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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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Measurements of radiated elastic wave energy from dynamic tensile cracks

The role of fracture-velocity, microstructure, and fracture-energy barriers in elastic wave radiation during a dynamic fracture was investigated in experiments in which dynamic tensile cracks of two fracture cofigurations of double cantilever beam geometry were propagating in glass samples. The first, referred to as primary fracture, consisted of fractures of intact glass specimens; the second configuration, referred to as secondary fracture, consisted of a refracture of primary fracture specimens which were rebonded with an intermittent pattern of adhesive to produce variations in fracture surface energy along the crack path. For primary fracture cases, measurable elastic waves were generated in 31 percent of the 16 fracture events observed; the condition for radiation of measurable waves appears to be a local abrupt change in the fracture path direction, such as occurs when the fracture intersects a surface flaw. For secondary fractures, 100 percent of events showed measurable elastic waves; in these fractures, the ratio of radiated elastic wave energy in the measured component to fracture surface energy was 10 times greater than for primary fracture.

Boler, Frances M.↗
NASA NTRS1990

Constraints on the subsurface structure of Europa

The wedge-shaped bands appearing near the anti-Jovian point on Europa are tension cracks which, after formation on an intact lithosphere, have facilitated the rotation of ice-lithosphere sections decoupled from the silicate interior. Such factors as fluid pressure, surface temperature, silicate impurities in the ice, and strain rates, would have affected the processes in question. A minimum degree of differentiation is required for Europa to mechanically decouple the rotated ice lithosphere from the underlying, predominantly silicate mantle.

Golombek, M. P.↗
NASA NTRS1990

Orbital debris environment for spacecraft in low earth orbit

Modeling and measurement results used in formulating an environment model that can be used for the engineering design of spacecraft are reviewed. Earth-based and space-based sensors are analyzed and it is noted that the effects of satellite breakups can be modeled to predict a uncatalogued population, if the nature of the breakup is understood. It is observed that the telescopic data indicate that the current model is too low for sizes slightly larger than 10 cm, and may be too low for sizes between 2 cm and 10 cm, while there is an uncertainty in the current development, especially for sizes smaller than 10 cm, and at altitudes different from 500 km. Projections for the catastrophic collision rate for different growth conditions are made, emphasizing that the rate of growth of fragments will be twice the rate of intact objects.

Kessler, Donald J.↗
NASA NTRS1990

Intrapericardial denervation - Radial artery blood flow and heart rate responses to LBNP

The effects of intrapericardial denervation on the radial artery blood flow velocity (RABFV) and heart rate (HR) responses to LBNP in rhesus monkeys were investigated by measuring the RABFV transcutaneously by a continuous-wave Doppler ultrasonic flowmeter in order to derive an index of forearm blood flow response to low (0 to -20 mm Hg) and high (0 to -60 mm Hg) ramp exposures during supine LBNP. Four of the eight subjects were subjected to efferent and afferent cardiac denervation. It was found that, during low levels of LBNP, monkeys with cardiac denervation exhibited no cardiopulmonary baroreceptor-mediated change in the RABFV or HR, unlike the intact animals, which showed steady decreases in RABFV during both high- and low-pressure protocols. It is suggested that forearm blood flow and HR responses to low-level LBNP, along with pharmacological challenge, are viable physiological tests for verifying the completeness of atrial and cardiopulmonary baroreceptor denervation.

Mckeever, Kenneth H.↗
NASA NTRS1990

Cometary delivery of organic molecules to the early earth

It has long been speculated that earth accreted prebiotic organic molecules important for the origins of life from impacts of carbonaceous asteroids and comets during the period of heavy bombardment 4.5 x 10 to the 9th to 3.8 x 10 to the 9th years ago. A comprehensive treatment of comet-asteroid interaction with the atmosphere, surface impact, and resulting organic pyrolysis demonstrates that organics will not survive impacts at velocities greater than about 10 kilometers per second and that even comets and asteroids as small as 100 meters in radius cannot be aerobraked to below this velocity in 1-bar atmospheres. However, for plausible dense (10-bar carbon dioxide) early atmospheres, it is found that 4.5 x 10 to the 9th years ago earth was accreting intact cometary organics at a rate of at least about 10 to the 6th to 10 to the 7th kilograms per year, a flux that thereafter declined with a half-life of about 10 to the 8th years. These results may be put in context by comparison with terrestrial oceanic and total biomasses, about 3 x 10 to the 12th kilograms and about 6 x 10 to the 14th kilograms, respectively.

Chyba, Christopher F.↗
NASA NTRS1989

Orbiter post-tire failure and skid testing results

An investigation was conducted at the NASA Langley Research Center's Aircraft Landing Dynamics Facility (ALDF) to define the post-tire failure drag characteristics of the Space Shuttle Orbiter main tire and wheel assembly. Skid tests on various materials were also conducted to define their friction and wear rate characteristics under higher speed and bearing pressures than any previous tests. The skid tests were conducted to support a feasibility study of adding a skid to the orbiter strut between the main tires to protect an intact tire from failure due to overload should one of the tires fail. Roll-on-rim tests were conducted to define the ability of a standard and a modified orbiter main wheel to roll without a tire. Results of the investigation are combined into a generic model of strut drag versus time under failure conditions for inclusion into rollout simulators used to train the shuttle astronauts.

Daugherty, Robert H.↗
NASA NTRS1990

A study of the kinematic dynamo equation with time-dependent coefficients

During an active star formation epoch the interstellar medium of a galaxy is in a hyperactive state, and the average turbulent velocity is higher than in the long periods between star formation epochs. The galactic magnetic field generated by dynamo action depends strongly on the turbulent velocity, so that generation of magnetic field should vary with star formation activity. This paper is a preliminary study of the kinematic dynamo equation with time-dependent coefficients simulating the time dependence of the star formation activities. Ko and Parker argued in a simple model that the thickness of the dynamo region is the most sensitive dynamo parameter. The present work shows that the effect of inflating the galactic disk suddenly is to transform a stationary magnetic field into a growing field while keeping the profile more or less intact. Plane wave solutions for a dynamo with power-law time-dependent parameters show that the field may decay first and then grow, and vice versa, which is quite different from a constant parameter dynamo.

Ko, Chung-Ming↗
NASA NTRS1990

A two-component volatile atmosphere for Pluto. I - The bulk hydrodynamic escape regime

The seasonal effects on Pluto's atmosphere of a simplified system of CH4 and N2 saturated over a solid solution are investigated, and the results are compared with previous CH4 models. It is found that bulk escape occurs for CH4 mole fractions less than 0.7 of Pluto's volatile reservoir. Greater CH4 abundance leads to diffusive separation during the escape of both species and an atmospheric mixing ratio of about Xc(0). If Xc(0) is in the range 0.02-0.10, Pluto's atmosphere remains largely intact at aphelion rather than virtually freezing out as it does for Xc(0) greater than 0.3 or less than 0.001, or form an atmosphere with only a single volatile gas. An upper limit for the CH4 mixing ratio is about 0.07 if N2 is the second gas. On the other hand, CH4 is the dominant surface constituent of the volatile deposit if Xc(0) is greater than 0.0001.

Trafton, L.↗
NASA NTRS1991

Neural-Network Control Of Prosthetic And Robotic Hands

Electronic neural networks proposed for use in controlling robotic and prosthetic hands and exoskeletal or glovelike electromechanical devices aiding intact but nonfunctional hands. Specific to patient, who activates grasping motion by voice command, by mechanical switch, or by myoelectric impulse. Patient retains higher-level control, while lower-level control provided by neural network analogous to that of miniature brain. During training, patient teaches miniature brain to perform specialized, anthropomorphic movements unique to himself or herself.

Buckley, Theresa M.↗
NASA NTRS1989

Stochastic histories of dust grains in the interstellar medium

The purpose is to study an evolving system of refractory dust grains within the Interstellar Medium (ISM). This is done via a combination of Monte Carlo processes and a system of partial differential equations, where refractory dust grains formed within supernova remnants and ejecta from high mass loss stars are subjected to the processes of sputtering and collisional fragmentation in the diffuse media and accretion within the cold molecular clouds. In order to record chemical detail, the authors take each new particle to consist of a superrefractory core plus a more massive refractory mantle. The particles are allowed to transfer to and fro between the different phases of the interstellar medium (ISM) - on a time scale of 10(exp 8) years - until either the particles are destroyed or the program finishes at a Galaxy time of 6x10(exp 9) years. The resulting chemical and size spectrum(s) are then applied to various astrophysical problems with the following results. For an ISM which has no collisional fragmentation of the dust grains, roughly 10 percent by mass of the most refractory material survives the rigors of the ISM intact, which leaves open the possibility that fossilized isotopically anomalous material may have been present within the primordial solar nebula. Stuctured or layered refractory dust grains within the model cannot explain the observed interstellar depletions of refractory material. Fragmentation due to grain-grain collisions in the diffuse phase plus the accretion of material in the molecular cloud phase can under certain circumstances cause a bimodal distribution in grain size.

Liffman, Kurt↗
NASA NTRS1991

An evaluation of GTAW-P versus GTA welding of alloy 718

Mechanical properties were evaluated to determine statistically whether the pulsed current gas tungsten arc welding (GTAW-P) process produces welds in alloy 718 with room temperature structural performance equivalent to current Space Shuttle Main Engine (SSME) welds manufactured by the constant current GTAW-P process. Evaluations were conducted on two base metal lots, two filler metal lots, two heat input levels, and two welding processes. The material form was 0.125-inch (3.175-mm) alloy 718 sheet. Prior to welding, sheets were treated to either the ST or STA-1 condition. After welding, panels were left as welded or heat treated to the STA-1 condition, and weld beads were left intact or machined flush. Statistical analyses were performed on yield strength, ultimate tensile strength (UTS), and high cycle fatigue (HCF) properties for all the post welded material conditions. Analyses of variance were performed on the data to determine if there were any significant effects on UTS or HCF life due to variations in base metal, filler metal, heat input level, or welding process. Statistical analyses showed that the GTAW-P process does produce welds with room temperature structural performance equivalent to current SSME welds manufactured by the GTAW process, regardless of prior material condition or post welding condition.

Gamwell, W. R.↗
NASA NTRS1990

MALEO: Modular Assembly in Low Earth Orbit. A strategy for an IOC lunar base

Modular Assembly in Low Earth Orbit (MALEO) is a new strategy for building an initial operational capability lunar habitation base. In this strategy, the modular lunar base components are brought up to Low Earth Orbit by the Space Transportation System/Heavy Lift Launch Vehicle fleet, and assembled there to form a complete lunar base. Modular propulsion systems are then used to transport the MALEO lunar base, complete and intact, all the way to the moon. Upon touchdown on the lunar surface, the MALEO lunar habitation base is operational. An exo-skeletal truss superstructure is employed in order to uniformly absorb and distribute the rocket engine thrusting forces incurred by the MALEO lunar base during translunar injection, lunar orbit insertion, and lunar surface touchdown. The components, configuration, and structural aspects of the MALEO lunar base are discussed. Advantages of the MALEO strategy over conventional strategies are pointed out. It is concluded that MALEO holds promise for lunar base deployment.

Thangavelu, M.↗
NASA NTRS1991

SIMS analysis of extended impact features on LDEF experiment

Discussed here are the first Secondary Ion Mass Spectroscopy (SIMS) analysis of projectile material deposited in extended impact features on Ge wafers from the trailing edge. Although most capture cells lost their plastic film covers, they contain extended impact features that apparently were produced by high velocity impacts when the plastic foils were still intact. Detailed optical scanning of all bare capture cells from the trailing edge revealed more than 100 impacts. Fifty-eight were selected by scanning electron microscope (SEM) inspection as prime candidates for SIMS analysis. Preliminary SIMS measurements were made on 15 impacts. More than half showed substantial enhancements of Mg, Al, Si, Ca, and Fe in the impact region, indicating micrometeorites as the projectiles.

Amari, S.↗
NASA NTRS1991

Guidance, navigation, and control subsystem equipment selection algorithm using expert system methods

Enhanced engineering tools can be obtained through the integration of expert system methodologies and existing design software. The application of these methodologies to the spacecraft design and cost model (SDCM) software provides an improved technique for the selection of hardware for unmanned spacecraft subsystem design. The knowledge engineering system (KES) expert system development tool was used to implement a smarter equipment section algorithm than that which is currently achievable through the use of a standard data base system. The guidance, navigation, and control subsystems of the SDCM software was chosen as the initial subsystem for implementation. The portions of the SDCM code which compute the selection criteria and constraints remain intact, and the expert system equipment selection algorithm is embedded within this existing code. The architecture of this new methodology is described and its implementation is reported. The project background and a brief overview of the expert system is described, and once the details of the design are characterized, an example of its implementation is demonstrated.

Allen, Cheryl L.↗
NASA NTRS1987

Method for fastening aircraft frame elements to sandwich skin panels covering same using woven fiber connectors

This invention relates to improvements in the method by which elongate frame elements such as the spars in aircraft wings are fastened to the skin panels covering same where these skin pane]s are of the sandwich type having inner and outer facesheets with a core bonded therebetween, such method consisting of preparing the panel to receive its frame elements by cutting elongate grooves spanwise through the inner facesheet and the core therebeneath while leaving the outer facesheet intact; bridging the gap thus produced in the inner facesheet with one bundle of filaments adhesively bonded thereto, the latter being contained in a woven connector in the form of a strap or band running lengthwise of the groove, and this filament bundle farming an endless strand of yarn that is laid back and forth transversely across the gap in side-by-side parallel rows but which are parted at intervals for the side-by-side lays of at least one other similar yarn strand to pass therebetween in intersecting relation; adhesive]y-bonding the skin panel core exposed within the groove to one or both sides of the frame element located proximal thereto using two endless strands of yarn laid back and forth to define a pair of intersecting webs arranged in spaced substantially parallel relation to one another that form a part of the connector and pass through the spaces between the first-mentioned yarn strands.

Paul J Jonas↗
NASA NTRS1990

Is thinking computable?

Strong artificial intelligence claims that conscious thought can arise in computers containing the right algorithms even though none of the programs or components of those computers understand which is going on. As proof, it asserts that brains are finite webs of neurons, each with a definite function governed by the laws of physics; this web has a set of equations that can be solved (or simulated) by a sufficiently powerful computer. Strong AI claims the Turing test as a criterion of success. A recent debate in Scientific American concludes that the Turing test is not sufficient, but leaves intact the underlying premise that thought is a computable process. The recent book by Roger Penrose, however, offers a sharp challenge, arguing that the laws of quantum physics may govern mental processes and that these laws may not be computable. In every area of mathematics and physics, Penrose finds evidence of nonalgorithmic human activity and concludes that mental processes are inherently more powerful than computational processes.

Denning, Peter J.↗
NASA NTRS1990

A Personnel Launch System for safe and efficient manned operations

Several Conceptual designs for a simple, rugged Personnel Launch System (PLS) are presented. This system could transport people to and from Low Earth Orbit (LEO) starting in the late 1990's using a new modular Advanced Launch System (ALS) developed for the Space Exploration Initiative (SEI). The PLS is designed to be one element of a new space transportation architecture including heavy-lift cargo vehicles, lunar transfer vehicles, and multiple-role spcecraft such as the current Space Shuttle. The primary role of the PLS would be to deliver crews embarking on lunar or planetary missions to the Space Station, but it would also be used for earth-orbit sortie missions, space rescue missions, and some satellite servicing missions. The PLS design takes advantage of emerging electronic and structures technologies to offer a robust vehicle with autonomous operating and quick turnaround capabilities. Key features include an intact abort capability anywhere in the operating envelope, and elimination of all toxic propellants to streamline ground operations.

Petro, Andrew J.↗
NASA NTRS1990

EMG analysis of human postural responses during parabolic flight microgravity episodes

Anticipatory postural activity in the trunk and legs precedes rapid shoulder flexion in unit gravity. The hypothesis that anticipatory activity is a component of a single neural command for arm movement was tested by monitoring the surface electromyographic activity of the biceps femoris, paraspinals, and deltoid muscles of three subjects during the microgravity phase of parabolic flight. If part of a single command, anticipatory postural activity would be expected to remain intact despite the absence of the body's center of gravity in a reduced gravity environment. However, in at least 75 percent of the microgravity trials anticipatory biceps femoris activity was absent, indicating a separation of postural and agonist muscle activity. Such a finding suggests that anticipatory postural biceps femoris activity may be initiated independently of agonist (deltoid) activity.

Layne, Charles S.↗