high pressure and temperature were recognized as a key issue in the design and operation of various liquid rocket engines of the current and future generations. Critical problem areas of radiation coupled with combustion of bipropellants are assessed and accounted for in the formulation of a universal scaling law incorporated with a radiation-enhanced vaporization combustion model. Numerical algorithms are developed and the pertaining data of the Variable Thrust Engine (VTE) and Space Shuttle Main Engine (SSME) are used to conduct parametric sensitivity studies to predict the principal intercoupling effects of radiation. The analysis reveals that low enthalpy engines, such as the VTE, are vulnerable to a substantial performance set back by the radiative loss, whereas the performance of high enthalpy engines such as the SSME, are hardly affected over a broad range of engine operation. Additionally, combustion enhancement by the radiative heating of the propellant has a significant impact in those propellants with high absorptivity. Finally, the areas of research related with radiation phenomena in bipropellant engines are identified.

Chiu, Huei-Huang↗
NASA NTRS1989

Deep space communications, weather effects, and error control

Deep space telemetry is and will remain signal-to-noise limited and vulnerable to interference. A need exists to increase received signal power and decrease noise. This includes going to Ka-band in the mid-1990's to increase directivity. The effects of a wet atmosphere can increase the noise temperature by a factor of 5 or more, even at X-band, but the order of magnitude increase in average data rate obtainable at Ka-band relative to X-band makes the increased uncertainty a good trade. Lowbit error probabilities required by data compression are available both theoretically and practically with coding, at an infinitesimal power penalty rather than the 10 to 15 dB more power required to reduce error probabilities without coding. Advances are coming rapidly in coding, as with the new constraint-length 15 rate 1/4 convolutional code concatenated with the already existing Reed-Solomon code to be demonstrated on Galileo. In addition, high density spacecraft data storage will allow selective retransmissions, even from the edge of the Solar System, to overcome weather effects. In general, deep space communication was able to operate, and will continue to operate, closer to theoretical limits than any other form of communication. These include limits in antenna area and directivity, system noise temperature, coding efficiency, and everything else. The deep space communication links of the mid-90's and beyond will be compatible with new instruments and compression algorithms and represent a sensible investment in an overall end-to-end information system design.

Posner, Edward C.↗
NASA NTRS1988

Orbital debris environment for spacecraft designed to operate in low Earth orbit

The orbital debris environment model is intended to be used by the spacecraft community for the design and operation of spacecraft in low Earth orbit. This environment, when combined with material-dependent impact tests and spacecraft failure analysis, is intended to be used to evaluate spacecraft vulnerability, reliability, and shielding requirements. The environment represents a compromise between existing data to measure the environment, modeling of this data to predict the future environment, the uncertainty in both measurements and modeling, and the need to describe the environment so that various options concerning spacecraft design and operations can be easily evaluated.

Kessler, Donald J.↗