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.     

Structure of cress root statocytes in microgravity (Bion-10 mission).

Experiments on primary roots of Lepidium sativum L. have been performed on board the Bion-10 satellite. The experimental set-up was extremely miniaturized and completely automatic. The results demonstrate the effectiveness of the instrumentation. The spatial orientation, growth, root cap differentiation and statocyte structure of roots grown under microgravity (MG) have been compared with control roots grown on the ground (GC) and in a 1G-reference centrifuge in space (RC). Root length and cap shape did not differ between MG and control samples. Under MG, the mean distance of the statoliths from the distal cell wall of the statocytes increased significantly, the mean distance of the mitochondria decreased and the nucleus did not change its position in comparison to both controls. The number and the shape of the amyloplasts (statoliths) were not influenced by the space flight factors, but their size as well as their relative area in the cell decreased. The number of starch grains per statolith as well as their size and shape changed under MG. In MG and RC samples the number of lipid bodies in the statocytes was higher and the relative area larger than in GC samples. The relative area occupied by vacuoles was greater in RC statocytes than in GC and MG statocytes. These results partly confirm and, in addition, extend the data from earlier experiments in space.     

Mass-spectrometric in situ studies of cometary organics for p/Halley and options for the future.

When the VEGA and GIOTTO spacecrafts flew by comet p/Halley in 1986 the mass-spectrometers Puma and PIA measured the composition of cometary dust particles impacting at speeds of well above 65 km/s. Ion formation upon impact lead to mostly atomic ions. However, a small fraction of the ions measured could be related to molecules. A sophisticated analysis allowed for the first time to point to the chemical nature of cometary organics based on actual mass spectra. With the instrument CoMA for the NASA-BMFT mission CRAF much higher mass-resolution and molecule masses become accessible for in situ measurement, and will yield complementary information to the gas chromatograph CIDEX also onboard CRAF.     

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.     

Foliage attenuation and backscatter analysis of SAR imagery

The ability of a synthetic aperture radar (SAR) to detect targets under foliage is in part determined by the attenuation suffered by radiation propagating through the foliage and the backscatter from the foliage. MIT Lincoln Laboratory made measurements of foliage attenuation and backscatter using the NASA/JPL-UHF, L-, C-band fully-polarimetric SAR in July 1990. In this experiment, a 48 km² forested area near Portage, Maine was imaged. Twenty-seven 8 ft trihedral corner reflectors were arrayed throughout the imaged area in order to measure foliage attenuation. Ground truth was recorded at the time of the experiment in order to correlate the attenuation and backscatter results with foliage biophysical properties. The probability densities for foliage attenuation and for backscatter are determined as functions of frequency, polarization, and depression angle     

Adaptive Estimation for a System with Unknown Measu rement Bias

An adaptive state estimator for passive underwater tracking of maneuvering targets is developed. The state estimator is designed specifically for a system containing unknown or randomly switching biased measurements. In modeling the stochastic system, it is assumed that the bias sequence dynamics can be modeled by a semi-Markov process. By incorporating the semi-Markovian concept into a Bayesian estimation technique, an estimator consisting of a bank of parallel, adaptively weighted, Kalman filters has been developed. Despite the large and randomly varying measurement biases, the proposed estimator, provides an accurate estimate of the system states.     

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.