9,292 research outputs found
Guidance methods for low-thrust space vehicles Cumulative progress report, 1 Jan. 1969 - 31 Jan. 1970
Guidance and control schemes for optimal low-thrust Earth-Mars transfer mission
Simple models for the shuttle remote manipulator system
The investigation is aimed at establishing a series of simple models which can be used to study the forces and moments which occur due to the reaction control system (RCS) jet plume firings during a deployment or retrieval of an IUS type payload. The models considered in this investigation are primarily planar in nature. In this study primary attention is given to the roles the payload play in determining the overall moments on the remote manipulator system arm
Proton-induced noise in digicons
The Space Telescope, which carries four Digicons, will pass several times per day through a low-altitude portion of the radiation belt called the South Atlantic Anomaly. This is expected to create interference in what is otherwise anticipated to be a noise-free device. Two essential components of the Digicon, the semiconductor diode array and the UV transmitting window, generate noise when subjected to medium-energy proton radiation, a primary component of the belt. These trapped protons, having energies ranging from 2 to 400 Mev and fluences at the Digicon up to 4,000 P+/sec-sq cm, pass through both the window and the diode array, depositing energy in each. In order to evaluate the effect of these protons, engineering test models of Digicon tubes to be flown on the High Resolution Spectrograph were irradiated with low-flux monoenergetic proton beams at the University of Maryland cyclotron. Electron-hole pairs produced by the protons passing through the diodes or the surrounding bulk caused a background count rate. This is the result of holes diffusing over a distance of many diode spacings, causing counts to be triggered simultaneously in the output circuits of several adjacent diodes. Pulse-height spectra of these proton-induced counts indicate that most of the bulk-related counts overlap the single photoelectron peak. A geometrical model will be presented of the charge collection characteristics of the diode array that accounts for most of the observed effects
Lattice-Gas Simulations of Ternary Amphiphilic Fluid Flow in Porous Media
We develop our existing two-dimensional lattice-gas model to simulate the
flow of single-phase, binary-immiscible and ternary-amphiphilic fluids. This
involves the inclusion of fixed obstacles on the lattice, together with the
inclusion of ``no-slip'' boundary conditions. Here we report on preliminary
applications of this model to the flow of such fluids within model porous
media. We also construct fluid invasion boundary conditions, and the effects of
invading aqueous solutions of surfactant on oil-saturated rock during
imbibition and drainage are described.Comment: 9 pages, 6 figures (1 and 6 are in color), RevTeX with epsf and
graphic
- …