VLSI processors for signal detection in SETI

The objective of the Search for Extraterrestrial Intelligence (SETI) is to locate an artificially created signal coming from a distant star. This is done in two steps: (1) spectral analysis of an incoming radio frequency band, and (2) pattern detection for narrow-band signals. Both steps are computationally expensive and require the development of specially designed computer architectures. To reduce the size and cost of the SETI signal detection machine, two custom VLSI chips are under development. The first chip, the SETI DSP Engine, is used in the spectrum analyzer and is specially designed to compute Discrete Fourier Transforms (DFTs). It is a high-speed arithmetic processor that has two adders, one multiplier-accumulator, and three four-port memories. The second chip is a new type of Content-Addressable Memory. It is the heart of an associative processor that is used for pattern detection. Both chips incorporate many innovative circuits and architectural features.     

Error Performance of Two-Channel Phase-Measurement Systems

The problem of measuring a constant phase difference between two sinusoids which have been corrupted by two additive noise processes is investigated. For the case in which both noise processes are Gaussian and the signal-to-noise ratio is high, the variance of the time-averaged phase-difference estimate is found as a single integral over the noise power spectral densities and cross spectral density. Arbitrary cross correlation is allowed between the two noise processes. Two cases of practical interest are considered: 1) the noise processes have identical, rectangular power spectral densities and are statistically independent; 2) an idealized radio direction finding situation in which two spatially separated sensors are immersed in an isotropic, planar noise field. For the statistically independent case, a universal curve is presented which permits determination of phase-estimate standard deviation for arbitrary signal-to-noise ratio and for a wide range of bandwidths and integration times.     

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.     

Human adaptation to simulated gravitational fields

We present the resuIts of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the role of functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g.     

Characterization of High-Rate QPSK Channel with Adaptive Equalization

A computer simulation model capable of predicting the performance nce of a high-dta-rate end-to-end communication system with adaptive equalization is described in this paper. The model is used to characterize the behavior of NASA's proposed tracking and data relay satellite system (TDRSS), while accounting for signal distortion effects due to operational conditions and the required hardware are components necessary to fulfill mission objectives. Specifically, the performance of the TDRSS high-dta-rate lik (300 Mbps) is defined, both with and without adaptive equalization.     

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.     

Comparisons of Sensitivity Improvement Techniques for Linear Optimal Control Systems

It is well known that there are several ways to define a sensitivity function in the time domain. The results are reported of a study in which these definitions are compared. Controllers designed on the basis of these sensitivity functions are related to each other and conclusions are drawn about their usefulness in control system design.     

Phase Detector Response to Noisy and Noisy Fading Signals

Transfer characteristics of sinusoidal, triangular, and sawtooth-type phase detectors in response to noisy and noisy fading signals have been studied in detail. A new analytical model of the swatooth-type phase detector has been suggested. Detailed experimental results have been supplemented in support of the theoretical findings. Both the theoretical findings and the experimental results clearly indicate that the superiority of a sawtooth-type phase detector over the other two varieties is completely lost in noisy and noisy fading environments.     

The benefits and dilemmas of an international space station

Serious recommendations have been made about the development and mutual manning of an international space station. The achievements of ESA show that such international organizations can work successfully in high technology projects, although with problems. However, other work on isolated and confined environments suggests that sustained cooperation in the unique quarters of a space station for long durations may have special inter-cultural difficulties that need to be examined before any long term commitment is made. Also, a careful look at international activities in general suggests that in spite of the fact that there are many potential benefits for cooperative activities, there are also many international obstacles. If such an effort is to be embarked upon, it is important to look candidly at the problems that can be generated from the multi-national social, economic, and cultural systems in order to do serious and direct analyses. Such a project might be strangled by unanticipated and complex problems of a socio-cultural nature.     

The future of balloons in cosmic-ray research

In spite of the availability of satellites, the possiblity of increasing basic knowledge of cosmic radiation with the help of balloons has not diminished. New detection techniques have made it possible to enter new areas of study which had been closed earlier.