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At least 613 records · Page 34

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NASA NTRS1989

Application of a hybrid generation/utility assessment heuristic to a class of scheduling problems

A two-stage heuristic solution approach for a class of multiobjective, n-job, 1-machine scheduling problems is described. Minimization of job-to-job interference for n jobs is sought. The first stage generates alternative schedule sequences by interchanging pairs of schedule elements. The set of alternative sequences can represent nodes of a decision tree; each node is reached via decision to interchange job elements. The second stage selects the parent node for the next generation of alternative sequences through automated paired comparison of objective performance for all current nodes. An application of the heuristic approach to communications satellite systems planning is presented.

Heyward, Ann O.↗

NASA NTRS1989

Integrating planning and reactive control

Artificial intelligence research on planning is concerned with designing control systems that choose actions by manipulating explicit descriptions of the world state, the goal to be achieved, and the effects of elementary operations available to the system. Because planning shifts much of the burden of reasoning to the machine, it holds great appeal as a high-level programming method. Experience shows, however, that it cannot be used indiscriminately because even moderately rich languages for describing goals, states, and the elementary operators lead to computational inefficiencies that render the approach unsuitable for realistic applications. This inadequacy has spawned a recent wave of research on reactive control or situated activity in which control systems are modeled as reacting directly to the current situation rather than as reasoning about the future effects of alternative action sequences. While this research has confronted the issue of run-time tractability head on, in many cases it has done so by sacrificing the advantages of declarative planning techniques. Ways in which the two approaches can be unified are discussed. The authors begin by modeling reactive control systems as state machines that map a stream of sensory inputs to a stream of control outputs. These machines can be decomposed into two continuously active subsystems: the planner and the execution module. The planner computes a plan, which can be seen as a set of bits that control the behavior of the execution module. An important element of this work is the formulation of a precise semantic interpretation for the inputs and outputs of the planning system. They show that the distinction between planned and reactive behavior is largely in the eye of the beholder: systems that seem to compute explicit plans can be redescribed in situation-action terms and vice versa. They also discuss practical programming techniques that allow the advantages of declarative programming and guaranteed reactive response to be achieved simultaneously.

Rosenschein, Stanley J.↗

NASA NTRS1989

A view toward future launch vehicles - A civil perspective

Prospective NASA launch vehicle development efforts, which in addition to follow-on developments of the Space Shuttle encompass the Shuttle-C cargo version, various possible Advanced Launch System (ALS) configurations, and various Heavy Lift Launch System (HLLS) design options. Fully and partially reusable manned vehicle alternatives are also under consideration. In addition to improving on the current Space Shuttle's reliability and flexibility, ALS and HLLV development efforts are expected to concentrate on the reduction of operating costs for the given payload-launch capability.

Darwin, Charles R.↗

NASA NTRS1992

Gamma ray burst astrometry 2: Numerical tests

Since the announcement of the discovery of sources of gamma ray radiation in 1973, many more reports of such bursts have been published. Numerous artificial satellites have been equipped with gamma ray detectors including GRO. Unfortunately, almost no progress has been made in identifying the sources of this high energy radiation. Only one visible counterpart is known. It is suspected that this is a consequence of the methods currently used to define gamma ray burst source 'error boxes'. An alternative procedure was proposed in 1988 by Taff. Herein, Monte Carlo simulations are reported of the efficacy of this technique using realistic burst timing uncertainties and satellite location errors as well as a variety of satellite constellations. Since these are controlled numerical experiments, the dependence is examined of the statistics of the errors in the deduced burst wavefront normal as a function of the timing inconsistencies, detector location standard deviations, and especially the number and distribution of the detectors. The results clearly show that an arc minute prediction of a unique burst location is routinely obtainable once there are at least two interplanetary detectors.

Taff, L. G.↗

NASA NTRS1992

High speed magneto-resistive random access memory

A high speed read MRAM memory element is configured from a sandwich of magnetizable, ferromagnetic film surrounding a magneto-resistive film which may be ferromagnetic or not. One outer ferromagnetic film has a higher coercive force than the other and therefore remains magnetized in one sense while the other may be switched in sense by a switching magnetic field. The magneto-resistive film is therefore sensitive to the amplitude of the resultant field between the outer ferromagnetic films and may be constructed of a high resistivity, high magneto-resistive material capable of higher sensing currents. This permits higher read voltages and therefore faster read operations. Alternate embodiments with perpendicular anisotropy, and in-plane anisotropy are shown, including an embodiment which uses high permeability guides to direct the closing flux path through the magneto-resistive material. High density, high speed, radiation hard, memory matrices may be constructed from these memory elements.

Wu, Jiin-Chuan↗

NASA NTRS1992

High bandwidth electro-optic technology for intersatellite optical communications

The research and development of electronic and electro-optic components for geosynchronous and low earth orbiting satellite optical high bandwidth communications at the NASA-Goddard Space Flight Center is reviewed. Intersatellite optical communications retains a strong reliance on microwave circuit technology in several areas - the microwave to optical interface, the laser transmitter modulation driver and the optical receiver. A microwave to optical interface is described requiring high bandwidth electronic downconverters and demodulators. Electrical bandwidth and current drive requirements for the laser modulation driver for three laser alternatives are discussed. Bandwidth and noise requirements are presented for optical receiver architectures.

Krainak, Michael A.↗

NASA NTRS1995

Design of a GaAs/Ge Solar Array for Unmanned Aerial Vehicles

Unmanned Aerial Vehicles (UAV) are being proposed for many applications including surveillance, mapping and atmospheric studies. These applications require a lightweight, low speed, medium to long duration airplane. Due to the weight, speed, and altitude constraints imposed on such aircraft, solar array generated electric power is a viable alternative to air-breathing engines. Development of such aircraft is currently being funded under the Environmental Research Aircraft and Sensor Technology (ERAST) program. NASA Lewis Research Center (LeRC) is currently building a Solar Electric Airplane to demonstrate UAV technology. This aircraft utilizes high efficiency Applied Solar Energy Corporation (ASEC) GaAs/Ge space solar cells. The cells have been provided by the Air Force through the ManTech Office. Expected completion of the plane is early 1995, with the airplane currently undergoing flight testing using battery power.

Scheiman, David A.↗

NASA NTRS1997

Massively Parallel and Scalable Implicit Time Integration Algorithms for Structural Dynamics

Explicit codes are often used to simulate the nonlinear dynamics of large-scale structural systems, even for low frequency response, because the storage and CPU requirements entailed by the repeated factorizations traditionally found in implicit codes rapidly overwhelm the available computing resources. With the advent of parallel processing, this trend is accelerating because of the following additional facts: (a) explicit schemes are easier to parallelize than implicit ones, and (b) explicit schemes induce short range interprocessor communications that are relatively inexpensive, while the factorization methods used in most implicit schemes induce long range interprocessor communications that often ruin the sought-after speed-up. However, the time step restriction imposed by the Courant stability condition on all explicit schemes cannot yet be offset by the speed of the currently available parallel hardware. Therefore, it is essential to develop efficient alternatives to direct methods that are also amenable to massively parallel processing because implicit codes using unconditionally stable time-integration algorithms are computationally more efficient when simulating the low-frequency dynamics of aerospace structures.

Farhat, Charbel↗

NASA NTRS2001

Stability and Control Properties of an Aeroelastic Fixed Wing Micro Aerial Vehicle

Micro aerial vehicles have been the subject of considerable interest and development over the last several years. The majority of current vehicle concepts rely on rigid fixed wings or rotors. An alternate design based on an aeroelastic membrane wing concept has also been developed that has exhibited desired characteristics in flight test demonstrations and competition. This paper presents results from a wind tunnel investigation that sought to quantify stability and control properties for a family of vehicles using the aeroelastic design. The results indicate that the membrane wing does exhibit potential benefits that could be exploited to enhance the design of future flight vehicles.

Waszak, Martin R.↗

NASA NTRS2002

Simulation and Flight Control of an Aeroelastic Fixed Wing Micro Aerial Vehicle

Micro aerial vehicles have been the subject of continued interest and development over the last several years. The majority of current vehicle concepts rely on rigid fixed wings or rotors. An alternate design based on an aeroelastic membrane wing has also been developed that exhibits desired characteristics in flight test demonstrations, competition, and in prior aerodynamics studies. This paper presents a simulation model and an assessment of flight control characteristics of the vehicle. Linear state space models of the vehicle associated with typical trimmed level flight conditions and which are suitable for control system design are presented as well. The simulation is used as the basis for the design of a measurement based nonlinear dynamic inversion control system and outer loop guidance system. The vehicle/controller system is the subject of ongoing investigations of autonomous and collaborative control schemes. The results indicate that the design represents a good basis for further development of the micro aerial vehicle for autonomous and collaborative controls research.

Waszak, Martin↗

NASA NTRS2003

Erosion Resistant Coatings for Polymer Matrix Composites in Propulsion Applications

Polymer Matrix Composites (PMCs) offer lightweight and frequently low cost alternatives to other materials in many applications. High temperature PMCs are currently used in limited propulsion applications replacing metals. Yet in most cases, PMC propulsion applications are not in the direct engine flow path since particulate erosion degrades PMC component performance and therefore restricts their use in gas turbine engines. This paper compares two erosion resistant coatings (SANRES and SANPRES) on PMCs that are useful for both low and high temperature propulsion applications. Collaborating over a multi-year period, researchers at NASA Glenn Research Center, Allison Advanced Developed Company, and Rolls-Royce Corporation have optimized these coatings in terms of adhesion, surface roughness, and erosion resistance. Results are described for vigorous hot gas/particulate erosion rig and engine testing of uncoated and coated PMC fan bypass vanes from the AE 3007 regional jet gas turbine engine. Moreover, the structural durability of these coatings is described in long-term high cycle fatigue tests. Overall, both coatings performed well in all tests and will be considered for applications in both commercial and defense propulsion applications.

Sutter, James K.↗

NASA NTRS2010

Methods for Estimating Environmental Effects and Constraints on NexGen: High Density Case Study

This document provides a summary of the current methods developed by Metron Aviation for the estimate of environmental effects and constraints on the Next Generation Air Transportation System (NextGen). This body of work incorporates many of the key elements necessary to achieve such an estimate. Each section contains the background and motivation for the technical elements of the work, a description of the methods used, and possible next steps. The current methods described in this document were selected in an attempt to provide a good balance between accuracy and fairly rapid turn around times to best advance Joint Planning and Development Office (JPDO) System Modeling and Analysis Division (SMAD) objectives while also supporting the needs of the JPDO Environmental Working Group (EWG). In particular this document describes methods applied to support the High Density (HD) Case Study performed during the spring of 2008. A reference day (in 2006) is modeled to describe current system capabilities while the future demand is applied to multiple alternatives to analyze system performance. The major variables in the alternatives are operational/procedural capabilities for airport, terminal, and en route airspace along with projected improvements to airframe, engine and navigational equipment.

Augustine, S.↗

NASA NTRS2010

A New Representative for Small-Body Gravity Estimation

One of the options proposed in the 2009 Review of the U. S. Human Spaceflight Plans Committee calls for the consideration of robotic and human missions to asteroids. Beginning in 2000, the NEAR Shoemaker spacecraft inserted into orbit about the asteroid 433 Eros, and studied it for a year before landing. The Hayabusa satellite journeyed to 25143 Itokawa, and operated in a proximity of the asteroid for several months before landing to collect a return sample. Additionally, the DAWN satellite, which was launched in 2007, will explore the dwarf-planet Ceres and the asteroid 4 Vesta in the next three years. These are just several examples of current interests in exploring asteroids. In this paper, we explore an alternative for estimating the gravity field of a small body using observations of an orbiting satellite. Our approach uses two new mathematical tools, the quadratures (on a sphere) invariant under the icosahedral group, and a multiresolution representation of the gravity potential. With the near optimal quadratures on the sphere, we minimize the number of parameters needed to recover a function. Also, instead of estimating the coefficients of the spherical harmonics, the new quadratures allow us to estimate directly the values of the gravity field since they offer an analogue of the Lagrange-type interpolation.

Jones, Brandon A.↗

NASA NTRS2010

Water Membrane Evaporator

A water membrane evaporator (WME) has been conceived and tested as an alternative to the contamination-sensitive and corrosion-prone evaporators currently used for dissipating heat from space vehicles. The WME consists mainly of the following components: An outer stainless-steel screen that provides structural support for the components mentioned next; Inside and in contact with the stainless-steel screen, a hydrophobic membrane that is permeable to water vapor; Inside and in contact with the hydrophobic membrane, a hydrophilic membrane that transports the liquid feedwater to the inner surface of the hydrophobic membrane; Inside and in contact with the hydrophilic membrane, an annular array of tubes through which flows the spacecraft coolant carrying the heat to be dissipated; and An inner exclusion tube that limits the volume of feedwater in the WME. In operation, a pressurized feedwater reservoir is connected to the volume between the exclusion tube and the coolant tubes. Feedwater fills the volume, saturates the hydrophilic membrane, and is retained by the hydrophobic membrane. The outside of the WME is exposed to space vacuum. Heat from the spacecraft coolant is conducted through the tube walls and the water-saturated hydrophilic membrane to the liquid/vapor interface at the hydrophobic membrane, causing water to evaporate to space. Makeup water flows into the hydrophilic membrane through gaps between the coolant tubes.

Ungar, Eugene K.↗

NASA NTRS2012

Aerothermal Testing of Woven TPS Ablative Materials

Woven Thermal Protection Systems (WTPS) is a new TPS concept that is funded by NASAs Office of the Chief Technologist (OCT) Game Changing Division. The WTPS project demonstrates the potential for manufacturing a variety of TPS materials capable of wide ranging performances demanded by a spectrum of solar system exploration missions. Currently, missions anticipated to encounter heat fluxes in the range of 1500 4000 Watts per square centimeter are limited to using one proven material fully dense Carbon Phenolic. However, fully dense carbon phenolic is only mass efficient at heat fluxes greater than 4000 Watts per square centimeter, and current mission designs suffer this mass inefficiency for lack of an alternative mid-density TPS. WTPS not only bridges this gap but also offers a replacement for carbon phenolic, which itself requires a significant and costly redevelopment effort to re-establish its capability for use in the high heat flux missions recently prioritized in the NRC Decadal survey, including probe missions to Venus, Saturn and Neptune. This poster will summarize some recent arc jet testing to evaluate the performance of WTPS. Both mid density and fully dense WTPS test results will be presented and results compared to heritage carbon phenolic where applicable.

Stackpoole, Mairead↗

NASA NTRS2010

Hypergolic Propellant Destruction Evaluation Cost Benefit Analysis

At space vehicle launch sites such as Vandenberg Air Force Base (VAFB), Cape Canaveral Air Force Station (CCAFS) and Kennedy Space Center (KSC), toxic vapors and hazardous liquid wastes result from the handling of commodities (hypergolic fuels and oxidizers), most notably from transfer operations where fuel and oxidizer are transferred from bulk storage tanks or transfer tankers to space launch vehicles. During commodity transfer at CCAFS and KSC, wet chemical scrubbers (typically containing four scrubbing towers) are used to neutralize fuel saturated vapors from vent systems on tanks and tanker trailers. For fuel vapors, a citric acid solution is used to scrub out most of the hydrazine. Operation of both the hypergolic fuel and oxidizer vapor scrubbers generates waste scrubber liquor. Currently, scrubber liquor from the fuel vapor scrubber is considered non-hazardous. The scrubber liquor is defined as spent citric acid scrubber solution; the solution contains complexed hydrazine I methylhydrazine and is used to neutralize nonspecification hypergolic fuel generated by CCAFS and KSC. This project is a collaborative effort between Air Force Space Command (AFSPC), Space and Missile Center (SMC), the CCAFS, and National Aeronautics and Space Administration (NASA) to evaluate microwave destruction technology for the treatment of non-specification hypergolic fuel generated at CCAFS and KSC. The project will capitalize on knowledge gained from microwave treatment work being accomplished by AFSPC and SMC at V AFB. This report focuses on the costs associated with the current non-specification hypergolic fuel neutralization process (Section 2.0) as well as the estimated costs of operating a mobile microwave unit to treat non-specification hypergolic fuel (Section 3.0), and compares the costs for each (Section 4.0).The purpose of this document is to assess the costs associated with waste hypergolic fuel. This document will report the costs associated with the current fuel neutralization process and also examine the costs of an alternative technology, microwave destruction of waste hypergolic fuel. The microwave destruction system is being designed as a mobile unit to treat non-specification hypergolic fuel at CCAFS and KSC.

Kessel, Kurt↗

NASA NTRS2013

Woven TPS Enabling Missions Beyond Heritage Carbon Phenolic

Woven Thermal Protection Systems (WTPS) is a new TPS concept that is funded by NASAs Office of the Chief Technologist (OCT) Game Changing Division. The WTPS project demonstrates the potential for manufacturing many TPS architectures capable of performances demanded by the many potential solar system exploration missions. Currently, missions that encounter heat fluxes in the range of 1500 4000 W/sq cm and pressures greater than 1.5 atm have very limited TPS options - only one proven material, fully dense Carbon Phenolic, is currently available for these missions. However, fully dense carbon phenolic is only mass efficient at heat fluxes greater than 4000 W/sq cm, and current mission designs suffer this mass inefficiency for lack of an alternative mid-density TPS. WTPS not only bridges this TPS gap but also offers a replacement for carbon phenolic, which itself requires a significant and costly redevelopment effort to re-establish its capability for use in the high heat flux missions recently prioritized in the NRC Decadal survey, including probe missions to Venus, Saturn and Neptune. This presentation will introduce some woven TPS architectures considered in this project and summarize some recent arc jet testing to evaluate the performance of fully dense and mid density WTPS. Performance comparisons to heritage carbon phenolic will be drawn where applicable.

Stackpoole, Mairead↗

NASA NTRS2014

Crude Oil Remote Sensing, Characterization and Cleaning with CW and Pulsed Lasers

For detection, identification and characterization of crude oil we combine several optical methods of remote sensing of crude oil films and emulsions (coherent fringe projection illumination (CFP), holographic in-line interferometry (HILI), and laser induced fluorescence). These methods allow the three-dimensional characterization of oil spills, important for practical applications. Combined methods of CFP and HILI are described in the frame of coherent superposition of partial interference patterns. It is shown, that in addition to detection/identification laser illumination in the green-blue region can also degrade oil slicks. Different types of surfaces contaminated by oil spills are tested: oil on the water, oil on the flat solid surfaces and oil on the curved surfaces of pipes. For the detection and monitoring of the laser-induced oil degradation in pipes, coherent fiber bundles were used. Both continuous-wave (CW) and pulsed lasers are tested using pump-probe schemes. This finding suggests that properly structured laser clean-up can be an alternative environmentally-friendly method of decontamination, as compared to the currently used chemical methods that are dangerous to environment.

Kukhtareva, Tatiana↗