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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

A Tactical Scheduler for Surface Metering Under Minimum Departure Interval Restrictions

Minimum Departure Interval (MDI) and Miles-In-Trail (MIT) are common traffic management tools. They both require minimum separation between departures to meet specific traffic conditions. The MDI restriction is a time separation requirement between departures, usually on the same Standard Instrument Departure (SID), whereas the MIT restriction is a distance separation requirement between aircraft, including but not limited to departure flights, to meet specific criteria associated with flight path or destination. At Incheon International Airport (IATA code: ICN) in South Korea, MDIs are imposed on 92% of departure flights. They involve specific criteria including not only having identical SID, but also satisfying other conditions, imposed on the flight path and destination. To address complicated MDI constraints, Korea Aerospace Research Institute (KARI) has been developing and improving a tactical scheduler for surface metering at ICN to provide appropriate target times for pushbacks and takeoffs for departure flights under MDIs. This paper describes the MDI requirements at ICN, the development of a heuristic scheduling algorithm to work with the MDI restrictions, and the performance evaluation of the algorithm through fast-time simulations. The performance evaluation results indicate that the proposed heuristic algorithm can provide the surface metering schedules that comply with the MDI restrictions without significant performance degradation.

DMAN (Departure Management)↗
NASA NTRS1964

Hybrid rocket propulsion <la propulsion par fusees hybrides<

The aim of the first part of this article is to demonstrate the potentialities of hybrids in the space program. These potentialities are applicable to all three main classes of chemical rockets currently in use, namely: (1) storable -propellant rockets, (2) cryogenic-propellant rockets, and (3) semistorable-propellant rockets, where the non-storable element is introduced at the time of firing. On the basis of these three categories, the properties of hybrid systems are discussed in relation to the specific impulse. The hybrid method of propulsion is compared with standard solid- and liquid-propellant propulsion systems. The second part of the article is concerned with the fundamental problems of combustion, the emphasis being placed on the rate of regression of the solid phase, which determines the performance of the system. Different theories of the regression rate are described and compared with various experimental results.

Cryogenic propellant↗
NASA NTRS1967

Workmanship standards for fusion welding

Workmanship standards manual defines practices, that adhere to rigid codes and specifications, for fusion welding of component piping, assemblies, and systems. With written and pictorial presentations, it is part of the operating procedure for fusion welding.

Phillips, M. D.↗
NASA NTRS1976

Status of research into lightning effects on aircraft

Developments in aircraft lightning protection since 1938 are reviewed. Potential lightning problems resulting from present trends toward the use of electronic controls and composite structures are discussed, along with presently available lightning test procedures for problem assessment. The validity of some procedures is being questioned because of pessimistic results and design implications. An in-flight measurement program is needed to provide statistics on lightning severity at flight altitudes and to enable more realistic tests, and operators are urged to supply researchers with more details on electronic components damaged by lightning strikes. A need for review of certain aspects of fuel system vulnerability is indicated by several recent accidents, and specific areas for examination are identified. New educational materials and standardization activities are also noted.

Plumer, J. A.↗
NASA NTRS1991

Compression of Martian atmosphere for production of oxygen

The compression of CO2 from the Martian atmosphere for production of O2 via an electrochemical cell is addressed. Design specifications call for an oxygen production rate of 10 kg per day and for compression of 50 times that mass of CO2. Those specifications require a compression rate of over 770 cfm at standard Martian temperature and pressure (SMTP). Much of the CO2 being compressed represents waste, unless it can be recycled. Recycling can reduce the volume of gas that must be compressed to 40 cfm at SMTP. That volume reduction represents significant mass savings in the compressor, heating equipment, filters, and energy source. Successful recycle of the gas requires separation of CO (produced in the electrochemical cell) from CO2, N2, and Ar found in the Martian atmosphere. That aspect was the focus of this work.

Lynch, D. C.↗
NASA NTRS1990

Time and frequency measuring metrological equipment in the USSR

The complex of the means of providing time and frequency traceability in the USSR includes the system of time and frequency standards of the National Time and Frequency Calibration Service, time and frequency transfer facilities and local time and frequency standards. Control on measurement correctness is performed by the All-Union State Standard calibration service. The hardware of most of the above-mentioned systems is provided by the instruments developed by our institute. A common scientific and technological approach allowed us to create a unified system of time-frequency equipment composed of widely used serial instruments, sets, automated systems and complexes. Primary frequency standards of different classes, time and frequency references and instruments are based on the unified system. CH1-70 hydrogen frequency standard and its CH1-70A, CH1-80 modifications are used in the group time and frequency standards. Measuring time and data processing techniques, and also instrumentation specifications on the results of 10-year operation are given. The existing system provides time-frequency measurements with 2 times 10(exp -13) plus or minus 1 times 10(exp -14) accuracy.

Uljanov, Adolph A.↗
NASA NTRS1991

Some partial-unit-memory convolutional codes

The results of a study on a class of error correcting codes called partial unit memory (PUM) codes are presented. This class of codes, though not entirely new, has until now remained relatively unexplored. The possibility of using the well developed theory of block codes to construct a large family of promising PUM codes is shown. The performance of several specific PUM codes are compared with that of the Voyager standard (2, 1, 6) convolutional code. It was found that these codes can outperform the Voyager code with little or no increase in decoder complexity. This suggests that there may very well be PUM codes that can be used for deep space telemetry that offer both increased performance and decreased implementational complexity over current coding systems.

Abdel-Ghaffar, K.↗
NASA NTRS1992

Comparison of dermal and inhalation routes of entry for organic chemicals

The quantitative comparison of the chemical concentration inside the body as the result of a dermal exposure versus an inhalation exposure is useful for assessing human health risks and deciding on an appropriate protective posture. In order to describe the relationship between dermal and inhalation routes of exposure, a variety of organic chemicals were evaluated. The types of chemicals chosen for the study were halogenated hydrocarbons, aromatic compounds, non-polar hydrocarbons and inhalation anesthetics. Both dermal and inhalation exposures were conducted in rats and the chemicals were in the form of vapors. Prior to the dermal exposure, rat fur was closely clipped and during the exposure rats were provided fresh breathing air through latex masks. Blood samples were taken during 4-hour exposures and analyzed for the chemical of interest. A physiologically based pharmacokinetic model was used to predict permeability constants (cm/hr) consistent with the observed blood concentrations of the chemical. The ratio of dermal exposure to inhalation exposure required to achieve the same internal dose of chemical was calculated for each test chemical. The calculated ratio in humans ranged from 18 for styrene to 1180 for isoflurane. This methodology can be used to estimate the dermal exposure required to reach the internal dose achieved by a specific inhalation exposure. Such extrapolation is important since allowable exposure standards are often set for inhalation exposures, but occupational exposures may be dermal.

Jepson, Gary W.↗
NASA NTRS1992

Electronic Still Camera

A handheld, programmable, digital camera is disclosed that supports a variety of sensors and has program control over the system components to provide versatility. The camera uses a high performance design which produces near film quality images from an electronic system. The optical system of the camera incorporates a conventional camera body that was slightly modified, thus permitting the use of conventional camera accessories, such as telephoto lenses, wide-angle lenses, auto-focusing circuitry, auto-exposure circuitry, flash units, and the like. An image sensor, such as a charge coupled device ('CCD') collects the photons that pass through the camera aperture when the shutter is opened, and produces an analog electrical signal indicative of the image. The analog image signal is read out of the CCD and is processed by preamplifier circuitry, a correlated double sampler, and a sample and hold circuit before it is converted to a digital signal. The analog-to-digital converter has an accuracy of eight bits to insure accuracy during the conversion. Two types of data ports are included for two different data transfer needs. One data port comprises a general purpose industrial standard port and the other a high speed/high performance application specific port. The system uses removable hard disks as its permanent storage media. The hard disk receives the digital image signal from the memory buffer and correlates the image signal with other sensed parameters, such as longitudinal or other information. When the storage capacity of the hard disk has been filled, the disk can be replaced with a new disk.

Holland, S. Douglas↗
NASA NTRS1994

Renaissance architecture for Ground Data Systems

The Mission Operations and Data Systems Directorate (MO&DSD) has embarked on a new approach for developing and operating Ground Data Systems (GDS) for flight mission support. This approach is driven by the goals of minimizing cost and maximizing customer satisfaction. Achievement of these goals is realized through the use of a standard set of capabilities which can be modified to meet specific user needs. This approach, which is called the Renaissance architecture, stresses the engineering of integrated systems, based upon workstation/local area network (LAN)/fileserver technology and reusable hardware and software components called 'building blocks.' These building blocks are integrated with mission specific capabilities to build the GDS for each individual mission. The building block approach is key to the reduction of development costs and schedules. Also, the Renaissance approach allows the integration of GDS functions that were previously provided via separate multi-mission facilities. With the Renaissance architecture, the GDS can be developed by the MO&DSD or all, or part, of the GDS can be operated by the user at their facility. Flexibility in operation configuration allows both selection of a cost-effective operations approach and the capability for customizing operations to user needs. Thus the focus of the MO&DSD is shifted from operating systems that we have built to building systems and, optionally, operations as separate services. Renaissance is actually a continuous process. Both the building blocks and the system architecture will evolve as user needs and technology change. Providing GDS on a per user basis enables this continuous refinement of the development process and product and allows the MO&DSD to remain a customer-focused organization. This paper will present the activities and results of the MO&DSD initial efforts toward the establishment of the Renaissance approach for the development of GDS, with a particular focus on both the technical and process implications posed by Renaissance to the MO&DSD.

Perkins, Dorothy C.↗
NASA NTRS1996

Observations on the Reliability of Rubidium Frequency Standards on Block 2/2A GPS Satellites

Currently, the block 2/2A Global Positioning System (GPS) satellites are equipped with two rubidium frequency standards. These frequency standards were originally intended to serve as the back-ups to two cesium frequency standards. As the constellation ages, the master Control Station is forced to initialize and increasing number or rubidium frequency standards. Unfortunately the operational use of these frequency standards has not lived up to initial expectations. Although the performance of these rubidium frequency standards has met and even exceeded GPS requirements, their reliability has not. The number of unscheduled outage times and the short operational lifetimes of the rubidium frequency standards compare poorly to the track record of the cesium frequency standards. Only a small number of rubidium frequency standards have actually been made operational. Of these, a large percentage have exhibited poor reliability. If this trend continues, it is unlikely that the rubidium frequency standards will help contribute to the navigation payload meeting program specification.

Dieter, Gary L.↗
NASA NTRS2001

Control and Observation in Distributed Environments

This viewgraph presentation gives an overview of the control and observation in distributed environments. No existing system meets all our needs (e.g., they cannot be embedded in tools or applications and have limited fault management functionality). The goals of our infrastructure include the following: (1) to develop a general framework for observation and control; (2) the framework should be extensible for specific tasks; and (3) it must be compatible with emerging standards.

Smith, Warren↗
NASA NTRS1996

Verification of IEEE Compliant Subtractive Division Algorithms

A parameterized definition of subtractive floating point division algorithms is presented and verified using PVS. The general algorithm is proven to satisfy a formal definition of an IEEE standard for floating point arithmetic. The utility of the general specification is illustrated using a number of different instances of the general algorithm.

Miner, Paul S.↗
NASA NTRS2001

Combining Information on Multiple Detection Techniques to Estimate the Effect of Patent Foramen Ovale on Susceptibility to Decompression Illness

The assembly and the maintenance of the International Space Station is expected to require hundreds of extravehicular excursions (EVA's) in the next 10 years. During an EVA, in order to allow movement and bending of limbs, spacesuit pressures are reduced to about 4.3 psi. as compared with about 14.7 psi. for normal atmospheric pressure at sea level. However, the exposure of astronauts to reduced pressures in spacesuits, is conducive to fonnation and growth of gas bubbles within venous blood or tissues, which could cause decompression illness (DCI), a pathology best known to occur among deep-sea divers when they return to the surface. To reduce the risk of DCI, astronauts adjust to the reduced pressure in stages for a prolonged time known as a "pre-breathe" period prior to their extravehicular activity. Despite the use of pre-breathe protocols, an increased risk of DCI can arise for about 25% of humans who have a small hole, known as a patent foramen ovale (PFO), between two chambers of the heart. The atrial septum's fossa oval is, an embryological remnant of a flap between the septae primum and secundum allows fetal right atrial blood to pass into the left atrium, and usually closes after birth (Hagen, et al,. 1984). If fusion does not occur, a valve-like opening, the foramen ovale persists between the two atria. It has been suggested that astronauts with PFO's might be at greater risk of stroke or other serious neurological DCI because bubbles from a venous site may traverse a PFO, travel to the aorta and then enter the cerebral circulatory system causing a stroke (Figure 1). Astronauts are not now screened for PFO's, however consideration is being given to doing so. Here, we study three main methods abbreviated here as "ITE", "TCD" and "TEE", for detecting PFO's in living subjects. All involve the introduction of bubbles into a vein, immediately after which a sensory probe attempts to detect the bubbles in systemic circulation. Presence of the injected bubbles in the systemic circulation is indicative of a PFO. More detailed descriptions are given after the explanation of PFO's under Figure I. Even if a true PFO affects the risk of DCI, there remains a question of how effective screening would be if the detection method has errors of omission and/or commission. Of the three methods studied here, TEE is the "gold standard", matching autopsy results with near-perfect sensitivity and specificity (Schneider, et al. , 1996). However TEE is also the most difficult method to implement, requiring an internal esophagal probe, and is therefore not widely used. Currently, the easiest to use and most common PFO detection method is TTE, which uses an external chest probe. This method has a specificity of near 100%, but suffers from a low sensitivity rate (about 30%). More recently, TCD has been developed, which uses ultrasound probes to detect the presence of bubbles in cerebral arteries. Studies indicate that TCD is quite effective, having a sensitivity of about 91% and a specificity of about 93% (Droste, et al., 1999) when applied correctly, however implementation is difficult and requires considerable training.

Feiveson, Alan H.↗
NASA NTRS2005

System for Processing Coded OFDM Under Doppler and Fading

An advanced communication system has been proposed for transmitting and receiving coded digital data conveyed as a form of quadrature amplitude modulation (QAM) on orthogonal frequency-division multiplexing (OFDM) signals in the presence of such adverse propagation-channel effects as large dynamic Doppler shifts and frequency-selective multipath fading. Such adverse channel effects are typical of data communications between mobile units or between mobile and stationary units (e.g., telemetric transmissions from aircraft to ground stations). The proposed system incorporates novel signal processing techniques intended to reduce the losses associated with adverse channel effects while maintaining compatibility with the high-speed physical layer specifications defined for wireless local area networks (LANs) as the standard 802.11a of the Institute of Electrical and Electronics Engineers (IEEE 802.11a). OFDM is a multi-carrier modulation technique that is widely used for wireless transmission of data in LANs and in metropolitan area networks (MANs). OFDM has been adopted in IEEE 802.11a and some other industry standards because it affords robust performance under frequency-selective fading. However, its intrinsic frequency-diversity feature is highly sensitive to synchronization errors; this sensitivity poses a challenge to preserve coherence between the component subcarriers of an OFDM system in order to avoid intercarrier interference in the presence of large dynamic Doppler shifts as well as frequency-selective fading. As a result, heretofore, the use of OFDM has been limited primarily to applications involving small or zero Doppler shifts. The proposed system includes a digital coherent OFDM communication system that would utilize enhanced 802.1la-compatible signal-processing algorithms to overcome effects of frequency-selective fading and large dynamic Doppler shifts. The overall transceiver design would implement a two-frequency-channel architecture (see figure) that would afford frequency diversity for reducing the adverse effects of multipath fading. By using parallel concatenated convolutional codes (also known as Turbo codes) across the dual-channel and advanced OFDM signal processing within each channel, the proposed system is intended to achieve at least an order of magnitude improvement in received signal-to-noise ratio under adverse channel effects while preserving spectral efficiency.

Tsou, Haiping↗
NASA NTRS2011

Strategic Ozone Sounding Networks: Review of Design and Accomplishments

Ozone soundings are used to integrate models, satellite, aircraft and ground-based measurements for better interpretation of ozone variability, including atmospheric losses (predominantly in the stratosphere) and pollution (troposphere). A well-designed network of ozonesonde stations gives information with high vertical and horizontal resolution on a number of dynamical and chemical processes, allowing us to answer questions not possible with aircraft campaigns or current satellite technology. Strategic ozonesonde networks are discussed for high, mid- and low latitude studies. The Match sounding network was designed specifically to follow ozone depletion within the polar vortex; the standard sites are at middle to high northern hemisphere latitudes and typically operate from December through mid-March. Three mid-latitude strategic networks (the IONS series) operated over North America in July-August 2004, March-May and August 2006, and April and June-July-2008. These were designed to address questions about tropospheric ozone budgets and sources, including stratosphere-troposphere transport, and to validate satellite instruments and models. A global network focusing on processes in the equatorial zone, SHADOZ (Southern Hemisphere Additional Ozonesondes), has operated since 1998 in partnership with NOAA, NASA and the Meteorological Services of host countries. Examples of important findings from these networks are described,

Thompson, Anne M.↗