Vol 15, No 2 (2016)

The problem of forming command control of the subhypersonic first stage of an aerospace system in climb is considered. Passive motion of spacecraft in conditions of maximum atmospheric density disturbance is analyzed. Achieving the prescribed value of the angle of climb is the terminal motion condition. Terminal height is a controlled value. An algorithm of terminal control for the formation of command value of aerodynamic lift coefficient is proposed. The Newton method with one or more iterations at the correction step is used in determining command control. The serviceability and efficiency of the algorithm compensating the influence of variations of atmospheric density on the preset terminal altitude condition of spacecraft motion are analyzed. The results of simulating spacecraft motion with terminal control for maximally «rarefied» and maximally «dense» atmosphere are discussed. Possible improvement of the terminal control algorithm is suggested. 

The article describes the equipment for the future spacecraft «Resource-PM». The main technical characteristics of the equipment are presented. The equipment includes an optical system, panchromatic and multispectral optoelectronic converters, a memory unit, a control unit and star sensors. The design specification for the equipment included unprecedented requirements for the resolution, efficiency, sensitivity and accuracy of coordinate referencing. In order to meet the requirements a new large-sized optical system, three types of large-format photo sensors, multichannel interference light filters, a high-speed large-format matrix for the star tracker, new algorithms of digital processing and compression of information, high-speed interfaces of data transmission with fiber-optic components had to be developed The structure of the optical system incorporates a carbon fiber dimension-stable structure, which, combined with lighter mirrors ensured light weight of the objective and high image quality. The equipment makes it possible to survey the Earth surface in panchromatic and eight narrow spectral channels with high spatial resolution. 

The study presents the principles of application of simulation modeling in conducting static tests of aerospace products using the small satellite (SS) «Aist-2D» as an example. Limitations of static tests that do not allow comprehensive analysis of the stress-strain state of a satellite are discussed. For example, it is not always possible to install sensors for measuring stress in remote locations. Simulation static tests using the finite element method with the use of the finite- element analysis MSC. Patran/Nastran package is proposed as an additional method of analyzing the stress-strain state of a product. The goals and tasks of the simulation tests are formulated and the main stages of the simulation modeling tests are described. To obtain consistent results of simulation modeling tests validation of the finite- element model of a satellite is required. The validation consists in confirming the adequacy of the model by analyzing the stress-strain state of the structure of the satellite. The main advantage of the simulation modeling test is the reduction of the cost of preparing and conducting the static tests. The efficiency of the method was confirmed in conducting the simulation modeling tests of the SS «Aist-2D», held in parallel with the static tests of the satellite. Thus, the application of the method of simulation modeling of static tests makes it possible to reduce the costs of static tests, improve the quality of static strength experiments and, consequently, increase the reliability of the satellite.

Obtaining a new optimal law of controlling onboard magnetic coils that would provide reduction of the angular momentum of nanosatellites and microsatellites to a predetermined small value and subsequently maintaining it is discussed in the paper. The study shows that the use of a new time-optimal control law contributes to a significant increase in the high speed performance of the magnetic attitude control system in the tasks of reducing angular momentum of satellites to small values. The problem of satellite angular rate damping in accordance with a reference model – a system of three independent linear homogeneous equations – is discussed as well. Some numerical results of the application of these laws to the problem of reduction of satellite angular momentum and angular velocity are presented. Advantages and drawbacks of the new time-optimal laws of control of angular momentum of nanosatellites and microsatellites are specified.

New optoelectronic telescopic complexes to be implemented are currently selected on the basis of painstaking  and long-term research in which scientific research institutes of the customer and space-rocket branch, as well as enterprises specializing in producing optoelectronic telescopic complexes and space vehicles of Earth remote sensing take part. A technique of ranking optoelectronic telescopic systems according to the degree of influence on the target characteristics of a space observation system (linear ground resolution, frequency of observation, accuracy of georeferencing, efficiency of delivery of remote sensing information etc.), taking into account possible changes in the design parameters of remote sensing spacecraft and the cost of new projects is proposed. The technique is based on the use of software for preliminary estimates of mass-dimensional and other design parameters of ERS satellites depending on the preset performance targets of space systems. The method proposed makes it possible to carry out prompt analysis of the efficiency of implementing some technology connected with choosing the design characteristics of Earth remote sensing space satellites equipped with optoelectronic telescopic systems.

The stability of motion of a space tether system with an atmospheric probe is investigated in the paper. The equilibrium position stability of a space tether system near the local vertical (static stability) and deployment stability (dynamic stability) is studied. A tether system consists of spacecraft from which the tether is deployed and an atmospheric probe. The Lagrangian method is used to derive a dynamic model of the tether system’s motion in a mobile orbital system of coordinates considering aerodynamic forces acting on the spacecraft and the probe. The conditions of tether system motion stability with respect to the local vertical are determined.  Analytical analysis is confirmed by numerical examples.

The paper presents the results of an experiment on the formation of thin films of barium disilicide (BaSi₂) – a promising material for solar cells using the method of solid-phase epitaxy.  BaSi₂ was formed in ultrahigh vacuum on silicon substrates with the use of template technology. At the final stage of the formation of nanostructures the films were recrystallized by annealing. The resulting thin films were investigated by in-situ methods: Auger electron spectroscopy and electron energy loss spectroscopy. Then ex-situ techniques were used: atomic force microscopy and X-ray diffraction. The latter method showed the presence of a-oriented barium disilicide in the film formed at the temperature of recrystallization T = 800 ⁰ C. The spectra of Auger electrons and electron energy loss for the film are presented. The analysis of surface topology nanostructure obtained by atomic force microscopy shows that its surface roughness is comparable with the roughness of thin BaSi₂ film samples formed by molecular beam epitaxy. The reason for a small amount of crystallites BaSi₂ formed, as we see it, is low interdiffusion of barium and silicon atoms in the case of using the chosen method of forming a film. The use of the Ba and Si co-deposition technique, followed by recrystallization of the film at temperatures close to the temperature specified in the paper appears to be the solution of this problem.

The study covers the development of a mathematical model of a micro gas turbine (MGTE) operating under transient conditions using a recurrent neural network. The compressor inlet temperature and pressure depending on the aircraft height and speed are taken into account explicitly. A full-size mathematical dynamic MGTE model based on engine per-unit description was used to verify the developed model. The obtained model was compared with the existing one employing normalized parameters of aircraft flight level and airspeed. The simulation suggests that the proposed model yields significantly smaller errors than the existing one, whereas the computation time of both models differs insignificantly.

The article suggests an empirical method of predicting noise of aircraft gasoline engines with carburetion used in light and unmanned aviation. The method is based on classical approaches of aeroacoustics to the calculation of environmental noise from different sources. The spectrum of acoustic power is proposed to be obtained on the basis of an empirical model similar to the known M. Khekl҆ model for the calculation of noise of internal combustion piston engines of ground application, but at the same time taking into account the key features of aircraft engines. The calculated and experimental data on integral characteristics of the acoustic field of aviation piston engines are shown to be in good agreement. Experimental data on the noise of aviation piston engines like Ash-62IR, M-14P, ROTAX-912ULS with and without cowling, ROTAX-582UL were obtained during acoustic tests of light propeller aircraft  An-2, Yak-18T, MAI-223M, MAI- 890U and MAI-890, respectively, under static conditions at a local aerodrome. At the same time the acoustic field of the piston engine was supposed to be axially symmetrical relative to the crankshaft axis and the noise of the engine was determined by the total radiation at the harmonics of flash recurrence rate in the cylinders.

A procedure of assessing the main characteristics of angular velocity inertial meters of middle and low accuracy classes, including measuring channel noise terms is proposed. The procedure is based on the processing of the meter output information by means of the Kalman discrete filter and the Allan variance method. The characteristics to be estimated are: scale coefficient errors and zero signal shifts, as well as series of standard noise terms. Estimates of the method error level for the procedure under consideration are given on the basis of mathematical simulation of the measurement information and its correction with different estimated errors. An example of approbation of the technique is processing the results of tests conducted for two inertial meters based on different operating principles. One of them is the ADIS16405 device developed by Analog Devices (USA) on the basis of three micromechanical gyroscopes of low- accuracy class and the other is the ВГ910-МК470 device designed by Fizoptika, CJSC (Arzamas city) which consists of one fiber-optic gyroscope of the middle -accuracy class.

The paper introduces a method of prompt orthotransformation of space images, based on the integration of the orbital and polynomial methods of photogrammetric image processing. The concept of the method consists in fragmentary formation of an orthoimage. Fragments (quadrangles) of a definite size are marked in space images, so that geometric constraints between their elements are adequately described by a bidimensional polynom of the first order. The adjacent fragments have common vertexes on the contact line, providing integrity of the orthoimage being formed. The location of the fragment (the coordinates of its vertexes) is defined by the orbital method with consideration for the configuration of terrain, thus, if the fragment is small enough, it provides terrain correction for all the points of the fragment. To use the orbital method we define initial values of the orientation angles of the on-board equipment of the spaceship and the laws of variations of these angles in course of survey with subsequent specification of these values in terms of the coordinates of four check points. The compliance between tolerance points of fragments of the initial image and the image being formed is achieved on the basis of the models, the implementation of which is computationally less complex than that based on orbital methods. Experimental approbation of the proposed method proved that the method of prompt orthotransformation makes possible four-fold reduction of the time of photogrammetric space image processing   while providing comparable accuracies of the resulting images.

The paper presents an analysis of approaches to using apriori information on relief to improve the quality of spaceborne SAR data interferometric processing. The impact of relief on geometric matching of SAR images is analyzed and an algorithm of fast and high-precision SAR image matching based on polynomial approximation of relief height impact is proposed. The necessity of perpendicular baseline refinement, given the current accuracy of navigation data, is shown. The need of using reference relief to refine the baseline is also shown. The expediency of baseline refinement before and after phase unwrapping is substantiated.  The impact of the steepness of relief slope on the coherence estimation is calculated. The existing methods of phase unwrapping are analyzed and an algorithm of their combining is proposed, based on apriori information on each method. A criterion for selecting areas on the interferogram where the true phase varies greatly from pixel to pixel because of the steep relief slope is presented. Phase – to - height conversion is also considered. Using publicly available global low resolution DEMs as apriori information on the relief is proposed.