Identification Techniques for SARSAT Signals

A process for the identification of emergency locator transmitter (ELT) signals related to search and rescue satellite-aided tracking (SARSAT) is presented. The ELT identification process is particularly important in order to increase the probability of detection and eliminate sources of interference from the data set. A set of ELT signal parameters is introduced and methods for estimating these parameters are developed. A theoretical analysis and performance evaluation of these methods is provided.     

The Delivery of Water During Terrestrial Planet Formation

The planetary building blocks that formed in the terrestrial planet region were likely very dry, yet water is comparatively abundant on Earth. Here we review the various mechanisms proposed for the origin of water on the terrestrial planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local planetesimals in the terrestrial planet region or into the planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the terrestrial planet region as the planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant planets begin roughly in their final locations and the disk of planetesimals and embryos in the terrestrial planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant planets implants material from beyond the snow line into the asteroid belt and terrestrial planet region, where it can be accreted by the growing planets. Sufficient water is delivered to the terrestrial planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the terrestrial planets.     

Adaptive Input Filter Compensation for Switching Regulators

An input filter is frequently employed between a switching regulator and its power source. However, its presence often results in degradation of dynamic performances and stability. The detrimental interaction is between an input filter and a switching regulator and is a function of the input filter parameters and also of the supply voltage. An earlier paper presented an analysis and design procedure aimed at developing a feed-forward loop to cancel this undesirable interaction. The feed-forward design is extended here to encompass a scheme that automatically accounts for changes in the supply voltage; the result is an adaptive compensation that tracks the input voltage variations. Experimental results are presented that confirm the adaptive nature of the design.     

A low cost steerable radio-telescope

We present the technical characteristics of a low-cost radio telescope for solar/non solar observations at decimetric (1200–1700 MHz) and centimetric (2700 and 5000 MHz) wavelengths known as Brazilian Decimetric Array (BDA). The technical specifications of the antenna, tracking system, log-periodic feed, preamplifier and the frequency-synthesised receiver with a Single Side Band (SSB) video output of 2.5 MHz are given.     

Ultra-reliable real-time control systems-future trends

Today's aircraft use ultra-reliable real-time controls for demanding functions such as Fly-By-Wire (FBW) flight control. Future aircraft, spacecraft and other vehicles will require greater use of these types of controls for functions that currently are allowed to fail, fail to degraded operation, or require human intervention in response to failure. Fully automated and autonomous functions will require ultra-reliable control. But ultra-reliable systems are very expensive to design and require large amounts of on-board equipment. This paper will discuss how the use of low-cost sensors with digital outputs, digitally commanded fault-tolerant actuation devices and interconnecting networks of low-cost data buses offer the promise of more affordable ultra-reliable systems. Specific technologies and concepts to be discussed include low-cost automotive and industrial data buses, “smart” actuation devices with integral fault masking capabilities, management of redundant sensors, and the fault detection and diagnosis of the data network. The advantages of integrating the control and distribution of electrical power with the control system will be illustrated. The design, installation, and upgrade flexibility benefits provided by an all-digital and shared network approach will be presented. The economic benefits of systems that can operate following failure and without immediate repair will be reviewed. The inherent ability of these redundant systems to provide effective built-in test and self-diagnostics capabilities will be described. The challenges associated with developing ultra-reliable software for these systems and the difficulties associated with exhaustive verification testing will be presented as will additional development hurdles that must be overcome     

Shock Wave Interaction with the Magnetopause

The magnetopause is in continuous motion and shock waves and impulsive acceleration events can occur. As an example, we show that the interaction of an interplanetary shock with the bow shock can generate a shock wave that after passing through the magnetosheath can interact with the magnetopause. In fluid dynamics, when a shock wave encounters a fluid discontinuity, the interface may become unstable and form bubbles and spikes. We consider this Richtmyer-Meshkov instability in magnetohydrodynamics. At the dayside magnetopause, the instability tends to be stabilized by the magnetic field. However, the shock wave interaction can initiate magnetic field reconnection for the southward IMF, which may be important in strong interplanetary shock events. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the convergence of iterative methods for bearings-only tracking

This paper deals with the analysis of the convergence of iterative methods for bearings only tracking (BOT). A geometric and unified framework is developed. Explicit sufficient conditions ensuring convergence of iterative methods for maximization of the likelihood functional are then derived