Current status, architecture, and future technologies for theInternational Space Station electric power system

The Electric Power System (EPS) being built for the International Space Station has undergone several significant changes over the last year, as major design decisions have been made for the overall station. While the basic topology and system elements have remained the same, there are important differences in connectivity, assembly sequence, and start-up. The key drivers for these changes in architecture have been the goal to simplify verification, and most significantly, the introduction of extensive Russian participation in the program. Having the Russians join the international community in this project has resulted in an expanded station size, larger crew, and almost doubled the observable surface of the Earth covered by the station. For the power system it has meant additional interfaces for power transfer, and new challenges for solar tracking at the higher inclination orbit. This paper reviews the current architecture and emphasizes the new features that have evolved, as the design for the new, larger station has developed. Additionally, the possible application of developing technology to the station, and other future missions is considered     

Neural networks in nonlinear aircraft flight control

This paper describes an approach for incorporating a neural network with real-time learning capability in a flight control architecture. The architecture is also applicable, in general, for the control of processes described by nonlinear differential equations of motion in which there exists a control for each degree of freedom. The main features are that the defining equations of motion for the process to be controlled are poorly known with respect to their functional forms, and that the functional forms, themselves, may undergo sudden and unexpected variation. It is well known that such systems are difficult to control, particularly when the effect of the control action enters nonlinearly. Numerical results based on 6DOF simulations of a high performance aircraft are presented to illustrate the potential benefits of incorporating neural networks as a part of a flight control system architecture     

The development of a series hybrid electric vehicle for near-termapplications

The design of a feasible hybrid electric vehicle for use in near-term applications is presented. The challenge involved cost effectiveness, acceleration, range, safety, and emissions, which were incorporated into the vehicle design. The relationship of the design goals was studied, and compromises were made to provide near-optimal system design. This process resulted in the selection and design of the major vehicle components. The design decisions and the actual vehicle components are reviewed     

Influence of gravity on the circadian timing system.

The circadian timing system (CTS) is responsible for daily temporal coordination of physiological and behavioral functions both internally and with the external environment. Experiments in altered gravitational environments have revealed changes in circadian rhythms of species ranging from fungi to primates. The altered gravitational environments examined included both the microgravity environment of spaceflight and hyperdynamic environments produced by centrifugation. Acute exposure to altered gravitational environments changed homeostatic parameters such as body temperature. These changes were time of day dependent. Exposure to gravitational alterations of relatively short duration produced changes in both the homeostatic level and the amplitude of circadian rhythms. Chronic exposure to a non-earth level of gravity resulted in changes in the period of the expressed rhythms as well as in the phase relationships between the rhythms and between the rhythms and the external environment. In addition, alterations in gravity appeared to act as a time cue for the CTS. Altered gravity also affected the sensitivity of the pacemaker to other aspects of the environment (i.e., light) and to shifts of time cues. Taken together, these studies lead to the conclusion that the CTS is indeed sensitive to gravity and its alterations. This finding has implications for both basic biology and space medicine.     

A modified Gaussian sum approach to estimation of non-Gaussiansignals

A Gaussian sum estimation algorithm has previously been developed to deal with noise processes that are non-Gaussian. Inherent in this algorithm is a serious growing memory problem that causes the number of terms in the Gaussian sum to increase exponentially at each iteration. A modified Gaussian sum estimation algorithm using an adaptive filter is developed that avoids the growing memory problem of the previous algorithm while providing effective state estimation. The adaptive filter is comprised of a fixed set of estimators operating in parallel with each individual estimate possessing its own corresponding weighting term. A simulation example illustrates the new non-Gaussian estimation technique     

Fuel cell technology status

Several major fuel cell projects and their status are described. The fuel cell types discussed are phosphoric acid, molten carbonate, solid oxide, and polymer. One of the technologies is very close to commercialization. Two others offer the possibility for higher efficiency and large capacity electric generation using coal. Still another may be the answer to the key issues facing the transportation sector     

Optimal radar threshold determination in Weibull clutter andGaussian noise

A technique is presented for determining the ideal detection threshold when Gaussian noise and Weibull distributed clutter returns are present on a radar receiver and neither is dominant. Quantitative data is presented for several clutter types and false alarm probabilities     

Fusion of sensors with dissimilar measurement/tracking accuracies

The case of data fusion of sensors dissimilar in their measurement/tracking errors is considered. It is shown that the fused track performance is similar whether the sensor data are fused at the track level or at the measurement level. The case of a cluster of targets, resolved by one sensor but not the other, is also considered. Under certain conditions the fused track may perform worse than the worst of the sensors. A remedy to this problem through modifications of the association algorithm is presented     

Partial pressures and nature of products. Application to the photolysis of PH3 and NH3 in the atmosphere of Jupiter and Saturn.

The photolysis of mixtures of gases containing NH3 or PH3 presents important differences mainly due to the strength of the X-H bond. On some examples, these differences are evidenced and the consequences for mixtures of gases containing these two compounds are shown: the photolysis of ammonia and ethylene mainly gives ethyl-, butyl- and hexylamine whereas the photolysis of phosphine and ethylene leads to ethyl- and vinylphosphine. When gaseous mixtures of NH3, PH3 and ethylene are photolyzed together, the presence of phosphine dramatically decreases the formation of nitrogen derivatives. The relevance of such lab studies to the atmospheres of Jupiter and Saturn is discussed.     

Formation of bioorganic compounds in simulated planetary atmospheres by high energy particles or photons.

Various types of organic compounds have been detected in Jupiter, Titan, and cometary coma. It is probable that organic compounds were formed in primitive Earth and Mars atmospheres. Cosmic rays and solar UV are believed to be two major energy sources for organic formation in space. We examined energetics of organic formation in simulated planetary atmospheres. Gas mixtures including a C-source (carbon monoxide or methane) and a N-source (nitrogen or ammonia) was irradiated with the followings: High energy protons or electrons from accelerators, gamma-rays from 60Co, UV light from a deuterium lamp, and soft X-rays or UV light from an electron synchrotron. Amino acids were detected in the products of particles, gamma-rays and soft X-rays irradiation from each gas mixture examined. UV light gave, however, no amino acid precursors in the gas mixture of carbon monoxide, nitrogen and nitrogen. It gave only a trace of them in the gas mixture of carbon monoxide, ammonia and water or that of methane, nitrogen and water. Yield of amino acid precursors by photons greatly depended on their wavelength. These results suggest that nitrogen-containing organic compounds like amino acid precursors were formed chiefly with high energy particles, not UV photons, in Titan or primitive Earth/Mars atmospheres where ammonia is not available as a predominant N-source.