Position Location from Sensors with Position Uncertainty

A statistical analysis of a mixed-mode position-location system with sensors position uncertainty is described. Expressions for the maximum likelihood estimator and its error statistics, under ?small errors? assumption, are derived.     

Accessing NASA technology with the World Wide Web

NASA Langley Research Center (LaRC) began using the World Wide Web (WWW) in the summer of 1993, becoming the first NASA installation to provide a center-wide home page. This coincided with a reorganization of LaRC to provide a more concentrated focus on technology transfer to both aerospace and non-aerospace industry. Use of WWW and NCSA Mosaic not only provides automated information dissemination, but also allows for the implementation, evolution and integration of many technology transfer and technology awareness applications. This paper describes several of these innovative applications, including the on-line presentation of the entire Technology Opportunities Showcase (TOPS), an industrial partnering showcase that exists on the Web long after the actual 3-day event ended. The NASA Technical Report Server (NTRS) provides uniform access to many logically similar, yet physically distributed NASA report servers. WWW is also the foundation of the Langley Software Server (LSS), an experimental software distribution system which will distribute LaRC-developed software. In addition to the more formal technology distribution projects, WWW has been successful in connecting people with technologies and people with other people     

Upstream waves and particles

A brief analysis is made of the interrelation of the intensity of cosmic-ray particles, the column density of gas and the intensity of cosmic γ-rays. It is shown that, locally, γ-ray data enable the calibration of H₂ densities to be inferred from CO data and elsewhere the variation of cosmic-ray intensity with position to be assessed. Finally, the importance of cosmic-ray irradiated molecular clouds in simulating γ-ray ‘sources’ is reiterated.     

Fuel Savings in the WHECON Attitude Control System Using an Asymmetric Controller

This paper investigates the possibility of generating an on-off limit cycle mode in the WHECON attitude control system. lt is shown that, by eliminating the off set angle ? in the roll-actuated control torquer, the WHECON system can be reduced to the structure considered earlier by Mendel and, therefore, an on-off limit cycle can be generated simply by introducing an appropriate amount of asymmetry into the deadzone characteristic of the WHECON controller. Because with this mode of on-off limit cycle the thruster jets will fire only once in each cycle of the oscillation, it is claimed that a considerable amount of fuel can be saved by the proposed modifications to the original WHECON design. Dynamic simulation study was conducted with the actual nonlinear model of the WHECON system considered and the results indicate that, for both zero and nonzero values of the off set angle ?, substantial fuel savings can be achieved by using the asymmetric controller.     

Recursive Computation of the Generalized Q Function

A recursive method of computing values of the generalized Q function is described. The Q function is also interpreted in terms of noncentral chi-square distributed random variables, and in terms of the difference between Poisson random variables.     

French research program on the physiological problems caused by weightlessness. Use of the primate model

The need to acquire a better knowledge of the main biological problems induced by microgravity implies--in addition to human experimentation--the use of animal models, and primates seem to be particularly well adapted to this type of research. The major areas of investigation to be considered are the phospho-calcium metabolism and the metabolism of supporting tissues, the hydroelectrolytic metabolism, the cardiovascular function, awakeness, sleep-awakeness cycles, the physiology of equilibrium and the pathophysiology of space sickness. Considering this program, the Centre d'Etudes et de Recherches de Medecine Aerospatiale, under the sponsorship of the Centre National d'Etudes Spatiales, developed both a program of research on restrained primates for the French-U.S. space cooperation (Spacelab program) and for the French-Soviet space cooperation (Bio-cosmos program), and simulation of the effects of microgravity by head-down bedrest. Its major characteristics are discussed in the study.     

X-ray scattering by intergalactic dust

The imaging capabilities of the Exosat and Einstein satellites at soft X-ray wavelengths have begun to show that suitable Galactic X-ray sources have extended ( 10 arcmin) haloes due to scattering of soft X-rays by interstellar dust. A simple argument suggests that similar haloes, due to scattering by intergalactic dust, should exist around distant (z 1) quasars and detailed analysis confirms this conclusion. A search for such haloes around suitable X-ray quasars could provide valuable, model-independent, constraints on the amount and origin of intergalactic dust.     

Biological studies of martian soil analogues

Results of the study of the influence of Martian soil analogues, both as described by American scientists and as prepared by us, and of hydrogen peroxide on the viability of microorganisms are presented. The experiments were carried out using mixtures of soil analogues with desert soil and black earth (chernozem) samples, and pure cultures of microorganism. Microorganisms capable of withstanding a concentration of hydrogen peroxide in the medium as high as 1.5–2.0% were isolated. None of the 40 strains of microorganisms studied, all belonging to different systematic and physiological groups, exhibited growth inhibition on solid media in the presence of Martian soil analogues. In view of the fact that Martian soil cannot contain microorganisms in great quantities, we suggest using electroadsorption for their concentration, to make detection reliable. A device was designed for this purpose, using the principle of electroadsorption on a polarisable carrier (sterile cotton wool or cheesecloth). The concentrated suspension of microorganisms thus obtained was then characterized by various physicochemical methods.