Telerobotics: problems and research needs

With major emphasis on simulation, a university laboratory telerobotics facility permits problems to be approached by groups of graduate students. Helmet-mounded displays provide realism; the slaving of the display to the human operator's viewpoint gives a sense of `telepresence' that may be useful for prolonged tasks. Using top-down 3-D model control of distant images allows distant images to be reduced to a few parameters to update the model used for display to the human operator in a preview model to circumvent, in part, the communication delay. Also, the model can be used as a format for supervisory control and permit short-term local autonomous operations. Image processing algorithms can be made simpler and faster without trying to construct sensible images from the bottom. Control studies of telerobots lead to preferential manual control modes and, in this university environment, to basic paradigms for human motion and thence, perhaps, to redesign of robotic control, trajectory path planning, and rehabilitation prosthetics. Speculation as to future industrial drives for this telerobotic field suggests efficient roles for government agencies such as NASA     

Silent energy source for tactical applications

Power source requirements for the Soldier System, which includes all items/equipment worn, consumed, or carried by the soldier in the field for his or her individual use, are discussed. The use of fuel cells, which offer silence and high efficiency, is considered. It is concluded that the proton exchange membrane (PEM) fuel cell coupled with a good hydrogen source offers a very attractive power source for the Soldier System and for other portable requirements needing power in the range of 50 to 500 W     

Atmospheric Attenuation Models for Satellite-To-Earth Links

In an earlier paper by the authors1 it was mentioned that atmospheric attenuation effects could be included by assuming that the attenuation is directly proportional to number of air masses. While this assumption is valid for the optical region, it is not true in the microwave region (1 to 40 GHz). For a clear atmosphere, the two constituents which absorb microwaves are oxygen and water vapor. An analysis of the atmospheric attenuation data for the microwave region has been made and some rather simple expressions for computing the attenuation as a function of zenith angle are developed with an accuracy suitable for satellite antenna footprint calculations.     

A polytropic model for the solar wind

The solar wind fills the heliosphere and is the background medium in which coronal mass ejections propagate. A realistic modelling of the solar wind is therefore essential for space weather research and for reliable predictions. Although the solar wind is highly anisotropic, magnetohydrodynamic (MHD) models are able to reproduce the global, average solar wind characteristics rather well. The modern computer power makes it possible to perform full three dimensional (3D) simulations in domains extending beyond the Earth’s orbit, to include observationally driven boundary conditions, and to implement even more realistic physics in the equations. In general, MHD models for the solar wind often make use of additional source and sink terms in order to mimic the observed solar wind parameters and/or they hide the not-explicitly modelled physical processes in a reduced or variable adiabatic index. Even the models that try to take as much as possible physics into account, still need additional source terms and fine tuning of the parameters in order to produce realistic results. In this paper we present a new and simple polytropic model for the solar wind, incorporating data from the ACE spacecraft to set the model parameters. This approach allows to reproduce the different types of solar wind, where the simulated plasma variables are in good correspondence with the observed solar wind plasma near 1 AU.     

Why should the latitude of the observer be considered when modeling gradual proton events? An insight using the concept of cobpoint

The shape of flux profiles of gradual solar energetic particle (SEP) events depends on several not well-understood factors, such as the strength of the associated shock, the relative position of the observer in space with respect to the traveling shock, the existence of a background seed particle population, the interplanetary conditions for particle transport, as well as the particle energy. Here, we focus on two of these factors: the influence of the shock strength and the relative position of the observer. We performed a 3D simulation of the propagation of a coronal/interplanetary CME-driven shock in the framework of ideal MHD modeling. We analyze the passage of this shock by nine spacecraft located at ∼0.4 AU (Mercury’s orbit) and at different longitudes and latitudes. We study the evolution of the plasma conditions in the shock front region magnetically connected to each spacecraft, that is the region of the shock front scanned by the “cobpoint” (Heras et al., 1995), as the shock propagates away from the Sun. Particularly, we discuss the influence of the latitude of the observer on the injection rate of shock-accelerated particles and, hence, on the resulting proton flux profiles to be detected by each spacecraft.     

Modelling of Solar Wind, CME Initiation and CME Propagation

Simulations of coronal mass ejections (CMEs) evolving in the interplanetary (IP) space from the Sun up to 1 AU are performed in the framework of ideal magnetohydrodynamics (MHD) by the means of a finite-volume, explicit solver. The aim is to quantify the effect of the background solar wind and of the CME initiation parameters, such as the initial magnetic polarity, on the evolution and on the geo-effectiveness of CMEs. First, three different solar wind models are reconstructed using the same numerical grid and the same numerical scheme. Then, different CME initiation models are considered: Magnetic foot point shearing and magnetic flux emergence. For the fast CME evolution studies, a very simple CME model is considered: A high-density and high-pressure magnetized plasma blob is superposed on a background steady state solar wind model with an initial velocity and launch direction. The simulations show that the initial magnetic polarity substantially affects the IP evolution of the CMEs influencing the propagation velocity, the shape, the trajectory (and thus, the geo-effectiveness).     

Portable power source needs of the future Army-batteries and fuelcells

This paper describes the US Army's future needs for silent portable power in the area of batteries and fuel cells. These needs will continue to increase as a result of the introduction of newer types of equipment, the increasing digitization of the battlefield, and future integrated Soldier Systems. Current battery programs are aimed at improved, low-cost primary batteries, and rechargeable batteries with increased energy densities. The Army fuel cell program aimed at portable systems capable of the order of 150 W is also described     

Ambiguity Resolution in Interferometry

A comprehensive theory of interferometry from a system viewpoint with particular emphasis on the ambiguity resolution problem is developed. The derived error equations include contributions from all system uncertainties, i.e., phase measurement, frequency, and element phase center position errors in three dimensions. The direction-of-arrival errors are inversely proportional to the interferometer baseline and it is customary to make the baseline large enough to meet the accuracy requirements. A system with a baseline greater than a half-wavelength results in the well known direction-of-arrival ambiguity problem with the addition of a third element to each baseline being a common method for resolving the ambiguity. It is shown that contrary to previous thinking there are many equally optimal positions for adding the third element to resolve the ambiguity. In addition, it is shown how the measurement made to resolve the ambiguity can also be applied to increase the accuracy of the angle-of-arrival measurement. A central result is the derivation of expressions specifying the probability of correct resolution of ambiguities as a function of system parameters and system errors. Moreover the concept of an acceptance criterion designed to reduce processing of erroneous measurements is developed. Narrowing the criterion reduces the percentage of data accepted for processing, but increases the probability of correct ambiguity resolution. This is analogous to the relationship between the probability of detection and the probability of false alarm in radar theory.     

迈卓诺光笔测量仪:树立了便携式大尺寸坐标测量系统的新基准

在航空行业的精密测量领域,用于大尺寸的光学测量仪得到了较多应用.