2,471 research outputs found
Fixed-Base Simulator Studies of the Ability of the Human Pilot to Provide Energy Management Along Abort and Deep-Space Entry Trajectories
A simulation study has been made to determine a pilot's ability to control a low L/D vehicle to a desired point on the earth with initial conditions ranging from parabolic orbits to abort conditions along the boost phase of a deep-space mission. The program was conducted to develop procedures which would allow the pilot to perform the energy management functions required while avoiding the high deceleration or skipout region and to determine the information display required to aid the pilot in flying these procedures. The abort conditions studied extend from a region of relatively high flight-path angles at suborbital velocities while leaving the atmosphere to a region between orbital and near-escape velocity outside the atmosphere. The conditions studied included guidance from suborbital and superorbital aborts as well as guidance following return from a deepspace mission. In this paper, the role of the human pilot?s ability to combine safe return abort procedures with guidance procedures has been investigated. The range capability from various abort and entry conditions is also presented
A comparison of laser based ranging systems for AR/C category 1: Hardware
This paper will present some aspects of the effect of inherent laser effects on the performance of CW-Tone modulated and FM-CW laser ranging techniques. It will be shown that performance of these techniques is affected in different ways by inherent laser characteristics and previous comparisons of the techniques should be modified to reflect more realistic conditions. An overall survey of laser ranging will be given to place the CW and FM-CW techniques in perspective. It will be seen that the newly introduced FM-CW laser radar has potentially far superior performance to CW-Tone modulated systems now proposed for use in space rendezvous and capture systems
A comparison of laser-based ranging systems for AR/C
The three most common types of laser target ranging (time-of-flight, tone modulated, and FM-CW) are discussed in terms of principle of operation. The first, time-of-flight, is shown to depend more on the ability of support electronics than the fundamentals of the concept. Examples in the literature are cited to show the remarkably good performance of time-of-flight systems. A system developed in Finland was shown to have an incremental ranging capability of a few millimeters. The system is not only robust; it does not include additions such as reference legs and the like, which are expected, for improvement in performance. Though not immediately obvious, the second technique, tone modulated ranging is somewhat of an extension of the time-of-flight technique. Finally, the FM-CW technique is presented. This is completely different from the tone or time-of-flight techniques, but is a direct translation of the same-named technique used in radar ranging systems
A Phase Space Approach to Gravitational Enropy
We examine the definition S = ln Omega as a candidate "gravitational entropy"
function. We calculate its behavior for gravitationl and density perturbations
in closed, open and flat cosmologies and find that in all cases it increases
monotonically. Using the formalism to calculate the gravitational entropy
produced during inflation gives the canonical answer. We compare the behavior
of S with the behavior of the square of the Weyl tensor. Applying the formalism
to black holes has proven more problematical.Comment: Talk delivered at South African Relativistic Cosmology Symposium, Feb
1999. Some new results over Rothman and Anninos 97. To appear in GRG, 17
page
Methods of fitting multivariant functional models in the area of large computer exploita- tion final report, 23 may 1963 - 23 jul. 1965
Methods of fitting multivariant functional models in area of large computer exploitatio
Building from the Ground Up: Creating Effective Programs to Mentor Children of Prisoners (The Amachi Model)
Drawing from P/PVs five years of hands-on experience designing and implementing Amachi programs around the country, Building From The Ground Up describes best practices for planning, developing and managing a mentoring-children-of-prisoners program. This guidebook is essential for learning the professional procedures, standards and administrative tools required to have an effective program
Sources of oscillation frequency increase with rising solar activity
We analyze and interpret SOHO/MDI data on oscillation frequency changes
between 1996 and 2004 focusing on differences between activity minimum and
maximum of solar cycle 23. We study only the behavior of the centroid
frequencies, which reflect changes averaged over spherical surfaces. Both the
f-mode and p-mode frequencies are correlated with general measures of the sun's
magnetic activity. However, the physics behind each of the two correlations is
quite different. We show that for the f-modes the dominant cause of the
frequency increase is the dynamical effect of the rising magnetic field. The
relevant rise must occur in subphotospheric layers reaching to some 0.5 - 0.7
kG at a depth of about 5 Mm. However, the implied constraints also require the
field change in the atmosphere to be so small that it has only a tiny dynamical
effect on p-mode frequencies. For p-modes, the most plausible explanation of
the frequency increase is a less than 2 percent decrease in the radial
component of the turbulent velocity in the outer layers. Lower velocity implies
a lower efficiency of the convective transport, hence lower temperature, which
also contributes to the p-mode frequency increase.Comment: ApJ, accepte
Gravitational Entropy and Quantum Cosmology
We investigate the evolution of different measures of ``Gravitational
Entropy'' in Bianchi type I and Lema\^itre-Tolman universe models.
A new quantity behaving in accordance with the second law of thermodynamics
is introduced. We then go on and investigate whether a quantum calculation of
initial conditions for the universe based upon the Wheeler-DeWitt equation
supports Penrose's Weyl Curvature Conjecture, according to which the Ricci part
of the curvature dominates over the Weyl part at the initial singularity of the
universe. The theory is applied to the Bianchi type I universe models with dust
and a cosmological constant and to the Lema\^itre-Tolman universe models. We
investigate two different versions of the conjecture. First we investigate a
local version which fails to support the conjecture. Thereafter we construct a
non-local entity which shows more promising behaviour concerning the
conjecture.Comment: 20 pages, 7 ps figure
Measures of gravitational entropy I. Self-similar spacetimes
We examine the possibility that the gravitational contribution to the entropy
of a system can be identified with some measure of the Weyl curvature. In this
paper we consider homothetically self-similar spacetimes. These are believed to
play an important role in describing the asymptotic properties of more general
models. By exploiting their symmetry properties we are able to impose
significant restrictions on measures of the Weyl curvature which could reflect
the gravitational entropy of a system. In particular, we are able to show, by
way of a more general relation, that the most widely used "dimensionless"
scalar is \textit{not} a candidate for this measure along homothetic
trajectories.Comment: revtex, minor clarifications, to appear in Physical Review
On the evolution of a large class of inhomogeneous scalar field cosmologies
The asymptotic behaviour of a family of inhomogeneous scalar field
cosmologies with exponential potential is studied. By introducing new variables
we can perform an almost complete analysis of the evolution of these
cosmologies. Unlike the homogeneous case (Bianchi type solutions), when k^2<2
the models do not isotropize due to the presence of the inhomogeneitiesComment: 23 pages, 1 figure. Submitted to Classical and Quantum Gravit
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