Space Reflection Research Articles

Structure, structural features, assembling, and bench testing of the deployable space reflector

Structure, structural features, assembling, and bench testing of the deployable space reflector

Control system of the radio-reflective surface shape of a large-size space reflector using its current-conducting structural parts

A comprehensive approach to creating a control system for the shape of the radio-reflecting surface of a large-size space reflector is considered. Large-aperture space antennas are used for satellite communications and space exploration. The design of these structures is one of the most promising areas. Ensuring the specified characteristics of the reflector is directly related to maintaining the specified shape of the radio-reflective netting. Developing a control system for the shape of the active antenna surface is an urgent task. Optimizing this process makes it possible to accomplish the mission during the operational period effectively. The paper evaluates the effects of perturbations on a large-scale structure operating in outer space. A method for adjusting the geometry of the frontal network is proposed. This allows for improved communication between spacecraft and ground stations, which is very important for the safety of space flights. The conductive parts of the reflector are considered to transmit energy and control signals to the actuators. The application results of various control algorithms of the executive device making it possible to correct the netting considering the minimization of energy costs and oscillations of the structure are shown. According to the simulation results, the optimal algorithm of the target criteria hierarchy showed greater stability in terms of convergence in the presence of measurement noise and disturbances, which allows it to be applied in real time. This algorithm is supposed to be used in the future when creating a prototype of the system for controlling the shape of the radio-reflective surface of a large-size space reflector using its current-conducting structural parts.

Electrostatically Actuated X-Band Mesh Reflector with Bend-Formed Support Structure

Increasing the size of radio frequency (RF) reflectors in space can enhance gain and spatial resolution in applications such as space-based communication and remote sensing. The size of current passive deployable reflectors is limited by a tradeoff between diameter and surface precision, which causes RF performance to degrade as size increases. A promising approach to overcome this tradeoff is to combine in-space manufacturing, which enables large structures, with distributed embedded actuation, which enables precise control over the reflector surface. Here we demonstrate a reflector antenna system that integrates these two technologies, using a candidate in-space manufacturing process, termed “Bend-Forming,” with embedded electrostatic actuators. We design and fabricate a 1-m-diam prototype of an electrostatically actuated X-band reflector with a knitted gold-molybdenum mesh as the reflector surface, carbon-fiber-reinforced plastic booms as electrodes, and a truss support structure fabricated with Bend-Forming. We characterize the RF performance of this reflector, successfully demonstrating i) control over a wide range of focal lengths by suppressing a pull-in instability and ii) beam steering over an angular range of 4.2° via asymmetric electrostatic actuation. This work lays the foundation for future space communication and remote sensing technologies, offering a scalable solution to enhance RF performance through in-space manufacturing and precision control.

Controlling the Focusing Ability of the Parabolic Graphene Reflector in Free Space at Microwave Frequencies

The studied configuration is a two-dimensional, very thin parabolic reflector made of graphene and illuminated by an H-polarized electromagnetic plane wave. We present basic scattering and focusing properties of such a graphene reflector depending on the graphene parameters at microwave frequencies, using the resistive boundary condition for very thin sheets. The scattering is formulated as an electromagnetic boundary-value problem; it is transformed to a singular integral equation that is further treated with the method of analytical regularization (MAR) based on the known solution of the Riemann–Hilbert Problem (RHP). The numerical results are computed by using a Fredholm second-kind matrix equation that guarantees convergence and provides easily controlled accuracy. Compared to THz range, in microwaves, the scattering pattern of reflector and the field level at geometrical focus can be controlled in a wide range by adjusting the chemical potential of graphene. Even though here no dielectric substrate supporting the graphene is considered, the practical realization can also be possible as a thin layer graphene material in GHz range. As we demonstrate, the variation of the chemical potential from 0 to 1 eV can improve the focusing ability within the factor of three. The high accuracy of the used method and the full wave formulation of the problem support our findings.

სხვადასხვა სიმრუდის ზედაპირზე აგებული ტრანსფორმირებადი, პანტოგრაფული სტრუქტურები

The possibilities to design expandable-foldable structures on various curvature surfaces are considered in the given paper. The presented geometrical layouts are unfolding structures with closed and open contours. The transformable designs are made by an interconnected set of elementary pantographic structure. The elementary transformable structure consists of two levers connected by a transverse cylindrical joint. The considered designs of transformable structures can be effectively used in space structures, in particular deployable space reflectors, also in ground-based transformable structures.

THE METHOD OF ADJUSTING THE MULTI-FREQUENCY PROBING RADAR SIGNAL PARAMETERS AND THE TROPOSPHERIC RADIO WAVEGUIDE CHARACTERISTICS

Peculiarities of air circulation in the coastal zone of large reservoirs (large lakes or inland seas such as the Black and Azov Seas) can lead to a significant departure from the standard spatial distribution of meteorological and, accordingly, radiophysical characteristics of air.
 As a result, it is possible for regions of space with an abnormally low attenuation level of radio waves of certain frequency ranges to appear – tropospheric radio waveguides (TWG). The appearance of TWG leads to multi-beam propagation of radio waves and fluctuations of radar signals. Fluctuations of the radar signal lead to a decrease in the range of detection of aerial objects by radars. For single-frequency radar signals, it is only possible to estimate the degree of distortion and the amount of radar detection range loss. A paradoxical situation arises when, due to TWG, it is possible to increase the range of detection of aerial objects, but due to the distortion of the radar signal in TWG, the detection performance decreases. For multi-frequency signals, it is potentially possible to adjust the parameters of the radar signal with the parameters of the radar channel (in this case, the tropospheric radio waveguide).
 The adjustable parameters of a multifrequency signal include: the number of frequency components; bandwidth of the frequency component; average frequency of the frequency component; signal duration; period.
 The characteristics of TWG, on which the parameters of the multifrequency signal depend, include: the lower transmission frequency of TWG; the upper transmission frequency of TWG; the delay time of the rays in the TWG.
 The bandwidth and beam delay values can be obtained directly by emitting and receiving a test multi- frequency pilot signal, but this method requires the presence of a reference reflector in space, which is difficult to implement in practice.
 The electrophysical characteristics of the tropospheric waveguide can be determined from the data of meteorological observations. The method developed in the article allows, based on the known characteristics of the tropospheric waveguide, to determine and adjust the parameters of a multi-frequency signal, which reduces the fluctuations of the sounding signal and increases the aerial objects detection rang.

Seismic imaging of medical ultrasound data: Towards in vivo applications

This study presents the application to medical ultrasonography of a high value-added imaging method developed in the context of geophysical exploration and based on the undulatory description of the physical process. Currently, the most serious limitation of conventional medical ultrasound systems is the implicit assumption of constant-velocity media stemming from the widespread use of geometrical ray-based imaging algorithms and leading to phase aberration phenomena in the case typical of the human body of two or more tissues with different velocities. As a result, imaging of targets underlying tissue layers can be severely degraded. To address this problem, the proposed algorithm is designed expressly for variable-velocity media, providing high-resolution images by implementing the solution of the one-way wave equation. From a macro-velocity model, the illuminated structures are imaged by correlating, in the frequency domain and for each source element, the simulated emitted wavefield with the back-propagated echoes sensed by the ultrasound transducer. The pointwise sum of the correlations reveals, constructively, all diffraction points and reflectors in the image space. The experiments conducted on in vitro laboratory data reveal remarkable spatial resolution and very accurate target positioning, even in the presence of an aberrant layer. A preliminary in vivo test also demonstrates the method's effectiveness in imaging echoes recorded on human tissues, giving a glimpse of its potentiality for clinical purposes.

A calculation method of the passive wireless surface acoustic wave sensor response phase

In this research, we propose a method to calculate the phase delay angle of the reflected wave compared to the wave emitted from the interdigital transducer (IDT) of a passive wireless surface acoustic wave (SAW) sensor by combining simulation of the finite element method (FEM) and MATLAB. Based on the result, we consider the influence of the reflector position on the phase delay of the SAW sensor consisting of an IDT and three equally spaced reflectors. The distances between the IDT and the first reflector are 870 micrometers, 939.6 micrometers, and 1009.2 micrometers, and the distances between the reflector positions are 452.4 micrometers, 522 micrometers, and 591.6 micrometers. The outputs of the FEM simulation, including delay time, amplitude loss, and the length of the reflected wave are put into the model in MATLAB to determine the phase delay of the response waves. The obtained phase delay results show that as the distance between the IDT and the reflectors increases, the phase delay angle increases to 4.49 degrees, 5.39 degrees, and 5.78 degrees, respectively.

New concept of ground based-space radio interferometer and modern technologies application for deployment simulation of precise petal space reflector

Radio interferometers make it possible to achieve high resolution of astronomical observations due to the large base of the measuring instrument. The ground-space radio telescope RadioAstron holds the record for angular resolution among radio interferometers, its maximum base was about 340 000. km. The project turned out to be very successful. The new concept is based on the experience of the RadioAstron project and proposes the use of several orbiting radio telescopes that work together in the cm and mm spectral regions. This will further increase the base of the radio interferometer and expand the viewing angle at each current moment of time. Modern technical means make it possible to launch into orbit several identical mirrors operating in the short-wavelength region of the spectrum with an effective area no worse than the effective area of the RadioAstron antenna at a wavelength of 1.35 cm. Thus, the project can be quite budgetary. Now 3D modeling and 3D printing technologies make it possible to speed up and simplify the development of physical models. The manufacture of complex parts used to take days of work. Now we can use 3D printing to make different parts in a matter of hours. In the physical model of a new petal mirror project, we used FDM and LCD printing technologies. The paper discusses examples of manufacturing petal mirror physical model components, limitations and features of these technologies.

Mathematical modeling of temperature fields in antenna reflectors of space vehicles

The main factor that determines the distortion of the shape of the reflectors in outer space is the temperature deformation due to the uneven distribution of heat fluxes in the structural elements. Therefore, it is important to develop models and methods for calculating temperature fields in reflectors with uneven distribution of heat fluxes on the surface. The use of such methods will reduce the number of expensive field experiments. The paper first constructs a mathematical model for calculating temperature fields in a parabolic reflex antenna, in the form of a paraboloid of rotation rotating at a constant angular velocity, taking into account the finite velocity of heat propagation as a boundary value problem of mathematical physics for the hyperbolic equation of thermal conductivity. that the thermophysical properties of the body are constant. At the initial moment of time, the body temperature is constant, and on the outer surface of the body are known values of heat flux which are continuous coordinate functions. To solve the obtained boundary value problem, a new integral transformation for a two-dimensional finite space was constructed. The formula of inverse transformation is given. Eigenvalues and eigenfunctions for the kernel of integral transformation are found using finite element methods and Galorkin. The division of the region into simplex elements was made. Thus the problem of finding eigenvalues and eigenfunctions was reduced to the algebraic problem of finding eigenvalues and eigenfunctions. After applying the constructed new integral transformation to the obtained boundary value problem, we obtained the Cauchy problem, the solution of which was found analytically. The obtained solution of the boundary value problem is twice continuously differentiated by spatial coordinates and once in time. The solution of the boundary value problem found can be used to modulate the temperature fields that occur in a parabolic reflex antenna. The paper first constructs a mathematical model for calculating temperature fields in a paraboloid rotating at a constant angular velocity, taking into account the finite velocity of heat propagation as a boundary value problem of mathematical physics for the hyperbolic equation of thermal conductivity with Neumann boundary conditions. Using the developed integral transformation, the temperature fields in the paraboloid in the form of convergent series by Fourier functions were found. The solution of the generalized boundary value problem of heat exchange of the paraboloid of rotation can be used to modulate the temperature fields that occur in the antenna reflectors of spacecraft.

The contact problem in FEM analysis of filiform structure for large deployable reflectors

Space reflectors need a continuous increase of size to improve the quality of the communication. Considering the small space available in launchers, the antenna must be assembled within the vector and deployed in the space environment. The antenna requires a thin metallic mesh sustained by an appropriate net structure. The best reflector efficiency is reached when all the metallic wires keep in stable contact, allowing the electrical field to be homogeneous. The number of wires involved is enormous, so that, the modelling requires a simple structural approach connected to a reliable contact tool. Single wires can be modelled by beams, but this opens a non-trivial contact managing. As a matter of fact, the wires describe a thin surface, but the contact is realized by 3D crossing. This point is the main objective of the present work which suggests a way to overcome the crossing while maintaining the structure modelling in a 2D field. The contact efficiency needs that the wires do not exceed the elastic strength, causing a lowering of loading contacts due to irreversible deformations. Taking advantage of the present approach, an investigation over the percentage of active contacts in a full mesh is performed, so that optimally applied tensile loads are identified.

Research and Experimental Verification on Topology-Optimization Design Method of Space Mirror Based on Additive-Manufacturing Technology

As one of the most-critical components in space optical cameras, the performance of space mirrors directly affects the imaging quality of space optical cameras, and the lightweight form of mirror blanks is a key factor affecting the structural quality and the surface-shape accuracy of mirrors. For the design requirements of lightweight and high surface-shape accuracy with space mirrors, this study proposes a design and manufacturing method that integrates topology-optimization with additive-manufacturing technology. This article firstly introduced the basic process and key technologies of space-mirror design and analyzed the superiority of combining a topology-optimized configuration design and additive-manufacturing technology; secondly, the topology-optimized design method of a back-open-structure mirror was used to complete the scheme design of a Φ260 mm aperture mirror; finally, the laser selective-melting manufacturing technology was used to complete the Φ260 mm aperture mirror blank. The mirror and its support structure were assembled and tested in a modal mode; the resonant frequencies of the mirror assembly were all over 600 Hz; and the deviation from the analytical results was within 2%. The optical surface of the mirror was turned by the single-point diamond-turning (SPDT) technique. The accuracy of the optical surface was checked by a Zygo interferometer. The RMS accuracy of the mirror surface was 0.041λ (λ is the wavelength; λ = 632 nm). In the test of the influence of gravity on the surface-shape accuracy, the mirror was turned over, which was equivalent to twice the gravity, and the RMS of the mirror surface-shape accuracy was 0.043λ, which met the requirement. The verification results show that the mirror designed and fabricated by the additive-manufacturing-based mirror-topology-optimization method can be prepared by the existing process, and the machinability and mechanical properties can meet the requirements, which provides an effective development method for improving the structural design and optimizing the manufacturing of space reflectors.

Modeling the deployment of a two-link spoke of a large-sized space reflector taking into account the backlash

This article discusses the process of deployment a two-link spoke of a large-sized transformable space-based reflector. In view of the high costs of carrying out field tests, the construction of correct mathematical models is an urgent task. Currently, the creation of large-sized systems is actively developing. Such systems consist of several interconnected links. When delivered to a given orbit, the large-sized system is folded for placement in the launch vehicle. After entering the orbit, it is deployed to the specified operating state. A mathematical model has been developed for the deployment of the spoke, improved in terms of taking into account the separation of parameters depending on the length and time, which makes it possible to study the arising vibrations of the structure. It is important to take into account the backlash in the connections. Even small gaps in the spoke link connections can lead to a manifold increase in the stabilization time of the system. The developed mathematical model makes it possible to consider various conditions for linking links, change the mass-dimensional parameters and materials of the spoke. The results of modeling are presented, showing the correctness of mathematical models. Conclusions are made about the admissibility of using mathematical models for spokes consisting of a larger number of links.

New design of precise deployable reflector. Technologies for manufacturing of physical model

The new design of petal space antenna is considered in the paper. Various versions of solid petal-type mirrors have been considered and investigated in a number of articles and space projects. The classical scheme of petal type deployable space reflector was proposed and developed by Dornier Corporation within FIRST space project and was used in the Radioastron project to create a 10-meter antenna of space radio telescope. However, the classical petal mirror design has two significant drawbacks. Firstly, in the open state, the petals are cantilevered on the central mirror, what leads to low rigidity of the structure in open state. Secondly, in the classical design, the accuracy of the reflecting surface of the open mirror strongly depends on small errors in the operation of the deployment system. To overcome these drawbacks a new design of petal type mirror and a new system for precise opening of the mirror were proposed and studied. To test a new technical solution, a physical model of a deployable reflector was developed. The model contains a central mirror, a set of petals, hinges, locks and actuators for opening the mirror. 3D printing technology, CNC (computer numerical control) milling, plastic injection molding and carbon fiber technologies have been tested for central mirror and petals of the model fabrication. The results of computer and physical simulation are presented in the paper.

Surface shape control of integrated paraboloid space reflector consisting of sub-reflectors exploiting modulated solar pressure

Reflectors are very critical space elements and can be used not only as solar collectors/reflectors, telecommunication radio antennas and telescopes but also for dual-usage such as solar sails and solar concentrators to probe and sublimate materials from asteroids when actively controlling the surface shape. In this paper, the surface shape of a slack reflector with negligible elastic deformations will be controlled to be a paraboloid by actively modulating the solar radiation pressure (SRP) force using reflectivity control devices (RCDs) across the reflector. Nonlinear static equilibrium equations for an arbitrary infinitesimal within the reflector along the radial, circumferential and transverse directions are established considering the external modulated SRP force and internal tensions respectively. The coupled radial stress differential governing equation and reflectivity algebraic equation are obtained for the paraboloid reflector by the help of the formulation of an inverse problem based on equilibrium equations previously established. Some analytical and numerical analysis for reflectors with ideal and non-perfect SRP force models are performed respectively. The conclusions concerning about how to control the reflector’s surface shape successfully using allowed reflectivity, resulting in reasonable stress range, moreover, how to get the feasible solutions influenced by the reflector’s size parameters, are all based on the presented analytical and numerical analysis.

Novel Surface Design of Deployable Reflector Antenna Based on Polar Scissor Structures

Space-deployable mechanisms can be used as supporting structures for large-diameter antennas in space engineering. This study proposes a novel method for constructing the surface design of space reflector antennas based on polar scissor units. The concurrency and deployability equations of the space scissor unit with definite surface constraints are derived using the rod and vector methods. Constraint equations of the spatial transformation for space n-edge polar scissor units are summarized. A new closed-loop deployable structure, called the polar scissor deployable antenna (PSDA), is designed by combining planar polar scissor units with spatial polar scissor units. The over-constrained problem is solved by releasing the curve constraint that locates at the end-point of the planar scissor mechanism. Kinematics simulation and error analysis are performed. The results show that the PSDA can effectively fit the paraboloid of revolution. Finally, deployment experiments verify the validity and feasibility of the proposed design method, which provides a new idea for the construction of large space-reflector antennas.

New design modifications of the supporting ring for a large deployable space reflector

Though theoretical and experimental studies of the design of large deployable antenna reflectors have already been carried out for quite a long time, the results obtained in this area of research still attract a lively interest and have good application prospects. In the present paper, two novel design modifications are described for the symmetric (i.e. with circular apertures) radio telescopes. The novelty consists in that improved stiffness and stability have been obtained by combining two conical pantograph systems and thus getting the whole hinged-bar structure consisting of cylindrical and sliding hinges only. Three FE models of the supporting ring structure are constructed and compared with one another using the NASTRAN FEA software. The degrees of freedom of hinges are simulated in local coordinate systems. A static, modal and buckling analysis had been done to investigate, strength and stiffness characteristics.

Electrostrictive PVDF-TrFE Thin Film Actuators for the Control of Adaptive Thin Shell Reflectors

This paper presents the technology to control the shape of thin polymer doubly curved shell structures with a unimorph layer of strain actuators to achieve high quality, light-weight, foldable space reflectors. The selected active material is PVDF-TrFE deposited by spin coating; it is electrostrictive, isotropic and enjoys an excellent piezoelectric coefficient d 31 ≃ 15 pC/N when properly annealed, but has a nonlinear, quadratic behavior. The strain actuation is controlled by an array of segmented electrodes. The purpose of this study is to evaluate the material properties achieved in the manufacturing process. A simple, unidirectional model of electrostrictive material is considered and the material constants (electrostrictive constant Q 33 , piezoelectric constant d 31 , spontaneous polarization P s and poling strain S P ) are estimated from various static and dynamic experiments. The final part of the paper illustrates the control authority on a small demonstrator with seven independent electrodes and compares the experimental results with numerical finite element simulations.

Study and prototyping of a permanent magnetic suspension for the alignment by gravity of the elevation angle for the next generation lunar reflector experiment

The research is focused on the design of a magnetic suspension employable to achieve Earth-pointing for a space reflector or other devices integrated on a lunar lander or rover deck just utilizing the local gravity. The classical solution is based on heavy and expensive actuators, still representing critical subsystems as their failure might often lead to severe or catastrophic effects on the mission. This proposal is based on a magnetic suspension realized with two small magnetic bearings. They can be contained in a cylinder smaller than 15 mm diameter and 20 mm height and capable of supporting 20 N. After designing, a prototype has been built employing commercially available neodymium permanent magnets. Preliminary results of carrying capacity have been correlated in good agreement both with analytical calculation and finite elements analysis. The study has showed that the goal of 20 N can be attainable. The structure stiffness and carrying load for the accurate alignment of each stator/rotor pack is crucial for the performance of the suspension. The next step is the design and build-up of an upgraded model to be qualified for the mission dynamic loads.

Coupling and Hysteresis Characteristics during Multiple Actuation in Shape-deformable Space Reflector

For the observation of microwave in space over 100 GHz by radio astronomical satellites, this study develops shape-deformable antenna reflectors. When a certain portion of the antenna reflector prototype is deformed, the entire reflector is affected by the partial deformation. The purpose of this study is firstly clarifying the effect of coupling in reflector displacement. Secondly, this study tries the performance evaluation of hysteresis elimination by a piezoelectric strain feedback system under the effect of the displacement coupling. To achieve these objectives, this study quantifies the displacement coupling, the relations between piezoelectric strain and reflector displacement, and the residual reflector displacement error under the feedback control when multiple actuators are driven simultaneously. As a result, this study clarifies that there is a non-negligible coupling effect and the stress history dependence in the reflector surface deformation, causing the limit in the accuracy of the feedback system. Based on these experimental observations, this paper presents three design improvement plans that will possibly solve these problems.