Stochastic battery discharge in portable communication devices

The objective of this work is to explore ways in which performance of battery systems can be enhanced through the use of energy-efficient battery management techniques. The phenomenon of charge recovery that takes place under pulsed discharge conditions is identified as a mechanism that can be exploited to enhance the capacity of a cell in a portable communication device. The bursty nature of many data traffic sources suggests that data transmissions in communication devices may provide natural opportunities for charge recovery. We model the data source as a stochastic process and let the cell discharge be driven by such a process. We use a model of a dual lithium ion insertion cell to identify the improvement to cell capacity that results from the stochastic discharge. The insight from this study leads us to propose discharge shaping techniques that tradeoff energy efficiency with delay in the required current supply     

ARTEMIS Mission Design

The ARTEMIS mission takes two of the five THEMIS spacecraft beyond their prime mission objectives and reuses them to study the Moon and the lunar space environment. Although the spacecraft and fuel resources were tailored to space observations from Earth orbit, sufficient fuel margins, spacecraft capability, and operational flexibility were present that with a circuitous, ballistic, constrained-thrust trajectory, new scientific information could be gleaned from the instruments near the Moon and in lunar orbit. We discuss the challenges of ARTEMIS trajectory design and describe its current implementation to address both heliophysics and planetary science objectives. In particular, we explain the challenges imposed by the constraints of the orbiting hardware and describe the trajectory solutions found in prolonged ballistic flight paths that include multiple lunar approaches, lunar flybys, low-energy trajectory segments, lunar Lissajous orbits, and low-lunar-periapse orbits. We conclude with a discussion of the risks that we took to enable the development and implementation of ARTEMIS.     

Dawn Science Planning, Operations and Archiving

The Dawn science operations team has designed the Vesta mission within the constraints of a low-cost Discovery mission, and will apply the same methodology to the Ceres mission. The design employs proactive mapping mission strategies and tactics such as functional redundancy, adaptability to trajectory uncertainties, and easy sequence updates to deliver reliable and robust sequences. Planning tools include the Science Opportunity Analyzer and other multi-mission tools, and the Science time-ordered listings. Science operations are conducted jointly by the Science Operations Support Team at the Jet Propulsion Laboratory (JPL) and the Dawn Science Center at the University of California, Los Angeles (UCLA). The UCLA Dawn Science Center has primary responsibility for data archiving while the JPL team has primary responsibility for spacecraft and instrument operations. Constraints and uncertainties in the planning and sequencing environment are described, and then details of the science plan are presented for each mission sub-phase. The plans indicate that Dawn has a high probability of meeting its science objectives and requirements within the imposed constraints.     

Geomagnetic Observations for Main Field Studies: From Ground to Space

Direct measurements of the geomagnetic field have been made for more than 400 years, beginning with individual determinations of the angle between geographic and magnetic North. This was followed by the start of continuous time series of full vector measurements at geomagnetic observatories and the beginning of geomagnetic repeat stations surveys in the 19th century. In the second half of the 20th century, true global coverage with geomagnetic field measurements was accomplished by magnetometer payloads on low-Earth-orbiting satellites. This article describes the procedures and instruments for magnetic field measurements on ground and in space and covers geomagnetic observatories, repeat stations, automatic observatories, satellites and historic observations. Special emphasis is laid on the global network of geomagnetic observatories.     

Shaping peace

Soviet General Secretary Gorbachev, in his January 1986 speech, expressed a hope that the level of nuclear weapons would before long be greatly reduced. The Soviet Embassy in Sri Lanka invited Arthur C. Clarke to comment on the General Secretary's speech. This article is his response.     

Effect of variable thermal properties of the solid phase on composite solid propellant combustion

Effects of variable thermal properties (specific heat and thermal conductivity) of the solid phase on the combustion of composite solid propellants are studied analytically. Both steady and unsteady burning are considered. It is shown that the effects of variable thermal properties are small and can be accounted for by choosing proper average values of specific heat and thermal conductivity.     

A relative navigation system for formation flight

A relative navigation system based on both the Inertial Navigation System (INS) and the Global Positioning System (GPS) is developed to support situational awareness during formation flight. The architecture of the system requires an INS/GPS integration across two aircraft via a data link. A fault-tolerant federated filter is used to estimate the relative INS errors based on relative GPS measurements and a range measurement obtained from the data link. The filter is constructed based on a reduced-order model of the relative INS error process. A method for analyzing the filter performance is presented. A case involving two helicopters in formation flight is studied under three different night trajectories to account for the effect of vehicle motion on the INS state transition matrix. The results of the covariance analysis are compared with actual night results over an instrumented test range.     

Advances in non-linear apodization

Selected new methods and applications of non-linear apodization for irregularly-shaped and parse coherent apertures and arrays are presented. The benefits include unproved impulse response performance, i.e., reduced peak sidelobes and integrated sidelobe power, along with improved mainlobe resolution, compared to classic windowing techniques. Nonlinear apodization (NLA) techniques can also serve as powerful engines for effective superresolution and bandwidth extrapolation of coherent data for filling sparse apertures. The sparse aperture filling property of superresolution algorithms for radar data forms the basis for a new concept which is introduced here: synthetic multiple aperture radar technology (SMART). Increased swath and/or reduced antenna size are some of the benefits postulated for SMART applied to synthetic aperture radar (SAR) systems. The benefits of these new methods and applications for nonlinear apodization are then demonstrated for two specific applications: 1) sidelobe control for Y-type synthetic aperture radiometers, such as the European Soil Moisture and Ocean Salinity (SMOS) system (Kerr et al.) and JPL's proposed GeoSTAR (Lambrigsten) concept; and, 2) filling of sparse synthetic aperture radar data by exploiting the bandwidth extrapolation properties of nonlinear apodization based superresolution techniques. The methods that have been developed and demonstrated herein have potential application to a wide range of passive and active microwave remote sensing and radar systems.     

Security Systems Research and Testing Laboratory at Edith Cowan University

The testing and evaluation of sophisticated security systems has remained in the domain of governments in national facilities and the commercial security industry through manufacturers and engineering consultants. As well, the production of testing protocols and industry standards has been developed by national organisations, professional security, and engineering bodies in the appropriate security fields. The Security Systems Research and Testing Laboratory in the School of Engineering and Mathematics at Edith Cowan University (ECU), Perth, Western Australia has commenced operations in research, testing, and evaluation of security systems. This paper wir describe the first year of operation of the Security Systems Research and Testing Laboratory, and will describe the role that testing and evaluation of security systems plays in the education and training of Security Science graduates, as well as the benefits that the Laboratory brings to the security industry through its testing programme.     

A novel resonant converter topology for DC-to-DC power supply

A class-E DC-to-DC converter with half-wave controlled current rectifier is proposed. Its output voltage is controlled by the conduction angle of the rectifier switch at constant switching frequency. Zero voltage switching for all the switches can be maintained from full load to no load. Its steady state characteristics are analyzed and the effects of the circuit parameters are studied. Some extensions of the proposed converter are also discussed. The analysis is verified by PSPICE simulation and an experimental prototype