Mapping the earth's magnetic and gravity fields from space: Current status and future prospects

Orbital potential field measurements are sensitive to regional variations in earth density and magnetization that occur over scales of a few hundred kilometers or greater. Global field models currently available are able to distinguish gravity variations of ±5 milligal over distances of ～1,000 km and magnetic variations of ±6 gamma over distances of ～300 km at the earth's surface. Regional variations in field strength have been detected in orbital measurements that are not apparent in higher resolution, low altitude surveys. NASA is presently studying a spacecraft mission known as GRAVSAT/MAGSAT, which would be the first satellite mission to perform a simultaneous survey of the earth's gravity and magnetic fields at low orbital altitudes. GRAVSAT/MAGSAT has been proposed for launch during the latter nineteen-eighties, and it would measure gravity field strength to an accuracy of 1 milligal and magnetic field strength to an accuracy of 2 gamma (scalar)/5 gamma (vector components) over a distance of roughly 100 km. Even greater improvements in the accuracy and spatial resolution of orbital surveys are anticipated during the nineteen-nineties with the development of potential field gradiometers and a tethered satellite system that can be deployed from the Space Shuttle to altitudes of 120 km above the earth's surface.     

Simplified Optimum Modulation Indices

The design of a narrowband, phase-modulated, multisubcarrier, phase-coherent, space-communication system requires that the subcarrier modulation indices be kept within close tolerance limits. This need arises since the modulation indices directly affect the division of power among the carrier and subcarriers. If the system is not designed in an optimum manner to handle large tolerance variation, the system performance may degrade sharply in an adverse environment. A universal graphical technique?modulation loss contours?is developed as a design tool for the ?optimum? selection of modulation indices. The technique is novel in that it yields solutions directly from the universal curves and does not require the drawing of additional curves. Two criteria of optimization are considered, simultaneous thresholding and minimal sensitivity. The minimally sensitive case is considered as weighted simultaneous thresholding and is solved by the aid of a graphical algorithm. The technique is applicable to k subcarriers (sinusoidal and/or square wave), considering three subcarriers at a time-two subcarriers as direct variables and the third as a parameter?all other subcarriers remaining constant. Previous techniques required trial and error methods, drawing of curves, or computerized search techniques to arrive at the proper modulation indices and maximum tolerance bands. This method allows a quick solution to the tolerance problem and optimum selection of modulation indices, facilitating the design and/or analysis of narrowband PM systems.     

Biological studies of martian soil analogues

Results of the study of the influence of Martian soil analogues, both as described by American scientists and as prepared by us, and of hydrogen peroxide on the viability of microorganisms are presented. The experiments were carried out using mixtures of soil analogues with desert soil and black earth (chernozem) samples, and pure cultures of microorganism. Microorganisms capable of withstanding a concentration of hydrogen peroxide in the medium as high as 1.5–2.0% were isolated. None of the 40 strains of microorganisms studied, all belonging to different systematic and physiological groups, exhibited growth inhibition on solid media in the presence of Martian soil analogues. In view of the fact that Martian soil cannot contain microorganisms in great quantities, we suggest using electroadsorption for their concentration, to make detection reliable. A device was designed for this purpose, using the principle of electroadsorption on a polarisable carrier (sterile cotton wool or cheesecloth). The concentrated suspension of microorganisms thus obtained was then characterized by various physicochemical methods.     

Experiments with injection of powerful plasma jet into the ionosphere

This paper describes two rocket experiments “Aelita” with high power lithium plasma injection. The results of onboard magnetometer, massspectrometer, photometer, plasma, corpuscular and ground radar measurements are given. Dynamics and structure of plasma formation are discussed.     

An Analysis of Helicopter Rotor Modulation Interference

In satellite-to-helicopter communications, interference exists on the incoming signal when the receiving antenna is located below the rotor blades. A bound is established for the performance of a coherent fixed-tone ranging system operating at L band in this interference environment. The scalar diffracted field beneath the rotating blades, at L band and above, is found to satisfy the criterion of Fresnel diffraction, and is computed using the techniques of Fourier optics. The diffracted field is expressed in terms of a narrow-band signal. The amplitude and phase components are calculated from a Fourier Series expansion using the FFT algorithm. The significant harmonics of the phase component of the interference combine with the baseband of the narrow-band, phase-modulated ranging signal. This results in CW interference, and in rearrangement of the first-order, sideband, ranging-tone channel powers. The degradation in ranging accuracy is evaluated by computing the signal-to-interference (SIR) ratio for a set of ranging tones. The post-detection (SIR)PD at the output of the correlator is shown to be a function of the amplitude of the phase harmonics of the interference, the relative difference between the ranging tone and interference center frequencies (a function of rotor speed), the rangetone modulation indices, and the post-detection filter noise bandwidth.     

Degradation of Probability of Error Due to IF Filtering

The probability of error P(e) is computed in a binary communication system with a single-pole IF filter. The effect of time-bandwidth product foT and IF frequency to band width ratio f1/Ifo on P(e) is shown. The sampling time is optimized and the effect of nonoptimal sampling time on P(e) is calculated.     

Formation and evolution of low-mass Algols

We discuss the origin, evolution and fate of low-mass Algols (LMA) that have components with initial masses less than 2.5 M₀. The semi-major axes of orbits of pre-LMA do not exceed 20–25 R₀. The rate of formation of Algol-type stars is 0.01/year. Magnetic stellar winds may be the factor that determines the evolution of LMA. Most LMA end their lives as double helium degenerate dwarfs with M₁/M₂ 0.88 (like L870-2). Some of them even merge through angular momentum loss caused by gravitational waves.     

Two-dimensional radiation-hydrodynamics calculations of the formation of O-B associations in dense molecular clouds

Two-dimensional calculations of ionization-shockwave propagation into a curved molecular cloud are presented. Density enhancement occurs due to the combined effects of cloud curvature and radiation flow. The star formation process is expected to be enhanced near the edges of irregularly shaped molecular clouds.Authors listed alphabetically