Will Tracz, our esteemed editor and Used-Program salesman, has written an entertaining, non-technical book dealing with the practice (and lack of) of software reuse. Its a collection of essays, mostly rehashed (reused?) and updated from various columns and papers published over the years.. Its a short (a bit over 200 pages) easy reading and enjoyable book (I read most of it in one sitting). Some of the essays discuss what was printed in the past and a discussion of the current status of the points.

Safeware: System Safety and Computers

Object-oriented analysis

This is cne of the r-are text books written in the discipline of Nuclear Reactor Analysis, where the author has considered the interests of both scientists and practising engineers, in addition to serving the needs of the academia. The most attractive feature of this book is a balanced treatment of theory and practice of the subject matter. The theoretical foundations of the reactor design methods are explained with simplified definitions and relevant practical illustrations. The author scans through quickly the traditional aspects of the so-called reactor physics and takes the reader through the details of the analytical aspects in a conventional manner. Hcwever, there is a definite departure from the classical method of approach in order to avoid lengthy and repetitive discussions, that are available in many standard text books on reactor physics. The chief departure fran tradition is the priority accorded to the treatment of the energy part of the problems as opposed to the spatial Dart normally devoted to by other authors . A similar unorthodox approach has been applied while dealing with the solution of the various equations by giving priority to computer oriented mrethods as opposed to the classical solutions.

Nuclear reactor analysis

Several satellite formation e ying designs and their evolution through time are investigated. Satellite formation e ying designs arederived from the linearized equations of relative motion under two-body dynamics better known as Hill’ s equations (Hill, G. W., “ Researches in the Lunar Theory,”American Journal of Mathematics , Vol. 1, No. 1, 1878, pp. 5‐26). The formations are then propagated forward in time in the presence of realistic perturbations to determine the stability of each design. Formations considered include in-plane, in-track, circular, and projected circular designs. The Draper Semianalytic Satellite Theory is used to propagate mean elements of the satellites. When perturbations disrupt the satellite formations, an effort is made to quantify the cost of formation-keeping maneuvers. The goal of this effort is to provide physical insight into satellite formation e ying design and outline the effects of realistic dynamics on those designs.

Satellite Formation Flying Design and Evolution

The operation of wireless power transfer systems with multiple transmitters (TXs) or receivers (RXs) is investigated. With multiple TXs or RXs in a limited space, couplings occur between TXs or between RXs. The frequency conditions for maximum efficiency and power transfer under such couplings are proposed. Effective resonant frequency of the TXs or the RXs is changed due to such couplings, and driving and/or resonant frequencies should therefore be adjusted accordingly. The amount and type of the required adjustments are provided. The efficiencies in these conditions are discussed. These concepts are supported by experiments with couplings between TXs or between RXs. Using the proposed frequency adjustments, 51-65-W power is transferred with 45%-57% efficiency, even with very low coupling coefficients of 0.025-0.063 from TX to RX. This improvement is significant compared to the unadjusted cases where less than 4 W is transferred with only 5%-33% efficiency.

Effect of Coupling Between Multiple Transmitters or Multiple Receivers on Wireless Power Transfer

With the recent flurry of research on satellite formation flight, a need has become apparent for a set of linearized equations that describe the relative motion of satellites under the effect of the J 2 geopotential disturbance. In the past, Hill's linearized equations of relative motion have been used to analyze relative motion between satellites, but they were not designed to capture the effect of the J 2 potential. A new set of constant-coefficient, linearized, differential equations of motion is derived. Although surprisingly similar in form to Hill's equations, they are able to capture the effects of the J 2 potential. A numerical simulator is employed to check the fidelity of the equations. It is shown that with the appropriate initial conditions, the new linearized equations of motion have periodic errors of only 0.4% over all inclinations, radii, and cluster configurations. The new linearized equations of motion also allow for insights into the effects of the J 2 disturbance on a satellite cluster including an effect called tumbling, where the cluster as a whole rotates about the vector normal to the orbital plane of the reference orbit. The differential J 2 effects are also analyzed, and the cluster configurations that minimize this effect can be determined from the new equations. Overall, a new high-fidelity set of linearized differential equations is produced that is well suited to model satellite relative motion in the presence of the J 2 potential.

High-Fidelity Linearized J Model for Satellite Formation Flight

A stereoscopic imaging system incorporates a plurality of imaging devices or cameras to generate a high resolution, wide field of view image database from which images can be combined in real time to provide wide field of view or panoramic or omni-directional still or video images.

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Stereoscopic wide field of view imaging system

The use of propellant to maintain the relative orientation of multiple spacecraft in a sparse aperture telescope such as NASA’s Terrestrial Planet Finder (TPF) poses several issues. These include fuel depletion, optical contamination, plume impingement, thermal emission, and vibration excitation. An alternative is to eliminate the need for propellant, except for orbit transfer, and replace it with electromagnetic control. Relative separation, relative attitude, and inertial rotation of the array can all be controlled by creating electromagnetic dipoles on each spacecraft, in concert with reaction wheels, and varying their strengths and orientations. Whereas this does not require the existence of any naturally occurring magnetic fields, such as the Earth’s, such fields can be exploited. Optimized designs are discussed for a generic system and a feasible design is shown to exist for a five-spacecraft, 75-m baseline TPF interferometer.

Electromagnetic Formation Flight for Multisatellite Arrays

In this paper, we consider the equations of motion of a two-spacecraft formation flying array that uses electromagnets as relative position actuators. The relative positions of the spacecraft are controlled by the forces generated between the electromagnets on the two spacecraft, and the attitudes of the spacecraft are controlled using reaction wheels. The nonlinear equations of motion for this system are linearized about a nominal operating trajectory, taken to be a steady-state spin maneuver used for deep-space interferometric observation. The linearized equations are analyzed for stability and controllability. Although the open-loop system proves to be unstable, a controllability analysis indicates that the system is fully controllable with the given suite of actuators, and is therefore stabilizable. An optimal linear feedback controller is then designed, and the closed-loop dynamics are simulated. The simulations demonstrate that the closed-loop system is indeed stable, and that linear control is a very promising technique for electromagnetic formation flight systems, despite the nonlinearity of the dynamics.

Raymond J. Sedwick

Papers

High-Fidelity Linearized J Model for Satellite Formation Flight

Stereoscopic wide field of view imaging system

Electromagnetic Formation Flight for Multisatellite Arrays

Electromagnetic formation flight dynamics including reaction wheel gyroscopic stiffening effects

Long range inductive power transfer with superconducting oscillators