Vol 15, No 1 (2016)

Modal testing is an efficient tool for checking and updating of computational dynamic models of aircraft. Test objects are fixed by special elastic suspension systems during the modal testing time. Stiffness characteristics of such systems are determined on the assumption that the impact of the suspension on the eigentones of elastic vibrations of a freely flying aircraft should not exceed the pre-arranged level. It is therefore considered that the vibration frequency of the structure as a rigid body on the suspension should be several times lower than the natural frequency of the first flexible mode. Besides, different sources recommend various ratios between these frequencies. As to the modal testing of large flexible space structures, the task of creating such a suspension becomes many times more difficult because such structures can have very low natural frequencies of flexible modes. The influence of the suspension system on the accuracy of the aircraft modal testing results manifests itself in two ways. On the one hand, the use of the suspension leads to an increase of all natural frequencies of the test object. On the other hand, the occurrence of modes of the object as a rigid body with non-zero frequencies leads to the aircraft phase resonance frequency shifts which determine the natural frequencies of flexible mode tones. The paper presents a technique for correcting an aircraft computational dynamic model taking into account the suspension system. The correction is based on the fact that the errors in measurement of displacements in modal tests (i.e. eigenmodes as well) are greater than the errors in determining natural frequencies by more than an order of magnitude. The effect of modes of an object as a rigid body on an elastic suspension system on the accuracy of determination of its natural frequencies, generalized masses and generalized damping factors of flexible modes is analyzed.

Currently, creation of space -based P-band radar systems is a vital problem in the development of Earth remote sensing systems. These systems make it possible to solve the problem of monitoring vegetation on the Earth’s surface, to carry out soil analysis and detect objects detecting hidden in foliage. Such systems are, however, difficult to produce due to the necessity of using large- aperture antenna systems. Expanding active phased arrays and reflector antennas are most common for the task. Structures of this kind are characterized by considerable mass and dimensions, which does not make it possible to regard small satellites as their carriers. A system with an array of four transceiving Yagis is proposed. The systems are shown to possess sufficient characteristics to solve the target tasks. The structure’s simplicity makes it possible to install the systems on small satellites, which drastically reduces the cost and time of production.

The paper deals with the problem of choosing the type and the main design parameters of the correcting propulsion system of spacecraft functioning in low near-circular Earth orbits. The efficiency of using chemical (impulse) and low-thrust electric propulsion engines is analyzed. Analytical relations for calculating spacecraft design parameters and specifying the areas of efficient use of electric propulsion engines are obtained for the criterion of useful load fraction and the assumption of constant power dependent acceleration. The results of calculating the areas of efficient use and design parameters of spacecraft for various operational altitudes are shown.

The paper presents various schemes of flight of a separated part of the first stage, equipped with the reactive recovery system taking a two-stage oxygen-kerosene medium class launch vehicle assembled on the basis of the results of ballistic design and similar to the“Falcon-9” launcher in its power mass characteristics. The results of assessing the change in the payload mass placed into the low-earth orbit by the launcher, estimating the change in the value of the mass ratio of the first-stage recovery system and limit values of aerodynamic and heat loads of the first stage in the phase of recovery depending on the flight scheme are presented. The values of the mass ratio of the recovery system depending on the flight scheme are compared with that of the mass ratio of an aircraft-type recovery system. The advantages of the reactive recovery system in comparison with the aircraft-type recovery system are pointed out. The necessity of using an additional retroburn by restarting the service propulsion system of the stage prior to the re-entry with the aim of reducing aerodynamic and heat loads. It is shown that the reactive way of recovery can be implemented with acceptable energy losses only by making an intermediate landing on the complex located along the flight course.

The paper presents an algorithm of damping the initial angular rate of the SamSat-218D nanosatellite after its separation from the transporting-launching container. Three mutually orthogonal magnetic coils are used as actuators that provide damping of the initial angular rate on board the nanosatellite. The traditional B-dot algorithm is used as the damping algorithm. Two operating modes are possible for the B-dot algorithm: a continuous mode and a discrete one. As the continuous operating mode of the magnetic coils onboard the nanosatellite in orbital flight is inexpedient because of the necessity of measuring the Earth magnetic field intensity vector the discrete mode of operating of the algorithm of damping the initial angular velocities acquired by the nanosatellite after its separation from the transporting-launching container is analyzed. The results of the mathematical simulation during the analysis of choosing discretization intervals in the algorithm of damping the initial angular rate of the SamSat-218D nanosatellite are presented.

The paper presents the results of an experiment using the «Space system of microacceleration compensation» (SSMC) scientific hardware. The SSMC hardware has been developed and manufactured at the Institute of Space Device Engineering of Samara State Aerospace University with the participation of the Joint Stock Company «Space Rocket Center «PROGRESS» and operated on the Photon-M №4 spacecraft in the period from July 18 to September 1, 2014. The experiment is dedicated to collecting information about the values of the magnetic field of the Earth and compensating accelerations by comparing the measured values with the calculated values for IRGF model. Characteristics of the SSMC scientific hardware and the basic data obtained in the analysis of telemetry data are presented. An averaged picture of distribution of the magnetic field of the Earth during the experiment is obtained.

The article discusses the option of using video images to determine the orientation and the position of the second nanosatellite relative to the first one by a series of snapshots made by the first nanosatellite. Optical cameras installed on the first nanosatellite are used as measuring devices. A new approach has been developed to solve the task set. The approach includes an image processing algorithm, a genetic algorithm of differential evolution and a model of motion relative to the center of mass. The approach takes into account the requirements imposed on the nanosatellite hardware that sets limitations on the computational resource of the airborne digital computer and on the quality of images obtained from the optical camera. The developed approach is more economic than similar algorithms. The approach was verified by the benchmark problem of separating two nanosatellites in a short time interval. The dependence of the coordinates of the center of mass of the second satellite on the current orientation and pixel orientation target coordinates in the shot is revealed. The paper includes graphs of the error of determining orientation and position of the center of mass of the second satellite relative to the first one. The approach demonstrates acceptable accuracy in the range of up to 10 seconds for the problem under consideration. The accuracy decreases dramatically as the distance between the two nanosatellites increases.

The paper presents technologies of reducing the technological environmental impact of man-made space launch vehicles (SLV) based on controlled descent and trajectories of deorbiting the spent stages, burning of the separated nose fairing halves and tail section in the atmosphere. Controlled descent of a spent stage is accomplished due to the installation of an active on-board recovery system that uses unexpended remnants of the liquid components of propellant in the tanks. The burning of the fairing and tail section is based on the introduction of pyrotechnic compositions in their designs. Practical possibility of implementing this technology is shown taking the SLV «Soyz-2.1.b» space rocket as an example. It makes it possible not only to provide a solution to the basic environmental requirements, but also to improve the performance characteristics of the SLVs, move to a new technical level of their designing and operation. Using the technology of gasification of liquid residual propellants  allows  controlled  descent  of  separating  SLV  stages  with  the  scatter  of impact points less than1 km, displacement of the impact range to 15% and increasing the mass of the payload due to the maneuver of the SLV lower stage to the intended impact area to 5% of the initial payload mass.  The mass of additional equipment required for the implementation of this technology can be up to 3-5% of the «dry» structure of the SLV separating part.

Elastic-damping supports are widely spread in the design of aviation gas-turbine engines. These supports include elastic elements of the «squirrel cage» type.  A methodology of calculating the flexibility matrix for the «squirrel cage» with straight rod elements of rectangular cross-section with account for groove rounding is presented in the paper. Determining the flexibility matrix is essential for constructing mathematical models of aviation gas turbine engines when solving problems of rotor dynamics. The methodology is based on the application of Mohr integral for beam constructions. The results obtained with the help of the methodology are compared with the results of calculations in the finite-element complex and with the results of calculation without regard for the rounding, as well as with results obtained by other authors.

The main principles of choosing the capacity of a high-speed radio data link for modern Earth remote sensing spacecraft are discussed in the paper. The following points are taken into account: overfilling of the onboard memory storage device; duration of communication sessions between the spacecraft and the downlink point; the required bandwidth and the reliability of the radio data link. Mathematical restrictions for the conditions of the overflow of the on-board memory storage of target information and the amount of information transmitted to the downlink points during a communication session between the spacecraft and the downlink point are specified. An expression is proposed for the estimation of radio data link capacity on the basis of the Shannon formula with account for the energy relations for satellite communication links, the required width of the passband and the probability of data transmission error. The influence of the probability of the information transmission error and the main parameters of the radio signal (the speed of protective coding and the phase deviation) on the value of high-speed radio data link capacity is analyzed. Changes in radio data link capacity in retrospect for the years immediately ahead are analyzed in accordance with the predicted value of the required volume of space information of Earth remote sensing for radio data links of different reliability.

A prototype of the hyperspectrometer based on the Offner scheme has been tested. Drawings have been produced and the main mirror elements of the hyperspectrometer including diffraction grating on a convex spherical surface have been fabricated. The profile of the grating groove has been measured and light energy distribution in diffraction orders has been modeled as a function of wavelength. Optomechanical elements for the necessary alignments of the hyperspectrometer elements have been designed and manufactured. Adjustment of the optical prototyping scheme has been implemented and point images for three wavelengths of monochromatic radiation have been obtained. Distribution of light energy in diffraction orders and maxima positions are in an agreement with the simulation results. The spectrometer has also been tested on test images in polychromatic radiation under the control of the developed software.

The paper deals with the possibility of application of generic concepts based on the use of multiple programming paradigms with the aim of providing uniform access to universal data storage. The investigation is conducted using the example of developing a library of software components within the framework of the project of creating an expert system using the information base of the Topos Pro software package. The aim of the paper is to check the possibility of forming mechanisms for construction of independent components for access and data processing that would make it possible to produce software products with a low level of coupling and high cohesion. In this case, the concrete implementation would be characterized by conceptual integrity and would provide better understanding of the design process. Storage structures and data access facilities should be associated with what is considered in the article as generic concepts of container class adapters and iterators. This makes it possible to present the program code as a set of elementary independent primitives forming the basis for application logic design in terms of generic abstractions implying the process of extending library components and their adaptation to the domain area. The approach of using multiple programming paradigms coupled with the possibility of extension and setting of newly-created components based on library abstractions provides a new level of understanding programming. The generic concepts in this case become the main tools, while implementations of specific classes on their basis can be set through the use of overloading, aggregation, inheritance and specification of requirements for an abstract data type. After the pre-implementation of some library components and specific classes of access to a universal data model a conclusion can be made that the chosen strategy of interaction with the universal storage based on generic concepts is the best. It makes possible to reduce the complexity level as well as the LOC and allows the developer to concentrate only on the domain logic of applications providing access to the databases supporting the universal data model.