Synchronous response modelling and control of an annular momentum control device

Research on the synchronous response modelling and control of an advanced Annular Momentun Control Device (AMCD) used to control the attitude of a spacecraft is described. For the flexible rotor AMCD, two sources of synchronous vibrations were identified. One source, which corresponds to the mass unbalance problem of rigid rotors suspended in conventional bearings, is caused by measurement errors of the rotor center of mass position. The other sources of synchronous vibrations is misalignment between the hub and flywheel masses of the AMCD. Four different control algorithms were examined. These were lead-lag compensators that mimic conventional bearing dynamics, tracking notch filters used in the feedback loop, tracking differential-notch filters, and model-based compensators. The tracking differential-notch filters were shown to have a number of advantages over more conventional approaches for both rigid-body rotor applications and flexible rotor applications such as the AMCD. Hardware implementation schemes for the tracking differential-notch filter were investigated. A simple design was developed that can be implemented with analog multipliers and low bandwidth, digital hardware

Culture, Efficacy, and Outcome Expectancy in Teacher Preparation;How Do the Beliefs of Pre-Service Interns, Mentor Teachers, University Supervisors and Teacher Educators Compare?

Researchers agree that teachers\u27 attitudes and efficacy beliefs play a significant role in student achievement (Armor et al., 1976 Hoy & Spero, 2005 Szabo & Mokhtari, 2004 Woolfolk & Hoy, 1990). Teachers with high self-efficacy: 1) believe they can positively influence students\u27 learning and achievement despite environmental conditions (Armor et al., 1976 Ashton & Webb, 1986 Gibson & Dembo, 1984) and 2) assume accountability for student learning (Gibson & Dembo, 1984 Ross, 1998 Siwatu, 2007). On the contrary, teachers with low teacher efficacy have minimal expectations for and fewer interactions with minority students. They are also more likely to feel teacher burnout and abandon the profession (Betoret, 2006 Friedman, 2004 Guerra, Attar, & Weissberg, 1997). Various studies have confirmed that even after successfully completing multicultural courses and field experiences, interns\u27 negative beliefs and low outcome expectancies for minority students remained (Garmon, 1996, 2004 Easter, Schultz, Neyhart & Reck, 1999). Although little is known about how teaching efficacy develops, it is possible that programs incorporating efficacy-building opportunities assist to create and maintain a pool of quality teachers in culturally diverse schools (Clark & Wegener, 2009 Garcia, 2004 Milner, 2005 Santoro & Allard, 2005 Tucker et al., 2005 Siwatu, 2007 Swearingen, 2009). The purpose of this study will be to examine patterns in culturally responsive teaching self efficacy and outcome expectancies between interns, mentor teachers, university supervisors, and teacher educators in an urban teacher education progra

Culture, Efficacy, and Outcome Expectancy in Teacher Preparation;How Do the Beliefs of Pre-Service Interns, Mentor Teachers, University Supervisors and Teacher Educators Compare?

Researchers agree that teachers\u27 attitudes and efficacy beliefs play a significant role in student achievement (Armor et al., 1976 Hoy & Spero, 2005 Szabo & Mokhtari, 2004 Woolfolk & Hoy, 1990). Teachers with high self-efficacy: 1) believe they can positively influence students\u27 learning and achievement despite environmental conditions (Armor et al., 1976 Ashton & Webb, 1986 Gibson & Dembo, 1984) and 2) assume accountability for student learning (Gibson & Dembo, 1984 Ross, 1998 Siwatu, 2007). On the contrary, teachers with low teacher efficacy have minimal expectations for and fewer interactions with minority students. They are also more likely to feel teacher burnout and abandon the profession (Betoret, 2006 Friedman, 2004 Guerra, Attar, & Weissberg, 1997). Various studies have confirmed that even after successfully completing multicultural courses and field experiences, interns\u27 negative beliefs and low outcome expectancies for minority students remained (Garmon, 1996, 2004 Easter, Schultz, Neyhart & Reck, 1999). Although little is known about how teaching efficacy develops, it is possible that programs incorporating efficacy-building opportunities assist to create and maintain a pool of quality teachers in culturally diverse schools (Clark & Wegener, 2009 Garcia, 2004 Milner, 2005 Santoro & Allard, 2005 Tucker et al., 2005 Siwatu, 2007 Swearingen, 2009). The purpose of this study will be to examine patterns in culturally responsive teaching self efficacy and outcome expectancies between interns, mentor teachers, university supervisors, and teacher educators in an urban teacher education progra

Assessment of flywheel energy storage for spacecraft power systems

The feasibility of inertial energy storage in a spacecraft power system is evaluated on the basis of a conceptual integrated design that encompasses a composite rotor, magnetic suspension, and a permanent magnet (PM) motor/generator for a 3-kW orbital average payload at a bus distribution voltage of 250 volts dc. The conceptual design, which evolved at the Goddard Space Flight Center (GSFC), is referred to as a Mechanical Capacitor. The baseline power system configuration selected is a series system employing peak-power-tracking for a Low Earth-Orbiting application. Power processing, required in the motor/generator, provides a potential alternative configurations that can only be achieved in systems with electrochemical energy storage by the addition of power processing components. One such alternative configuration provides for peak-power-tracking of the solar array and still maintains a regulated bus, without the expense of additional power processing components. Precise speed control of the two counterrotating wheels is required to reduce interaction with the attitude control system (ACS) or alternatively, used to perform attitude control functions. Critical technologies identified are those pertaining to the energy storage element and are prioritized as composite wheel development, magnetic suspension, motor/generator, containment, and momentum control. Comparison with a 3-kW, 250-Vdc power system using either NiCd or NiH2 for energy storage results in a system in which inertial energy storage offers potential advantages in lifetime, operating temperature, voltage regulation, energy density, charge control, and overall system weight reduction

Fluidic Momentum Controller

Large angular control moments and torques are developed by controllably circulating a relatively small mass of liquid through small diameter pipes describing a large diameter loop. The loop, by generating and storing angular momentum, can thereby provide efficient cancellation of periodic, non-accumulating, externally induced rotational disturbances. The loop is preferably located on or near the periphery of a structure which is to be stabilized

Experimental validation of a smart-bias active magnetic bearing controller

Active magnetic bearings (AMBs) are being increasingly employed in the aerospace industry in a variety of devices including compressors, turbines, pumps, and flywheels. One application of great interest to future space missions is the Integrated Power and Attitude Control System (IPACS). The IPACS consists of an arrangement of flywheels that integrates the energy storage and attitude control functions into a single system; thereby, reducing the spacecraft mass, volume, launching cost, and maintenance. Like any energy storage system, flywheels need to be operated with low power losses. AMBs are ideally suited for flywheels because they eliminate mechanical losses (friction). Nevertheless, AMBs are subject to electrical losses, which are proportional to the bias flux. We recently developed an innovative solution to the problem of AMB control with reduced electrical power losses. The controller incorporates a smart, time-varying bias flux that reduces power losses without affecting the rotor stabilization. The novelty of the smart-bias controller strongly motivated the pursuit of the next step in this research – an experimental validation. To that end, the objectives of this project were: · Design and build an experimental AMB test rig. · Conduct tests to validate the smart-bias controller and its power-loss reduction mechanism in comparison to a standard constant-bias AMB controller. The experimental results show that the smart-bias controller clearly reduces the electrical power losses and energy dissipation of the AMB system in comparison to the constant-bias approach, without significantly affecting the stabilization performance. These results confirm, in a qualitative manner, the theoretical and numerical results obtained earlier

Integrated Flywheel Technology, 1983

Topics of discussion included: technology assessment of the integrated flywheel systems, potential of system concepts, identification of critical areas needing development and, to scope and define an appropriate program for coordinated activity

Advanced Integrated Power and Attitude Control System (IPACS) study

Integrated Power and Attitude Control System (IPACS) studies performed over a decade ago established the feasibility of simultaneously satisfying the demands of energy storage and attitude control through the use of rotating flywheels. It was demonstrated that, for a wide spectrum of applications, such a system possessed many advantages over contemporary energy storage and attitude control approaches. More recent technology advances in composite material rotors, magnetic suspension systems, and power control electronics have triggered new optimism regarding the applicability and merits of this concept. This study is undertaken to define an advanced IPACS and to evaluate its merits for a space station application. System and component designs are developed to establish the performance of this concept and system trade studies conducted to examine the viability of this approach relative to conventional candidate systems. It is clearly demonstrated that an advanced IPACS concept is not only feasible, but also offers substantial savings in mass and life-cycle cost for the space station mission

A Feasibility Study on the Control of a Generic Air Vehicle Using Control Moment Gyros

This paper examines feasibility and performance issues in using Control Moment Gyroscopes (CMGs) to control the attitude of a fixed-wing aircraft. The paper describes a control system structure that permits allocating control authority and bandwidth between a CMG system and conventional aerodynamic control surfaces to stabilize a vehicle with neutral aerodynamic stability. A simulation study explores the interplay between aerodynamic and CMG effects, and indicates desirable physical characteristics for a CMG system to be used for aircraft attitude control