Long term changes in Venus sulfur dioxide

Pioneer Venus data from the first 5 years of operation show a decline by more than a factor of ten in SO₂ at the cloud tops. A consistent decline has also recurred in the amount of sub-micron haze above the clouds. The correlation between these two observables is 0.8 over this period. A plausible explanation is injection of SO₂ from episodic volcanism. The episodic behavior implies that steady state models of the Venus cloud chemistry and dynamics may be of limited use.     

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.     

Synthetic aperture radar imaging systems

This paper presents profiles of 12 airborne and spaceborne Synthetic Aperture Radar (SAR) imaging systems. This information is intended to help potential users evaluate the systems for specific applications. The systems profiled in this article can be used for commercial purposes; some have been built specifically for commercial use while others also serve as science and research tools, Both domestic and foreign systems designed for government agencies and private industry are profiled. Nine of these systems are currently operational; two systems are scheduled to begin service in the near future. A third system is no longer active, but archive data are commercially available     

Shielding against galactic cosmic rays.

Ions of galactic origin are modified but not attenuated by the presence of shielding materials. Indeed, the number of particles and the absorbed energy behind most shield materials increases as a function of shield thickness. The modification of the galactic cosmic ray composition upon interaction with shielding is the only effective means of providing astronaut protection. This modification is intimately connected with the shield transport properties and is a strong function of shield composition. The systematic behavior of the shield properties in terms of microscopic energy absorption events will be discussed. The shield effectiveness is examined with respect to conventional protection practice and in terms of a biological endpoint: the efficiency for reduction of the probability of transformation of shielded C3H10T1/2 mouse cells. The relative advantage of developing new shielding technologies is discussed in terms of a shield performance as related to biological effect and the resulting uncertainty in estimating astronaut risk.     

Consideration in selecting crops for the human-rated life support system: a Linear Programming model.

A Linear Programming model has been constructed which aids in selecting appropriate crops for CELSS (Controlled Environment Life Support System) food production. A team of Controlled Environment Agriculture (CEA) faculty, staff, graduate students and invited experts representing more than a dozen disciplines, provided a wide range of expertise in developing the model and the crop production program. The model incorporates nutritional content and controlled-environment based production yields of carefully chosen crops into a framework where a crop mix can be constructed to suit the astronauts' needs. The crew's nutritional requirements can be adequately satisfied with only a few crops (assuming vitamin mineral supplements are provided) but this will not be satisfactory from a culinary standpoint. This model is flexible enough that taste and variety driven food choices can be built into the model.     

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.     

Tests of Direct-Sampling Coherent Detection with a Laboratory Analog-to-Digital Converter

Phase accuracy and simplicity advantages of a direct-sampling coherent detection (DCD) system were demonstrated by computer simulation in earlier correspondence. This correspondence reviews the DCD approach and reports the results of experiments involving digitized samples of analog signals taken by a high-quality, off-the-shelf A/Dconverter. IF signals near 10, 20, and 30 MHz were sampled at 5 MHzresulting in rms DCD phase errors generally below 0.50 compared witherrors less than 0.20 computed in the earlier simulations.     

Overview of nuclear fragmentation models and needs.

It has been known for some time that adequate assessment of spacecraft shield requirements and concomitant estimates of astronauts radiation exposures from galactic cosmic radiation requires accurate, quantitative methods for characterizing these radiation fields as they pass through thick absorbers. The main nuclear interaction processes involved are (1) nuclear elastic and inelastic collisions, and (2) nuclear breakup (fragmentation) and electromagnetic dissociation (EMD). Nuclear fragmentation and EMD are important because they alter the elemental and isotopic composition of the transported radiation fields. At present, there is no suitably accurate theory for predicting nuclear fragmentation cross sections for all collision pairs and energies of interest in space radiation protection. Typical cross-section differences between theory and experiment range from about 25 percent to a factor of two. The resulting errors in transported flux, for high linear energy transfer (LET) particles, are comparble to these cross-section errors. In this overview, theoretical models of heavy ion fragmentation currently used to generate input data bases for cosmic-ray transport and shielding codes are reviewed. Their shortcomings are discussed. Further actions needed to improve their accuracy and generality are presented.     

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.