Performance Evaluation of Suboptimal Filters

The use of a Kalman filter in an applications problem requires a detailed model of both the system dynamics and the measurement dynamics. The model for many problems may be extremely large in dimensionality. However, in many instances one has a limited computer capability and, thus, must purposely introduce modeling errors into the filter in order to gain a computational advantage. However, as is well known, this may lead to the phenomenon of filter divergence. This paper considers the development of equations which allow one to evaluate a filter of reduced state. The equations are based upon using covariance analysis techniques in order to determine the true root-mean-square estimation error. These equations are computationally more advantageous than others appearing in the literature.     

Statistics of Focused and Defocused Radar Maps

Coherent high-resolution synthetic-aperture radar systems achieve their range resolution by pulse compression and azimuth resolution by compression of naturally generated FM coding due to Doppler shifts as the aircraft flies by the target. If the data is left unprocessed, it is, in effect, a defocused map of the terrain. As such, it should exhibit less dynamic range than if the data is compressed. This paper describes an experimental study to verify the above conjecture. The results of this study indicate that if dynamic range of the data link is a problem, the radar data should be transmitted in its unprocessed form. This might very well be the case for planetary mapping by means of satellites.     

Accuracy Limitations of Hyperbolic Multilateration Systems

A recently developed procedure [1] for assessing the accuracy of hyperbolic multilateration systems makes it easy to determine basic limitations on accuracy. This paper illustrates how such bounds can be derived. The results include bounds for a variety of geometries that are representative of practical ground-based and satellite-based hyperbolic systems. The results are applicable whenever the ranging errors can be treated as uncorrelated zeromean random variables. In some cases the bounds quantify general knowledge (e. g., the directional dependence of errors). In other cases the bounds represent entirely new limitations (e. g., optimum accuracies for sector-restricted and cone-restricted transmitter/receiver configurations).     

The Impact of Integrated Electronics on Aerospace Avionic Subsystems

Integrated electronics or microelectronics is one of today's major technical frontiers. Possibilities offered to the designer of avionics subsystems, for aerospace vehicles, by these techniques, are almost limitless, from the point of view of performance capabilities as well as reliability and maintainability. Application will change current engineering practices in avionics design. Some changes will be easy; in others, problems will appear. This paper discusses these changes, indicating potential gains to be expected as well as potential problem areas. The rise in the application of integrated electronics is expected to be high for the next 10 to 15 years. By 1980, integrated circuitry will have largely replaced the use of discrete components, and the rate-of-increase-of-application curves will level off.     

Source processes in the high-latitude ionosphere

Space Science Reviews -     

Some peculiarities of the wave beams in wireless power transmission

Some wave beam peculiarities which usually are wasted are useful in wireless power transmission systems. These peculiarities-the focusing of the beam, the taper distribution of the radiating field, and the discontinuous antenna-are discussed     

A Lower Bound on Prediction Errors for Randomly Accelerating Targets

A lower bound exists for the accuracy with which the future position of a randomly accelerating target can be predicted. This bound applies even when noiseless data is optimally processed. In this correspondence, the prediction error bound is evaluated and presented as a universal curve for the case of a stationary random acceleration process with an exponential autocorrelation function.     

ATS-6 Significance

The Applications Technology Satellite (ATS-6), the most powerful, most sophisticated, most versatile communications satellite flown to date, is the last of NASA's experimental satellites intended to demonstrate major advances in communications and spacecraft technology. It is a multipurpose, multidisciplinary spacecraft whose principal objectives were to demonstrate a large, unfurlable antenna structure and precise pointing and attitude control in the synchronous orbit The spacecraft carries 27 different experiments, 3 of which demonstrate users' applications of satellite communications. Significant advances in antenna technology, precise attitude control, materials technology, spacecraft structures, and thermal control have been successfully demonstrated. The most significant accomplishments of the ATS-6 mission are the demonstration of the practicality of satellite broadcasting to small, simple, inexpensive ground stations and the uses of this potential service in the solution of social problems involving education and health care. The success of these initial demonstrations has led ATS-6 experimenters and potential users to incorporate a Public Service Satellite Consortium dedicated to the provision of satellite broadcasting services for educational and health-care applications.