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In this paper, we obtain sufficient and necessary conditions for big truncated Hankel operators on model spaces to be zero, or of finite rank or compact. Our main tools are the properties of Hardy Hankel operators and function algebras. [ABSTRACT FROM AUTHOR]

Let u be a nonconstant inner function. In this paper, we study the dual truncated Toeplitz operators on the orthogonal complement of the model space K u 2 . This is a new class of Toeplitz operator. We show the product of two dual truncated Toeplitz operators D f D g to be zero if and only if either f or g is zero. We give a necessary and sufficient condition for the product of two dual truncated Toeplitz operators to be a finite rank operator. Furthermore, a necessary and sufficient condition is found for the product of two dual truncated Toeplitz operators to be a dual truncated Toeplitz operator. The last two results are different from the classical Toeplitz operator theory. [ABSTRACT FROM AUTHOR]

The research for global climate changes calls for high quality satellite data and imageries regarding the Polar Regions. In recent years, the emerging Earth-Observation micro/nano satellite technology provides new data sources for polar region observations. The STU-2A, also named TW-1A, is such a nano satellite designed for polar region observation activities. It is a 3U CubeSat of 2.9 kg with a size of 30 × 10 × 10 cm carrying an Earth observation camera, launched into a Sun Synchronous Orbit (SSO) at 481 km with an inclination of 97.3°, on September 25, 2015. During the Antarctic summer of 2015/16, it has acquired visible-light true color images with a resolution of 94 m, covering different sea and coastal regions including Amundsen Sea, Ross Sea and Vincennes Bay. These images were used to analyze the change of glacier and sea ice, compared and calibrated with reference to the publically available MODIS images with a resolution of 250 m. As the camera was specially designed for the Polar regions which have an environment of low solar elevation angle and high surface reflectance, it eliminates the oversaturation problem of the MODIS sensors and can provide high quality images. Based on data analysis and assessment, it is confirmed that this satellite data can meet the demand of glacier and sea ice observation. This paper presents the Cubesat system design and configuration, the payload camera design, and its application in Antarctic glacier and sea ice observation. [ABSTRACT FROM AUTHOR]

This paper presents a novel non-certainty-equivalence adaptive control method for the attitude tracking control problem of spacecraft with inertia uncertainties. The proposed immersion and invariance (I&I) based adaptation law provides a more direct and flexible approach to circumvent the limitations of the basic I&I method without employing any filter signal. By virtue of the adaptation high-gain equivalence property derived from the proposed adaptive method, the closed-loop adaptive system with a low adaptation gain could recover the high adaptation gain performance of the filter-based I&I method, and the resulting control torque demands during the initial transient has been significantly reduced. A special feature of this method is that the convergence of the parameter estimation error has been observably improved by utilizing an adaptation gain matrix instead of a single adaptation gain value. Numerical simulations are presented to highlight the various benefits of the proposed method compared with the certainty-equivalence-based control method and filter-based I&I control schemes. [ABSTRACT FROM AUTHOR]

Truncated Toeplitz operators are compressions of multiplication operators on L 2 to model spaces (that is, subspaces of H 2 which are invariant with respect to the backward shift). For this class of operators we prove certain Szegö type theorems concerning the asymptotics of their compressions to an increasing chain of finite dimensional model spaces. [ABSTRACT FROM AUTHOR]

Next generation spacecraft will bring back heavier payloads from explored planets. Advance in the modeling of the thermo-chemical ablation of carbon-based thermal protection system materials is fundamental to improve the design capabilities of these vehicles. Computational fluid dynamic approaches are extensively used to model the gas-surface interaction phenomena over ablative materials. The advantage of such kind of approaches is the accurate description of the aerothermal environment obtained through the full resolution of the mechanical, thermal, and chemical boundary layers that develop over an ablative surface when exposed to a high-enthalpy flow. This paper is devoted to the assessment of the uncertainties of such kind of thermo-chemical ablation model and to study their effect on the model final outcomes. A sphere of non-pyrolyzing carbon-based material, exposed to conditions similar to those of a typical plasma wind tunnel test, is the selected test case for the analysis. Two forward non-intrusive uncertainty quantification techniques are used to analyze the influence of the defined set of uncertain parameters on the estimate of steady-state mass blowing flux and surface temperature. Our results show that for the selected conditions, and uncertainty ranges, the surface nitridation reaction probability has the strongest impact on the model outcomes. [ABSTRACT FROM AUTHOR]

The article focuses on the flyby issue involving large-size space debris (LSSD) objects in low Earth orbits. The data on overall sizes of the known upper-stages and last stages of launch-vehicles make it possible to emphasize five compact groups of such objects from the Satellite catalogue in 600–2000 km altitude interval. The flyby maneuvers are executed by a single space vehicle (SV) that transfers the current captured LSSD object to the specially selected circular or elliptical disposal orbit (DO) and after a period of time returns to capture a new one. The flight is always realized when a value of the Right Ascension of the Ascending Node (RAAN) is approximately the same for the current DO and for an orbit of the following LSSD object. Distinctive features of changes in mutual distribution of orbital planes of LSSD within a group are shown on the RAAN deviations’ evolution portrait. In case of the first three groups (inclinations 71°, 74° and 81°), the lines describing the relative orientation of orbital planes are quasi-parallel. Such configuration allows easy identification of the flyby order within a group, and calculation of the mission duration and the required total Δ V . In case of the 4th and the 5th groups the RAAN deviations’ evolution portrait represents a conjunction of lines chaotically intersecting. The article studies changes in mission duration and in the required Δ V depending on the catalogue number of the first object in the flyby order. The article also contains a comparative efficiency analysis of the two world-wide known schemes applicable to LSSD objects’ de-orbiting; the analysis is carried out for all 5 distinguished LSSD groups. [ABSTRACT FROM AUTHOR]

Aim of the work is to present a method to evaluate the electromagnetic absorption properties of spacecraft and space debris. For these objects, the radar detection ability depends mainly on volume, shape, materials type and other electromagnetic reflecting behaviour of spacecraft surface components, such as antennas or thermal blankets, and of metallic components in space debris. The higher the electromagnetic reflection coefficient of such parts, the greater the radar detection possibility. In this research an electromagnetic reverberation chamber is used to measure the absorption cross section (ACS) of four objects which may represent space structure operating components as well as examples of space debris: a small satellite, a composite antenna dish, a Thermal Protection System (TPS) tile and a carbon-based composite missile shell. The ACS mainly depends on geometrical characteristics like apertures, face numbers and bulk porosity, as well as on the type of the material itself. The ACS, which is an electromagnetic measurement, is expressed in squared meters and thus can be compared with the objects geometrical cross section. A small ACS means a quite electromagnetic reflective tendency, which is beneficial for radar observations; on the contrary, high values of ACS indicate a strong absorption of the electromagnetic field, which in turn can result a critical hindering of radar tracking. [ABSTRACT FROM AUTHOR]

An improved time-varying optimal controller based on parameter optimization is proposed for the stabilization of spacecraft missions on nominal libration-point orbits of the Sun-Earth system. Because of the importance of the weighting matrices in the design of the time-varying controller, based on a genetic algorithm and the sequential quadratic programming method, two optimization models (for time-invariant and piecewise-constant weighting matrices) are used to determine the weighting matrices to improve the performance of the time-varying optimal controller. Practical missions are presented for a spacecraft moving steadily on a reference orbit. Numerical simulations of these missions demonstrate that the parameter-optimization methods provide a smaller overshoot and faster convergence time than when trial-and-error or Bryson's rule are used to select the weighting matrices. Piecewise-constant weighting matrices calculated for the time-varying controller using the parameter-optimization method provide better control performance than time-invariant weighting matrices. Additionally, for both optimization models, the genetic algorithm combined with sequential quadratic programming produces a shorter injection period and lower fuel consumption than the other optimization methods that are compared in this paper. [ABSTRACT FROM AUTHOR]

The objective of the present research is to study the accuracy of the double- and single-averaged models that are usually considered to predict the motion of spacecrafts or celestial bodies that have their motion perturbed by a third-body. Those two models are compared with each other and then validated against the complete elliptic restricted three-body problem. Those models are developed to give a faster but general behaviour of the motion of the perturbed body in a medium or longer time scale. The researches performed here verify the accuracy of those methods for shorter time scales by showing the differences in terms of the values of the inclination and eccentricity of the perturbed body predicted by those models. Those differences are calculated both at every instant of time and as an integral over the time. The use of the integral along the time for the errors is a new form to study those differences and show a more complete comparison of the accuracy of those approximations, completing the instantaneous picture given by the usual approach of looking at the instantaneous measurement. If the value of the integral is divided by the time integration, the mean error is obtained. The results show that the single-averaged model is better in the short time scale and the difference among those models is smaller when predicting the eccentricity than the inclination. The effects of the time scale is verified by varying the study to values from 2 days up to 50 revolutions of the Moon (1,366 days). Another important point found in the present paper is the range of the eccentricities of the perturbing body that accelerates the dynamics. [ABSTRACT FROM AUTHOR]

Based on the L1 adaptive control theory, a novel three-axis attitude control system for an axisymmetric spacecraft with uncertain dynamics moving in elliptic orbits, using solar radiation pressure, is derived. The nonaffine-in-control nonlinear spacecraft model includes the gravity gradient torque, the control torque produced by four solar flaps, and external time-varying disturbance moments. For the three-axis attitude control, an L1 adaptive control system is designed, which includes a state predictor. A smooth projection algorithm is used to confine the estimated parameters within a desirable set. In the closed-loop system, the designed adaptive law accomplishes three-dimensional attitude control. A special feature of the attitude control system is that it is possible to select large adaptation gains for fast adaptation and to obtain quantifiable performance bounds. Simulation results show that in the closed-loop system, precise roll, yaw, and pitch angle control is accomplished, despite unmodeled nonlinearities, parameter uncertainty, and external disturbance inputs in the model. [ABSTRACT FROM PUBLISHER]

Five spacecraft-plasma models are used to simulate the interaction of a simplified geometry Solar Probe Plus (SPP) satellite with the space environment under representative solar wind conditions near perihelion. By considering similarities and differences between results obtained with different numerical approaches under well defined conditions, the consistency and validity of our models can be assessed. The impact on model predictions of physical effects of importance in the SPP mission is also considered by comparing results obtained with and without these effects. Simulation results are presented and compared with increasing levels of complexity in the physics of interaction between solar environment and the SPP spacecraft. The comparisons focus particularly on spacecraft floating potentials, contributions to the currents collected and emitted by the spacecraft, and on the potential and density spatial profiles near the satellite. The physical effects considered include spacecraft charging, photoelectron and secondary electron emission, and the presence of a background magnetic field. Model predictions obtained with our different computational approaches are found to be in agreement within 2% when the same physical processes are taken into account and treated similarly. The comparisons thus indicate that, with the correct description of important physical effects, our simulation models should have the required skill to predict details of satellite-plasma interaction physics under relevant conditions, with a good level of confidence. Our models concur in predicting a negative floating potential Vfl ~ -10V for SPP at perihelion. They also predict a "saturated emission regime" whereby most emitted photo- and secondary electron will be reflected by a potential barrier near the surface, back to the spacecraft where they will be recollected. [ABSTRACT FROM AUTHOR]

A dynamic model for the launching system incorporating the influence of the clamp band joint is developed using the finite element method, where both of the launch vehicle and the spacecraft are modeled as Timoshenko beams. The clamp band joint is represented by a massless beam element, of which the element stiffness matrix is developed based on the expressions for the axial and bending stiffnesses of the joint deduced by the authors in the previous works. Dynamic analyses are performed to evaluate the joint influence on the launching system, where the variations of the mass and length of the launching system due to the fuel combustion and stage jettisons during the ascent flight are considered. The dynamic model presented here can be applied to investigate dynamics of launching systems involving the influence of clamp band joints conveniently. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of a model of the earth-returning vehicle (HTV-R) were investigated in a supersonic wind tunnel. The free rotational technique was employed in the test. Two kinds of the test devices were prepared with different degrees of freedom. The 1-DOF device allowed the model to rotate only around a pitch axis, and the 3-DOF device allowed the model to rotate around the pitch, yaw and roll axes. The dynamic tests were carried out in a flow of Mach 1.5. Both the 1-DOF and 3-DOF tests gave the similar results on the damping and static aerodynamic properties in pitch. The rolling behavior was observed in 3-DOF test which was considered related to the uneven inertial properties. [ABSTRACT FROM AUTHOR]

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Abstract: The severe mechanical environment that electronic components experience during spacecraft launch necessitates that their failure probability be assessed. One possible approach is to create an accurate model of the printed circuit board''s (PCBs) dynamic response; subsequently, the failure probability can be determined by comparing the response model with corresponding failure criteria for the electronic components. In principle the response model can be achieved by a very detailed finite element (FE) model of the PCB which would include the mass and stiffness of all components present on the PCB. Unfortunately this approach requires an excessive effort; therefore, it is rarely pursued by the designer. Past research has shown that assumptions can be made about the mass and stiffness that allow simpler models to be created that still achieve appropriate levels of accuracy. However, the accuracy of these simplified models has not yet been quantified over a range of possible design cases. This paper will quantify how increasing levels of modelling simplifications decrease the accuracy of PCB FE models. [Copyright &y& Elsevier]

Air-bearing-based spacecraft simulators are widely used to develop and verify spacecraft control techniques required by modern spacecraft applications. To create a spacelike environment with ground spacecraft simulators, the effects of gravity should be minimized. For a spherical air-bearing system with 3 rotational degrees of freedom, the center of rotation of the spacecraft simulator should be exactly aligned with the center of gravity. This paper presents the automatic mass balancing method, which compensates for the center of gravity offset from the center of rotation by actuating three proof masses on linear motion stages. Adaptive control of the automatic mass balancing system is used while the balancing masses are actuated in real time. The proposed techniques are implemented on the ground-based three-axis spacecraft simulator for the bifocal relay mirror spacecraft. [ABSTRACT FROM AUTHOR]

Abstract: In the given article scientific and technical complex for modeling, researching and testing of rocket-space vehicles’ power installations which was created in Power Source Laboratory of National Aerospace University “KhAI” is described. This scientific and technical complex gives the opportunity to replace the full-sized tests on model tests and to reduce financial and temporary inputs at modeling, researching and testing of rocket-space vehicles’ power installations. Using the given complex it is possible to solve the problems of designing and researching of rocket-space vehicles’ power installations efficiently, and also to provide experimental researches of physical processes and tests of solar and chemical batteries of rocket-space complexes and space vehicles. Scientific and technical complex also allows providing accelerated tests, diagnostics, life-time control and restoring of chemical accumulators for rocket-space vehicles’ power supply systems. [Copyright &y& Elsevier]

Fluid viscous damper is an important component of a whole spacecraft vibration isolator and many other isolators applied in different areas. In this paper, the interaction between viscous heating and damping force in a fluid viscous damper is considered. And a thermodynamic model of the fluid viscous damper, which includes a dynamic equation and the thermal balance equation, is developed. As the system is time varying in the application of whole spacecraft vibration isolation, the effect of viscous heating on the vibration isolation performance is numerically studied both in the frequency domain and the time domain. From the numerical analysis, it is found that the temperature rise mainly causes shifts of resonant frequencies and larger amplification factors at resonances. [Copyright &y& Elsevier]

The pedagogical experience with adolescent students in 9 th, 10 th, and 11 th of basic education levels (H.S.) in the Astronomy class is narrated herein; astronomy field practices, conceptualization exercises, audiovisual aids, construction of paper model spaceships, and visits to specialized sites, among other activities. In the process, relevant facts of the education of scientific attitude in the students stand out. A Center of scientific interest, where the passion for the study of physics is motivated has been created. The Ovidio Decroly legacy guides this process; highlighting globalization, base ideas and force ideas. [ABSTRACT FROM AUTHOR]

Develops a method that used patterns to model variability and applied it to spacecraft mission-planning software system. Reuse in product family engineering; Types of discriminants in family systems; Discussion. INSET: Approaches to Family Model Development.

In this article, three models in two different spaces are compared for use with an image processing system working in real time. A static geometric model of a robot work-cell is held in computer memory as several solid polyhedra. This model is updated as new objects enter or leave the workplace. Similar 2-D slices in joint space, spheres, and simple polyhedra are used to model these objects. The three models are compared for their ability to be updated with new information and for the efficiency of the whole system in accessing data concerning new objects. The system supplies data to a ‘Path Planner.’ The path planner contains a geometric model of the static environment and a robot. The robot machinery structure is modeled as connected cylinders and spheres and the range of motion is quantized. © 1995 John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The code observable of global navigation satellite systems (GNSS) is influenced by group delay variations (GDV) of transmitter and receiver antennas. For the Global Positioning System (GPS), the variations can sum up to 1 m in the ionosphere-free linear combination and thus can significantly affect precise code applications. The contribution of the GPS transmitters can amount to 0.8 m peak-to-peak over the entire nadir angle range. To verify the assumption of their time-invariance, we determined daily individual satellite GDV for GPS transmitter antennas over a period of more than two years. Dual-frequency observations of globally distributed reference stations and their multipath combination form the basis for our analysis. The resulting GPS GDV are stable on the level of a few centimeters for C1, P2, and for the ionosphere-free linear combination. Our study reveals that the inconsistencies of the GDV of space vehicle number (SVN) 55 with respect to earlier studies are not caused by temporal instabilities, but are rather related to receiver properties. [ABSTRACT FROM AUTHOR]

The article offers information on the collection of printing files from the U.S. National Aeronautics & Space Administration (NASA) including three-dimensional (3D) models of spacecraft, a rock from the planet Mars, and asteroid Vesta.