Permanent-Magnet Linear Alternators Part 1: Fundamental Equations

Powered by free-piston Stirling engines, linear alternators are proposed for space power stations as well as for isolated domestic applications, automotive, and on-Earth solar power plants. As the literature on the subject is sparse and base-design oriented, we present the general equations for both three-phase and single-phase winding configurations having permanent-magnet field excitations.     

An Adaptive Multiple-Beam Transmitter for Satellite Communications

A multiple-beam satellite communications system that can adaptbeam power to varying beam traffic is proposed. A new type active-array fed, single reflector antenna design and an S band, 5-beamsystem concept including interbeam exchange are described. Basedon these concepts, a high EIRP multiple-beam system with trafficadaptability similar to a single-beam system is realized.     

Software intensive systems safety analysis

Two important elements in the avionics suite of modern aircraft are: the flight control system (FCS) and the flight management system (FMS). The FCS provides the capability to stabilize and control the aircraft, while the FMS is responsible for flight planning and navigation. A clear trend in the aerospace industry is to place greater reliance on software systems, and many FCS and FMS subsystems are implemented primarily in software. For example, within the FCS is the flight guidance system (FGS) that generates roll and pitch guidance commands. Similarly, within the FMS is the vertical navigation (VNAV) function that acts like a third crew member in the cockpit, ordering mode change requests and resetting target altitude values to enable the aircraft to track the vertical flight plan. We have developed formal, executable models of the requirements for the mode logic of a FGS and for portions of the VNAV functionality. We have also conducted a comprehensive software safety analysis on the FGS mode logic model, and are completing the analysis of the VNAV model. This analysis uses as its starting point several "traditional" safety analysis techniques such as a functional hazard assessment (FHA), a fault tree analysis (FTA), and a failure mode effects analysis (FMEA). However, we are also using formal methods techniques known as model checking and theorem proving to verify the presence of safety properties in the model. This paper summarizes the (now completed) safety analysis that was performed on the FGS model, and highlights the similarities and differences with the (still on-going) safety analysis of the FMS model. In particular, we summarize progress made to date in the use of formal methods to verify the presence of the required safety properties in the models themselves.     

Broadband light source for fiber-optic measurement system in spaceborne applications

Measuring temperatures, mechanical loads and derived quantities precisely and reliably play an important role in spaceflight. With spacecraft becoming increasingly complex, upscaling of present telemetry techniques can become cumbersome. Additionally, there are entirely new sensory requirements, resulting from emerging technologies such as smart structures, active vibration damping and composite material health monitoring. It has been demonstrated in preceding studies that these measurements can be advantageously and efficiently carried out by means of fiber-optic systems. The most prominent fiber-optic strain and temperature sensor is the fiber Bragg grating. Typically, multiple fiber Bragg gratings are used to translate entire temperature and strain fields into an optical wavelength information. For the interrogation of these sensors, a broadband or scanning light source is required. Additional requirements with respect to the light source are high intensity and unpolarized illumination of the gratings. These constraints can be met by a light source that is based on amplified spontaneous emission in a rare-earth-doped fiber. In the presented work, a compact light source, adapted for measurement applications and targeted towards space applications, has been developed. The design of this light source is presented, as well as its implementation. The light source has been designed and tested for selected core aspects of space robustness and the results of these tests are summarized.     

Spatial Thinking Across the College Curriculum: A Report on a Specialist Meeting

This report presents findings from a specialist meeting of spatially-minded researchers and administrators from education and industry to consider prospects for introducing courses and curricula on spatial thinking in higher education. More than 40 participants explored the rationale for expanding student exposure to concepts, tools, and applications of spatial reasoning across a range of science, engineering, and humanities disciplines. The focus was on what we know and what we need to know to make the case for space, underscoring basic research on what is meant by spatial thinking and on variations in the spatial reasoning skills required in different domains of knowledge. The need for rigorous assessments of learning outcomes associated with different approaches to teaching spatial thinking was emphasized.     

Earth–Moon libration point orbit stationkeeping: Theory,modeling, and operations

Collinear Earth–Moon libration points have emerged as locations with immediate applications. These libration point orbits are inherently unstable and must be maintained regularly which constrains operations and maneuver locations. Stationkeeping is challenging due to relatively short time scales for divergence, effects of large orbital eccentricity of the secondary body, and third-body perturbations. Using the Acceleration Reconnection and Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission orbit as a platform, the fundamental behavior of the trajectories is explored using Poincaré maps in the circular restricted three-body problem. Operational stationkeeping results obtained using the Optimal Continuation Strategy are presented and compared to orbit stability information generated from mode analysis based in dynamical systems theory.     

On the Measurements of D/H in QSO Absorption Systems Closing in on the primordial abundance of deuterium

We present our measurements of the deuterium to hydrogen ratio (D/H) in QSO absorption systems, which give D/H = 3.40 ± 0.25 × 10-5 based on analysis of four independent systems. We discuss the properties of two systems which provide the strongest constraints on D/H. We outline the systematic effects involved in measurements of D/H and introduce a sophisticated method of analysis which properly accounts for these effects.     

Solar Models with Non-Standard Chemical Composition

The OPAL monochromatic opacity tables are used to evaluate the impact of a non-standard chemical composition on solar models. A calibrated solar model with consistent diffusion including the effect of radiative forces and ionization on drift velocities is presented. It is shown that surface abundances are predicted to change slightly more than in traditional solar models where these refinements are not included. All elements included in the model settle at similar rates which is reflected in the relative variation in surface abundances ranging from 7.5% for calcium to 8.8% for argon. The structural difference between the consistent model and the traditional model is small, with a maximum effect of 0.3% for the isothermal sound speed at the base of the convection zone. The settling of CNO is only marginally affected. Opacity profiles have also been calculated with varying abundances for volatile elements, for which the abundances are poorly known, and other selected elements. It is shown that if one allows a 10% variation of these elements individually one can expect a peak Rosseland mean opacity variation of 3% for oxygen, a little less 2% for Si and Ne, and around 1% for Mg and S in the radiative zone. Other light metals and volatile elements have no significant impact on the opacity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of track structure and radioprotectors on the induction of oncogenic transformation in murine fibroblasts by heavy ions

The oncogenic potential of high-energy ⁵⁶Fe particles (1 GeV/nucleon) accelerated with the Alternating Gradient Synchrotron at the Brookhaven National Laboratory was examined utilizing the mouse C3H 10T1/2 cell model. The dose-averaged LET for high-energy ⁵⁶Fe is estimated to be 143 keV/μm with the exposure conditions used in this study. For ⁵⁶Fe ions, the maximum relative biological effectiveness (RBE_max) values for cell survival and oncogenic transformation were 7.71 and 16.5 respectively. Compared to 150 keV/μm ⁴He nuclei, high-energy ⁵⁶Fe nuclei were significantly less effective in cell killing and oncogenic induction. The prostaglandin E₁ analog misoprostol, an effective oncoprotector of C3H 10T1/2 cells exposed to X rays, was evaluated for its potential as a radioprotector of oncogenic transformation with high-energy ⁵⁶Fe. Exposure of cells to misoprostol did not alter ⁵⁶Fe cytotoxicity or the rate of ⁵⁶Fe-induced oncogenic transformation.