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.     

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.     

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.     

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.     

A Parametric Technique for Time Delay Estimation

The problem of estimating the time difference of arrival of a signal with unknown spectrum to two receivers is treated. A signal model containing both spectral and delay parameters is derived. The model parameters are computed by a two-step procedure: (1) the modified Yule-Walker equations are used to estimate the autoregressive spectrum of the source signal, and (2) a frequency domain squared error criterion is minimized to provide the delay estimate. The performance of the proposed technique is illustrated by simulation results.     

Radiation environments and absorbed dose estimations on manned space missions.

In order to make an assessment of radiation risk during manned missions in space, it is necessary first to have as accurate an estimation as possible of the radiation environment within the spacecraft to which the astronauts will be exposed. Then, with this knowledge and the inclusion of body self-shielding, estimations can be made of absorbed doses for various body organs (skin, eye, blood-forming organs, etc.). A review is presented of our present knowledge of the radiation environments and absorbed doses expected for several space mission scenarios selected for our development of the new radiation protection guidelines. The scenarios selected are a 90-day mission at an altitude (450 km) and orbital inclinations (28.5 degrees, 57 degrees and 90 degrees) appropriate for NASA's Space Station, a 15-day sortie to geosynchronous orbit and a 90-day lunar mission. All scenarios chosen yielded dose equivalents between five and ten rem to the blood forming organs if no large solar particle event were encountered. Such particle events could add considerable exposure particularly to the skin and eye for all scenarios except the one at 28.5 degrees orbital inclination.     

The low energy gamma-ray experiments on GRO in perspective

The NASA Gamma-Ray Observatory, GRO, will carry two instruments for low energy gamma-ray astronomy. The ‘Oriented Scintillation Spectrometer Experiment - OSSE’ represents the latest step in the evolution of collimated detectors. A large detection area, simultaneous source and background observation and rigorous control over systematic errors yield significant improvements in sensitivity over earlier instruments. The ‘Imaging Compton Telescope - COMPTEL’ brings the proven concept of the Compton telescope to the state of the art level. Position sensitive scintillation detectors make it possible to generate sky images with a resolution of about 2° over a f.o.v. of about 1 sr. The complementary nature of these two experiments promises a first in-depth exploration of the sky in a wavelength range which covers the transition from the X-ray sky to the apparently unrelated high energy gamma-ray sky. Possible directions of further evolution of these experiments will be discussed.