Usefulness of daily +2Gz load as a countermeasure against physiological problems during weightlessness.

Adaptation to head-down-tilt bed rest as a simulated microgravity leads to an abnormality of reflex control of circulation, hypovolemia and reduction of exercise capacity. We hypothesized that this cardiovascular deconditioning and reduction of exercise capacity could be prevented by a daily 1 hr centrifugation at +2Gz. To test this hypothesis, twenty healthy male subjects underwent 4 day of 6 degrees head-down-tilt bed rest. Ten of them were exposed to a +2Gz load for up to 30 min twice per day (the Gz group). The remaining 10 were not exposed to a Gz load (the no-Gz group). We estimated autonomic cardiovascular control by power spectral analysis of blood pressure and R-R interval variability, and baroreflex regulation by the transfer function analysis and the sequence method, before and after bed rest. Further, we measured hematocrit as an index of changes in plasma volume and maximal oxygen consumption as an index of exercise capacity, before and after bed rest. Result: In the no-Gz group, heart rate increased after bed rest. The high frequency power of R-R interval variability as an index of cardiac parasympathetic nervous activity, baroreflex gains estimated by transfer function analysis and the sequence method as index of the integrated arterial-cardiac baroreflex function decreased significantly. Associated with these changes, the ratio of low to high frequency power of R-R as an indicator of cardiac sympathovagal balance tended to increase after bed rest in the no-Gz group. However, those showed no significant changes after bed rest in the Gz group. Hematocrit increased after bed rest in the no-Gz group. It also tended to increase in the Gz group, however it did not achieve statistical significance. Maximal oxygen consumption decreased significantly to similar extent in both the groups. Conclusion: This result suggested that 1) a daily 1hr +2Gz load produced by a centrifuge might eliminate the changes in autonomic cardiovascular control during simulated weightlessness; 2) furthermore, it might partly reverse hypovolemia induced by bed rest; 3) however, it could not prevent the decreases in exercise capacity.     

Location and sampling of aqueous and hydrothermal deposits in martian impact craters

Do large craters on Mars represent sites that contain aqueous and hydrothermal deposits that provide clues to astrobiological processes? Are these materials available for sampling in large craters? Several lines of evidence strongly support the exploration of large impact craters to study deposits important for astrobiology. The great depth of impact craters, up to several kilometers relative to the surrounding terrain, can allow the breaching of local aquifers, providing a source of water for lakes and hydrothermal systems. Craters can also be filled with water from outflow channels and valley networks to form large lakes with accompanying sedimentation. Impact melt and uplifted basement heat sources in craters > 50 km in diameter should be sufficient to drive substantial hydrothermal activity and keep crater lakes from freezing for thousands of years, even under cold climatic conditions. Fluid flow in hydrothermal systems is focused at the edges of large planar impact melt sheets, suggesting that the edge of the melt sheets will have experienced substantial hydrothermal alteration and mineral deposition. Hydrothermal deposits, fine-grained lacustrine sediments, and playa evaporite deposits may preserve evidence for biogeochemical processes that occurred in the aquifers and craters. Therefore, large craters may represent giant Petri dishes for culturing preexisting life on Mars and promoting biogeochemical processes. Landing sites must be identified in craters where access to the buried lacustrine sediments and impact melt deposits is provided by processes such as erosion from outflow channels, faulting, aeolian erosion, or excavation by later superimposed cratering events. Very recent gully formation and small impacts within craters may allow surface sampling of organic materials exposed only recently to the harsh oxidizing surface environment.     

Modeling the Modification of the Nighttime High-Latitude F-Region by Powerful HF Radiowaves

A mathematical model of the high-latitude F-region, taking the ionospheric plasma convection into account, is used for modeling a response of the auroral F-region to irradiation by powerful high-frequency (HF) radiowaves. The model enables us to calculate the time variations in the profiles of the electron concentration, the velocity of positive ions, and the ion and electron temperatures in the part of a magnetic-flux tube moving over an artificial ionospheric heater under the action of a convective electric field. The modeling was carried out for a part of the magnetic flux tube intersecting the F-layer irradiated by the Norwegian heater at Tromsö when it is located near the midnight magnetic meridian. The calculations were made for the equinox conditions under the high solar and low geomagnetic activity. The results of our modeling show that substantial variations in the profiles of the electron temperature, the velocity of positive ions, and the electron concentration can be produced in the nighttime high-latitude F-layer due to HF heating. The perturbation caused by a 20 s rectangular pulse should exist for about 20 min at the level of the F-layer maximum. The disturbed plasma volume can leave the region irradiated by the heater and move away for over 500 km within the above-mentioned time period.     

Planetary Missions of the 20th Century*

Among of the highlights of the 20^th century were flights of spacecraft to other bodies of the Solar System. This paper describes briefly the missions attempted, their goals, and fate. Information is presented in five tables on the missions launched, their goals, mission designations, dates, discoveries when successful, and what happened if they failed. More detailed explanations are given in the accompanying text. It is shown how this enterprise developed and evolved step by step from a politically driven competition to intense scientific investigations and international cooperation. Initially, only the USA and USSR sent missions to the Moon and planets. Europe and Japan joined later. The USSR carried out significant research in Solar System exploration until the end of the 1980s. The Russian Federation no longer supports robotic planetary exploration for economic reasons, and it remains to be seen whether the invaluable Russian experience in planetary space flight will be lost. Collaboration between Russian and other national space agencies may be a solution.     

Using the PROGRESS transport spacecraft in structure of the International Space Station for realization of scientific experiments under microgravity conditions

The problem is considered of using the PROGRESS transport spacecraft, which will deliver the payload on the ISS, as a free flying platform for realization of space experiments. For maintenance of the ISS 5-6 PROGRESS flights per year are planned. Usually after delivery of the payload the PROGRESS undocks from the ISS and burns down in the Earth atmosphere. However, the operating conditions of its onboard systems allow to prolong operation and to make free flight near to the station and repeatedly to be docked to it. It is offered to use this possibility for performing experiments on Material Science.     

Synthesis of biomass and utilization of plants wastes in a physical model of biological life-support system

The paper considers problems of biosynthesis of higher plants' biomass and "biological incineration" of plant wastes in a working physical model of biological LSS. The plant wastes are "biologically incinerated" in a special heterotrophic block involving Californian worms, mushrooms and straw. The block processes plant wastes (straw, haulms) to produce soil-like substrate (SLS) on which plants (wheat, radish) are grown. Gas exchange in such a system consists of respiratory gas exchange of SLS and photosynthesis and respiration of plants. Specifics of gas exchange dynamics of high plants--SLS complex has been considered. Relationship between such a gas exchange and PAR irradiance and age of plants has been established. Nitrogen and iron were found to the first to limit plants' growth on SLS when process conditions are deranged. The SLS microflora has been found to have different kinds of ammonifying and denitrifying bacteria which is indicative of intensive transformation of nitrogen-containing compounds. The number of physiological groups of microorganisms in SLS was, on the whole, steady. As a result, organic substances--products of exchange of plants and microorganisms were not accumulated in the medium, but mineralized and assimilated by the biocenosis. Experiments showed that the developed model of a man-made ecosystem realized complete utilization of plant wastes and involved them into the intrasystem turnover.     

Electrostatic Noise Spectrum at the Electron Cyclotron Frequency and Electromagnetic Emission in the Inhomogeneous Plasma of the Topside Ionosphere

Measurements of the wave emission of the topside ionosphere made onboard the APEX satellite using the electric component of the wave field in the 0.1–10 MHz frequency band are presented. At middle latitudes a wave intensity decrease was observed in the broad-band spectrum of the electrostatic noise at the electron cyclotron frequency. It is shown that a break in the spectrum of electrostatic modes at the electron cyclotron frequency (the absence of the plasma eigen-frequencies) may be a cause of the observed effect. The increase of the intensity at the electron cyclotron frequency in the ionospheric trough and at latitudes above the trough region as compared to middle latitudes may be explained by the capture by plasma irregularities of the electromagnetic emission of the auroral electron fluxes.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 3, 2005, pp. 201–208.Original Russian Text Copyright © 2005 by Izhovkina, Prutensky, Pulinets, Kiraga, Klos, Rothkael.     

Statistical study of interplanetary condition effect on geomagnetic storms: 2. Variations of parameters

We investigate the behavior of mean values of the solar wind’s and interplanetary magnetic field’s (IMF) parameters and their absolute and relative variations during the magnetic storms generated by various types of the solar wind. In this paper, which is a continuation of paper [1], we, on the basis of the OMNI data archive for the period of 1976–2000, have analyzed 798 geomagnetic storms with D _st ≤ −50 nT and their interplanetary sources: corotating interaction regions CIR, compression regions Sheath before the interplanetary CMEs; magnetic clouds MC; “Pistons” Ejecta, and an uncertain type of a source. For the analysis the double superposed epoch analysis method was used, in which the instants of the magnetic storm onset and the minimum of the D _st index were taken as reference times. It is shown that the set of interplanetary sources of magnetic storms can be sub-divided into two basic groups according to their slowly and fast varying characteristics: (1) ICME (MC and Ejecta) and (2) CIR and Sheath. The mean values, the absolute and relative variations in MC and Ejecta for all parameters appeared to be either mean or lower than the mean value (the mean values of the electric field E _y and of the B _z component of IMF are higher in absolute value), while in CIR and Sheath they are higher than the mean value. High values of the relative density variation sN/〈N〉 are observed in MC. At the same time, the high values for relative variations of the velocity, B _z component, and IMF magnitude are observed in Sheath and CIR. No noticeable distinctions in the relationships between considered parameters for moderate and strong magnetic storms were observed.     

On the structure of the floating zone in melting

Floating zone melting is used in crystal growth and purification of high melting materials. The use of a reduced gravity environment will remove the constraint imposed on the length of the zone by the hydrostatic pressure. The equilibrium of the floating zone may involve, (1) Hydrostatic forces, when the zone rotates as a whole. (2) Convective driving forces, when the zone is stationary but fluid property gradients appear. (3) Hydrodynamic forces, when some parts of the zone are set into motion with respect to others. The last effects are considered in this paper. The flow pattern of a floating zone held between two discs in relative motion is complicated, and thence the solution of the problem is difficult even assuming a constant property-newtonian liquid. Nevertheless, when a small parameter appears in the problem, the complete flow field can be split into zones where simple solutions are found. To illustrate this approach, the spin-up from rest of an initially cylindrical floating zone is considered with detail. Here the small parameter is the time elapsed from the impulsive starting of motion. Since the problem which has been considered, as well as some others which can be tackled by use of similar methods, concern the viscous layer close to either plate, they can be simulated experimentally in the ground laboratory with short floating zones. Procedures to produce these zones are indicated.     

Erratum to: Postvolcanic Aerosols: Measurements of Altitude and Particle Sizes with Twilight-Sky Polarimetry

Cosmic Research - An Erratum to this paper has been published: https://doi.org/10.1134/S0010952521110010