Communicating across the solar system

The technological advances of the Space Age have enabled us to project our senses through complex instruments to the edge of the Solar System and beyond. The link back to Earth by the communication channel has provided us with a wealth of information. The vast improvement in communication capability, by a factor of 10¹⁸, from the launching of the first earth satellites to the capacity of the Voyager telecommunications link across the Solar System, is symbolic of both our technical prowess and our cultural development. The combination of data rate and extreme distance at the Voyager 2 encounters with Uranus and Neptune in 1986 and 1989 will require the ground network to perform an engineering feat of unequalled magnitude. This paper describes the engineering challenge of communicating with spacecraft at the limits of the Solar System and the engineering responses to that challenge.     

Photometric calibration and first results obtained with the UFT experiment on board the astron satellite

The UV telescope of 30 cm diameter equipped with a three channel scanner spectrometer aboard the highly eccentric orbit space station “ASTRON” is describedAbsolute calibration of the whole device is performed using spectra of standard stars, of which absolute values were obtained by TDI or IUE experiments. Several photometric controls have been made on the stability of the equipment after one year of operation which demonstrate reliability of some first results obtained by the UFT.The sensitivity curve of the spectrophotometric system has been observed with a reproducibility of 2σ = 10% or better.The repeated observation of one star (139 Tau) indicates that the overall performance exhibits the same quality after one year in orbit. The low resolution mode ($\text{Δ λ = 28}\text{A}\text{?}$) leads to a powerful new investigation of faint extended sources.     

Measurements of trace contaminants in closed-type plant cultivation chambers.

Trace contaminants generated in closed facilities can cause abnormal plant growth. We present measurement data of trace contaminants released from soils, plants, and construction materials. We mainly used two closed chambers, a Closed-type Plant and Mushroom Cultivation Chamber (PMCC) and Closed-type Plant Cultivation Equipment (CPCE). Although trace gas budgets from soils obtained in this experiment are only one example, the results indicate that the budgets of trace gases, as well as CO2 and O2, change greatly with the degree of soil maturation and are dependent on the kind of substances in the soil. Both in the PMCC and in the CPCE, trace gases such as dioctyl phthalate (DOP), dibutyl phthalate (DBP), toluene and xylene were detected. These gases seemed to be released from various materials used in the construction of these chambers. The degree of increase in these trace gas levels was dependent on the relationship between chamber capacity and plant quantity. Results of trace gas measurement in the PMCC, in which lettuce and shiitake mushroom were cultivated, showed that ethylene was released both from lettuce and from the mushroom culture bed. The release rates were about 90 ng bed-1 h-1 for the shiitake mushroom culture bed (volume is 1700 cm3) and 4.1 approximately 17.3 ng dm-2 h-1 (leaf area basis) for lettuce. Higher ethylene release rates per plant and per unit leaf area were observed in mature plants than in young plants.     

Hemispheric differences in the earth radiation budget derived from Nimbus-7 related to climate studies

Earth Radiation Budget (ERB) data from Nimbus-7 over the period November 1978 – June 1980 has consistently shown strong hemispheric differences when analyzed over different temporal and spatial scales. Hemispheric variations in time latitude cross sections of net and emitted radiation were found to be caused by changes in the Earth-Sun distance and continental effects.Maps of annual range for the entire Earth calculated from monthly averages showed areas of high and low variability of the different ERB parameters. The ERB of these regional areas were examined and most of the variability was found to lay in the large amplitude of the annual solar cycle. Variations in the global annual cycle of albedo /1/ are studied with respect to differences in latitudinal averaged albedo. The anomaly in the annual cycle of global averaged albedo was found to be caused by tropical albedo changes.     

The cometary contribution to prebiotic chemistry.

Different estimates based on dynamical considerations, lunar cratering rates, Solar System chemical abundances, and the single-impact theory on the origin of the Earth-Moon system suggest that comets and other related small, volatile-rich primitive minor bodies captured by the Earth during the early Archean must have been a major source of volatiles on our planet. It is likely that a substantial fraction of the organic molecules present in the colliding cometary nuclei, which may have included nitrogen bases and the precursors of amino acids, were destroyed due to the high temperatures and shock wave energy associated with the collision. However, the presence of H2O, CN, CH, CO, CO2 and other carbon-bearing molecules and radicals in the atmosphere of the Sun and in circumstellar shells around carbon-rich stars suggests that at least simple carbon species could have survived the cometary collisions. Under the anoxic conditions thought to prevail in the prebiotic terrestrial paleoatmosphere, the post-collisional formation of a large number of excited molecules and radicals, and the rapid quenching of the expanding gaseous ball may have led, upon rapid cooling, to the formation of molecules of biogenic elements and to their eventual deposition in localized environments where complex organic compounds of biochemical significance may have been produced and accumulated.     

Spacecraft on-orbit deployment anomalies: What can be done?

On-orbit anomalies related to the deployment of spacecraft appendage and possible causes of such failures are considered. The discussion covers mechanical launch loading, on-orbit thermal and solar concerns, reliability of spacecraft pyrotechnics, and practical limitations of ground-based deployment testing. Lessons learned from the successful recovery of the Telesat Canada Anik-E2 satellite in 1991 are examined     

Angle and polarization estimation in a coherent signal environment

It is shown how a uniform linear array of crossed dipoles may be used with the ESPRIT algorithm and spatial smoothing techniques to estimate the arrival directions and polarizations of incoming coherent plane waves. Some examples showing typical performance are presented. One method of smoothing can be used where it is necessary to estimate both the arrival angles and polarizations of signals. Two other methods can be used when only the arrival angles are of interest     

A model of radiation conditions during spacecraft flights in the interplanetary space and in the Earth's magnetosphere.

Based on the available measurement data, simulations of radiation conditions during spacecraft flights in the interplanetary space and in the Earth's and Jupiter's radiation belts has been carried out. The > or = 10 MeV and > or = 30 MeV solar flare proton fluence forecast has been proposed for Cycle 22. Radiation conditions due to both magnetospheric electrons and protons and to solar flare protons, magnetic rigidity cutoff being taken into account, have been evaluated on spacecraft trajectories in the Earth's and Jupiter's magnetospheres.     

Image understanding research for automatic target recognition

Automatic target recognition (ATR) is an important capability for defense applications. Many aspects of image understanding (IU) research are traditionally used to solve ATR problems. The authors discuss ATR applications and problems in developing real-world ATR systems and present the status of technology for these systems. They identify several IU problems that need to be resolved in order to enhance the effectiveness of ATR-based weapon systems. They conclude that technological gains in developing robust ATR systems will lead to significant advances in many other areas of applications of image understanding