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At least 1,315 records · Page 73
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NASA NTRS2015

Testing Secondary Models for the Origin of Radio Mini-Halos in Galaxy Clusters

We present an MHD simulation of the emergence of a radio minihalo in a galaxy cluster core in a "secondary" model, where the source of the synchrotron-emitting electrons is hadronic interactions between cosmic-ray protons with the thermal intracluster gas, an alternative to the "reacceleration model" where the cosmic ray electrons are reaccelerated by turbulence induced by core sloshing, which we discussed in an earlier work. We follow the evolution of cosmic-ray electron spectra and their radio emission using passive tracer particles, taking into account the time-dependent injection of electrons from hadronic interactions and their energy losses. We find that secondary electrons in a sloshing cluster core can generate diffuse synchrotron emission with luminosity and extent similar to observed radio minihalos. However, we also find important differences with our previous work. We find that the drop in radio emission at cold fronts is less prominent than that in our reacceleration-based simulations, indicating that in this flavor of the secondary model the emission is more spatially extended than in some observed minihalos. We also explore the effect of rapid changes in the magnetic field on the radio spectrum. While the resulting spectra in some regions are steeper than expected from stationary conditions, the change is marginal, with differences in the synchrotron spectral index of delta(spectral index) less than approximately 0.15-0.25, depending on the frequency band. This is a much narrower range than claimed in the best-observed minihalos and produced in the reacceleration model. Our results provide important suggestions to constrain these models with future observations.

clusters: general aEuro" magnetohydrodynamics (MHD↗
NASA NTRS1980

Evaluation of a bulk calorimeter and heat balance for determination of supersonic combustor efficiency

Results are presented from the shakedown and evaluation test of a bulk calorimeter. The calorimeter is designed to quench the combustion at the exit of a direct-connect, hydrogen fueled, scramjet combustor model, and to provide the measurements necessary to perform an analysis of combustion efficiency. Results indicate that the calorimeter quenches reaction, that reasonable response times are obtained, and that the calculated combustion efficiency is repeatable within + or -3 percent and varies in a regular way with combustor model parameters such as injected fuel equivalence ratio.

Mcclinton, C. R.↗
NASA NTRS1981

Human factors in equipment development for the Space Shuttle - A study of the general purpose work station

The results of a human factors test to assay the suitability of a prototype general purpose work station (GPWS) for biosciences experiments on the fourth Spacelab mission are reported. The evaluation was performed to verify that users of the GPWS would optimally interact with the GPWS configuration and instrumentation. Six male subjects sat on stools positioned to allow assimilation of the zero-g body posture. Trials were run concerning the operator viewing angles facing the console, the console color, procedures for injecting rates with dye, a rat blood cell count, mouse dissection, squirrel monkey transfer, and plant fixation. The trials were run for several days in order to gage improvement or poor performance conditions. Better access to the work surface was found necessary, together with more distinct and better located LEDs, better access window latches, clearer sequences on control buttons, color-coded sequential buttons, and provisions made for an intercom system when operators of the GPWS work in tandem.

Junge, M. K.↗
NASA NTRS1985

A tandem mirror plasma source for a hybrid plume plasma propulsion concept

This paper describes a tandem mirror magnetic plasma confinement device to be considered as a hot plasma source for the hybrid plume rocket concept. The hot plasma from this device is injected into an exhaust duct, which will interact with an annular layer of hypersonic neutral gas. Such a device can be used to study the dynamics of the hybrid plume and to experimentally verify the numerical predictions obtained with computer codes. The basic system design is also geared toward being lightweight and compact, as well as having high power density (i.e., several kW/sq cm) at the exhaust. This feature is aimed toward the feasibility of 'space testing'. The plasma is heated by microwaves. A 50 percent heating efficiency can be obtained by using two half-circle antennas. The preliminary Monte Carlo modeling of test particles result reported here indicates that interaction does take place in the exhaust duct. Neutrals gain energy from the ion, which confirms the hybrid plume concept.

Yang, T. F.↗
NASA NTRS1994

Surface characterization through shape oscillations of drops in microgravity and 1-g

The goal of these experiments is to determine the rheological properties of liquid drops of single or multiple components in the presence or absence of surface active materials by exciting drops into their quadrupole resonance and observing their free decay. The resulting data coupled with appropriate theory should give a better description of the physics of the underlying phenomena, providing a better foundation than earlier empirical results could. The space environment makes an idealized geometry available (spherical drops) so that theory and experiment can be properly compared, and allows a 'clean' environment, by which is meant an environment in which no solid surfaces come in contact with the drops during the test period. Moreover, by considering the oscillations of intentionally deformed drops in microgravity, a baseline is established for interpreting surface characterization experiments done on the ground by other groups and ours. Experiments performed on the United States Microgravity Laboratory Laboratory (USML-1) demonstrated that shape oscillation experiments could be performed over a wide parameter range, and with a variety of surfactant materials. Results, however, were compromised by an unexpected, slow drop tumbling, some problems with droplet injection, and the presence of bubbles in the drop samples. Nevertheless, initial data suggests that the space environment will be useful in providing baseline data that can serve to validate theory and permit quantitative materials characterization at 1-g.

Apfel, Robert E.↗
NASA NTRS1995

Delta wing vortex manipulation using pulsed and steady blowing during ramp pitching

The effectiveness of steady and pulsed blowing as a method of controlling delta wing vortices during ramp pitching has been investigated in flow visualization experiments conducted in a water tunnel. The recessed angled spanwise blowing technique was utilized for vortex manipulation. This technique was implemented on a beveled 60 delta wing using a pair of blowing ports located beneath the vortex core at 40% chord. The flow was injected primarily in the spanwise direction but was also composed of a component normal to the wing surface. The location of vortex burst was measured as a function of blowing intensity and pulsing frequency under static conditions, and the optimum blowing case was applied at three different wing pitching rates. Experimental results have shown that, when the burst location is upstream of the blowing port, pulsed blowing delays vortex breakdown in static and dynamic cases. Dynamic tests verified the existence of a hysteresis effect and demonstrated the improvements offered by pulsed blowing over both steady blowing and no-blowing scenarios. The application of blowing, at the optimum pulsing frequency, made the vortex breakdown location comparable in static and ramp pitch-up conditions.

Moreira, J.↗
NASA NTRS2001

"2001: A Space Odyssey" Revisited: The Feasibility of 24 Hour Commuter Flights to the Moon Using NTR Propulsion with LUNOX Afterburners

The prospects for "24 hour" commuter flights to the Moon. similar to that portrayed in 2001: A Space Odyssey but on a more Spartan scale. are examined using two near term. "high leverage" technologies-liquid oxygen (LOX)-augmented nuclear thermal rocket (NTR) propulsion and "lunar-derived" oxygen (LUNOX) production. Iron-rich volcanic glass. or "orange soil," discovered during the Apollo 17 mission to Taurus-Littrow. has produced a 4% oxygen yield in recent NASA experiments using hydrogen reduction. LUNOX development and utilization would eliminate the need to transport oxygen supplies from Earth and is expected to dramatically reduce the size, cost and complexity of space transportation systems. The LOX-augmented NTR concept (LANTR) exploits the high performance capability of the conventional liquid hydrogen (LH2)-cooled NTR and the mission leverage provided by LUNOX in a unique way. LANTR utilizes the large divergent section of its nozzle as an "afterburner" into which oxygen is injected and supersonically combusted with nuclear preheated hydrogen emerging from the engine's choked sonic throat-essentially "scramjet propulsion in reverse." By varying the oxygen-to-hydrogen mixture ratio, the LANTR engine can operate over a wide range of thrust and specific impulse (Isp) values while the reactor core power level remains relatively constant. The thrust augmentation feature of LANTR means that "big engine" performance can be obtained using smaller. more affordable. easier to test NTR engines. The use of high-density LOX in place of low-density LH2 also reduces hydrogen mass and tank volume resulting in smaller space vehicles. An implementation strategy and evolutionary lunar mission architecture is outlined which requires only Shuttle C or "in-line" Shuttle-derived launch vehicles, and utilizes conventional NTR-powered lunar transfer vehicles (LTVs), operating in an "expendable mode" initially, to maximize delivered surface payload on each mission. The increased payload is dedicated to installing "modular" LUNOX production units with the intent of supplying LUNOX to lunar landing vehicles (LLVs) and then LTVs at the earliest possible opportunity. Once LUNOX becomes available in low lunar orbit (LLO), monopropellant NTRs would be outfitted with an oxygen propellant module, feed system and afterburner nozzle for "bipropellant" operation. Transition to a "reusable" mission architecture now occurs with smaller, LANTR-powered LTVs delivering approximately 400% more payload on each piloted round trip mission than earlier expendable "all LH2" NTR systems. As initial lunar outposts grow to eventual lunar settlements and LUNOX production capacity increases, the LANTR concept can enable a rapid "commuter" shuttle capable of 24 hour "one way" trips to and from the Moon. A vast deposit of "iron-rich" volcanic glass beads identified at just one candidate site - located at the southeastern edge of Mare Serenitatis - could supply sufficient LUNOX to support daily commuter flights to the Moon for the next 9000 years'.

Borowski, Stanley K.↗
NASA NTRS1998

Modeling of a Two-Phase Jet Pump with Phase Change, Shocks and Temperature-Dependent Properties

One of the primary motivations behind this work is the attempt to understand the physics of a two-phase jet pump which constitutes part of a flow boiling test facility at NASA-Marshall. The flow boiling apparatus is intended to provide data necessary to design highly efficient two-phase thermal control systems for aerospace applications. The facility will also be capable of testing alternative refrigerants and evaluate their performance using various heat exchangers with enhanced surfaces. The test facility is also intended for use in evaluating single-phase performance of systems currently using CFC refrigerants. Literature dealing with jet pumps is abundant and covers a very wide array of application areas. Example application areas include vacuum pumps which are used in the food industry, power station work, and the chemical industry; ejector systems which have applications in the aircraft industry as cabin ventilators and for purposes of jet thrust augmentation; jet pumps which are used in the oil industry for oil well pumping; and steam-jet ejector refrigeration, to just name a few. Examples of work relevant to this investigation includes those of Fairuzov and Bredikhin (1995). While past researchers have been able to model the two-phase flow jet pump using the one-dimensional assumption with no shock waves and no phase change, there is no research known to the author apart from that of Anand (1992) who was able to account for condensation shocks. Thus, one of the objectives of this work is to model the dynamics of fluid interaction between a two-phase primary fluid and a subcooled liquid secondary fluid which is being injected employing atomizing spray injectors. The model developed accounts for phase transformations due to expansion, compression, and mixing. It also accounts for shock waves developing in the different parts of the jet pump as well as temperature and pressure dependencies of the fluid properties for both the primary two-phase mixture and the secondary subcooled liquid. The research effort on which this document partly reports described a relatively simple model capable of describing the performance of a two-phase flow jet pump. The model is based on the isentropic homogeneous expansion/compression hypothesis and is capable of fully incorporating the effects of shocks in both the mixing chamber and the throat/diffuser parts of the pump. The physical system chosen is identical to that experimentally tested by Fairuzov and Bredikhin (1995) and should therefore be relatively easy to validate.

Sherif, S. A.↗
NASA NTRS1976

Test particle propagation in magnetostatic turbulence. 1. Failure of the diffusion approximation

The equation which governs the quasi-linear approximation to the ensemble and gyro-phase averaged one-body probability distribution function is constructed from first principles. This derived equation is subjected to a thorough investigation in order to calculate the possible limitations of the quasi-linear approximation. It is shown that the reduction of this equation to a standard diffusion equation in the Markovian limit can be accomplished through the application of the adiabatic approximation. A numerical solution of the standard diffusion equation in the Markovian limit is obtained for the narrow parallel beam injection. Comparison of the diabatic and adiabatic results explicitly demonstrates the failure of the Markovian description of the probability distribution function. Through the use of a linear time-scale extension the failure of the adiabatic approximation, which leads to the Markovian limit, is shown to be due to mixing of the relaxation and interaction time scales in the presence of the strong mean field.

Klimas, A. J.↗
NASA NTRS1986

Investigation of a repetitive pulsed electrothermal thruster

A pulsed electrothermal (PET) thruster with 1000:1 ratio nozzle is tested in a repetitive mode on water propellant. The thruster is driven by a 60J pulse forming network at repetition rates up to 10 Hz (600W). The pulse forming network has a .31 ohm impedance, well matched to the capillary discharge resistance of .40 ohm, and is directly coupled to the thruster electrodes without a switch. The discharge is initiated by high voltage breakdown, typically at 2500V, through the water vapor in the interelectrode gap. Water is injected as a jet through a .37 mm orifice on the thruster axis. Thruster voltage, current and impulse bit are recorded for several seconds at various power supply currents. Thruster to power ratio is typically T/P = .07 N/kW. Tank background pressure precludes direct measurement of exhaust velocity which is inferred from calculated pressure and temperature in the discharge to be about 14 km/sec. Efficiency, based on this velocity and measured T/P is .54 + or - .07. Thruster ablation is zero at the throat and becomes measurable further upstream, indicating that radiative ablation is occurring late in the pulse.

Burton, R. L.↗
NASA NTRS1994

Time-dependent evolution of cosmic-ray-modified shock structure: Transition to steady state

Steady state solutions to the two-fluid equations of cosmic-ray-modified shock structure were investigated first by Drury and Volk (1981). Their analysis revealed, among other properties, that there exist regions of upstream parameter space where the equations possess three different downstream solutions for a given upstream state. In this paper we investigate whether or not all these solutions can occur as time-asymptotic states in a physically realistic evolution. To do this, we investigate the time-dependent evolution of the two-fluid cosmic-ray equations in going from a specified initial condition to a steady state. Our results indicate that the time-asymptotic solution is strictly single-valued, and it undergoes a transition from weakly to strongly cosmic-ray-modified at a critical value of the upstream cosmic ray energy density. The expansion of supernova remnant shocks is considered as an example, and it is shown that the strong to weak transition is in fact more likely. The third intermediate solution is shown to influence the time-dependent evolution of the shock, but it is not found to be a stable time-asymptotic state. Timescales for convergence to these states and their implications for the efficiency of shock acceleration are considered. We also investigate the effects of a recently introduced model for the injection of seed particles into the shock accelerated cosmic-ray population. The injection is found to result in a more strongly cosmic-ray-dominated shock, which supports our conclusion that for most classes of intermediate and strong cosmic-ray-modified shocks, the downstream cosmic-ray pressure component is at least as large as the thermal gas pressure, independent of the upstream state. As a result, cosmic rays almost always play a significant role in determining the shock structure and dissipation and they cannot be regarded as test particles.

Donohue, D. J.↗
NASA NTRS2016

Enabling International Data Relay at Mars

The most commonly used mode of communications be-tween Earth and a Mars surface mission is ultra-high fre-quency (UHF) radio relay via a Mars orbiter. There are four orbiters and two surface rovers operating at Mars and by October there should be five orbiters and three landers or rovers. There has been some collaboration between ESA’s Mars Express orbiter and NASA’s rovers, but 2016 is when Mars relay becomes fully international. In October, ESA will deliver the ExoMars Trace Gas Orbiter (TGO) and En-try, Descent, and Landing (EDL) Demonstrator Module (EDM) lander to Mars. The ExoMars program includes both ESA and ROSCOSMOS, with NASA participation (the Electra UHF transceiver on TGO). NASA orbiters will pro-vide relay for EDM and future ESA Mars landers and rov-ers. TGO will provide relay for NASA's current and future surface assets (as Mars Express will continue to do). Inter-national collaboration is enabled in several steps. At the in-struction of the space agencies, the Mars mission projects negotiate and write a “Service Agreement.” This describes at a high level how a new Mars orbiter would operate with its corresponding surface missions or how a new surface mis-sion would operate with its corresponding orbiters. It in-cludes the roles of the different projects, how the new mis-sion would communicate with existing or planned missions, the general flow of data and commands, and the capabilities or requirements of the new mission. After completing the Service Agreement, the projects write Interface Control Doc-uments (ICDs), each of which describes data and command flow in greater detail and quantitative aspects of the relay link and operations timeline between an orbiter and a cor-responding lander/rover. Interfaces and operations are test-ed before a new mission arrives at Mars. Once at Mars, a new orbiter performs some “practice” relay contacts with its partners. For a new lander (e.g. EDM), relay operations gen-erally begin before atmospheric entry at Mars, with record-ing of the UHF relay signal from the lander (including open-loop wide-bandwidth recording) as it enters and traverses Mars’s atmosphere and lands on its surface. After Mars EDL or orbit injection, each relay contact is negotiat-ed and scheduled using the Mars Relay Operations Service (MaROS). This paper describes the international approach to develop inter-agency agreements, inter-project interfaces, and specifics of how MaROS is used in actual relay opera-tions between international partners.

Winton, Alistair J.↗
NASA NTRS1997

Ejector Noise Suppression with Auxiliary Jet Injection

An experimental program to reduce aircraft jet turbulence noise investigated the interaction of small auxiliary jets with a larger main jet. Significant reductions in the far field jet noise were obtained over a range of auxiliary jet pressures and flow rates when used in conjunction with an acoustically lined ejector. While the concept is similar to that of conventional ejector suppressors that use mechanical mixing devices, the present approach should improve thrust and lead to lower weight and less complex noise suppression systems since no hardware needs to be located in the main jet flow. A variety of auxiliary jet and ejector configurations and operating conditions were studied. The best conditions tested produced peak to peak noise reductions ranging from 11 to 16 dB, depending on measurement angle, for auxiliary jet mass flows that were 6.6% of the main jet flow with ejectors that were 8 times the main jet diameter in length. Much larger reductions in noise were found at the original peak frequencies of the unsuppressed jet over a range of far field measurement angles.

Berman, Charles H.↗
NASA NTRS1991

Experimental and theoretical comparison of the Probe Thrust Vector Control concept

A concept that offers an alternate method for thrust vector control of liquid or solid propellant rockets is the use of a solid body or probe that is inserted on demand through the wall of the rocket nozzle. This Probe Thrust Vector Control (PTVC) concept is an alternative to that of a gimbaled nozzle or a Liquid Injection Thrust Vector control system. The viability of the PTVC concept can be assessed either experimentally and/or with the use of CFD. A purely experimental assessment is time consuming and expensive, whereas a CFD assessment is time- and cost-effective. Two key requirements of the concept are PTVC vectoring performance and active cooling requirements for the probe to maintain its thermal and structural integrity. The objective of the work reported here is presentation of experimental subscale cold flow tests and comparison of these tests with CFD predictions and the response time of the PTVC system.

Cavalleri, Robert↗
NASA NTRS1998

Passively Adaptive Inflatable Structure for the Shooting Star Experiment

An inflatable structural system is described for the Shooting Star Experiment that is a technology demonstrator flight for solar thermal propulsion. The inflatable structure is a pressurized assembly used in orbit to support a fresnel lens for focusing sunlight into a thermal storage engine. When the engine temperature reaches a preset level, the propellant is injected into the storage engine, absorbs heat from a heat exchanger, and is expanded through the nozzle to produce thrust. The inflatable structure is an adaptive system in that a regulator and relief valve are utilized to maintain pressure within design limits during the full range of orbital conditions. Further, the polyimide film material used for construction of the inflatable is highly nonlinear, with modulus varying as a function of frequency, temperature, and level of excitation. A series of tests is described for characterizing the structure in response to various operating conditions.

Tinker, Michael L..↗
NASA NTRS2004

Single-Stage, 3.4:1-Pressure-Ratio Aspirated Fan Developed and Demonstrated

Researchers are constantly pursuing technologies that will increase the performance of gas turbine engines. The aspirated compressor concept discussed here would allow the compression system to perform its task with about one-half of the compressor blades. To accomplish this, the researchers applied boundary layer control to the blades, casing, and hub. This method of boundary layer control consisted of removing small amounts of air from the main flow path at critical areas of the compressor. This bleed air could be used by other systems such as engine cooling or could be re-injected into lower pressure areas that require air for enhanced performance. This effort was initiated by the Massachusetts Institute of Technology (MIT) in response to a solicitation from the Defense Advanced Research Projects Agency (DARPA) who sought to advance research in flow control technology. The NASA Glenn Research Center partnered with MIT (principal investigator), Honeywell Aircraft Engines (cycle analysis, structural analysis, and mechanical design), and Pratt & Whitney (cycle analysis and aero-analysis) to conceptualize, design, analyze, build, and test the aspirated fan stage. The aero-design and aero-analysis of this fan stage were jointly executed by MIT and Glenn to minimize the amount of bleed flow needed and to maintain the highest efficiency possible (ref. 1). Mechanical design issues were complicated by the need to have a shrouded rotor with hollow blades, with rotor stress levels beyond the capabilities of titanium. The high stress issues were addressed by designing a shroud that was filament wound with a carbon fiber/epoxy matrix, resulting in an assembly that was strong enough to handle the high stresses. Both the rotor (preceding photographs) and stator (following photograph) were fabricated in two halves and then bolted together at the hub and tip, permitting the bleed passages to be machined into each half before assembly.

Braunscheidel, Edward P.↗
NASA NTRS1967

Lunar Orbiter II - Photographic Mission Summary

Lunar Orbiter II photography of landing sites, and spacecraft systems performance. The second of five Lunar Orbiter spacecraft was successfully launched from Launch Complex 13 at the Air Force Eastern Test Range by an Atlas-Agena launch vehicle at 23:21 GMT on November 6, 1966. Tracking data from the Cape Kennedy and Grand Bahama tracking stations were used to control and guide the launch vehicle during Atlas powered flight. The Agena spacecraft combination was maneuvered into a 100-nautical-mile-altitude Earth orbit by the preset on-board Agena computer. In addition, the Agena computer determined the maneuver 1 and engine-bum period required to inject the spacecraft on the cislunar trajectory 20 minutes after launch. Tracking data from the downrange stations and the Johannesburg, South Africa station were used to monitor the entire boost trajectory.

LUNAR ORBITER↗
NASA NTRS1973

Cavity temperature and flow characteristics in a gas-core test reactor

A test reactor concept for conducting basic studies on a fissioning uranium plasma and for testing various gas-core reactor concepts is analyzed. The test reactor consists of a conventional fuel-element region surrounding a 61-cm-(2-ft-) diameter cavity region which contains the plasma experiment. The fuel elements provide the neutron flux for the cavity region. The design operating conditions include 60-MW reactor power, 2.7-MW cavity power, 200-atm cavity pressure, and an average uranium plasma temperature of 15,000 K. The analytical results are given for cavity radiant heat transfer, hydrogen transpiration cooling, and uranium wire or powder injection.

Putre, H. A.↗