Attitude and Oribit Estimation Using Stars and Landmarks

An extended Kalman filter is used to process line-of-sight measurements to stars and known landmarks providing a statistical indication of performance in estimating spacecraft attitude, orbital ephemeris, and the bias drift of a set of three strapdown gyros. The landmark measurements were assumed to have been taken from the imagery of an Earth-observing multispectral scanner. It is shown that filtering of these noisy measurements results in highly accurate estimates of the above parameters. Results are given showing the sensitivity of performance to various system parameters such as star tracker accuracy, errors in the knowledge of landmark position, and number of stars and landmarks processed.     

The structural features of the germanium-silicon solid solution crystals obtained under microgravity

Structural features of germanium-silicon solid solution crystals have been investigated and silicon distribution in the crystals has been studied. All the crystals obtained under microgravity had, in spite of good external shape and facetting, a poorer internal structure than those obtained on Earth. The distribution of silicon have been shown to be non-uniform. High dislocation densities were observed.     

Interference Immunity Effects in CPSK Systems with Hard-Limiting Transponders

Transmission characteristics are described for M-ary coherent phase-shift keyed (CPSK) systems with N-stage hard-limiting transponders where noise and multiple continuous wave (CW) interference sources are additively combined in each link. A general expression for the probability density function of the composite phase at the final link is derived; the overall error probability is then obtained from this general expression. Comparisons with N-cascaded linear amplifier systems clearly show the noise and interference immunity that result from the use of bandpass hard limiters (BPHLs). The BPHL system's error probability improvement versus interference sources is shown to be much larger than the improvement versus noise.     

Selected examples of profitable applications of remote sensing for resources inventories and monitoring

The Remote Sensing Centre of the Institute of Geodesy and Cartography in Warsaw has been operating since 1976. It has multi-disciplinary character; carries out scientific research, elaborates technologies of remote sensing investigations, applies remote sensing methods for solving various practical problems, coordinates national activities in this field, developes and disseminates remote sensing knowledge at both national and international levels offering various types of specialized training.The authors discuss the role of remote sensing investigations in the process of development planning. Examples of projects executed at the Remote Sensing Centre and concerning topographic and land use mapping, geological investigations, agricultural crop area determination, forest research, environmental monitoring and studies of climatic conditions in urban environment are described and extensively discussed in the paper. The authors emphasize these areas of the application of remote sensing and these interpretation techniques which are of potential interest for the developing countries.     

Nonlinear analysis of hydrodynamic instability in laminar flames—II. Numerical experiments

We consider a nonstationary nonlinear integrodifferential equation describing the evolution of a disturbed plane flame front. The following two-dimensional problems are solved numerically: (i) The formation of a wrinkled noncellular laminar flame front under conditions of spontaneous hydrodynamic instability. (ii) The formation of a turbulent cellular flame front under conditions of spontaneous diffusional-thermal instability. (iii) The formation of a turbulent wrinkled-cellular flame front under conditions of spontaneous hydrodynamic and diffusional-thermal instability. We compute the flame front velocity in laminar and turbulent propagation.     

Recent developments in ultraviolet filters and coatings

A number of new high efficiency optical coatings have recently been developed at wavelengths in the ultraviolet and vacuum ultraviolet for use in space science experiments. The development of these coatings has resulted in the design and manufacture of wavelength selective filters used in reflectance at near normal incidence that have high VUV reflectance with little near-UV and visible reflectance. Very narrow band transmission filters are now available at wavelengths as short as 1500Å with bandwidths as narrow as 35–40Å. In addition, high efficiency anti-reflection coatings as well as neutral density filters are now available at many wavelengths in this region.Material limitations, more severe than those in the visible, place certain restrictions on the size, wavelength, and degree of selectivity that is achievable with present technology. A summary of the current commercial technology along with the material limitations is presented.     

Comparative economics of very high capacity communications satellites

Technology advances expected by the late 1980 or early 1990 time period will allow the construction of powerful and complex communications satellites with large multibeam antennas and very many transponders, and their operation and maintenance in geostationary orbit. The high sensitivity and effective radiated power of such satellites will enable the Earth stations using them to shrink dramatically in size and cost, thus becoming readily available to very large numbers of users as well as making possible new kinds and levels of communications services simply not possible with smaller satellites. This paper briefly describes three such new designs, concerning electronic mail transmission, educational TV distribution, and mass personal communications; it compares the users' service costs with those of terrestrial networks designed for the same performance.     

Lightweight (AlGaAs)GaAs/CuInSe2 tandem junction solarcells for space applications

Mechanically stacked tandem cells consisting of GaAs thin-film upper cells and CuInSe₂ thin-film lower cells have been developed to meet the increasing power needs projected for future spacecraft. The authors report the fabrication of the first highly efficient lightweight GaAs/CuInSe₂ tandem cell on a 2-mil thick substrate, update recent performance improvements in thin-film GaAs/CuInSe₂ tandem cells, and discuss their application to space power systems. The efficiency of 4-cm² cells has improved to 21.6% AM0, the highest ever reported for a thin-film photovoltaic cell. Lightweight 4-cm² tandem cells have been successfully fabricated with efficiencies as high as 20.8%. These cells weighed about 180 mg without optimized substrate trimming. Radiation and operating temperature effects on GaAs/CuInSe₂ tandem cells are also discussed, and an interconnect scheme to form a voltage-matched string is described     

Radiation stability of organic matter in liquid and frozen H2O, NH3 and water-ammonia mixtures

The redox properties of irradiated liquid and frozen H₂O, NH₃ and H₂O/NH₃ mixtures at 298 K and 77 K, resp., towards some simple organic molecules have been checked by injecting carrierfree ¹¹C atoms and analyzing their chemical state by means of radiochromatography. The reactions and the stability of organic products versus radiation dose (in this study by MeV protons) depend on temperature, phase state, mobility of radicals, their concentration and reactivity. Especially dangerous are the reactive OH and O₂H radicals which oxidize organic material to inorganic CO₂. Highest stability has been found at low temperatures (solid state, reduced mobility of radicals) and for systems containing H-donors (H₂O/NH₃ mixtures), which reduce the concentration of oxidizing radicals. The fact that many bodies in space consist of H₂O-ice with NH₃ and CH₄ additives at temperatures between 10 and 150 K is promising in view of the survival of organic matter under high doses of radiation.