Методы сохранения оптических свойств поверхности зеркал космического телескопа Т-170М проекта «Спектр-УФ» на этапе предполётной подготовки

Astrophysical observations in the ultraviolet band have many advantages. At present, the «Spektr-UF» project is under implementation to create a large space observatory for operation in the ultraviolet spectrum.Requirements for the ultraviolet telescope optics quality are extremely high. Therefore, both to manufacture such a large space telescope as the T-170M and to transport it to the launch complex are rather difficult challenges in terms of technology.When manufacturing optical elements of the telescope T-170M, a combination of Al+MgF2 coatings has been preferred. At the same time, atmospheric oxygen penetrates through the pores in the magnesium fluoride, thereby forming a Al2O3 oxide layer on the sputtered aluminum, which significantly degrades the UV reflectivity of the mirror surface. It is also necessary to fulfill the requirements for surface cleanliness of optical system elements of the telescope during the finished product transportation and its storage and to provide for the autonomous operation of the system that maintains atmosphere control.To solve the set tasks:1)    a dust-proof-and-moisture-proof sheath (DPAMPS) was designed to prevent the optical system mirror surfaces of the telescope from coming in contact with atmosphere;2)    to provide a controlled atmosphere inside the DPAMPS the need is justified to blow gaseous nitrogen of special purity (grade 1) in accordance with GOST 9293-74 with a dew point temperature of -50°С, at most, inside the telescope; calculations have proved that charging with the super-atmospheric pressure of 10 kPa provides the optimal conditions for maintaining the optical properties of the space telescope mirrors surface, and also minimizes the loads on the easily damaging elements of the telescope;3)    to ensure the required cleanliness of the optical system elements surfaces of the telescope inside the DPAMPS, a class of purity Class 7 ISO, at worst, is established in accordance with GOST ISO 14644-1-2002; contamination tolerance of optical system components being, at most, 0.03% of the total surface area (300 p.p.m.) is provided by the rational choice of the blow-down scheme of the telescope with feeding nitrogen through the equipment bay;4)    a rational design of the supercharger using a gas analyzer and boost valves with external feedback provides driving pressure and operation autonomy of the system that maintains atmosphere control.Астрофизические наблюдения в УФ-диапазоне обладают многими преимуществами. В настоящее время идёт выполнение проекта «Спектр-УФ», направленного на создание крупной космической обсерватории для работы в ультрафиолетовом участке спектра.Требования к качеству оптики ультрафиолетового телескопа предельно высоки, поэтому изготовление такого крупного космического телескопа, как Т-170М, а также его транспортировка на стартовый комплекс – весьма сложные технологические задачи.При изготовлении оптических элементов телескопа Т-170М сделан выбор в пользу сочетания покрытий Al+MgF2. При этом через поры во фториде магния проникает атмосферный кислород, приводя к образованию на напылённом алюминии слоя оксида (Al2O3), который значительно ухудшает УФ-отражательную способность поверхности зеркала. Также необходимо выполнить требования к чистоте поверхностей элементов оптической системы телескопа при транспортировке готового изделия и его хранении и предусмотреть автономность работы системы поддержания контролируемой атмосферы.Для решения поставленных задач:1) был разработан пылевлагозащитный чехол (ПВЗЧ), предотвращающий контакт поверхностей зеркал оптической системы телескопа с атмосферой;2) для создания внутри ПВЗЧ контролируемой атмосферы обоснована необходимость выполнения поддува внутрь телескопа газообразного азота особой чистоты (сорт 1) в соответствии с ГОСТ 9293-74 с температурой точки росы не выше -50°С; расчётами подтверждено, что наддув избыточным давлением 10 кПа обеспечивает оптимальные условия сохранения оптических свойств поверхности зеркал космического телескопа, а также минимизирует нагрузки на легкоповреждаемые элементы телескопа;3) для обеспечения требуемой чистоты поверхностей элементов оптической системы телескопа внутри ПВЗЧ установлен класс чистоты не хуже класса 7 ИСО в соответствии с ГОСТ ИСО 14644-1-2002; допустимое загрязнение деталей оптической системы не более 0,03% от общей площади поверхности (300 p.p.m.) обеспечено рациональным выбором схемы продува телескопа подачей азота через инструментальный отсек;4) рабочее давление и автономность работы системы поддержания контролируемой атмосферы обеспечены рациональной конструкцией агрегата наддува с использованием газоанализатора и клапанов наддува с внешней обратной связью

Microarc Oxidation of Product Surfaces without Using a Bath

While using an electrochemical method to cover the large-sized work-pieces, units, and products up to 6 м3 by protective coating, there is a certain difficulty to apply traditional anodizing techniques in a plating vat, and it is necessary to find various processing techniques.To use the existing micro-arc oxide coating (MOC) methods for work-pieces of various forms and sizes in a plating vat is complicated in case it is required to provide oxide layers in separate places rather than over entire surface of a work-piece. The challenge is to treat flat surfaces in various directions, external and internal surfaces of rotation bodies, profiled surfaces, intersections, closed and through holes, pipes, as well as spline and thread openings for ensuring anti-seize properties in individual or small-scale production to meet technical requirements and operational properties of products.A design of tools to provide MOC-process of all possible surfaces of various engineering box-type products depends on many factors and can be considerably different even when processing the surfaces of the same forms. An attachment to be used is fixed directly on a large-sized design (a work-piece, a product) or fastened in the special tool. The features of technological process, design shape, and arrangement of the processed surfaces define a fastening method of the attachment. Therefore it is necessary to pay much attention to a choice of the processing pattern and a design of tools.The Kaluga-branch of Bauman Moscow State Technical University is an original proposer of methods to form MOC-coatings on the separate surfaces of large-sized work-pieces using the moved and stationary electrodes to solve the above listed tasks.The following results of work will have an impact on development of the offered processing methods and their early implementation in real production:1. To provide oxide coatings on the surfaces of large-sized products or assemblies in a single or small-scale type of production by the other methods is impossible.2. There is a developed method to calculate volume electrolyte velocity while processing the large-sized work-pieces by means of moved electrode, taking into consideration the modes of MOC-coating formation and a design of the moved electrode. When processing a surface of 1dm2 depending on the modes of MOC-coating formation and a design of the moved electrode the volume electrolyte velocity will make 4 − 6 l/min.3. A descriptive design-engineering classification of methods for micro-arc oxide coating of separate surfaces of large-sized work-pieces is created on the basis of coated surface geometry, used electrode design, and formation method of a plating vat.4. The classified methods can be successfully used in creating technologies of large-sized products from titanic alloys, and the offered table is useful both for experts, and for students when studying electrochemical methods of processing.</p

Application of micro-arc oxidation methods in making the structure elements of spacecraft

When designing any spacecraft, the opening elements of the structure are applied in which deployment and locking units are used.There is a transporting step i.e. an insertion of the deployment unit in the folded state into orbit. During this step the deployment unit is under considerable vibratory loads, which are accepted by thrusts. Since the thrusts at this step work under increased wear conditions it is offered, considering a protuberant surface hardness of the micro-arc oxide (MAO) coating, to replace a constructional material of the thrusts with a larger density for the MAO-coated aluminium alloy.The step of deploying, at which required angle of deployment is provided by the rolling unit, is realized after the spacecraft has been placed into calculated orbit. This unit contains the target sleeve with the bearing, which provides reliable locking by means of the penetration in the inner cone of beam sector. To increase the product reliability and avoid a possibility for occurring the wear slot and burrs it is necessary to increase the hardness of the sector surface on which the target sleeve bearing rolls. The most rational solution is to form the local micro-arc oxide coating on the beam sector surface.Application of the micro-arc oxidation of aluminium alloys and research of the micro-arc oxidation specificities enable us:1) to decrease the typical deployment unit mass (by 0.221 kg or 0.85 %);2) to increase the rolling unit operation reliability;3) to design the schemes and select the conditions to form the micro-arc oxide coating on the parts of the typical deployment unit.The micro-arc oxide coating formed on the aluminium alloy is of significance for the aerospace industry that uses a diversity of aluminium alloys and prefers the structure mass decrease as much as possible. It should be appreciated that the process to form the micro-arc oxide coating is production friendly because it does not need the complex expensive equipment and is easily regulated by changing the electrolyte composition and the current conditions.</p

Investigating the Influence of Micro-Arc Oxide Coating on Rigidity and Strength of Long Force Elements of Spacecraft

Outboard elements (arms, towers) are widely used in spacecraft structure for setting-out of a payload; their high stiffness-weight ratio provides an opportunity to decrease the mass. The deployment unit is considered as an example of outboard structure. Its strength beams work under special conditions in operation. At the transportation stage beams are under considerable vibration loads. Therefore for increasing the natural resonance frequency it is rational to increase their rigidity. Using the micro-arc oxide coating suggests itself because the modulus of elasticity of the micro-arc oxide coating is more than that of the aluminium alloy. The beams suffer considerable bending load at the step of deploying; therefore the aluminium alloy with the micro-arc oxide coating must have suitable loading capacity, in addition to increased rigidity.Influence of micro-arc oxide coating on the rigidity and strength of tubes f rom aluminium alloy is investigated. It is determined that forming the micro-arc oxide coating on thin-walled tubes with a ratio of the coating area to the cross-section area of more than 25% is the most rational. In this case the rigidity of composite material considerably exceeds the rigidity of the aluminium alloy of the same cross-section while the redistribution of stresses in the surface coating of heterogeneous elasticity cross-section doesn’t cause the sudden increase of stresses. Also forming an attainable thickness of the micro-arc oxide coating on the surface of tube from aluminium alloy will be rational solution because the increase of attainable thickness of the microarc oxide coating provides an opportunity to form it on thick-walled tubes saving an acceptable, in the context of the strength, ratio of the coating area to the overall cross-section area.Micro-arc oxidation is an advanced method to form the wear resistant, resistant to corrosion, heat-shielding and electrically insulating coatings, but depending on the operating conditions, type of structures, and dominant type of deformations the choice of the micro-arc oxide coating thickness can have a considerable effect on the loading capacity of structure.</p

Zirconium Micro-Arc Oxidation as a Method for Producing Heat Insulation Elements in Spacecraft

Application of coatings on the surface of materials as well as their composition and structure control in the near-surface layer enables us to use properties of base material and modified layers in the most rational and profitable way and save expensive and rare metals and alloys.The space telescope of T-170M will be the main tool of the international space observatory "Spektr-UF".It is being understood that the main mirror shade, which is in the outer space and has a considerable height will act as a radiator cooling a unit (cage) of the main mirror. Therefore it is necessary to create heat insulation between the shade of the main mirror and the frame of the main mirror unit. From the thermal calculations a detail to provide heat insulation must possess thermal conductivity, at most, 2,5 and a conditional limit of fluidity for compression, at least, 125 MPas to ensure that the shade diaphragms position of the main mirror is stable with respect to the optical system of telescope.Considering that oxide of zirconium possesses one of the lowest thermal conductivities among oxides of metals, it is offered to use zirconium, as a material of base, and to put the MAO-covering (micro-arc oxide) on its surface.As a result of studying the features of MAO-coverings on zirconium it is:1) found that the composite material consisting of zirconium and MAO-covering on it, has low thermal conductivity (less than 2 ), and thus, because of small oxide layer thickness against the thickness of base material, possesses the mechanical properties which are slightly different from the pure zirconium ones;2) found that the composite material possesses the low gas release, allowing its use in the outer space conditions; the material processed in two electrolytes i.e. phosphate and acid ones has the lowest gas release;3) found that with growing thickness of MAO-covering its porosity decreases, thus the average pore diameter grows thereby leading to increasing thermal conductivity of MAO-covering. Therefore it is inexpedient to use thick MAO-coverings. Besides, adhesion between the covering and the base decreases;4) advisable to use a stack of thin washers in case it is necessary to apply the heat insulation of considerable thickness.</p

Optical Property Retention Methods for the T-170M Space Telescope Mirrors Surface in the Project «Spektr-UF» at the Preflight Preparation Stage

Astrophysical observations in the ultraviolet band have many advantages. At present, the «Spektr-UF» project is under implementation to create a large space observatory for operation in the ultraviolet spectrum.Requirements for the ultraviolet telescope optics quality are extremely high. Therefore, both to manufacture such a large space telescope as the T-170M and to transport it to the launch complex are rather difficult challenges in terms of technology.When manufacturing optical elements of the telescope T-170M, a combination of Al+MgF2 coatings has been preferred. At the same time, atmospheric oxygen penetrates through the pores in the magnesium fluoride, thereby forming a Al2O3 oxide layer on the sputtered aluminum, which significantly degrades the UV reflectivity of the mirror surface. It is also necessary to fulfill the requirements for surface cleanliness of optical system elements of the telescope during the finished product transportation and its storage and to provide for the autonomous operation of the system that maintains atmosphere control.To solve the set tasks:1)    a dust-proof-and-moisture-proof sheath (DPAMPS) was designed to prevent the optical system mirror surfaces of the telescope from coming in contact with atmosphere;2)    to provide a controlled atmosphere inside the DPAMPS the need is justified to blow gaseous nitrogen of special purity (grade 1) in accordance with GOST 9293-74 with a dew point temperature of -50°С, at most, inside the telescope; calculations have proved that charging with the super-atmospheric pressure of 10 kPa provides the optimal conditions for maintaining the optical properties of the space telescope mirrors surface, and also minimizes the loads on the easily damaging elements of the telescope;3)    to ensure the required cleanliness of the optical system elements surfaces of the telescope inside the DPAMPS, a class of purity Class 7 ISO, at worst, is established in accordance with GOST ISO 14644-1-2002; contamination tolerance of optical system components being, at most, 0.03% of the total surface area (300 p.p.m.) is provided by the rational choice of the blow-down scheme of the telescope with feeding nitrogen through the equipment bay;4)    a rational design of the supercharger using a gas analyzer and boost valves with external feedback provides driving pressure and operation autonomy of the system that maintains atmosphere control