J. L. Norman Violette
Associate Editor
This book is part of a three-volume series that “cover introductory and advanced concepts in interference analysis and mitigation for wireless personal communications.” The first volume provides a generalized description of launch vehicles including several satellite systems being built for worldwide access to personal communication services, such as Iridium, Globalstar, Teledesic, and Odyssey systems. Concepts of LEO, MEO, and GEO orbits used by these satellite systems are also presented.
The multiple uses of satellite systems (navigation, surveillance, communications, broadcast applications, etc.) are briefly described. The basic spacecraft structural and power distribution requirements are described and illustrated. The attitude and articulation control subsystem (AACS) that assures that the spacecraft is placed in a precise orbital location and maintains the required attitude is described. Other subsystems presented as introduction include command and data handling, thermal, and propulsion control, and a variety of mechanical devices, instruments, and sensors. Payload functions and electrical connections for signal and power distribution are described briefly.
Overviews of personal and mobile satellite communications provides descriptions and illustrations of satellite communications networks including descriptions of launch vehicles and launch scenarios. The advantages and disadvantages of geostationary earth orbits (GEO) and low earth orbits (LEO) are described.
Fundamental concepts of space mechanics are presented to help understand the inner workings of the attitude and articulation control (guidance) subsystem (AACS). Chapter sections describe the two-body central force motion; orbital determination; Keplerian (circular, elliptical, parabolic, and hyperbolic) orbits; and satellite earth area coverage. Descriptions of orbital terminology conclude the chapter.
This chapter contains detailed descriptions of space concepts and subsystems and associated basic electronic circuits. The techniques and subsystems that essentially control the attitude and stabilization of a satellite are described. The physical principles and electrical functional block diagrams of a satellite AACS and sun sensors are presented and illustrated.
Oscillation problems and possible solutions in sun-sensor operational amplifier circuits are described. Grounding techniques for proper operational amplifier performance are illustrated.
The physical principles of momentum/reaction wheels that add stability against distorting torques, absorb cyclic torques, and transfer momentum to the satellite body are described and the drive electronics functionally illustrated. The noise problems generated in these reaction wheel assemblies are introduced and addressed in more detail later in the book. Noise generation and suppression in motor drive circuits are described and illustrated.
Other topics developed include intrinsic noise in operational amplifiers; a description of the physical principles of a star camera and associated noise concerns; noise in amplifier circuits; spectral (Fourier) representation of digital waveforms; simple electromagnetic noise coupling; descriptions of common-mode and differential-mode currents; satellite inertial measurement unit (IMU); noise issues in analog-to-digital (A/D) converters; noise concerns in high- speed A/D converters; noise figure in op- amps; total noise output; proper power supply decoupling in op-amps; and fundamentals of op-amp grounding.
This chapter addresses the various elements of satellite power systems including: solar energy and power; solar cells and radiation; solar arrays; the space environment and radiation damage to solar cells; noise in switching-mode power supplies (SMPS), including input noise, input ripple noise, input inrush current limit, conducted interference, and sources of interference generated in the SMPS including EMI from diodes, silicon-controlled rectifiers, and power transistors. Interference paths in SMPS are described and illustrated. A section is provided on a study in the proper design of grounding for SMPS converters in printed circuit boards (PCBs). This includes transient effects in SMPSs, and proper grounding to suppress these transient effects. Energy storage (batteries) and battery charging and power control are described. Stresses on satellite power systems due to wide temperature variations are described.
This (C&DH) subsystem provides communications to and from the spacecraft. A brief overview is presented of satellite command C&DH systems including requirements for such a system with block diagrams provided to illustrate parts of the system. Fundamentals of modulation theory and coding are presented. Worst-case analysis guidelines are included for analog and digital design with examples of use in C&DH subsystems. Details of factors affecting propagation delays are addressed including timing analysis. Noise issues in satellite telecommunications subsystems are addressed, including uplink/downlink models.
Detailed developments are provided on transponder functions. Included are descriptions of travelling wave tube amplifiers (TWTAs), intermodulation distortion, and multiple access techniques in satellites (TDMA, CDMA, FDMA).
Some fundamentals of antenna theory are presented which provide basic concepts useful for understanding more specific satellite antenna developments that follow. Antenna basics presented include near-field and far-field concepts, antenna gain, power relationships, electromagnetic wave propagation, antenna factor, and antenna interference coupling model. Satellite antenna concepts include satellite coverage area, phased array antennas, lens and reflector antennas, feed systems, pulse-forming networks, unfurlable antennas, and multibeam frequency reuse in mobile communications.
Concepts of space physics are introduced that describe the natural electromagnetic environment encountered by orbiting spacecraft. The presence of plasmas that result in spacecraft charging is briefly described. Typical environmental parameters encountered at geosynchronous altitudes, and those encountered during auroral activity in low-altitude polar orbits, are presented. The effects of electron energy, and other factors due to spacecraft charging, are described. The author suggests assuming that the spacecraft be visualized as a Langmuir probe, used in laboratory plasma experiments, in order to facilitate understanding spacecraft charging. The remainder of the chapter provides additional descriptions of charging environments and charging currents, differential charging, surface potential differences, and arcing (electrostatic discharge, or ESD). The latter discharging is the primary mechanism by which charging disturbs spacecraft. Methods and models are provided to analyze the coupling of the discharge transient to the spacecraft structure and cables. A recommended analysis approach is illustrated. Parameters and threshold levels for component/circuit upset and damage are provided.
A list of References and an Index are included.
The book is well-written by a knowledgeable author. This Volume I provides an excellent, easy-to-read introduction to space communication systems. It can be used by itself for an introductory course at the college undergraduate level and as a ready-reference for practicing engineers. It also leads to Volumes II and III for more details on space communication techniques.