2,016 research outputs found
Space Shuttle Orbiter And Subsystems
Considerable progress has been made in designing the Space Shuttle orbiter and defining its subsystems since the development contract was awarded by NASA to Rockwell International in August, 1972. During the past two years, NASA and Rockwell International, Space Division have been engaged in an intensive effort to refine orbiter preliminary design concepts and to translate them into reality. This paper describes the orbiter \u27s configuration and its major subsystems. The general arrangement of the vehicle and its major assemblies are described. Orbiter flight characteristics and mission profiles are summarized. Selected subsystems including structure, thermal protection, propulsion, power, reaction control, orbital maneuvering, environmental control and life support, hydraulics, avionics, and accommodations for crew and payloads are described
Recommended from our members
HSST crack-arrest studies overview
An overview is given of the efforts underway in the Heavy-Section Steel Technology (HSST) Program to better understand and model crack-arrest behavior in reactor pressure vessel steels. The efforts are both experimental and analytical. The experimental work provides K/sub Ia/ data from laboratory-sized specimens, from thick-wall cylinders which exhibit essentially-full restraint and from nonisothermal wide-plate specimens. These data serve to define toughness-temperature trends and to provide validation data under prototypical reactor conditions. The analytical efforts interpret and correlate the data, plus provide LEFM, elastodynamic and viscoplastic methods for analyzing crack run-arrest behavior in reactor vessels. The analysis methods are incorporated into finite element computer programs which are under development at three separate laboratories. 22 refs., 10 figs
Mars and the early Sun
Global mean temperatures near 273 K on early Mars are difficult to explain in the context of standards solar evolution models. Even assuming maximum CO2 greenhouse warming, the required flux is approximately 15 percent too low. Here we consider two astrophysical models that could increase the flux by this amount. The first model is a nonstandard solar model in which the early Sun had a mass somewhat greater than today's mass (1.02-1.06 solar mass). The second model is based on a standard evolutionary solar model, but the ecliptic flux is increased due to focusing by an (expected) heavily spotted early Sun
Axisymmetric Stationary Solutions as Harmonic Maps
We present a method for generating exact solutions of Einstein equations in
vacuum using harmonic maps, when the spacetime possesses two commutating
Killing vectors. This method consists in writing the axisymmetric stationry
Einstein equations in vacuum as a harmonic map which belongs to the group
SL(2,R), and decomposing it in its harmonic "submaps". This method provides a
natural classification of the solutions in classes (Weil's class, Lewis' class
etc).Comment: 17 TeX pages, one table,( CINVESTAV- preprint 12/93
A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree Survey
We have measured the surface density of galaxies toward 14 X-ray-selected
cluster candidates at redshifts greater than z=0.46, and we show that they are
associated with rich galaxy concentrations. We find that the clusters range
between Abell richness classes 0-2, and have a most probable richness class of
one. We compare the richness distribution of our distant clusters to those for
three samples of nearby clusters with similar X-ray luminosities. We find that
the nearby and distant samples have similar richness distributions, which shows
that clusters have apparently not evolved substantially in richness since
redshift z =0.5. We compare the distribution of distant X-ray clusters in the
L_x--richness plane to the distribution of optically-selected clusters from the
Palomar Distant Cluster Survey. The optically-selected clusters appear overly
rich for their X-ray luminosities when compared to X-ray-selected clusters.
Apparently, X-ray and optical surveys do not necessarily sample identical mass
concentrations at large redshifts. This may indicate the existence of a
population of optically rich clusters with anomalously low X-ray emission. More
likely, however, it reflects the tendency for optical surveys to select
unvirialized mass concentrations, as might be expected when peering along
large-scale filaments.Comment: The abstract has been abridged. Accepted for publication in the
Astrophysical Journa
Flowering of kiwifruit (Actinidia deliciosa) is reduced by long photoperiods
Mature kiwifruit (Actinidia deliciosa âHaywardâ) vines grown under standard orchard management were exposed to 16-h photoperiods from the longest day in summer until after leaf fall in autumn. Photoperiod extension was achieved with tungsten halogen lamps that produced 2â8 ”mols mâ2 sâ1 photosynthetically active radiation. Long day treatments did not affect fruit dry matter or fruit weight at harvest during the growing season that the treatments were applied or during the following growing season. However, flowering was reduced by 22% during the spring following treatment application. As this reduction in flowering was not accompanied by a decrease in budbreak, the long day effect is not consistent with a delay in the onset of winter chilling. It is suggested therefore, that the observed reduction in flowering may be because of a diminution of floral evocation
Characterization of the JWST Pathfinder Mirror Dynamics Using the Center of Curvature Optical Assembly (CoCOA)
The JWST (James Webb Space Telescope) Optical Telescope Element (OTE) consists of a 6.6 meter clear aperture, 18-segment primary mirror, all-reflective, three-mirror anastigmat operating at cryogenic temperatures. To verify performance of the primary mirror, a full aperture center of curvature optical null test is performed under cryogenic conditions in Chamber A at NASA Johnson Space Center using an instantaneous phase measuring interferometer. After phasing the mirrors during the JWST Pathfinder testing, the interferometer is utilized to characterize the mirror relative piston and tilt dynamics under different facility configurations. The correlation between the motions seen on detectors at the focal plane and the interferometer validates the use of the interferometer for dynamic investigations. The success of planned test hardware improvements will be characterized by the multi-wavelength interferometer (MWIF) at the Center of Curvature Optical Assembly (CoCOA)
First principles theory of inelastic currents in a scanning tunneling microscope
A first principles theory of inelastic tunneling between a model probe tip
and an atom adsorbed on a surface is presented, extending the elastic tunneling
theory of Tersoff and Hamann. The inelastic current is proportional to the
change in the local density of states at the center of the tip due to the
addition of the adsorbate. We use the theory to investigate the vibrational
heating of an adsorbate below an STM tip. We calculate the desorption rate of H
from Si(100)-H(21) as function of the sample bias and tunnel current,
and find excellent agreement with recent experimental data.Comment: 5 pages, RevTeX, epsf file
Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces
Electron-hole excitations in the surface bands of GaAs(110) are analyzed
using constrained density-functional theory calculations. The results show that
Frenkel-type autolocalized excitons are formed. The excitons induce a local
surface unrelaxation which results in a strong exciton-exciton attraction and
makes complexes of two or three electron-hole pairs more favorable than
separate excitons. In such microscopic exciton "droplets" the
electron density is mainly concentrated in the dangling orbital of a surface Ga
atom whereas the holes are distributed over the bonds of this atom to its As
neighbors thus weakening the bonding to the substrate. This finding suggests
the microscopic mechanism of a laser-induced emission of neutral Ga atoms from
GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from:
[email protected]
Asymptotic Structure of Symmetry Reduced General Relativity
Gravitational waves with a space-translation Killing field are considered. In
this case, the 4-dimensional Einstein vacuum equations are equivalent to the
3-dimensional Einstein equations with certain matter sources. This interplay
between 4- and 3- dimensional general relativity can be exploited effectively
to analyze issues pertaining to 4 dimensions in terms of the 3-dimensional
structures. An example is provided by the asymptotic structure at null
infinity: While these space-times fail to be asymptotically flat in 4
dimensions, they can admit a regular completion at null infinity in 3
dimensions. This completion is used to analyze the asymptotic symmetries,
introduce the analog of the 4-dimensional Bondi energy-momentum and write down
a flux formula.
The analysis is also of interest from a purely 3-dimensional perspective
because it pertains to a diffeomorphism invariant 3-dimensional field theory
with {\it local} degrees of freedom, i.e., to a midi-superspace. Furthermore,
due to certain peculiarities of 3 dimensions, the description of null infinity
does have a number of features that are quite surprising because they do not
arise in the Bondi-Penrose description in 4 dimensions.Comment: 39 Pages, REVTEX, CGPG-96/5-
- âŠ