Ultimate IR Horizon Sensor

The accuracy of presently available IR horizon sensors is not sufficient to meet the stringent attitude sensing and control requirements for future remote sensing and meteorological satellites. The different sources of error in a horizon sensor are analyzed. The accuracy of the sensor is presently limited by the detector noise. Use of HgCdTe in place of an immersed bolometer detector, which is used in conventional horizon sensors eliminates many of the errors. Hence, it is possible to design an ultimate IR horizon sensor whose accuracy is limited only by the uncertainty of the Earth horizon. Comparison of performances of the two types of detectors for horizon sensing is given and possible configurations of sensor using this detector are discussed.     

Evaluation of Geometric Performance of Global Positioning System

The global positioning system (GPS) is a satellite-based radio navigation system to provide extremely accurate three-dimensional position fixes and system time to users anywhere on the Earth at any time regardless of weather conditions. The most significant performance parameter of the GPS is the degree of navigation accuracy which is strongly coupled to the choice of orbit configuration. The 3 X 8 orbit configuration has been considered as an operational GPS which consists of 24 satellites deployed in circular 63° inclined, subsynchronous 12-h orbits. In this paper, the geometric performance of several orbit configuration, including a 3 X 8 orbit configuration, is analyzed numerically by altering orbit period and elevation mask, respectively. It will be shown that 1) there are a few orbit configurations which are comparable to or better than the baseline 3 X 8 orbit configuration, and 2) for higher elevation mask, the geometric performance can be improved effectively by increasing orbit period to some extent.     

Unsupervised Tracking of Maneuvering Vehicles

The design of adaptive filters for the tracking of high-performance maneuvering targets is a fundamental problem in real-time surveillance systems. As is well known, a filter which provides heavy smoothing can not accurately track an evasive maneuver, and conversely. Consequently, one is led to the consideration of adaptive methods of filter design. This paper presents an improved self-adaptive filter algorithm for on-line solution of the above problem. Basically, this algorithm utilizes the orthogonality property of the residual time series to force the filter to automatically track the optimal gain levels in a changing environment.     

Analysis of Limit Cycles in a Two-Transistor Saturable-Core Parallel Inverter

A familiar two-transistor saturable-core parallel inverter is modeled as a nonlinear negative resistance in parallel with energy-storage elements. The techniques of singular-point analysis are combined with piecewise linear techniques to permit determination of solution trajectories on the phase plane. Clear insight is provided, not only into steady-state oscillation, but also into transient behavior of the circuit. Experimental results confirming the analytical model are included.     

Radar Calibration Test Satellite

A satellite has been designed for application to radar calibration. Electromagnetic and mechanical characteristics of the satellite and their influence on the selection of shape and other parameters are discussed. Theoretical and experimental scattering data are included.     

Comments on "The GYROLITE: A New Generation Synchronous Satellite"

The effectiveness of the GYROLITE attitude stabilization is discussed on the basis of the basic mathematical equations in [1], and an avenue towards improved performance is indicated.     

Excitation of the Lyman-α in the night sky

The experiments pertaining to the excitations of Lyman- radiation in the night sky are reviewed. Various possible modes of excitation are considered. Scattering of solar L in interplanetary hydrogen is not suitable because of an insufficient amount of hydrogen and difficulty in accounting for the large night time albedo contrasted with the small daytime value. Transport by multiple scattering in the exosphere produces an appreciable excitation as well as the correct variation of intensity as function of zenith angle. However, the process fails by a factor of 4 for a solar flux of 6 ergs/cm² sec and the 3 × 10¹² atoms/cm² geocorona consistent with absorption measurements. A direct scattering in a geocoma far from the earth overcomes the albedo and thin atmosphere problems. However, there is difficulty in accounting for the presence of the amount of hydrogen necessary beyond 15 earth radii. Also the absence of H excitation by Lyman- is a problem. No explanation so far proposed appears adequate. Experiments are suggested.     

Population dynamics of an algal-bacterial cenosis in closed ecological system.

The paper deals with microalgae-bacteria interrelationships in the "autotroph-heterotroph" aquatic biotic cycle. Explanations of why and how algal-bacterial ecosystems are formed still remain controversial. The paper presents results of experimental and theoretical investigations of the functioning of the algal-bacterial cenosis (the microalga Chlorella vulgaris and concomitant microflora). The Chlorella microbial community is dominated by representatives of the genus Pseudomonas. Experiments with non-sterile batch cultures of Chlorella on Tamiya medium showed that the biomass of microorganisms increases simultaneously with the increase in microalgal biomass. The microflora of Chlorella can grow on organic substances released by photosynthesizing Chlorella. Microorganisms can also use dying Chlorella cells, i.e. form a "producer-reducer" biocycle. To get a better insight into the cenosis-forming role of microalgae, a mathematical model of the "autotroph-heterotroph" aquatic biotic cycle has been constructed, taking into account the utilization of Chlorella photosynthates and dead cells by microorganisms and the contribution of the components to the nitrogen cycle. A theoretical study showed that the biomass of concomitant bacteria grown on glucose and detritus is larger than the biomass of bacteria utilizing only microalgal photosynthates, which agrees well with the experimental data.