Typical Satellite Research Articles

B/PS bulges and barlenses from a kinematic viewpoint – II

ABSTRACT Internal dynamics and kinematics of galaxies have imprints on the line-of-sight velocity distribution (LOSVD). Gauss–Hermite parametrization allows one to identify the kinematics features of the system in terms of skewness (h3) and broadness (h4) deviations of an LOSVD. Such a method provides information about the type of orbits since a $h_3\!-\!\overline{V}$ correlation is a sign of elongated orbits, and the anticorrelation is a sign of circular or near-circular orbits. In previous works, analysis of the $h_3\!-\!\overline{V}$ relation provided a tool to identify a hidden bar or B/PS bulge (edge-on, PA = 90°) and to probe their strength. We prepared two N-body galaxy models with clear B/PS bulges: one has an ordinary bar (the X model), and the second one has a barlens embedded into a bar (the BL model) to investigate the mechanism of formation of h3 features at any position of an observer. We show that the $h_3\!-\!\overline{V}$ correlation appears in the regions where bar and disc particles are mixing. We also reveal that the model with a barlens has an $h_3\!-\!\overline{V}$ anticorrelation in the centre, and we show that barlens-specific orbits are responsible for this signal. Moreover, this feature can be observed only for galaxies with compact bulges and barlenses. The results of this work are applicable for the interpretation of future integral-field unit (IFU) data for real galaxies with B/PS bulges, especially for objects with barlenses.

Homotopy type of the nilpotent orbits in classical Lie algebras

Homotopy type of the nilpotent orbits in classical Lie algebras

Numerical study of alpha particle loss with toroidal field ripple based on CFETR steady-state scenario

Abstract Effects of plasma equilibrium parameters on the alpha particle loss with the toroidal field ripple based on the CFETR steady-state scenario have been numerically investigated by the orbit-following code GYCAVA. It is found that alpha particle losses decrease and loss regions become narrower with the plasma current increasing or with the magnetic field decreasing. It is because the ripple stochastic transport and the ripple well loss of alpha particle are reduced with the safety factor decreasing. Decrease of the plasma density and temperature can reduce alpha particle losses due to enhancement of the slowing-down effect. The direction of the toroidal magnetic field can significantly affect heat loads induced by lost alpha particle. The vertical asymmetry of heat loads induced by the clockwise and counter-clockwise toroidal magnetic fields are due to the fact that the ripple distribution is asymmetric about the mid-plane, which can be explained by the typical orbits of alpha particle. The maximal heat load of alpha particle for the clockwise toroidal magnetic field is much smaller than that for the counter-clockwise one.

Use of Simple Skull Radiographs in Orbital Correlations in Nigeria

Introduction: Anthropometric measurements have been carried out in many studies to segregate people into races, ethnicity and various biological traits in the past. Such studies include cephalometry being deployed because of its significance in forensic and clinical evaluations of individuals. The objective of this study is to determine the correlation between the shape types of the orbit with different age groups and their prevalence using simple skull X-rays.
 Materials and Methods: Plain X-rays of the skull with posteroanterior exposures were obtained for a retrospective period of 5-year period from 2004 to 2009. The selected radiographs were those based on clear recognition of their orbital margins assessed by 2 experienced Radiologist who determined the shapes of the orbits as being oval, circular or quadrangular. Out of total of five hundred (500) plain X-rays of the skull obtained, only 255 satisfied the inclusion criteria.
 The data was analyzed statistically using INSTAT software to compare the mean values in relation to age distribution of the subjects with the Student’s T-Test. Chi-Square (with Yates correction) was used for the comparison of proportions.
 Results: In the first 30 years of postnatal life, the oval shape orbit had been found to be more predominant with values of 22(64.7%), 17(30.9%), and 27(38.0%) respectively. As from the age of 30 to 70 years, the circular type had values of 16(34.0%), 8(33.3%), and 8(61.5%) respectively in each of the decades. Between the age of 60 to 70 years, the oval and circular types had equal prevalences.
 Conclusions: In addition to the known oval and quadrangular (triangular) types of orbital shape, this study revealed a 3rd type of orbit which we described as circular in shaped. The oval type of orbit is found to be more common from birth to age of 30 years but from but from 40 to 70 years the circular type predominates.

Reference Dynamic Models for Space Debris Orbit Prediction

In different orbit prediction scenarios, the dynamic models used are also different. For example, atmospheric drag is a very important perturbation force in the prediction of space debris in low orbits, but at mid-to-high orbits, the atmospheric drag can be ignored. To select the most suitable dynamic models for orbit prediction in different scenarios, this article provides a large number of orbits for different accuracy requirements and different orbit types. By comparing the prediction results with different dynamic models, the optimal dynamic models for various prediction scenarios are recommended. This work can serve as a reference and standard for the selection of reference dynamics models for different orbital types of space debris in orbit prediction.

Determination of Gender Variations Based on Anatomical Shapes of the Orbit on Plain Radiographs of Nigerians: A 5-Year Retrospective Cross-Sectional Study

Introduction: Cephalometry has been widely used in substantial aspects of medicine. There exist obvious differences between male and female bony features from early development to adulthood. The morphometric examination of the orbit and familiarity with its anatomy are important clinically in the diagnosis of orbital lesions and face reconstructive surgery. Diagnostic radiology and ophthalmology have a close relationship. Most prior research assessed orbital dimensions using direct approaches on living, cadaveric, or dry bones.
 Aim: To determine the gender variations based on the shapes of the orbit using Plain Radiographs.
 Materials and Methods: A 5-year retrospective cross-sectional study using 255 normal skull radiographs obtained from the Department of Diagnostic Radiology of Usmanu Danfodiyo University Teaching Hospital Sokoto from 2004 40 2009 was carried out with male to female ratio of 4:1. The radiographs were mounted on a viewing box, and the orbital shapes were noted. Results: In the male subjects, the shape of the orbit was oval in 68 (33.0%), quadrangular in 55 (26.7%), and round in 83 (40.3%). In the female subjects, the oval-shaped orbit was found in 27 (55.1%), quadrangular shape in 12 (24.5%), and in round shape 10 (20.4%).
 Conclusions: The commonest type of orbit seen in males is the round type, followed by the oval type with the quadrangular being the least type. In females the predominant type of orbit seen was oval, followed by the quadrangular type, with the round type being the least common. However, the differences were not statistically significant. The round type of orbit shows the strongest tendency in sex identification.

Low-Thrust Transfer to Quasi-Synchronous Martian Elliptic Orbit via Nonlinear Feedback Control

This study considers the problem of injecting a spacecraft into an elliptic, repeating-ground-track orbit about Mars, starting from a 4-sol highly elliptical orbit, which is a typical Martian capture orbit, entered at the end of the interplanetary transfer. The final operational orbit has apoares corresponding to the maximum (or minimum) latitude, and nine nodal periods are flown in 5 Martian nodal days. The orbit at hand is proven to guarantee coverage properties similar to the Molniya orbit about Earth; therefore, it is especially suitable for satellites that form constellations. Low-thrust nonlinear orbit control is proposed as an affordable and effective option for orbit injection, capable of attaining significant propellant reduction if compared to alternative strategies based on chemical propulsion. This work introduces a new, saturated feedback law for the low-thrust direction and magnitude that is capable of driving the spacecraft of interest toward the operational orbit. Remarkable stability properties are proven to hold using the Lyapunov stability theory. Because no reference path is to be identified a priori, this technique represents a viable autonomous guidance strategy, even in the case of temporary unavailability of the low-thrust propulsion system or in the presence of widely dispersed initial conditions and errors on estimating orbit perturbations. Monte Carlo simulations prove that the feedback guidance strategy at hand is effective and accurate for injecting a spacecraft into the desired, repeating-ground-track operational orbit without requiring any reference transfer path.

BDS Dual-Frequency Carrier Phase Multipath Hemispherical Map Model and Its Application in Real-Time Deformation Monitoring.

The BDS multipath delay error is highly related to the surrounding monitoring environment, which cannot be eliminated or mitigated by applying the double difference observation model. In the actual monitoring environment, due to the complexity of the BDS constellation, it is difficult for existing algorithms to consider GEO, IGSO, MEO and other different orbital types of satellites for real-time and efficient multipath error reduction. Therefore, we propose a novel BDS dual-frequency multipath error reduction method for real deformation monitoring for BDS considering various satellite orbit types. This method extracts the single error residual of each satellite based on the assumption of "zero mean" and divides the appropriate grid density of GEO and IGSO/MEO, respectively, to construct a dual-frequency multipath hemispherical map model suitable for BDS satellites with different orbital types. This method can realize the multipath error elimination of the observed values of different orbits and different frequencies. The results of simulation experiments and real deformation monitoring data demonstrate that this method can effectively eliminate low-frequency multipath delay errors in the observation domain and coordinate domain. After multipath correction, the precision of the horizontal coordinates and height coordinates are 1.7 mm and 4.6 mm. The precision of the horizontal coordinate and height coordinate is increased by 50% and 60%, respectively. The fixed rate of ambiguity increased by 5-7%.

Boosting the thermal management performance of a PCM-based module using novel metallic pin fin geometries: Numerical study

Satellite avionics and electronic components are getting compact and have high power density. Thermal management systems are essential for their optimal operational performance and survival. Thermal management systems keep the electronic components within a safe temperature range. Phase change materials (PCMs) have high thermal capacity, so they are promising for thermal control applications. This work adopted a PCM-integrated thermal control device (TCD) to manage the small satellite subsystems under zero gravity conditions thermally. The TCD's outer dimensions were selected upon a typical small satellite subsystem. The PCM adopted was the organic PCM of RT 35. Pin fins with different geometries were adopted to boost the lower thermal conductivity of the PCM. Six-pin fins geometries were used. First, the conventional geometries were square, circular, and triangular. Second, the novel geometries were cross-shaped, I-shaped, and V-shaped fins. The fins were designed at two-volume fractions of 20% and 50%. The electronic subsystem was assumed to be "ON" for 10 min releasing 20 W of heat, and "OFF" for 80 min. The findings show a remarkable decrease in the TCD's base plate temperature by 5.7 ℃ as the fins' number changed from 15 to 80 for square fins. The results also show that the novel cross-shaped, I-shaped, and V-shaped pin fins could significantly enhance thermal performance. The cross-shaped, I-shaped, and V-shaped reported a decrease in the temperature by about 1.6%, 2.6%, and 6.6%, respectively, relative to the circular fin geometry. V-shaped fins could also increase the PCM melt fraction by 32.3%.

Integrable Multi-Hamiltonian Systems from Reduction of an Extended Quasi-Poisson Double of {text {U}}(n)

We construct a master dynamical system on a {text {U}}(n) quasi-Poisson manifold, {mathcal {M}}_d, built from the double {text {U}}(n) times {text {U}}(n) and dge 2 open balls in mathbb {C}^n, whose quasi-Poisson structures are obtained from T^* mathbb {R}^n by exponentiation. A pencil of quasi-Poisson bivectors P_{underline{z}} is defined on {mathcal {M}}_d that depends on d(d-1)/2 arbitrary real parameters and gives rise to pairwise compatible Poisson brackets on the {text {U}}(n)-invariant functions. The master system on {mathcal {M}}_d is a quasi-Poisson analogue of the degenerate integrable system of free motion on the extended cotangent bundle T^*!{text {U}}(n) times mathbb {C}^{ntimes d}. Its commuting Hamiltonians are pullbacks of the class functions on one of the {text {U}}(n) factors. We prove that the master system descends to a degenerate integrable system on a dense open subset of the smooth component of the quotient space {mathcal {M}}_d/{text {U}}(n) associated with the principal orbit type. Any reduced Hamiltonian arising from a class function generates the same flow via any of the compatible Poisson structures stemming from the bivectors P_{underline{z}}. The restrictions of the reduced system on minimal symplectic leaves parameterized by generic elements of the center of {text {U}}(n) provide a new real form of the complex, trigonometric spin Ruijsenaars–Schneider model of Krichever and Zabrodin. This generalizes the derivation of the compactified trigonometric RS model found previously in the d=1 case.

Understanding chemistry with the symmetry-decomposed Voronoi deformation density charge analysis.

The symmetry-decomposed Voronoi deformation density (VDD) charge analysis is an insightful and robust computational tool to aid the understanding of chemical bonding throughout all fields of chemistry. This method quantifies the atomic charge flow associated with chemical-bond formation and enables decomposition of this charge flow into contributions of (1) orbital interaction types, that is, Pauli repulsive or bonding orbital interactions; (2) per irreducible representation (irrep) of any point-group symmetry of interacting closed-shell molecular fragments; and now also (3) interacting open-shell (i.e., radical) molecular fragments. The symmetry-decomposed VDD charge analysis augments the symmetry-decomposed energy decomposition analysis (EDA) so that the charge flow associated with Pauli repulsion and orbital interactions can be quantified both per atom and per irrep, for example, for σ, π, and δ electrons. This provides detailed insights into fundamental aspects of chemical bonding that are not accessible from EDA.

Small satellite Extracurricular projects – Implementing a context‐driven SysEng engine for improved adaptability and student agency

AbstractUniversity student projects usually attempt to follow, and often fail to follow, industry frameworks and standards to ensure the success of their development effort. The typical student satellite project follows ESA ECSS or NASA project frameworks, prescribing document artefacts, project reviews, the project life cycle, and typical project processes. In the case of Orbit NTNU, this was done without understanding the underlying dependencies and supporting connections between artefacts, design steps, and project phases. This paper presents a framework for increased understanding of the purpose of common design artefacts and their interdependencies by applying model‐centric system thinking and systemigrams as a tool for highlighting relationships and dependencies within the SysEng discipline, thus enabling the students to complete well‐informed and planned design iterations that build a solid and coherent system understanding throughout the project lifecycle. The method is built to be adapted to the needs of the project team and can readily be used by 1st year university students with one semester of SysEng experience.

Analysis performance of navigation constellation satellite failure and enhancement of LEO navigation

The stable operation of navigation satellite constellation is related to national economy and national defense security. The failure of any one or two satellites has little impact on the overall performance of the global navigation satellite constellation, and the availability of the navigation constellation decreases with the increase of the number of failed satellites. First, a typical medium earth orbit Walker-δ 24/3/1 constellation configuration was designed. Second, the service performance of the navigation constellation under different failure modes was analyzed. The weaknesses of the constellation were identified in combination with the availability data of the navigation constellation. Then, the overall performance of the navigation constellation after the low earth orbit satellite constellation compensates for the failure of the medium earth orbit satellite constellation is analyzed. The simulation results show that the failure of 5 global navigation satellites will reduce the availability of navigation constellation to 71%, and the hybrid navigation constellation can recover the availability to more than 97%. The orbital altitude and inclination of low orbit satellites affect the overall performance of the hybrid navigation constellation. The research results can provide reference for the demonstration of hybrid navigation constellation scheme.

Dynamics in the Vicinity of the Stable Halo Orbits

This work presents a study of the dynamics in the vicinity of the stable L2 halo orbits in the Earth-Moon system of the circular restricted three-body problem. These solutions include partially elliptic, partially hyperbolic, and elliptic quasi-halo orbits. The first two types of orbits are 2-dimensional quasi-periodic tori, whereas the elliptic orbits are 3-dimensional quasi-periodic tori. Motivated by the Lunar Gateway, this work computes these orbits to explore the 3-parameter family of solutions lying in the vicinity of the stable halo orbits. An algorithm is presented to quantify the size of the invariant surfaces which gives perspective on the size of the orbits. A stability bifurcation is detected where the partially elliptic tori become partially hyperbolic. A nonlinear behavior of the Jacobi constant is observed which differs from the behavior of the quasi-halo orbits emanating from the unstable halo orbits which makeup the majority of the quasi-halo family. Uses of the orbits in the vicinity of the stable L2 halo orbits are identified, and the results highlight characteristics and structure of the family to broaden the understanding of the dynamical structure of the circular restricted three-body problem.

Fast and accurate adaptive collocation iteration method for orbit dynamic problems

For over half a century, numerical integration methods based on finite difference, such as the Runge-Kutta method and the Euler method, have been popular and widely used for solving orbit dynamic problems. In general, a small integration step size is always required to suppress the increase of the accumulated computation error, which leads to a relatively slow computation speed. Recently, a collocation iteration method, approximating the solutions of orbit dynamic problems iteratively, has been developed. This method achieves high computation accuracy with extremely large step size. Although efficient, the collocation iteration method suffers from two limitations: (A) the computational error limit of the approximate solution is not clear; (B) extensive trials and errors are always required in tuning parameters. To overcome these problems, the influence mechanism of how the dynamic problems and parameters affect the error limit of the collocation iteration method is explored. On this basis, a parameter adjustment method known as the “polishing method” is proposed to improve the computation speed. The method proposed is demonstrated in three typical orbit dynamic problems in aerospace engineering: a low Earth orbit propagation problem, a Molniya orbit propagation problem, and a geostationary orbit propagation problem. Numerical simulations show that the proposed polishing method is faster and more accurate than the finite-difference-based method and the most advanced collocation iteration method.

Multi-orbit lunar GNSS constellation design with distant retrograde orbit and Halo orbit combination

The Moon is the closest natural satellite to mankind, with valuable resources on it, and is an important base station for mankind to enter deep space. How to establish a reasonable lunar Global Navigation Satellite System (GNSS) to provide real-time positioning, navigation, and timing (PNT) services for Moon exploration and development has become a hot topic for many international scholars. Based on the special spatial configuration characteristics of Libration point orbits (LPOs), the coverage capability of Halo orbits and Distant Retrograde Orbit (DRO) in LPOs is discussed and analyzed in detail. It is concluded that the Halo orbit with a period of 8 days has a better coverage effect on the lunar polar regions and the DRO has a more stable coverage effect on the lunar equatorial regions, and the multi-orbital lunar GNSS constellation with the optimized combination of DRO and Halo orbits is proposed by combining the advantages of both. This multi-orbital constellation can make up for the fact that a single type of orbit requires a larger number of satellites to fully cover the Moon, using a smaller number of satellites for the purpose of providing PNT services to the entire lunar surface. We designed simulation experiments to test whether the multi-orbital constellations meet the full lunar surface positioning requirements, and compare the coverage, positioning, and occultation effects of the four constellation designs that pass the test, and finally obtain a set of well-performing lunar GNSS constellations. The results indicate that the multi-orbital lunar GNSS constellation combining DRO and Halo orbits can cover 100% of the Moon surface, provides there are more than 4 visible satellites at any time on the Moon surface, which meets the navigation and positioning requirements, and the Position Dilution of Precision (PDOP) value is stable within 2.0, which can meet the demand for higher precision Moon surface navigation and positioning.

Digitally Mitigating Doppler Shift in High-Capacity Coherent FSO LEO-to-Earth Links

The range of applications enabled by the low-Earth orbit (LEO) constellations continues to increase, going from providing worldwide broadband internet access, to the transmission of enormous quantities of data gathered from space sensing and exploration. Therefore, it is imperative to find a technology for Earth-satellite and inter-satellite links that is able to provide ultra-high capacity and reliability. The alliance of coherent optical systems with free-space optics (FSO) can be considered a solution for these links, bringing the ultra-high capacity of fiber optic transmission systems to the wireless domain. However, the free-space channel brings some challenges to the telecommunication system, namely the atmospheric turbulence that can hinder data transmission, mainly when associated with typical satellite communication features such as the Doppler effect. Driven by this challenge, in this work, we propose a technique for mitigation of the impact of Doppler effect by dynamically adapting the transmitted signal symbol-rate while keeping the system bit-rate fixed through probabilistic constellation shaping (PCS). This methodology significantly increases the range of supported frequency shifts imposed by the Doppler effect in an experimental 600 Gbps transmission. Moreover, we address the reliability problem imposed by atmospheric turbulence, considering two different scenarios: i) a continuous transmission system with guaranteed reliability and ii) a bursty transmission without reliability constraints that solely aims at the maximization of the overall throughput of the system. In both scenarios, we show that the proposed methodology of adapting the system symbol-rate together with the transmitted constellation shaping can increase the supported bit-rate by more than 70 Gbps.

Modulated multi-sliding-surface attitude tracking control for all-electric propulsion satellites

This work presents an attitude tracking control method suitable for satellites only using on–off electric thrusters of constant magnitude. It is practically a globally stable finite-time controller modulated by the Pulse-Width-Pulse-Frequency (PWPF) algorithm. Two sliding surfaces are designed to insure a finite-time convergence property. An automatic generator for producing the time-related key parameter is proposed, leaving only two scalar parameters to fine tune values. Typical satellite control modes are used to validate the effectiveness of the proposed method. Results show that it is feasible not only for attitude tracking problem with various errors taken into account, but also for six degree-of-freedom control. Flexibility of trading-off the control accuracy and number of thruster firings can be achieved by the PWPF parameter tuning, which makes it a promising candidate for future use in real practise.

Geometry of sample spaces

In statistics, independent, identically distributed random samples do not carry a natural ordering, and their statistics are typically invariant with respect to permutations of their order. Thus, an n-sample in a space M can be considered as an element of the quotient space of Mn modulo the permutation group. The present paper takes this definition of sample space and the related concept of orbit types as a starting point for developing a geometric perspective on statistics. We aim at deriving a general mathematical setting for studying the behavior of empirical and population means in spaces ranging from smooth Riemannian manifolds to general stratified spaces.We fully describe the orbifold and path-metric structure of the sample space when M is a manifold or path-metric space, respectively. These results are non-trivial even when M is Euclidean. We show that the infinite sample space exists in a Gromov–Hausdorff type sense and coincides with the Wasserstein space of probability distributions on M. We exhibit Fréchet means and k-means as metric projections onto 1-skeleta or k-skeleta in Wasserstein space, and we define a new and more general notion of polymeans. This geometric characterization via metric projections applies equally to sample and population means, and we use it to establish asymptotic properties of polymeans such as consistency and asymptotic normality.

CMOS-based observation of Resident Space Objects using short-exposure stacking mode

To meet the growing demand for the surveillance of resident space objects, the Shanghai Astronomical Observatory has developed a new observation method for monitoring resident space objects using a high frame rate astronomical CMOS camera, called the short-exposure stacking mode. This method can be used to observe objects of various orbit types with high observation accuracy. This paper describes the implementation of this new method of RSO observation, and the observation experiment of one MEO satellite and two GEO satellites using this method with a 40 cm telescope, the observation system has a 0.5°×0.5° field of view. The observation results show that the accuracy of the sensor calibration is 0.3-0.4 arc-second. Compared with the external precision ephemeris, the standard deviation of the residual differences is better than 0.5 arc-second, which means that the precise orbit of space objects can be obtained with enough observation. And compared with the method that uses drift scan CCD, the observation time efficiency of the short-exposure stacking mode is better.