Engineering topics

Smith, D. A.

Publications and source records attributed to Smith, D. A..

At least 19 records

NASA NTRS2016

Space Launch System Trans Lunar Payload Delivery Capability

NASA Marshall Space Flight Center (MSFC) has successfully completed the Critical Design Review (CDR) of the heavy lift Space Launch System (SLS) and is working towards first flight of the vehicle in 2018. SLS will begin flying crewed missions with an Orion to a lunar vicinity every year after the first 2 flights starting in the early 2020's. So as early as 2021 these Orion flights will deliver ancillary payload, termed "Co-Manifested Payload", with a mass of at least 5.5 metric tons and volume up to 280 cubic meters to a cis-lunar destination. Later SLS flights have a goal of delivering as much as 10 metric tons to a cis-lunar destination. This presentation will describe the ground and flight accommodations, interfaces, and resources planned to be made available to Co-Manifested Payload providers as part of the SLS system. An additional intention is to promote a two-way dialogue between vehicle developers and potential payload users in order to most efficiently evolve required SLS capabilities to meet diverse payload requirements.

Jackman, A. L.↗

NASA NTRS2016

A New, Low Braking Index for the LMC Pulsar B0540-69

We report the results of a 16-month monitoring campaign using the Swift satellite of PSR 0540, a young pulsar in the Large Magellanic Cloud. Phase connection was maintained throughout the campaign so that a reliable ephemeris could be determined, and the length of the campaign is adequate to accurately determine the spin frequency and its first and second derivatives. The braking index n is 0.031 +/- 0.013 (90% confidence), a value much lower than previously reported for 0 540 and almost all other young pulsars. We use data from the extensive monitoring campaign with RXTE to showt hat timing noise is unlikely to significantly affect the measurement. This is the first measurement of the braking index in the pulsars recently discovered high spin-down state. We discuss possible mechanisms for producing the low braking index.

pulsars individual (PSR B0540âˆ’69)↗

NASA NTRS2014

Constraints On the Emission Geometries and Spin Evolution Of Gamma-Ray Millisecond Pulsars

Millisecond pulsars (MSPs) are a growing class of gamma-ray emitters. Pulsed gamma-ray signals have been detected from more than 40 MSPs with the Fermi Large Area Telescope (LAT). The wider radio beams and more compact magnetospheres of MSPs enable studies of emission geometries over a broader range of phase space than non-recycled radio-loud gamma-ray pulsars. We have modeled the gamma-ray light curves of 40 LAT-detected MSPs using geometric emission models assuming a vacuum retarded-dipole magnetic field. We modeled the radio profiles using a single-altitude hollow-cone beam, with a core component when indicated by polarimetry; however, for MSPs with gamma-ray and radio light curve peaks occurring at nearly the same rotational phase, we assume that the radio emission is co-located with the gamma rays and caustic in nature. The best-fit parameters and confidence intervals are determined using amaximum likelihood technique.We divide the light curves into three model classes, with gamma-ray peaks trailing (Class I), aligned (Class II), or leading (Class III) the radio peaks. Outer gap and slot gap (two-pole caustic) models best fit roughly equal numbers of Class I and II, while Class III are exclusively fit with pair-starved polar cap models. Distinguishing between the model classes based on typical derived parameters is difficult. We explore the evolution of the magnetic inclination angle with period and spin-down power, finding possible correlations. While the presence of significant off-peak emission can often be used as a discriminator between outer gap and slot gap models, a hybrid model may be needed.

pulsars: general↗

NASA NTRS2012

Discovery of the Millisecond Pulsar PSR J2043+1711 in a Fermi Source with the Nancay Radio Telescope

We report the discovery of the millisecond pulsar PSR J2043+1711 in a search of a Fermi Large Area Telescope (LAT) source with no known associations, with the Nancay Radio Telescope. The new pulsar, confirmed with the Green Bank Telescope, has a spin period of 2.38 ms, is relatively nearby (d approx. < 2 kpc) and is in a 1.48-d orbit around a low-mass companion, probably an He-type white dwarf. Using an ephemeris based on Arecibo, Nancay and Westerbork timing measurements, pulsed gamma-ray emission was detected in the data recorded by the Fermi LAT. The gamma-ray light curve and spectral properties are typical of other gamma-ray millisecond pulsars seen with Fermi. X-ray observations of the pulsar with Suzaku and the Swift X-ray Telescope yielded no detection. At 1.4 GHz, we observe strong flux density variations because of interstellar diffractive scintillation; however, a sharp peak can be observed at this frequency during bright scintillation states. At 327 MHz, the pulsar is detected with a much higher signal-to-noise ratio and its flux density is far more steady. However, at that frequency the Arecibo instrumentation cannot yet fully resolve the pulse profile. Despite that, our pulse time-of-arrival measurements have a post-fit residual rms of 2 micro s. This and the expected stability of this system have made PSR J2043+1711 one of the first new Fermi-selected millisecond pulsars to be added to pulsar gravitational wave timing arrays. It has also allowed a significant measurement of relativistic delays in the times of arrival of the pulses due to the curvature of space-time near the companion, but not yet with enough precision to derive useful masses for the pulsar and the companion. Nevertheless, a mass for the pulsar between 1.7 and 2.0 solar Mass can be derived if a standard millisecond pulsar formation model is assumed. In this paper, we also present a comprehensive summary of pulsar searches in Fermi LAT sources with the Nancay Radio Telescope to date.

general aEuro" pulsars↗

NASA NTRS2012

Fermi-LAT Constraints on the Pulsar Wind Nebula Nature of HESS J1857+026

Since its launch, the Fermi satellite has firmly identified 5 pulsar wind nebulae plus a large number of candidates, all powered by young and energetic pulsars. HESS J1857+026 is a spatially extended gamma-ray source detected by H.E.S.S. and classified as a possible pulsar wind nebula candidate powered by PSR J1856+0245. Aims. We search for -ray pulsations from PSR J1856+0245 and explore the characteristics of its associated pulsar wind nebula. Methods. Using a rotational ephemeris obtained from the Lovell telescope at Jodrell Bank Observatory at 1.5 GHz, we phase.fold 36 months of gamma-ray data acquired by the Large Area Telescope (LAT) aboard Fermi. We also perform a complete gamma-ray spectral and morphological analysis. Results. No pulsation was detected from PSR J1856+0245. However, significant emission is detected at a position coincident with the TeV source HESS J1857+026. The gamma-ray spectrum is well described by a simple power law with a spectral index of Gamma = 1.53 +/- 0.11(sub stat) +/- 0.55(sub syst) and an energy flux of G(0.1 C100 GeV) = (2.71 +/- 0.52(sub stat) +/- 1.51(sub syst) X 10(exp -11) ergs/ sq cm/s. This implies a gamma.ray efficiency of approx 5 %, assuming a distance of 9 kpc, the gamma-ray luminosity of L(sub gamma) (sub PWN) (0.1 C100 GeV) = (2.5 +/- 0.5(sub stat) +/- 1.5(sub syst)) X 10(exp 35)(d/(9kpc))(exp 2) ergs/s and E-dot = 4.6 X 10(exp 36) erg /s, in the range expected for pulsar wind nebulae. Detailed multi-wavelength modeling provides new constraints on its pulsar wind nebula nature.

Rousseau, R.↗

NASA NTRS2011

Pulsed Gamma Rays from the Original Millisecond and Black Widow Pulsars: A Case for Caustic Radio Emission?

We report the detection of pulsed gamma-ray emission from the fast millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20 (J1959+2048) using 18 months of survey data recorded by the Fermi Large Area Telescope (LAT) and timing solutions based on radio observations conducted at the Westerbork and Nancay radio telescopes. In addition, we analyzed archival RXTE and XMM-Newton X-ray data for the two MSPs, confirming the X-ray emission properties of PSR B1937+21 and finding evidence (approx. 4(sigma)) for pulsed emission from PSR B1957+20 for the first time. In both cases the gamma-ray emission profile is characterized by two peaks separated by half a rotation and are in close alignment with components observed in radio and X-rays. These two pulsars join PSRs J0034..0534 and J2214+3000 to form an emerging class of gamma-ray MSPs with phase-aligned peaks in different energy bands. The modeling of the radio and gamma-ray emission pro les suggests co-located emission regions in the outer magnetosphere.

Guillemot, L.↗

NASA NTRS2007

Programmable Thermostat Module Upgrade for the Multipurpose Logistics Module

The STS-121/ULF 1.1 mission was the maiden flight of the programmable thermostat module (PTM) system used to control the 28 V shell heaters on the multi-purpose logistics module (MPLM). These PTMs, in conjunction with a data recorder module (DRM), provide continuous closed loop temperature control and data recording of MPLM on-orbit heater operations. This Technical Memorandum discusses the hardware design, development, test, and verification (DDT&V) activities performed at the Marshall Space Flight Center as well as the operational implementation and mission performance.

Clark, D. W.↗

NASA NTRS2007

GRO J1655-40: Early Stages of the 2005 Outburst

The black-hole X-ray binary transient GRO J1655-40 underwent an outburst beginning in early 2005. We present the results of our multi-wavelength observational campaign to study the early outburst spectral and temporal evolution, which combines data from X-ray (RXTE, INTEGRAL), radio (VLA) and optical (ROTSE, SMARTS) instruments. During the reported period the source left quiescence and went through four major accreting black hole states: low-hard, hard intermediate, soft intermediate and high-soft. We investigated dipping behavior in the RXTE band and compare our results to the 1996-1997 case, when the source was predominantly in the high-soft state, finding significant differences. We consider the evolution of the low frequency quasi-periodic oscillations and find that the frequency strongly correlates with the spectral characteristics, before shutting off prior to the transition to the high-soft state. We model the broad-band high-energy spectrum in the context of empirical models, as well as more physically motivated thermal and bulk-motion Comptonization and Compton reflection models. RXTE and INTEGRAL data together support a statistically significant high energy cut-off in the energy spectrum at approximately equal to 100 - 200 keV during the low-hard state. The RXTE data alone also show it very significantly during the transition, but cannot see one in the high-soft state spectra. We consider radio, optical and X-ray connections in the context of possible synchrotron and synchrotron self-Compton origins of X-ray emission in low-hard and intermediate states. In this outburst of GRO J1655-40, the radio flux does not rise strongly with the X-ray flux.

Shaposhnikov, N.↗

NASA NTRS2007

Gamma-Ray Pulsar Candidates for GLAST

The Gamma-ray Large Area Space Telescope (GLAST) will be launched less than a year from now, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio Erequencies, are likely to emit greater than l00 MeV gamma rays with intensities detectable by the LAT. The main figure of merit used to select gamma-ray pulsar candidates is sqrt(E-dot)/d^2, where E-dot is the energy loss due to rotational spindown, and d is the distance to the pulsar. The figure of merit incorporates spin-down flux at earth (proportional to E-dot/d^2) times efficiency, assumed proportional to 1/sqrt(E-dot). A few individual objects are cited to illustrate the issues. Since large E-dot pulsars also tend to have large timing noise and occasional glitches, their ephemerides can become inaccurate in weeks to months. To detect and study the gamma-ray emission the photons must be accurately tagged with the pulse phase. With hours to days between gamma-ray photon arrival times from a pulsar and months to years of LAT exposure needed for good detections, GLAST will need timing measurements throughout the continuous gamma-ray observations. The poster will describe efforts to coordinate pulsar timing of the candidate gamma-ray pulsars.

Thompson, David J.↗

NASA NTRS2006

The Onset Phase of "Soft" X-ray Transients

Transient outbursts of black holes and neutron stars in X-ray binaries with low-mass companions start with a flickering hard power-law flux that contains a low frequency quasi-periodic oscillation (QPO). The frequency of the QPO may reflect the outer boundary of the coronal emission and its inward motion toward the compact object. It has also been proposed that the hard flux is related to the base of a radio emitting outflow or compact jet. We had detailed observations of the beginning of the 2005 outburst of GRO J165.5-40 with RXTE, INTEGRAL, the VLA and ROTSE. We use the X-ray, radio, and optical results in the context of these models to address their applicability to the onset of the outburst and to specify the physical parameters. Decline of the radio flux as both the power-law and disk flux increased constrains the amount of synchrotron self-Compton emission. Values are compared to those of other black hole and neutron star transients. We are glad to acknowledge support by a NASA INTEGRAL Guest Observer Grant and by the UTE project, NRAO, and ROTSE.

Swank, Jean Hebb↗

NASA NTRS2005

Advanced Sensor Concepts

The Advanced Sensor Concepts project was conducted under the Center Director's Discretionary Fund at the Marshall Space Flight Center. Its objective was to advance the technology originally developed for the Glovebox Integrated Microgravity Isolation Technology project. The objective of this effort was to develop and test several new motion sensors. To date, the investigators have invented seven new technologies during this endeavor and have conceived several others. The innovative basic sensor technology is an absolute position sensor. It employs only two active components, and it is simple, inexpensive, reliable, repeatable, lightweight, and relatively unobtrusive. Two sensors can be utilized in the same physical space to achieve redundancy. The sensor has micrometer positional accuracy and can be configured as a two- or three-dimensional sensor. The sensor technology has the potential to pioneer a new class of linear and rotary sensors. This sensor is the enabling technology for autonomous assembly of modular structures in space and on extraterrestrial locations.

Alhorn, D. C.↗

NASA NTRS2001

Geometrical Effects on the Electromagnetic Radiation from Lightning Return Strokes

The morphological difference between the electromagnetic radiation-field waveforms of "first" and "subsequent" return strokes in cloud-to-ground lightning flashes is well known and can be used to identify the formation of new channels to ground. This difference is generally believed due to the existence of branches on first-stroke channels, whereas subsequent strokes re-illuminate only the main channel of a previous stroke; but experimental evidence for this hypothesis is relatively weak. It has been argued for the influence of channel geometry on the fine structure of radiation from subsequent return strokes by comparing the field-change waveforms recorded at the same station from strokes within the same flash and between different flashes of both natural and triggered lightning. The present paper introduces new evidence for both of these hypotheses from a comparison of waveforms between sensors in different directions from the same stroke.

Willett, J. C.↗

NASA NTRS1999

A New Probe of the Molecular Gas Content in Galaxies: Application to M101

Studies of nearby spiral galaxies suggest that photodissociation regions (PDRs) are capable of producing the observed large--scale distribution of HI (Allen et al.- 1997, and references therein). The column density of HI in a PDR is fundamentally linked to the amount of far--ultraviolet (FUV) emission produced by nearby young stars and the local molecular gas volume density. Measurements of the HI column density and the FUV emission associated with PDRs thus provide a new probe of the molecular gas distribution in nearby galaxies. Advantages of this method include its insensitivity to assumptions about the CO/{\rm H2} conversion factor or the gas temperature. We discuss the application of this method to M101. The HI column density and FUV emission have been measured for 35 PDRs from VLA data (Braun 1997) and Ultraviolet Imaging Telescope data (Waller et al.-1997). We derive volume densities ranging from n-100 {\rm cm(exp -3)} in the central HI--poor regions of M101 to n -3000 {\rm cm(exp -3)} in the HI--rich periphery of the galaxy.

Smith, D. A.↗

NASA NTRS1998

XTE J1946+274 = GRO J1944+26

C. A. Wilson, M. H. Finger, R. S. Wilson, and D. M. Scott, Marshall Space Flight Center, NASA, report for the BATSE team: "Pulsations from a previously-uncatalogued x-ray pulsar in the Vul-Cyg region have been detected with BATSE in the energy band 20-50 keV from Sept. 8 through Sept. 14. A preliminary location (95-percent confidence) is bounded by R.A. = 19h 34m to 19h 54m and Decl. = +22o.5 to +30o.5 (equinox 2000.0). GRO J1944+26 rose from a 20-50-keV rms pulsed flux of < 15 mCrab on Sept. 7 to 27 +/- 3 mCrab on Sept. 13. Observations between Sept. 8 and 14 are consistent with a barycentric pulse frequency of 0.06315331 (6) Hz on Sept. 11.0 UT, with a frequency derivative of 2.2(2) x 10(exp -12) Hz/s. The pulse profile in the band 20-50 keV has a single asymmetric peak.

Smith, D. A.↗

NASA NTRS1994

A programmable heater control circuit for spacecraft

Spacecraft thermal control is accomplished for many components through use of multilayer insulation systems, electrical heaters, and radiator systems. The heaters are commanded to maintain component temperatures within design specifications. The programmable heater control circuit (PHCC) was designed to obtain an effective and efficient means of spacecraft thermal control. The hybrid circuit provides use of control instrumentation as temperature data, available to the spacecraft central data system, reprogramming capability of the local microprocessor during the spacecraft's mission, and the elimination of significant spacecraft wiring. The hybrid integrated circuit has a temperature sensing and conditioning circuit, a microprocessor, and a heater power and control circuit. The device is miniature and housed in a volume which allows physical integration with the component to be controlled. Applications might include alternate battery-powered logic-circuit configurations. A prototype unit with appropriate physical and functional interfaces was procured for testing. The physical functionality and the feasibility of fabrication of the hybrid integrated circuit were successfully verified. The remaining work to develop a flight-qualified device includes fabrication and testing of a Mil-certified part. An option for completing the PHCC flight qualification testing is to enter into a joint venture with industry.

Nguyen, D. D.↗

NASA NTRS1993

Jovian electron propagation in three dimensions of the heliosphere: The Ulysses investigations

We report investigations of Jovian relativistic electrons in the interplanetary medium that provide new insights into both the physical processes by which the Jovian magnetosphere releases its trapped, relativistic electrons into the interplanetary medium, and the modes of their interplanetary propagation. These studies were dependent on the unique postencounter trajectory for Ulysses. The spacecraft remained close to the radial distance of Jupiter (approximately 5.2 AU) and moved southward on the duskside by only approximately 12 deg in heliographic latitude and less than 8 deg in the heliographic azimuth relative to Jupiter for the period of approximately 100 deg days of this study. During this period the nominal Parker spiral interplanetary magnetic field with its alternating polarities sector structure established direct magnetic field line connections frequently between Jupiter and the spacecraft. These unique conditions made it possible to investigate in detail, for approximately four solar rotations, both the Jovian electron burst phenomenon and the continuous, diffusive interplanetary propagation of Jovian electrons.

Simpson, J. A.↗

NASA NTRS1993

Infrared images of Monoceros R2 IRS 3 - Evidence for a circumstellar disk

Diffraction-limited IR images of the protostellar system Mon R2 IRS 3 reveal a bright conical nebula which extends about 0.5 arcsec south from the southern component of the previously known star pair. The bright nebula is probably dust scattering the starlight which emerges along the polar axis of a large (greater than 500 AU) circumstellar disk. We estimate a lower limit to the disk mass of 3 X 10 exp -2 solar masses. A faint, previously unknown pointlike source lies 0.37 arcsec east of the northern star.

Koresko, C. D.↗

NASA NTRS1986

Acceleration of convergence of vector sequences

A general approach to the construction of convergence acceleration methods for vector sequence is proposed. Using this approach, one can generate some known methods, such as the minimal polynomial extrapolation, the reduced rank extrapolation, and the topological epsilon algorithm, and also some new ones. Some of the new methods are easier to implement than the known methods and are observed to have similar numerical properties. The convergence analysis of these new methods is carried out, and it is shown that they are especially suitable for accelerating the convergence of vector sequences that are obtained when one solves linear systems of equations iterative. A stability analysis is also given, and numerical examples are provided. The convergence and stability properties of the topological epsilon algorithm are likewise given.

Sidi, A.↗