SPS structures and control: A perspective

The characteristics and design requirements for the structure and control systems for a solar power satellite were evaluated. A simplistic, indicative analysis on a representative configuration was developed. Representative configuration masses and dimensions are given in convenient approximate magnitudes. The significance of structure control interaction and the significance of stiffness to the minimization of dynamic energy was demonstrated. It was found that the thermal environment for the SPS was dominated by solar radiation and waste heat rejection by the antenna. A more in-depth assessment of the control system design and associated system performance is still needed, specifically the inter-relatonships between control sensors, actuators, and structural response

Shape control of large space structures

A survey has been conducted to determine the types of control strategies which have been proposed for controlling the vibrations in large space structures. From this survey several representative control strategies were singled out for detailed analyses. The application of these strategies to a simplified model of a large space structure has been simulated. These simulations demonstrate the implementation of the control algorithms and provide a basis for a preliminary comparison of their suitability for large space structure control

Special coatings control temperature of structures

Special coatings in the form of paints that exhibit controlled ratios of sunlight absorptivity to grey-body emissivity control the temperature of structures in space flight. These finishes exhibit good resistance to ultraviolet radiation and do not discolor

Control Structures and Payout Policy

This paper examines the payout policies of UK firms listed on the London Stock Exchange during the 1990s.It complements the existing literature by analyzing the trends in both dividends and total payouts (including share repurchases).In a dynamic panel data regression setting, we relate target payout ratios to control structure variables.Profitability drives payout decisions of the UK companies, but the presence of strong block holders or block holder coalitions considerably weakens the relationship between corporate earnings and payout dynamics.While the impact of the voting power of shareholders coalitions on payout ratios is found to be always negative, the magnitude of this effect differs across different categories of block holders (i.e. industrial firms, outside individuals, directors, financial institutions).The controlling shareholders appear to trade off the agency problems of free cash flow against the risk of underinvestment, and try to enforce payout policies that optimally balance these two costs.Finally, the paper improves upon some methodological flaws of the recent empirical studies of payout policy.Payout policy;dividend payout;share repurchases;partial adjustment;ownership and control;voting power;Banzhaf power indices;corporate governance;free cash flow;pecking order

Control of large space structures

The control of large space structures was studied to determine what, if any, limitations are imposed on the size of spacecraft which may be controlled using current control system design technology. Using a typical structure in the 35 to 70 meter size category, a control system design that used actuators that are currently available was designed. The amount of control power required to maintain the vehicle in a stabilized gravity gradient pointing orientation that also damped various structural motions was determined. The moment of inertia and mass properties of this structure were varied to verify that stability and performance were maintained. The study concludes that the structure's size is required to change by at least a factor of two before any stability problems arise. The stability margin that is lost is due to the scaling of the gravity gradient torques (the rigid body control) and as such can easily be corrected by changing the control gains associated with the rigid body control. A secondary conclusion from the study is that the control design that accommodates the structural motions (to damp them) is a little more sensitive than the design that works on attitude control of the rigid body only

Control of structures in space

Various topics related to the control of large space structures are discussed. Equations of motion for distributed systems, eigenvalue problems, modal equations, control implementation, and the Langley beam experiment are discussed

Space Structures: Issues in Dynamics and Control

A selective technical overview is presented on the vibration and control of large space structures, the analysis, design, and construction of which will require major technical contributions from the civil/structural, mechanical, and extended engineering communities. The immediacy of the U.S. space station makes the particular emphasis placed on large space structures and their control appropriate. The space station is but one part of the space program, and includes the lunar base, which the space station is to service. This paper attempts to summarize some of the key technical issues and hence provide a starting point for further involvement. The first half of this paper provides an introduction and overview of large space structures and their dynamics; the latter half discusses structural control, including control‐system design and nonlinearities. A crucial aspect of the large space structures problem is that dynamics and control must be considered simultaneously; the problems cannot be addressed individually and coupled as an afterthought

Design and fabrication of 3-D printed conductive polymer structures for THz polarization control

In this paper, we numerically and experimentally demonstrate the inverse polarization effect in three-dimensional (3-D) printed polarizers for the frequency range of 0.5 - 2.7 THz. The polarizers simply consist of 3-D printed strip lines of conductive polylactic acid (CPLA, Proto-Pasta) and do not require a substrate or any further metallic deposition. The experimental and numerical results show that the proposed structure acts as a broadband polarizer between the range of 0.3 THz to 2.7 THz, in which the inverse polarization effect is clearly seen for frequencies above 0.5 THz. In the inverse polarization effect, the transmission of the transverse electric (TE) component exceeds that of the TM component, in contrast to the behavior of a typical wire-grid polarizer. We show how the performance of the polarizers depends on the spacing and thickness of the CPLA structure; extinction ratios higher than 20 dB are achieved. This is the first report using CPLA to fabricate THz polarizers, demonstrating the potential of using conductive polymers to design THz components efficiently and robustly

Identification of flexible structures for robust control

Documentation is provided of the authors' experience with modeling and identification of an experimental flexible structure for the purpose of control design, with the primary aim being to motivate some important research directions in this area. A multi-input/multi-output (MIMO) model of the structure is generated using the finite element method. This model is inadequate for control design, due to its large variation from the experimental data. Chebyshev polynomials are employed to fit the data with single-input/multi-output (SIMO) transfer function models. Combining these SIMO models leads to a MIMO model with more modes than the original finite element model. To find a physically motivated model, an ad hoc model reduction technique which uses a priori knowledge of the structure is developed. The ad hoc approach is compared with balanced realization model reduction to determine its benefits. Descriptions of the errors between the model and experimental data are formulated for robust control design. Plots of select transfer function models and experimental data are included