Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ThS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2

Dynamic Modulus and Damping of Boron, Silicon Carbide, and Alumina Fibers

The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide coated boron fibers were measured from-190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamics fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron based fibers are strongly anelastic, displaying frequency dependent moduli and very high microstructural damping. Ths single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.

Dicarlo, J. A.↗

Performance predictions for an SSME configuration with an enlarged throat

The Two Dimensional Kinetics (TDK) computer program that was recently developed for NASA was used to predict the performance of a Large Throat Configuration of the Space Shuttle Main Engine (SSME). Calculations indicate that the current design SSME contains a shock wave that is induced by the nozzle wall shape. In the Large Throat design an even stronger shock wave is predicted. Because of the presence of this shock wave, earlier performance predictions that have neglected shock wave effects have been questioned. The JANNAF thrust chamber performance prediction procedures given in a reference were applied. The analysis includes the effects of two dimensional reacting flow with a shock wave. The effects of the boundary layer with a regenatively cooled wall are also included. A Purdue computer program was used to compute axially symmetric supersonic nozzle flows with an induced shock, but is restricted to flows with a constant ratio of specific heats. Thus, the TDK program was also run with ths assumption and the results of the two programs were compared.

Nickerson, G. R.↗

Alternative cometary targets for the Giotto extended mission

The plan to use an Earth gravity-assist maneuver to redirect the Giotto spacecraft toward Comet Grigg-Skjellerup (GS) for an encounter in July 1992, and 2 additional cometary opportunities are discussed. The first is an encounter with Comet Hartley-2 (H2) in Aug., 1991. The H2 is intrinsically brighter than GS and the encounter would take place much closer to the Earth. The other potential target is Comet du Toit-Hartley (DTH), which is of considerable scientific interest because it split into 2 pieces during its 1979 apparition. Ths GS and H2 missions are the most viable; DTH is eliminated because its aphelion of transfer orbit and Sun distance at encounter (both 1.2 AU) are incompatible with Giotto's degraded thermal insulation.

Farquhar, R. W.↗

Rainfall index over oceans derived from SSM/I data

Ths Special Sensor Microwave/Imager radiometer on board the DMSP satellite measured microwave radiation at 19.35, 22.235, 37.0, and 85.5 GHz with a swath width of 1400 km, providing an opportunity to study global precipitation distributions. A monthly averaged rainfall index was derived using only the 19.35 GHz data. It covers the + or - 50 deg portion of the world with a 5 deg x 5 deg grid. The brightness temperature histogram is analyzed to derive the rainfall distribution. Estimates of the freezing level heights and the water vapor contents are utilized to understand the rainfall distribution better. Log normal and gamma distribution functions are fitted to the data and the derived monthly rainfall index compares favorably with historical precipitation patterns.

Chang, A. T. C.↗

Numerical study of external burning flowfields

This paper demonstrates the successful application of CFD to modeling an external burning flowfield. The study used the 2D, 3D, and PNS versions of the SPARK code. Various grids, boundary conditions, and ignition methodologies have been employed. Flameholding was achieved through the use of a subsonic outflow condition and a hot block located behind the step to ignite the fuel. Since the resulting burning produces a large subsonic region downstream of the cowl, this entire surface can be pressurized to the level of the back pressure. An evaluation of interactions between the ramjet exhaust and the external burning products demonstrate the complexity of this design issue. Ths code is now capable of evaluating the external burning effectiveness for flight vehicles using simple injector schemes, and the methodology can be readily applied to other external burning designs.

Bittner, Robert D.↗

A new transient pulsar in the Small Magellanic Cloud with an unusual x-ray spectrum

This article reports the discovery of a luminous (3.5 x 10(exp 37) ergs/sec over the 0.2 to 2 keV band) transient X-ray pulsar in the Small Magellanic Cloud (SMC) with an extremely soft component to its X-ray spectrum. This is the first time that a spectrum of this type has been seen in this class of X-ray source. The pulse period is 2.7632 s, and the pulse modulation appears to vary with energy from nearly unpulsed in the low-energy band of the ROSAT Position Sensitive Proportional Counter (PSPC) (0.07 to 0.4 keV) to about 50% in the high-energy band (1.0 to 2.4 keV). The object, RX J0059.2-7138, also shows flickering variability in its X-ray emission on timescales of 50 to 100s. The pulse-phase-averaged PSPC X-ray spectrum can be well described by a two-component source model seen through an absorbing column density of approximately 10(exp 21) atoms cm(exp -2). One spectral component is a power law with photon index 2.4. The other component is significantly softer and can be described by either a steeply falling power law or a blackbody with a temperature KT(sub BB) approximately 35 eV. Ths component is transient, but evidently upulsed, and, for the blackbody model fits, requires a large bolometric luminosity: near, or even several times greater than, the Eddington luminosity for a 1.4 solar mass object. When these characteristics of its soft emission are considered, RX J0059.2-7138 appears quite similar to other X-ray sources in the magellanic Clouds, such as CAL 83, CAL 87, and RX J0527.8-6954, which show only extreme ultrasoft (EUS) X-ray spectra. The discovery of RX J0059.2-7138, a probably high-mass X-ray binary, clearly indicates that EUS spectra may arise from accretion-powered neutron-star X-ray sources. This result lends support to the idea that some of the 'pure' EUS sources may be shrouded low-mass X-ray binaries rather than accreting white dwarfs.

Hughes, John P.↗

Intraseasonal Oscillations over South America: A Study with a Regional Climate Model

The National Center for Atmospheric Research (NCAR) regional climate model version 2 (RegCM2) is used to investigate the observed characteristics of intraseasonal oscillations over South America. Our study is mainly concentrated on an intraseaonal mode, which is observed to account for a large portion of the intraseasonal variation, to have a standing feature and to be independent of the MJO. The NCEPDOE AMIP-II reanalysis is utilized to provide initial and lateral boundary conditions for the RegCM2 based upon the OOZ, 062, 122 and 182 data.Our results indicate that the intraseasonal oscillation still exists with time- averaged lateral boundary condition, which prevents the MJO and other outside disturbances from entering the model's domain, suggesting a locally forced oscillation responsible for ths intraseasonal mode independent of the MJO. Further experiments show that the annual and daily variabilities and a radiative-convective interaction are not essential to the locally forced intraseasonal oscillation. The intraseasonal oscillations over Amazon in our model essentially result from interactions among atmospheric continental- scale circulation, surface radiation, surface sensible and latent heat fluxes, and cumulus convection. The wavelet analyses of various surface energy fluxes and surface energy budget also verify that the primary cause of intraseasonal oscillation is the interaction of land surface processes with the atmosphere.

Chen, Baode↗

Development of Particulates and Aerosols Research

During the past year several accomplishments were made for both the Particulate Matter Characterization and Measurement System, (PMCMS) and PAGEMS projects. The PAGEMS focus is to measure particulate emissions as a function of combustor parameters such as inlet temperature, inlet pressure and fuel air ratio. These measurements are used to evaluate combustor performance in hopes of correlating particulate emissions with engine conditions. These measurements have taken place at in-house NASA combustor facilities and off-site facilities. Ths work is unique because particulate measurements at high- pressure conditions are not commonly made. Some calibration of the PAGEMS instrumentation was done as well as minor modifications to the PAGEMS plumbing setup. These led to measurement improvements. The instrumentation and measurement process for PAGEMS was assessed and new instruments such as a thermodenuder, thermal mass flow meters and a cyclone separator were purchased to improve the PAGEMS instrumentation and measurement process. A worksheet was created to simulate varying inlet conditions to the DMA. This worksheet allows the user to assess the error in the measurements when certain conditions exist. Two technical papers were written with the PAGEMS team for the EXCAVATE field project. A paper was also reviewed for an in house publication. Also data was processed and analyzed for another field project (PAX) and will be part of a third PAGEMS paper. Accomplishments were also made with the PMCMS project. The calibration of the radial differential mobility analyzer, (RDMA) in the particle sizing system in the PMCMS was completed and provided satisfactory results. The voltages used for the RDMA depending on the particle of interest were corrected. The measurement capability of the PMCMS was increased by replacing the MetOne CPC with a TSI CPC. Lastly, assistance was provided to three college summer students with calibration of their particulate equipment and Monica Rivera shared her understanding of the aerosol technology with them. She also provided input for their end of the summer presentations. And attended the Aviation and Particle Emissions workshop. This workshop brought together experts in the aircraft particulate emissions field. As a result Ms. Rivera made two significant contacts with academia (UMR) and government (WPAFB) which could lead to future collaboration. She also attended the Aerosol and Particle Measurement Class held at the University of Minnesota. This class refreshed her particulate knowledge and introduced her to new aerosol applications and technology. Furthermore at the class contacts were made with private industry (TSI) and government (WPAFB). Ms. Rivera also enhanced her education by taking an in-house class on aircraft design and operation.

DeWitt, Kenneth↗

In Situ Aerosol Profile Measurements and Comparisons with SAGE 3 Aerosol Extinction and Surface Area Profiles at 68 deg North

Under funding from this proposal three in situ profile measurements of stratospheric sulfate aerosol and ozone were completed from balloon-borne platforms. The measured quantities are aerosol size resolved number concentration and ozone. The one derived product is aerosol size distribution, from which aerosol moments, such as surface area, volume, and extinction can be calculated for comparison with SAGE III measurements and SAGE III derived products, such as surface area. The analysis of these profiles and comparison with SAGE III extinction measurements and SAGE III derived surface areas are provided in Yongxiao (2005), which comprised the research thesis component of Mr. Jian Yongxiao's M.S. degree in Atmospheric Science at the University of Wyoming. In addition analysis continues on using principal component analysis (PCA) to derive aerosol surface area from the 9 wavelength extinction measurements available from SAGE III. Ths paper will present PCA components to calculate surface area from SAGE III measurements and compare these derived surface areas with those available directly from in situ size distribution measurements, as well as surface areas which would be derived from PCA and Thomason's algorithm applied to the four wavelength SAGE II extinction measurements.

Source record↗

A NASA Strategy for Leveraging Emerging Launch Vehicles for Routine, Small Payload Missions

Orbital flight opportunities for small payloads have always been few and far between, and then on February 1, 2002, the situation got worse. In the wake of the loss of the Columbia during STS- 107, changing NASA missions and priorities led to the termination of the Shuttle Small Payloads Projects, including Get-Away Special, Hitcbker, and Space Experiment Module. In spite of the limited opportunities, long queue, and restrictions associated with flying experiments on a man-rated transportation system; the carriers provided a sustained, high quality experiment services for education, science, and technology payloads, and was one of the few games in town. Attempts to establish routine opportunities aboard existing ELVs have been unsuccessful, as the cost-per-pound on small ELVs and conflicts with primary spacecraft on larger vehicles have proven prohibitive. Ths has led to a backlog of existing NASA-sponsored payloads and no prospects or plans for fbture opportunities within the NASA community. The prospects for breaking out of this paradigm appear promising as a result of NASA s partnership with DARPA in pursuit of low-cost, responsive small ELVs under the Falcon Program. Through this partnership several new small ELVs, providing 1000 lbs. to LEO will be demonstrated in less than two years that promise costs that are reasonable enough that NASA, DoD, and other sponsors can once again invest in small payload opportunities. Within NASA, planning has already begun. NASA will be populating one or more of the Falcon demonstration flights with small payloads that are already under development. To accommodate these experiments, Goddard s Wallops Flight Facility has been tasked to develop a multi-payload ejector (MPE) to accommodate the needs of these payloads. The MPE capabilities and design is described in detail in a separately submitted abstract. Beyond use of the demonstration flights however, Goddard has already begun developing strategies to leverage these new ELVs as elements of a larger system designed to provide routine, low-cost end-to-end services for small science, Exploration, and education payloads. The plan leverages the management approaches of the successful Sounding Rocket Program and Shuttle Small Payloads Projects. The strategy consists of using a systems implementation approach of elements, including 1) Falcon ELVs, 2) advanced launch site technologies and processes, 3) suite of experiment carriers accommodating different mission requirements, 4) streamlined integration and test operations, 5 ) experiment brokering and management, and 6) standardized, distributed payload operations. The envisioned suite of carriers includes the MPE, a standard interface experiment carrier, and potentially a reentry fieeflyer experiment carrier. Key to the success of this strategy is standard experiment interfaces within the carriers to limit mission- unique tasks, establishmg and managing a program of scheduled reoccurring flights rather than discrete missions, and streamlined, centralized implementation of the elements. These individual elements are each under development and Goddard will demonstrate the overall system strategy low-cost small payload missions on the initial Falcon demonstration launches from Wallops. goal is to show that this model should be converted to a sustained NASA program supporting science, technology, and education, with annual flight opportunities. The paper will define in detail the various elements of the overall program, as well as provide status, philosophy, and strategy for the program that will hopefully once-and-for-all provide low-cost, routine access to space for the small payloads community.

Underwood, Bruce E.↗

Using Transmission Control Protocol in the Trans-Pacific High Definition Video Satellite Communication Experiment - the Next Test

Ths paper describes a future Transmission Control Protocol (TCP) test which was planned as a part of the Trans-Pacific High Definition Video Satellite Communications Experiment. The TCP test portion of the Trans-Pacific High Definition Video Satellite Communications Experiment intends to examine the correlation between the underlying assumptions of come TCP algorithms and the performance shortfalls observed when the algorithms are used in a stellite-based environment, and to make experimental changes to existing TCP variants to study the effects of the modifications.

global information infrastructure (GII) satellites↗

Control of Telerobots with Variable Communication Delay

Ths paper proposes two solutions for the control of telerobots, in which master and slave are connected through a communication system that introduces a variable delay. This is the typical case of packet-switched networks (e.g. Internet), in which the delay varies in an unpredictible way.

stabilization of telerobots controllers Lyapunov f↗

A PC-based Workstation for Robotic Discectomy

Ths paper describes a PC-based controller for robot-assisted minimally invasive surgery. The development is motivated by the need of reducing the exposure of operating room personnel to X-rays during surgical procedures such as percutanrous discectomy.

control force monitoring small system envelope↗

The X-ray Evidence that the 51 Peg Companion is a Planet

51 Pegasi is a nearby G2-3 V star, which is similar to the Sun. Observers have recently detected and confirmed that 51 Pegasi has sinusoidal radial velocity variations with a period of 4.2 days and amplitude of 59 m/s. The radial velocity, if due to orbital motion around the system center-of-mass, implies a minimum companion mass of 0.47 Jupiter masses, which results from the assumption that the inclination angle of ths system is 90(sup 0) from the line of sight. We argue that the X-ray luminosity on the 51 Peg system implies that the unseen companion is a planet, independent of any assumption about the inclination angle.

51 pegasi 51 peg G2-3 V star↗

Conceptual Design of the TPF-O SC Buses

The Terrestrial Planet Finder - Occulter (TPF-O) mission has two Spacecraft (SC) buses, one for a space telescope and the other for a formation-flying occulter. SC buses typically supply the utilities (support structures, propulsion, attitude control, power, communications, etc) required by the payloads. Unique requirements for the occulter SC bus are to provide the large delta V required for the slewing maneuvers of the occulter, and comunications for formation flying. The TPF-O telescope SC bus shares some key features of the one for the Hubble Space Telescope (HST): both support space telescopes designed to observe in the visible to near infrared range of wavelengths with comparable primary mirror apertures (2.4 m for HST, 2.4 - 4.0 m for TPF-O). However, TPF-O is expected to have a Wide Field Camera (WFC) with a Field of View (FOV) much larger than that of HST. Ths WFC is also expected to provide fine guidance. TPF-O is designed to operate in an orbit around the Sun-Earth Lagrange 2 (SEL2) point. The longer communications range to SEL2 and the large science FOV require higher performance communications than HST. Maintaining a SEL2 orbit requires TPF-O, unlike HST, to have a propulsion system. The velocity required for reachng SEL2 and the limited capabilities of affordable launch vehicles require both TPF-O elements to have compact, low-mass designs. Finally, it is possible that TPF-O may utilize a modular design derived fiom that of HST to allow servicing in the SEL2 orbit.

Purves, Lloyd R.↗

LSP Composite Susbtrate Manufacturing Processing Guide

This document is intended to define Carbon Fiber Reinforced Plastic (CFRP) test panel configurations that can be employed for the purposes of evaluating the protection capabilities of Lightning Strike Protection (LSP) materials developed by the Aerospace Industry. The configurations are intended to provide consistent behavior in their response to simulated lightning strikes at pre-defined levels when tested by a capable vendor according to a test procedure written to enable consistent results (ref section 2.1.2). In response to an attachment of a simulated lightning strike on a CFRP panel, one can expect to see various levels of ablation and delamination, both through the thickness of the panel and with respect to the amount of panel surface area that exhibits damage. Panel configurations defined in this document include: An "unprotected" configuration 128694-1 (ref section 4.1), consisting of a cured CFRP laminate stackup of tape and fabric prepregs, coated with a typical aerospace primer and paint finishing scheme, attached to aluminum grounding bars intended to draw electrical current from the lightning attachment point to the panel edges and thus to ground. A "protected" configuration 128694-2 (ref section 4.1), wherein a layer of an LSP material form often used in the Aerospace Industry is included in the laminate stackup prior to cure. The CFRP materials, finishes and grounding arrangement for ths configuration are the same as for the "unprotected" configuration.

Kovach, Daniel J.↗

Iodine Hall Thruster Propellant Feed System for a CubeSat

There has been significant work recently in the development of iodine-fed Hall thrusters for in-space propulsion applications.1 The use of iodine as a propellant provides many advantages over present xenon-gas-fed Hall thruster systems. Iodine is a solid at ambient temperature (no pressurization required) and has no special handling requirements, making it safe for secondary flight opportunities. It has exceptionally high ρI sp (density times specific impulse), making it an enabling technology for small satellite near-term applications and providing system level advantages over mid-term high power electric propulsion options. Iodine provides thrust and efficiency that are comparable to xenonfed Hall thrusters while operating in the same discharge current and voltage regime, making it possible to leverage the development of flight-qualified xenon Hall thruster power processing units for the iodine application. Work at MSFC is presently aimed at designing, integrating, and demonstrating a flight-like iodine feed system suitable for the Hall thruster application. This effort represents a significant advancement in state-of-the-art. Though Iodine thrusters have demonstrated high performance with mission enabling potential, a flight-like feed system has never been demonstrated and iodine compatible components do not yet exist. Presented in this paper is the end-to-end integrated feed system demonstration. The system includes a propellant tank with active feedback-control heating, fill and drain interfaces, latching and proportional flow control valves (PFCV), flow resistors, and flight-like CubeSat power and control electronics. Hardware is integrated into a CubeSat-sized structure, calibrated and tested under vacuum conditions, and operated under under hot-fire conditions using a Busek BHT-200 thruster designed for iodine. Performance of the system is evaluated thorugh accurate measurement of thrust and a calibrated of mass flow rate measurement, which is a function of reservoir temperature/pressure, the flow resistors, and the setting of the PFCV. The calibration is performed using independent flow control monitoring techniques, providing an in situ measure of the flowrate as a function of controllable parameters. The reservoir temperature controls the iodine sublimation rate, providing propellant to ths thruster by pressurizing the propellant feed system to approx.1-2 psi. Control of the temperature and the PFCV are used to maintain reservoir pressure and keep the thruster discharge current constant.

Polzin, Kurt A.↗

The New NASA Ames Infrared Optical Constant Facility. Determinations for Titan Aerosol-, and Exoplanet and Brown Dwarf Cloud Particle Analogs

Here we present a new optical constant facility developed at NASA Ames that will allow the determination of optical constants in the infrared of various materials, analogs of hazes and cloud particles in (exo)planet atmospheres and brown dwarfs. Our facility is composed of a Fourier Transform Infrared (FTIR) spectrometer continuously covering the Near-IR, mid-IR and Far-IR range (from 0.74 to 200 µm), coupled to variable angle transmittance and reflectance accessories that allow the characterization of the scattering properties of nonhomogeneous samples (laboratory planetary aerosol analogs, films, slabs of material, crystals, powders...) over a wide incidence and emittance angle range (0-90 degrees). This permits the angular light distribution in both transmission and reflection measurements to be characterized, enabling the determination of the complex indices of refraction, n and k, over the full NIR-FIR range via modeling of the laboratory observations. The resulting refractive indices are critical input parameters in radiative transfer models, exoplanet and brown dwarf cloud models, protoplanetary disk simulations and other models used for the interpretation of observational data from past, current and future (exo)planetary NASA missions. We will present preliminary data obtained on Titan aerosol analogs produced in the Titan Haze Simulation (THS) experiment on COSmIC, a unique experimental platform developed at NASA Ames that allows the simulation of Titan's complex atmospheric chemistry at Titan-like temperature (200 K). We will also introduce a new study of the optical properties of ammonium-bearing phosphates, potential cloud particles forming in temperate exoplanets and brown dwarfs.

Planetary Science↗