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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Repairing Fractured Bones by Use of Bioabsorbable Composites

A proposed method of surgical repair of fractured bones would incorporate recent and future advances in the art of composite materials. The composite materials used in this method would be biocompatible and at least partly bioabsorbable: that is, during the healing process following surgery, they would be wholly or at least partly absorbed into the bones and other tissues in which they were implanted. Relative to the traditional method, the proposed method would involve less surgery, pose less of a risk of infection, provide for better transfer of loads across fracture sites, and thereby promote better healing while reducing the need for immobilization by casts and other external devices. One requirement that both the traditional and proposed methods must satisfy is to fix the multiple segments of a broken bone in the correct relative positions. Mechanical fixing techniques used in the traditional method include the use of plates spanning the fracture site and secured to the bone by screws, serving of wire along the bone across the fracture site, insertion of metallic intramedullary rods through the hollow portion of the fractured bone, and/or inserting transverse rods through the bone, muscle, and skin to stabilize the fractured members. After the bone heals, a second surgical operation is needed to remove the mechanical fixture(s). In the proposed method, there would be no need for a second surgical operation. The proposed method is based partly on the observation that in the fabrication of a structural member, it is generally more efficient and reliable to use multiple small fasteners to transfer load across a joint than to use a single or smaller number of larger fasteners, provided that the stress fields of neighboring small fasteners do not overlap or interact. Also, multiple smaller fasteners are more reliable than are larger and fewer fasteners. However, there is a trade-off between structural efficiency and the cost of insertion time and materials. The proposed method is further based partly on the conjecture that through-the-thickness reinforcements could be excellent for fixing bone segments for surgical repair. The through-the-thickness reinforcements would superficially resemble nails in both form and function. Denoted small-diameter rods (SDRs) to distinguish them from other narrow rods, these reinforcements would be shot or otherwise inserted through adjacent segments of fractured bone to fix them in their correct relative positions (see figure). Shot insertion would be effected by use an applicator that would amount to a miniaturized and highly refined version of the pneumatic guns often used in carpentry to drive nails and brads. The applicator, envisioned to be about the size of a ball-point-pen, would be driven by pressurized carbon dioxide. To further promote stabilization of the segments, layers of bone glue could be applied to the fracture surfaces prior to insertion of the SDRs. The bone glue could be therapeutically loaded with chemicals to promote growth of bone and fight infection

Farley, Gary L.↗
NASA NTRS1968

Improved fluid dynamics similarity, analysis and verification. Part 5: Analytical and experimental studies of thermal stratification phenomena

The stratification behavior of a contained fluid subjected to transient free convection heat transfer was studied. A rectangular vessel was employed with heat transfer from two opposite walls of the vessel to the fluid. The wall temperature was increased suddenly to initiate the process and was then maintained constant throughout the transient stratification period. Thermocouples were positioned on a post at the center of the vessel. They were adjusted so that temperatures could be measured at the fluid surface and at specific depths beneath the surface. The predicted values of the surface temperature and the stratified layer thickness were found to agree reasonably well with the experimental measurements. The experiments also provided information on the transient centerline temperature distribution and the transient flow distribution.

Winter, E. R. F.↗
NASA NTRS1979

Limb blood flow - Rest and heavy exercise in sitting and supine positions in man

The objectives of the study were twofold: (1) to determine the effect of body position (hydrostatic pressure) on total blood flow in active and passive limbs at rest and after severe exercise; and (2) to further evaluate the impedance technique for measurement of blood flow. To this end, the effect of body position on the redistribution of total blood flow in active (leg) and passive (forearm) limbs during exercise was determined by measuring total limb impedance (blood flow) in five male and one female subjects in sitting and supine positions with a modified Beckman BR-100 rheograph. The results show that, at rest and after exercise, the supine position induces significantly greater flows in the leg but not in the forearm. With severe exercise, blood flows are increased in both passive and active limbs, so that there is probably no net transfer of blood volume from passive to active muscles. The advantages of the impedance technique over other methods are stressed.

Greenleaf, J. E.↗
NASA NTRS2006

Chill Down Process of Hydrogen Transport Pipelines

A pseudo-steady model has been developed to predict the chilldown history of pipe wall temperature in the horizontal transport pipeline for cryogenic fluids. A new film boiling heat transfer model is developed by incorporating the stratified flow structure for cryogenic chilldown. A modified nucleate boiling heat transfer correlation for cryogenic chilldown process inside a horizontal pipe is proposed. The efficacy of the correlations is assessed by comparing the model predictions with measured values of wall temperature in several azimuthal positions in a well controlled experiment by Chung et al. (2004). The computed pipe wall temperature histories match well with the measured results. The present model captures important features of thermal interaction between the pipe wall and the cryogenic fluid, provides a simple and robust platform for predicting pipe wall chilldown history in long horizontal pipe at relatively low computational cost, and builds a foundation to incorporate the two-phase hydrodynamic interaction in the chilldown process.

Mei, Renwei↗
NASA NTRSDate not supplied

Simulation-Aided Design and Interpretation of Results of Microgravity-Based Solidification Experiments

The preparation and interpretation of microgravity experiments conducted on the International Space Station (ISS) can be challenging because of the remote location of the equipment. Although a “ground unit” is typically available on Earth, it is not located in the laboratory of the principal investigator. Furthermore, test experiments in the ground unit cannot fully duplicate heat transfer conditions of the weightless environment, and thus be a reliable reference for experiment design. Under such conditions, numerical simulations are a valuable tool both for preparing the experiments and interpreting the results obtained under terrestrial and micro-gravity conditions. In this work, we developed a detailed 3D model of the “SUBSA” furnace located at the ISS, and demonstrate its use in our present investigation which includes melt growth and vapor growth of InI crystals on the ISS. In 2002, the SUBSA furnace was designed and built for the growth of InSb crystals in the Microgravity Science Glovebox (MSG) at the ISS. The SUBSA furnace features a transparent section without heating elements, where the axial temperature gradient is high. In our present investigation, we have used the same furnace to grow four InI crystals from the melt, and two InI crystals from the vapor phase (2018-2021). InI crystals have ~20 times lower thermal conductivity than InSb crystals. As a result, during melt growth, the InI crystals were exposed to extremely high temperature gradients. To reduce the axial temperature gradient, we added external jackets made from high thermal conductivity material to the growth ampoules. The SUBSA furnace could not be modeled as asymmetric because of its rectangular shape and right-angled transparent section, which contains a convoluted geometry. The rectangular shape of the transparent section further complicates modelling of radiative heat transfer, which dominates in the zone. At present, numerical simulations are being conducted to resolve an apparent discrepancy between the readings of the 5 thermocouples located in the SUBSA furnace, and the observed position of the solid and molten material. The 3D simulation will be presented, along with the calibration and growth experiment results conducted in microgravity and in the SUBSA ground unit. The developed model should be useful for upcoming microgravity investigations planned to be conducted in the SUBSA facility.

V Riabov↗
NASA NTRSDate not supplied

From Simulation to Reality With Random Noise

The challenging environment of autonomous vehicle (AV) navigation necessitates certain functions be performed by deep neural networks. Optimizing these models involves collecting vast quantities of domain-specific training data and ensuring that the dataset is representative of expected conditions. High-fidelity simulation plays a vital role in making this process feasible, allowing a wide range of scenarios to be explored at low cost. However, learning from simulation introduces subtle biases into models, which can degrade real-world performance in unpredictable ways. This effect can be mitigated with learning schemes specialized to bridge distributional shifts (transfer learning). Given the complex nature of these methods, the underlying models, and their environments, meaningfully evaluating performance is notstraight forward. Many unrelated factors can effect an improvement in generalization accuracy, but a full ablation analysis is often difficult. To tease out signal from noise, it is necessary to understand how transfer learning performance is affected by noise itself. The goals of this paper are (i) to establish a domain randomization baseline for a simple classification transfer learning task and (ii) to validate the RRAV testbed as a platform for further research in sim-to-real learning. We generate imagery from a simulation of NASA Ames Research Center and train a small convolutional neural network (ConvNet) to classify position relative to a centerline. Further models are trained with different types of noise progressively added to the data. The models are deployed aboard the on-site test vehicle to test real-world performance. In our experiments, we find that such naive domain randomization raises sim-to-real accuracy from 64% to 79%, while training directly on real data yields an 89% accuracy ceiling. These results suggest that the isolated mechanism of domain randomization can significantly improve generalization.

simulation↗
NASA NTRS2012

Effects of Cloud Horizontal Inhomogeneity and Drizzle on Remote Sensing of Cloud Droplet Effective Radius: Case Studies Based on Large-eddy Simulations

This study investigates effects of drizzle and cloud horizontal inhomogeneity on cloud effective radius (re) retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS). In order to identify the relative importance of various factors, we developed a MODIS cloud property retrieval simulator based on the combination of large-eddy simulations (LES) and radiative transfer computations. The case studies based on synthetic LES cloud fields indicate that at high spatial resolution (100 m) 3-D radiative transfer effects, such as illumination and shadowing, can induce significant differences between retrievals ofre based on reflectance at 2.1 m (re,2.1) and 3.7 m (re,3.7). It is also found that 3-D effects tend to have stronger impact onre,2.1 than re,3.7, leading to positive difference between the two (re,3.72.1) from illumination and negative re,3.72.1from shadowing. The cancellation of opposing 3-D effects leads to overall reasonable agreement betweenre,2.1 and re,3.7 at high spatial resolution as far as domain averages are concerned. At resolutions similar to MODIS, however, re,2.1 is systematically larger than re,3.7when averaged over the LES domain, with the difference exhibiting a threshold-like dependence on bothre,2.1and an index of the sub-pixel variability in reflectance (H), consistent with MODIS observations. In the LES cases studied, drizzle does not strongly impact reretrievals at either wavelength. It is also found that opposing 3-D radiative transfer effects partly cancel each other when cloud reflectance is aggregated from high spatial resolution to MODIS resolution, resulting in a weaker net impact of 3-D radiative effects onre retrievals. The large difference at MODIS resolution between re,3.7 and re,2.1 for highly inhomogeneous pixels with H 0.4 can be largely attributed to what we refer to as the plane-parallelrebias, which is attributable to the impact of sub-pixel level horizontal variability of cloud optical thickness onre retrievals and is greater for re,2.1 than re,3.7. These results suggest that there are substantial uncertainties attributable to 3-D radiative effects and plane-parallelre bias in the MODIS re,2.1retrievals for pixels with strong sub-pixel scale variability, and theH index can be used to identify these uncertainties.

Zhang, Zhibo↗
NASA NTRS1979

Orbit Transfer Vehicle Engine Study. Phase A, extension 1: Advanced expander cycle engine optimization

The performance optimization of expander cycle engines at vacuum thrust levels of 10K, 15K, and 20K lb is discussed. The optimization is conducted for a maximum engine length with an extendible nozzle in the retracted position of 60 inches and an engine mixture ratio of 6.0:1. The thrust chamber geometry and cycle analyses are documented. In addition, the sensitivity of a recommended baseline expander cycle to component performance variations is determined and chilldown/start propellant consumptions are estimated.

Mellish, J. A.↗
NASA NTRS2000

The Charge Transfer Efficiency and Calibration of WFPC2

A new determination of WFPC2 photometric corrections is presented, using HSTphot reduction of the WFPC2 Omega Centauri and NGC 2419 observations from January 1994 through March 2000 and a comparison with ground-based photometry. No evidence is seen for any position-independent photometric offsets (the "long-short anomaly"); all systematic errors appear to be corrected with the CTE and zero point solution. The CTE loss time dependence is determined to be very significant in the Y direction, causing time-independent CTE solutions to be valid only for a small range of times. On average, the present solution produces corrections similar to Whitmore, Heyer, & Casertano, although with an improved functional form that produces less scatter in the residuals and determined with roughly a year of additional data. In addition to the CTE loss characterization, zero point corrections are also determined as functions of chip, gain, filter, and temperature. Of interest, there are chip-to-chip differences of order 0.01 - 0.02 magnitudes relative to the Holtzman et al. calibrations, and the present study provides empirical zero point determinations for the non-standard filters such as the frequently-used F450W, F606W, and F702W.

Dolphin, Andrew E.↗
NASA NTRS1972

Improvement of a geodetic triangulation through control points established by means of satellite or precision traversing

Whether any significant increment to accuracy could be transferred from a super-control continental net (continental satellite net or super-transcontinental traverse) to the fundamental geodetic net (first-order triangulation) is discussed. This objective was accomplished by evaluating the positional accuracy improvement for a triangulation station, which is near the middle of the investigated geodetic triangulation net, by using various station constraints over its geodetic position. This investigation on a 1858 kilometer long triangulation chain shows that the super-control net can provide a useful constraint to the investigated geodetic triangulation net, and thus can improve it only when the accuracy of super-control net is at least 1 part in 500,000.

Saxena, N. K.↗
NASA NTRS1974

Electric propulsion - Past history and future prospects

Studies of feasibility and flight mechanics of electric propulsion systems began around 1946. Conceptual systems design started in 1954, experimental developments in 1958; flight tests in 1964 and 1970 proved the functioning of electric thrusters in space. Further development of ion thruster systems has concentrated on bombardment ionization in the U.S., and on radiofrequency, bombardment, and surface contact ionization in West Germany, Great Britain, France and Russia. Electrothermal, plasma, and colloid thruster development has been pursued in many contries. Electric thrusters were used successfully during past years for satellite attitude control, and for prime propulsion of the Russian spacecraft Yantar. Further applications for attitude and position control of satellites are planned. Studies are presently underway for solar electric missions to planets, planetary moons, comets, asteroids, and toward the sun, and also for missions in near-earth space involving transfer, servicing, and repair of orbiting spacecraft.

Stuhlinger, E.↗
NASA NTRS1980

Three-dimensional structure of Escherichia coli initiator tRNA/f//Met/

The crystal structure of Escherichia coli tRNA(f)(Met), an initiator transfer RNA, has been determined. While grossly similar to that of the chain-elongating yeast tRNA(Phe), there are three major differences. One involves the folding of the anticodon loop; in particular, the position of the constant uridine, U33. This difference was unexpected and may be of functional significance.

Woo, N. H.↗
NASA NTRS1991

SSSFD manipulator engineering using statistical experiment design techniques

The Satellite Servicer System Flight Demonstration (SSSFD) program is a series of Shuttle flights designed to verify major on-orbit satellite servicing capabilities, such as rendezvous and docking of free flyers, Orbital Replacement Unit (ORU) exchange, and fluid transfer. A major part of this system is the manipulator system that will perform the ORU exchange. The manipulator must possess adequate toolplate dexterity to maneuver a variety of EVA-type tools into position to interface with ORU fasteners, connectors, latches, and handles on the satellite, and to move workpieces and ORUs through 6 degree of freedom (dof) space from the Target Vehicle (TV) to the Support Module (SM) and back. Two cost efficient tools were combined to perform a study of robot manipulator design parameters. These tools are graphical computer simulations and Taguchi Design of Experiment methods. Using a graphics platform, an off-the-shelf robot simulation software package, and an experiment designed with Taguchi's approach, the sensitivities of various manipulator kinematic design parameters to performance characteristics are determined with minimal cost.

Barnes, John↗
NASA NTRS1992

A plan for spacecraft automated rendezvous

An automated rendezvous approach has been developed that utilizes advances in technology to reduce real-time/near real-time flight operations support personnel to an acceptable level that is near the minimum without jeopardizing the success of the mission. The on-board flight targeting uses a rule-based system to select the pursuit vehicle phasing orbits and uses precise navigation updates from the pursuit/target spacecraft made possible by the global positioning system receivers/processors on both spacecraft to adjust the phasing orbits and achieve rendezvous. The ascent-to-orbit targeting for the pursuit vehicle has been successfully decoupled from the on-orbit orbit transfer phasing targeting. Typical launch window data have been developed for the heavy lift launch vehicle and cargo transfer vehicle for a Space Station Freedom rendezvous mission.

Deaton, A. W.↗
NASA NTRS2008

Delay Banking for Managing Air Traffic

Delay banking has been invented to enhance air-traffic management in a way that would increase the degree of fairness in assigning arrival, departure, and en-route delays and trajectory deviations to aircraft impacted by congestion in the national airspace system. In delay banking, an aircraft operator (airline, military, general aviation, etc.) would be assigned a numerical credit when any of their flights are delayed because of an air-traffic flow restriction. The operator could subsequently bid against other operators competing for access to congested airspace to utilize part or all of its accumulated credit. Operators utilize credits to obtain higher priority for the same flight, or other flights operating at the same time, or later, in the same airspace, or elsewhere. Operators could also trade delay credits, according to market rules that would be determined by stakeholders in the national airspace system. Delay banking would be administered by an independent third party who would use delay banking automation to continually monitor flights, allocate delay credits, maintain accounts of delay credits for participating airlines, mediate bidding and the consumption of credits of winning bidders, analyze potential transfers of credits within and between operators, implement accepted transfers, and ensure fair treatment of all participating operators. A flow restriction can manifest itself in the form of a delay in assigned takeoff time, a reduction in assigned airspeed, a change in the position for the aircraft in a queue of all aircraft in a common stream of traffic (e.g., similar route), a change in the planned altitude profile for an aircraft, or change in the planned route for the aircraft. Flow restrictions are typically imposed to mitigate traffic congestion at an airport or in a region of airspace, particularly congestion due to inclement weather, or the unavailability of a runway or region of airspace. A delay credit would be allocated to an operator of a flight that has accepted, or upon which was imposed, a flow restriction. The amount of the credit would increase with the amount of delay caused by the flow restriction, the exact amount depending on which of several candidate formulas is eventually chosen. For example, according to one formula, there would be no credit for a delay smaller than some threshold value (e.g., 30 seconds) and the amount of the credit for a longer delay would be set at the amount of the delay minus the threshold value. Optionally, the value of a delay credit could be made to decay with time according to a suitable formula (e.g., an exponential decay). Also, optionally, a transaction charge could be assessed against the value of a delay credit that an operator used on a flight different from the one for which the delay originated or that was traded with a different operator. The delay credits accumulated by a given airline could be utilized in various ways. For example, an operator could enter a bid for priority handling in a new flow restriction that impacts one or more of the operator s flights; if the bid were unsuccessful, all or a portion of the credit would be returned to the bidder. If the bid pertained to a single aircraft that was in a queue, delay credits could be consumed in moving the aircraft to an earlier position within the queue. In the case of a flow restriction involving a choice of alternate routes, planned altitude profile, aircraft spacing, or other non-queue flow restrictions, delay credits could be used to bid for an alternative assignment.

Green, Steve↗
NASA NTRS2012

Performance Requirements for Emergency Responder Interoperable and Compatible Electronic Safety Equipment

Firefighters and other emergency response personnel are presented with an increasing array of technologies to improve their health and safety. This includes real-time bidirectional communication, navigation and positional information, data on physiological and metabolic functions, as well as data on their surrounding environment. The emerging challenge is to integrate these elements into a practical system, addressing such features as power, data transfer, and inter-element coordination and communication. In many respects, NASA has addressed these aspects in the context of Extra Vehicular Activity (EVA). The EVA environment shares many common attributes with that of emergency response scenarios. A similar situation exists in terms of the need for interoperability among the various system sub-elements. A brief overview is presented on the similarities and differences in these two applications, as well as the technical approach adopted by NASA in terms of system design philosophy.

Greenberg, Paul S.↗
NASA NTRS2015

Pathfinder Lander Rover Recharge System, and MARCO POLO Controls and ACME Regolith Feed System Controls and Integration

This project stems from the Exploration, Research, and Technology Directorate (UB) Projects Division, and one of their main initiatives is the "Journey to Mars". Landing on the surface of Mars which is millions of miles away is an incredibly large challenge. The terrain is covered in boulders, deep canyons, volcanic mountains, and spotted with sand dunes. The robotic lander is a kind of spacecraft with multiple purposes. One purpose is to be the protective shell for the Martian rover and absorb the impact from the landing forces; another purpose is to be a place where the rovers can come back to, actively communicate with, and recharge their batteries from. Rovers have been instrumental to the Journey to Mars initiative. They have been performing key research on the terrain of the red planet, trying to unlock the mysteries of the land for over a decade. The rovers that will need charging will not all have the same kind of internal battery either. RASSOR batteries may differ from the PbAC batteries inside Red Rover's chassis. NASA has invested heavily in the exploration of the surface of Mars. A driving force behind further exploration is the need for a more efficient operation of Martian rovers. One way is to reduce the weight as much as possible to reduce power consumption given the same mission parameters. In order to reduce the mass of the rovers, power generation, communication, and sample analysis systems currently onboard Martian rovers can be moved to a stationary lander deck. Positioning these systems from the rover to the Lander deck allows a taskforce of smaller, lighter rovers to perform the same tasks currently performed by or planned for larger rovers. A major task in transferring these systems to a stationary lander deck is ensuring that power can be transferred to the rovers.

Internship↗