Engineering topics

White, N.

Publications and source records attributed to White, N..

9 records

NASA NTRS2012

ORIGIN: Metal Creation and Evolution from the Cosmic Dawn

ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z=10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z approx. 0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a Transient Event Detector (coded mask with a sensitivity of 0.4 photon/sq cm/s in 10 s in the 5-150 keV band) to identify and localize 2000 GRBs over a five year mission, of which approx.65 GRBs have a redshift >7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5 eV, a field of view of 30 arcmin and large effective area below 1 keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background is achieved by the selected low Earth orbit.

Kouveliotou, C.↗

NASA NTRS2012

Low-Latency Telerobotics from Mars Orbit: The Case for Synergy Between Science and Human Exploration

Initial, science-directed human exploration of Mars will benefit from capabilities in which human explorers remain in orbit to control telerobotic systems on the surface (Figure 1). Low-latency, high-bandwidth telerobotics (LLT) from Mars orbit offers opportunities for what the terrestrial robotics community considers to be high-quality telepresence. Such telepresence would provide high quality sensory perception and situation awareness, and even capabilities for dexterous manipulation as required for adaptive, informed selection of scientific samples [1]. Astronauts on orbit in close communication proximity to a surface exploration site (in order to minimize communication latency) represent a capability that would extend human cognition to Mars (and potentially for other bodies such as asteroids, Venus, the Moon, etc.) without the challenges, expense, and risk of putting those humans on hazardous surfaces or within deep gravity wells. Such a strategy may be consistent with goals for a human space flight program that, are currently being developed within NASA.

Valinia, A.↗

NASA NTRS2006

Broadband X-ray Spectroscopy of the ADC Source 4U 1822-37 with Suzaku

We will present the broadband spectra of the low mass x-ray binary 4U 1822-37, recently observed with Suzaku. 4U 1822-37 is the canonical accretion disk corona (ADC) source where the compact object is obscured by an extended corona that intercepts and scatters the central continuum emission, some of which is then reprocessed in the outer regions of the accretion disk. 4U 1822-37 therefore serves as an important link between x-ray binaries and AGN. The broadband x-ray spectra from the Suzaku XIS and HXD provide a unique opportunity to probe the physical conditions in the corona and the accretion disk for this important accretion geometry.

Cottam, J.↗

NASA NTRS2003

Imagine the Universe!

Welcome to the 2004 edition of the education CD from the Laboratory for High Energy Astrophysics at NASA Goddard Space Flight Center. We hope that you will find it to be an exciting and fun learning experience. We have tried very hard to make this CD as user-friendly as possible and along the way we have discovered some things that every user may need to know. Please read the README file found on the CD if you have any questions or problems using the disk. Then, after that, if you still have problems, email us at itu@athena.gsfc.nasa.gov. We will be happy to help you 'get going'! Below are links to all of the sites included on the CD. You will also find the addresses for the on-line version of each of these sites. If you have a good Internet connection available, we recommend that you view the sites on-line. There you will find the latest updated information, interactive activities, and active links to other sites. Included on the disk are: Imagine The Universe! This site is dedicated to a discussion about our Universe... what we know about it, how it is evolving, and the kinds of objects and phenomena it contains. Emphasizing the X-ray and gamma-ray parts of the electromagnetic spectrum, it also discusses how scientists know what they know, what mysteries remain, and how the answers to remaining mysteries may one day be found. Lots of movies, quizzes, and a special section for educators. Geared for ages 14 and up. This site can be viewed on-line at http://imagine.gsfc.nasa.gov/. StarChild: A learning center for young astronomers The 1998 Webby Award Winner for Best Education Website, StarChild is aimed at ages 4-14. It contains easy-to-understand information about our Solar System, the Universe, and space exploration. There are also activities, songs, movies, and puzzles! This site can be viewed on-line at http://starchild.gsfc.nasa.gov/. Astronomy Picture of the Day APOD offers a new astronomical image and caption each calendar day. We have captured the year 2003 entries of this award-winning site and included them on the disk. The images and information provide a wonderful resource for all ages. This site can be viewed on-line at http://apod.gsfc.nasa.gov/apod/astropix.html.

White, N.↗

NASA NTRS1996

Optimization of Operations Resources via Discrete Event Simulation Modeling

The resource levels required for operation and support of reusable launch vehicles are typically defined through discrete event simulation modeling. Minimizing these resources constitutes an optimization problem involving discrete variables and simulation. Conventional approaches to solve such optimization problems involving integer valued decision variables are the pattern search and statistical methods. However, in a simulation environment that is characterized by search spaces of unknown topology and stochastic measures, these optimization approaches often prove inadequate. In this paper, we have explored the applicability of genetic algorithms to the simulation domain. Genetic algorithms provide a robust search strategy that does not require continuity and differentiability of the problem domain. The genetic algorithm successfully minimized the operation and support activities for a space vehicle, through a discrete event simulation model. The practical issues associated with simulation optimization, such as stochastic variables and constraints, were also taken into consideration.

Joshi, B.↗

NASA NTRS1992

The HEASARC graphical user interface

An OSF/Motif-based graphical user interface has been developed to facilitate the use of the database and data analysis software packages available from the High Energy Astrophysics Science Archive Research Center (HEASARC). It can also be used as an interface to other, similar, routines. A small number of tables are constructed to specify the possible commands and command parameters for a given set of analysis routines. These tables can be modified by a designer to affect the appearance of the interface screens. They can also be dynamically changed in response to parameter adjustments made while the underlying program is running. Additionally, a communication protocol has been designed so that the interface can operate locally or across a network. It is intended that this software be able to run on a variety of workstations and X terminals.

White, N.↗

NASA NTRS1992

XPI: The Xanadu Parameter Interface

XPI is a table driven parameter interface which greatly simplifies both command driven programs such as BROWSE and XIMAGE as well as stand alone single-task programs. It moves all of the syntax and semantic parsing of commands and parameters out of the users code into common code and externally defined tables. This allows the programmer to concentrate on writing the code unique to the application rather than reinventing the user interface and for external graphical interfaces to interface with no changes to the command driven program. XPI also includes a compatibility library which allows programs written using the IRAF host interface (Mandel and Roll) to use XPI in place of the IRAF host interface.

White, N.↗

NASA NTRS1985

Bimodal quasi-oscillatory and spectral behavior in Sco X-1

X-ray observations were made to follow up the discovery of quasi-periodic oscillations (QPO) in Sco X-1. The QPO is observed in the quiescent state, and between flares in the active state. When the source is quiescent, the QPO frequency is 6 Hz and anticorrelated with intensity; in the active state, the frequency ranges from 10 to 20 Hz and is strongly correlated with intensity. At high intensities the QPO dissolves into continuum noise. The QPO rms amplitude decreases with count rate, and increases with photon energy. There are two modes of spectral behavior, with a one-to-one correspondence to the two modes of QPO: the spectral hardness ratio varies more steeply with intensity when the source shows 6 Hz QPO, than for 10 to 20 Hz QPO. Transitions between QPO modes, which occur when the flux is at its lowest levels, correspond to transitions between hardness ratio modes. The QPO frequency changes continuously through the transitions, which last a few hundred seconds.

Priedhorsky, W.↗

NASA NTRS1979

Elemental abundances in a type I SNR

The solid state spectrometer on the HEAO-2 X-ray observatory observed the X-ray spectrum of Tycho's SNR. The observations show a relative excess of line emission from Si, S, and Ar by or = 6 compared to that expected from a plasma of solar composition in collisional equilibrium and by a factor of or = 3 compared to Cas A. Similar excesses are not found for line emission from Mg and Fe. The data suggest that the SN observed by Tycho in 1572 produced significant amounts of Si group elements but did not eject large amounts of Fe as predicted by some models of Type I SN events.

Becker, R. H.↗