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PREREQUISITES FOR MODELING NANOSATELLITE ELEMENTS IN SEMI-NATURAL MODE Juziyeva Sh.A.1, Yensebayeva M.R.2 (Republic of Kazakhstan) Em ail: Juziyeva571@scientifictext.ru
'Juziyeva Shynar Aitkozhayevna — Student; 2Yensebayeva Madina Rishatovna — Student, SPECIALTY: SPACE TECHNIQUE AND TECHNOLOGIES, KAZAKH NATIONAL RESEARCH TECHNICAL UNIVERSITY NAMED AFTER K.I. SATPAYEV, ALMATY, REPUBLIC OF KAZAKHSTAN
Abstract: to launch a satellite with a magnetic orientation system into orbit, it is necessary to work out how to control it in semi-natural conditions, this requires the creation of a ground stand. To create such conditions, it is necessary to simulate a geomagnetic field with a pattern of change similar to the movement of the satellite in orbit. Such stands already exist and are actively used for testing. Their functionality allows you to perform all the necessary manipulations to test the operation of the nanosatellite before its operation in real space conditions.
This senior thesis analyzes the capabilities of the SX025 stand, as well as simulations of testing nanosatellites in semi-natural mode, carried out in stages using three main control algorithms. Keywords: unloading of flywheels, initial spin damping.
МОДЕЛИРОВАНИЕ ЭЛЕМЕНТОВ НАНОСПУТНИКОВ
В ПОЛУНАТУРНОМ РЕЖИМЕ Джузиева Ш.А.1, Енсебаева М.Р.2 (Республика Казахстан)
'Джузиева Шынар Айткожаевна - студент; 2Енсебаева Мадина Ришатовна — студент, специальность: космическая техника и технологии, Казахский национальный исследовательский технический университет им. К.И. Сатпаева, г. Алматы, Республика Казахстан
Аннотация: чтобы запустить на орбиту спутник с магнитной системой ориентации, необходимо отработать, как управлять им в полунатурных условиях, для этого требуется создание наземного стенда. Для создания таких условий необходимо смоделировать геомагнитное поле с закономерностью изменения, аналогичной движению спутника по орбите. Такие стенды уже существуют и активно используются для проведения испытаний. Их функциональность позволяет выполнять все необходимые манипуляции для проверки работы наноспутника перед его эксплуатацией в реальных космических условиях.
В работе анализируются возможности стенда SX025, а также моделирование испытаний наноспутников в полунатурном режиме, выполненных поэтапно с использованием трех основных алгоритмов управления.
Ключевые слова: разгрузка маховиков, демпфирование начальной закрутки.
Introduction. Modem production of small space satellites requires minimization of costs for its design and operation. Most of these cost savings occur when the satellite's design characteristics are selected correctly, i.e. when its systems are optimized at the initial design stage. In this case, it is necessary to correctly evaluate the composition and characteristics of the orientation and stabilization system, which is difficult to do without modeling. Control algorithms and computer modeling play an important role, but it is very important to check their operation, feasibility and effectiveness in practice for a specific hardware composition at the first stages. In this case, an above-ground test bench is required. It is advisable to use it, in particular, for testing the onboard orientation control system at the first stages of design. Working at the stand is extremely useful for training students engaged in the development of nanosatellites.
The instrument structure of the satellite requires a three-axis orientation of the device relative to the orbital coordinate system, so it is necessary to dampen the initial angular velocity of the satellite after separation from the carrier. This process is performed using electromagnetic coils interacting with a geomagnetic field. This is followed by stabilization of the apparatus in the desired position with the help of flywheels.
Fig. 1. General view of the SX-025 test stand
The purpose of this article is to analyze the capabilities of the stand, as well as simulations of testing nanosatellites in semi-natural mode, conducted through two stages: an algorithm for damping the initial spin using current coils and an algorithm for controlling the layout orientation using flywheels.
Semi-natural simulation stands are widely used both in industry and in educational institutions, and play an important role in the design and simulation of real satellite systems, teaching students to create and test systems in conditions close to real operating conditions.
1. Analysis of the capabilities of the laboratory stand, taking into account its technical characteristics.
The General view of the SX-025 test stand is shown in Fig. 1. the stand includes: a layout of the orientation system, a magnetic field simulator, a Sun simulator, an aerodynamic suspension, a stationary control computer. The layout of the orientation system consists of the orientation and stabilization system itself, a single-Board computer with a wireless communication channel for transmitting data to a stationary computer, batteries, a software-controlled current source, and a platform balancing system on which all the system elements are installed.
The orientation and stabilization system consists of orientation detection sensors, Executive bodies, and an orientation system control unit [1]. As Executive elements of the orientation control system on the layout, electromagnetic current coils and control motor-flywheels are used. Current coils induce a controlled magnetic moment, which, when interacting with an external magnetic field, creates a controlling mechanical moment. The orientation and stabilization system control unit is the link between sensors and controls.
To simulate the geomagnetic field, the stand uses a system of three pairs of mutually perpendicular square coils (Helmholtz rings) The sun simulator creates a constant parallel luminous flux at a distance of up to 1.5 m with a power of at least 80,000 Lux. The par-64 searchlight with a Philips 1000W230V lamp was chosen as a Sun simulator. Thanks to the aerodynamic suspension, the movement of the layout has three degrees of freedom, namely rotation around three axes with minimal friction. The vertical axis can be rotated 360°, and the two horizontal axes can be rotated ±30°.The aerodynamic suspension consists of a pedestal and a bearing in the form of a hemisphere (Fig. 2). the Layout of the orientation system is attached to the bearing.
Fig. 2. Defining individual parts of the stand
One of the problems when implementing a successful test is the presence of air flows. That is, if there are no air flows in the laboratory and the layout equipment is working (which does not create large magnetic moments), the only problem is the unbalance of the layout. In turn, an unbalance can be caused by heating the layout elements (which causes the layout's center of mass to shift).
The total maximum error in determining the layout position using orientation sensors is up to 5°.
2A. Algorithm for controlling the layout orientation by unloading the flywheels.
This section provides a study of the controlled movement of the layout of the orientation system by unloading the flywheels. The following coordinate systems are used to describe the dynamics of an object.
OXYZ-laboratory coordinate system. The axis Lies in the horizontal plane and is directed along the vector of the magnetic field, which during experiments is set constant in the direction, OY-vertically down, and Ozdostraivaet this system to the right orthogonal coordinate system.
Oxyz-related coordinate system. Its axes are the main Central axes of inertia of the layout of the microsatellite orientation system.[4]
The dynamics of an object is described by the equation
Jro + rox Jro = Moutside - H- rox H.
Here J is the inertia tensor, w is the angular velocity vector, H is the vector, and Moutside is the moment of gravity associated with non- ideal layout balancing.
If the system is in equilibrium, the control determined by the second equation of the system will take the form
H= kaS,
The moment of gravity force is excluded from the control law, since it is unknown in advance (or rather, the displacement of the center of mass relative to the suspension point is unknown) and is considered as a perturbation. Thus, the presence of such a moment will affect the deviation of the Oyaxis from the vertical (axisOT). The lower thery(ry> 0), the greater the deviation.
The final deviation of the layout from the zero position is due to the fact that the unloading of the flywheels and stabilization occur during fixed consecutive time intervals.
2b. Algorithm for damping the initial spin using current coils.
One of the most frequently used Executive elements is magnetic coils. With their help, the satellite's own dipole moment m is created, which when interacting with the geomagnetic field with induction A mechanical moment is generated [11]
M= mx B.
The use of current coils has a number of advantages: no consumption of the working fluid, low cost compared to other common Executive elements (flywheels, jet engines), low energy consumption.
The use of magnetic coils is complicated by the inability to create any mechanical moment specified in the direction. As can be seen, the mechanical moment at any time lies in a plane perpendicular to the geomagnetic induction vector. Choosing the satellite's own dipole moment by changing the current in the coils allows you to determine the direction and magnitude of the mechanical moment vector in this plane. In addition, the accuracy of magnetic orientation systems is noticeably lower than the accuracy of, say, flywheels. This leads
to the fact that the magnetic coils are installed either together with other Executive elements, or at the stage of quenching the initial angular velocity after separation of the satellite from the launch vehicle. Conclusion.
Creating the article on a small satellite requires setting the minimal cost of design and operation stages. Essential savings in these expenses occur when the necessary design characteristics of the satellite are implemented, as well as when optimizing its systems at the first design stage. It is very important to be able to correctly assess the composition and characteristics of the orientation and stabilization system, and this is complicated process without the modeling. Nevertheless, mathematical and computer modeling plays a significant role, but it is very important to check their functionality, accessibility and effectiveness in practice for a specific hardware implementation at the initial stages. This requires a ground-based test bench. It is advisable to use it, in particular, for functional testing of the onboard orientation control system at the early stages of design. It is obtainable through correct implementation of the software on to the hardware system. To reach desirable results it's also significant to create the algorithms for the simulation program. The ground-based testing of orientation control algorithms led to the creation of a stand for semi-natural modeling, consisting of a magnetic field simulator and a layout suspended from a string. String suspension actually provides an imitation of one degree of freedom (rotation of the layout in a horizontal plane) or, if the suspension point coincides with the center of mass, three rotational degrees of freedom. Through the fix of all three elements of working stand (hardware, software and algorithms), the experimental results will play out the best for the final version of the satellite.
The SU satellites stand is very helpful as a training base for students dealing with the problems of orientation. Due to the fact that the new versions of satellites are announced every year, it's also essential to implement new software and update the hardware, to gain better results in shorter periods of time. Therefore, there is a great potential for the development of the existing stand. Previous research on the topic has determined that the use of two stands makes it possible to study the relative movement of two control objects, which is of interest in the task of joint flight of several satellites (formation flying configuration). It proves that SU stand is up to date, modern technology efficient in satellites testing and effective in improving the satellites' work in natural space environment. The importance for ground-based testing of orientation control algorithms led to existing stand for semi-natural modeling at the Department of Space engineering and technology at Satbayev University.
References / Список литературы
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