Synthesis of a combined system for precise stabilization of the Spektr-UF observatory: II

The paper presents the second part of the results of search studies for the development of a combined system of high-precision stabilization of the optical telescope for the designed Spectr-UF international observatory [1]. A new modification of the strict method of the synthesis of nonlinear discrete-continuous stabilization systems with uncertainties is described, which is based on the minimization of the guaranteed accuracy estimate calculated using vector Lyapunov functions. Using this method, the synthesis of the feedback parameters in the mode of precise inertial stabilization of the optical telescope axis is performed taking the design nonrigidity, quantization of signals over time and level, and errors of orientation meters, as well as the errors and limitation of control moments of executive engine-flywheels into account. The results of numerical experiments that demonstrate the quality of the synthesized system are presented.     

Criteria of applicability of a gas-dynamic approximation of a continuous medium to describing the dispersion of combustion products of rocket propellants

Two criteria for the applicability of a gas-dynamic approximation of continuous medium to describing the dispersion of combustion products of rocket propellants at high altitudes are formulated. Related numerical estimates are given for different launch vehicles and one upper stage with fairly extended boost phases. The use of a continuous medium approximation is shown to have a clear altitude restriction.     

Approaches to the development of biomedical support systems for piloted exploration missions

Many aspects of the biomedical systems developed and realized aboard orbital stations, the International space station in the first place, deserve to be regarded as predecessors of the systems for health monitoring and maintenance of future exploration crews. At the same time, there are issues and tasks which have not been yet fully resolved. Specifically, these are prevention of the adverse changes in body systems and organs due to microgravity, reliable protection from the spectrum of space radiation, and elucidation of possible effects of hypomagnetic environment. We should not walk away from search and development of key biomedical technologies such as a system of automated fitness evaluation and a psychodiagnostic complex for testing and optimization of operator′s efficiency, and others. We have to address a large number of issues related to designing the composite life support systems of the utmost autonomy, closure and ecological safety of the human environment that will provide transformation of all kinds of waste. Another crucial task is to define a concept of the onboard medical center and dataware including the telemedicine technology. All the above developments should assimilate the most recent achievements in physiology, molecular biology, genetics, and advanced medical technologies. Biomedical researches on biosatellites also do not lose topicality.     

Hypervelocity fragment formation technology for ground-based laboratory tests

Cumulative jet formation was regarded aimed at the formation of hypervelocity fragments up to 14 km/s for the investigation of space debris effects on shielding screens. The basic physical problems of jet formation process are analyzed. It is shown that in process of realization of hyper-cumulation conditions for jet formation without complete stagnation point involving formation of the inner zone of constant pressure (dead zone), the flow mass is always greater than slug mass. That opens wide the possibilities for increasing fragment mass in laboratory tests.     

Physical–chemical properties of plasma membrane and function of erythrocytes of cosmonauts after long-term space flight

We studied microfluidity and selective ion permeability of plasma membranes and O₂-binding properties of erythrocytes of cosmonauts during early rehabilitation after a long-term space flight (LTSF). Microfluidity of plasma membranes in surface regions was found to undergo a reversible decrease during 13–15 days following LTSF, which was accompanied by a reversible increase in relative cholesterol content. Cosmonauts’ erythrocytes revealed an increased activity of Na/H-exchanger and K_Ca-channel as well as a decrease in number of discocytes and increase in number of echinocytes, stomatocytes and knizocytes. Total hemoglobin content as well as oxyhemoglobin content were lowered after the LTSF, while the affinity of hemoglobin to O₂ was advanced. It is suggested that the changes in Hb properties, microfluidity and selective permeability of plasma membranes following the elevated cholesterol content in the membranes can decrease tissue supply with O₂.     

Non-linear methods in remotely sensed multispectral data classification

The aim of this research is to develop an effective approach being able to deal with the stochastic nature of remote sensing data. In order to achieve this objective it is necessary to structure the methodological knowledge in the area of data mining and reveal the most suitable methods for the prediction and decision support based on large amounts of multispectral data. The idea is to establish a framework by decomposing the task into functionality objectives and to allow the end-user to experiment with a set of classification methods and select the best methods for specific applications. As a first step, we compare our results from Bayesian classification based on non-parametric probability density estimates of the data to the results obtained from other classification methods. Tree scenarios are considered, making use of a small benchmark dataset, a larger dataset from Corine land cover project for Bulgaria and analyzing different features and feature selection methods. We show that the theoretically optimal Bayesian classification can also achieve optimal classification in practice and provides a realistic interpretation of the world where land cover classes intergrade gradually.     

PEGASO: An ultra light long duration stratospheric payload for polar regions flights

Stratospheric balloons are powerful and affordable tools for a wide spectrum of scientific investigations that are carried out at the stratosphere level. They are less expensive compared to satellite projects and have the capability to lift payloads from a few kilograms to a couple of tons or more, well above the troposphere, for more than a month. Another interesting feature of these balloons, which is not viable in satellites, is the short turnaround time, which enables frequent flights.     

On the motions of RHESSI flare footpoints

The footpoint motions of flare hard X-ray (HXR) sources are directly related to the reconnection scenario of a solar flare. In this work, we tried to extract the information of footpoint motions for a number of flares observed with RHESSI. We found that the RHESSI flare results of the footpoint motions strongly support the classification proposed from the observations of YOHKOH/HXT. Furthermore, it is found that a flare can consist of two types of footpoint motions. We discussed the connections of the footpoint motions with the two-dimensional reconnection models.     

Electron temperature anisotropy effects on tearing mode in ion-scale current sheets

Recent two-dimensional (2-D) particle-in-cell (PIC) simulations have shown that there is a critical thickness of a current sheet, above which no significant saturation amplitude of the 2-D tearing (TI) mode can be expected. Here, we have introduced the initial electron temperature anisotropy (α_e0 = T_e⊥/T_e|| > 1), which is known to raise significantly the linear growth rates, and inspected if α_e0 > 1 can change the saturation level of the TI in a super-critical current sheet. Varying α_e0 and D (D: the current sheet half-thickness) systematically, we have found that while α_e0 boosts up the linear growth rate in both sub- and super-critical current sheets, macroscopic effects are obtained only in sub-critical current sheets, that is, energy transfer from the fastest growing short wavelength modes to longer wavelength modes are available only in the sub-critical regime. Since the critical thickness is a fraction of the ion inertial length, the tearing mode assisted by the electron temperature anisotropy alone, despite its significant boost in the linear growth rate, cannot be the agent for reconnection triggering in a current sheet of ion-scale thickness.