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Satellite communication, in over half a century have attained remarkable breakthrough in high speed transmission. These innovations, on the other hand, have come in tandem with significant performance improvements in other IT and telecommunications systems. As a result, these significant benefits are not as visible to the broader public as they would be as if this burst of performance had occurred in isolation. In nutshell, space satellite communication using optical technology provide powerful alternative to radio frequency (RF) and make communication reliable and cost effective. Satellite communications systems allow a whole new race of civilian and defence operations in surveillance, telecommunications, object tracking and space exploration. Since independent satellites are restricted by volume, space and strength, small satellites production in bulk clusters may be effective for a range of wildfire monitoring, science missions, mapping in gravity and water management exploration, among others. The development of communications satellites would provide for a more comprehensive understanding of the near-earth environment as well as a more efficient and cost-effective way of reaching space, thanks to the utilisation of multi-satellite systems. As a result, when satellites are designing, IsOWC is an utmost point to be considered. The numerous researches being performed in the satellite communications for introducing multi communications based on different orbits are described in this study. IsOWC systems over radio frequency based communication are preferred due to large bandwidth, high speed, absence of electromagnetic interference (EMI), lower transmission losses and improved security. We also present a detailed listing of challenges in Is-OWC such as Doppler shift, point ahead angle, satellite vibration and tracking, acquisition tracking and pointing (ATP) and background noise sources. [ABSTRACT FROM AUTHOR]

We show that the set of m × m complex skew-symmetric matrix polynomials of even grade d , i.e., of degree at most d , and (normal) rank at most 2 r is the closure of the single set of matrix polynomials with certain, explicitly described, complete eigenstructure. This complete eigenstructure corresponds to the most generic m × m complex skew-symmetric matrix polynomials of even grade d and rank at most 2 r. The analogous problem for the case of skew-symmetric matrix polynomials of odd grade is solved in [24]. [ABSTRACT FROM AUTHOR]

We discovered 83 asteroids at the Baldone Astrophysical Observatory (MPC code 069) in 2017–2022. We studied one of the dynamically interesting Apollo (Near Earth object) observed at the Baldone Astronomical Observatory, namely 428694 Saule (2008 OS9) and the Centaur-type asteroid 330836 Orius (2009 HW77). We studied the evolution of the asteroid Saule’s rotation period, obliquity, and spin axis together with its non-gravitational parameter da∕dt{\rm{d}}a/{\rm{d}}t connected with the Yarkovsky effect. Additionally, we studied the orbit of the Amor-type asteroid 2017 UW42, which has the significant non-gravitational parameter A2A2.

In this paper, we characterize and classify the orbits of the fixed-point group on the unipotent elements of the generalized symmetric spaces for inner involutions of SL 3 (k) and SL 4 (k) where k is a finite field of odd characteristic. We provide some generalized results for SL n (k). [ABSTRACT FROM AUTHOR]

In 1951 Łojasiewicz found a necessary and sufficient condition for the existence of a q-iterative root of an arbitrary bijective function g for any q ≥ 2 . In this article we extend this result to the injective case. More precisely, a necessary and sufficient condition for the existence of an iterative root of an injective function is proved, and in the case of existence, the characterization and enumeration of all iterative roots are given. Furthermore, we devise a construction by which all iterative roots of an injective function can be constructed (provided that the considered function has at least one iterative root). As an illustration, we apply the developed theory to several results from the literature to obtain somewhat more elegant and shorter proofs of those results. [ABSTRACT FROM AUTHOR]

Let R be a finite commutative ring with unity, and let G = (V , E) be a simple graph. The zero-divisor graph, denoted by Γ (R) is a simple graph with vertex set as R, and two vertices x , y ∈ R are adjacent in Γ (R) if and only if x y = 0 . In [5], the authors have studied the Laplacian eigenvalues of the graph Γ (Z n) and for distinct proper divisors d 1 , d 2 , ⋯ , d k of n, they defined the sets as, A d i = { x ∈ Z n : (x , n) = d i } , where (x, n) denotes the greatest common divisor of x and n. In this paper, we show that the sets A d i , 1 ≤ i ≤ k are actually orbits of the group action: A u t (Γ (R)) × R ⟶ R , where A u t (Γ (R)) denotes the automorphism group of Γ (R) . Our main objective is to determine new classes of threshold graphs, since these graphs play an important role in several applied areas. For a reduced ring R, we prove that Γ (R) is a connected threshold graph if and only if R ≅ F q or R ≅ F 2 × F q . We provide classes of threshold graphs realized by some classes of local rings. Finally, we characterize all finite commutative rings with unity of which zero-divisor graphs are not threshold. [ABSTRACT FROM AUTHOR]

Fractures of the orbit are frequently noted in craniomaxillofacial trauma. The complexity of the anatomy and the proximity to various vital structures often complicates the surgical management of these fractures. The authors have thus attempted to review the literature on anatomy of the bony orbit and its soft tissue envelope in a simplified manner with due emphasis on surgical anatomy and exploration of the orbit with a surgical perspective. The contents of this narrative literature review may be useful for young maxillofacial surgeons and will aid in the process of management of orbital fractures. [ABSTRACT FROM AUTHOR]

Despite a growing interest in developing and launching CubeSats, areas related to their testing and simulation still need to improve systematization, especially within universities. Regarding the temperature of CubeSats, the battery is one of the most critical components, which is why it is common to use active control techniques, such as heaters, based on the Joule effect, which impacts the satellite’s task scheduling. Despite previous works in the literature, no study simultaneously contemplates the scheduling of tasks and the thermal control of the battery, under varying energy, with the rigor and advantages of exact optimization algorithms. This letter proposes to address these two combined features: 1) the analysis and modeling of the nanosatellite scheduling problem to optimize the use of energy resources and 2) the maximize the mission value extraction while considering the battery temperature. In order to include the battery temperature control in the modeling, a proxy model will be used considering a finite volume method based on the heat transfer equations that govern the thermal models of a battery. Thus, a mathematical model of task scheduling capable of considering the thermal control of the battery will be introduced. [ABSTRACT FROM AUTHOR]

Two vertices |$u$| and |$v$| in a graph |$G=(V,E)$| are in the same orbit if there exists an automorphism |$\phi $| of |$G$| such that |$\phi (u)=v$|⁠. The orbit number of a graph |$G$|⁠ , denoted by |$Orb(G)$|⁠ , is the smallest number of orbits, which form a partition of |$V(G)$|⁠ , in |$G$|⁠. All vertex-transitive graphs |$G$| are with |$Orb(G)=1$|⁠. Since the |$n$| -dimensional hypercube, denoted by |$Q_{n}$|⁠ , is vertex-transitive, it follows that |$Orb(Q_{n})=1$| for |$n\geq 1$|⁠. Pai, Chang, and Yang proved that the |$n$| -dimensional folded crossed cube, denoted by |$FCQ_{n}$|⁠ , is vertex-transitive if and only if |$n\in \{1,2,4\}$|⁠ , namely |$Orb(FCQ_{1})=Orb(FCQ_{2})=Orb(FCQ_{4})=1$|⁠. In this paper, we prove that |$Orb(FCQ_{n})=2^{\lceil \frac{n}{2}\rceil -2}$| if |$n\geq 6$| is even and |$Orb(FCQ_{n}) = 2^{\lceil \frac{n}{2}\rceil -1}$| if |$n\geq 3$| is odd. [ABSTRACT FROM AUTHOR]

Any system with vectors from which spans is called a frame. The tight frame gives a representation of a vector from that looks like the representation in a orthonormal basis. The unitary equivalence up to a permutation on the set of tight frames preserves the inner products and is independent on the indexing of frame vectors. We present invariants of equivalence classes on the set of tight frames in , that separate classes of equivalence in general position. We describe a reconstruction of an equal norm tight frame up to permutational unitary equivalence from values of the invariants. The results are received by using the action of the symmetric group on the space of symmetric matrices. More precisely, we show algebraically independent generators of the field of invariants for this action. [ABSTRACT FROM AUTHOR]

CubeSats must endure the extreme temperature and radiation changes that are a result of the environment in orbit. The power system of CubeSats, which produces the electrical energy required to carry out the activities, is a crucial component. The photovoltaic effect, a phenomenon whose maximum power point decreases as temperature rises while the peak rises with solar radiation intensity rises, is used by the majority of satellites, including CubeSats, to convert solar radiation into electrical energy. High temperatures should be avoided since they decrease the effectiveness of this photovoltaic phenomenon, whereas high solar radiation levels are required to produce more energy. This study evaluates a simulation of a CubeSat 1U with solar panels mounted on all of its faces to examine the impact of orbit, attitude, and temperature management on power generation. The outcomes show that higher performance may be obtained by carefully choosing these factors. [ABSTRACT FROM AUTHOR]

LabOSat is an applied research group whose main objective is to increase the technology readiness level of electronic devices and systems for their use in satellite missions. Since 2013 the Group has participated in nine low-Earth orbit missions in collaboration with Satellogic. Its flagship payload, LabOSat-01, is a Source-Measurement-Unit instrument dedicated to the electrical characterization of electronic devices. In this brief communication, results of in-orbit operation of LabOSat-01 are presented. A summary of the Group activities in the period 2013–2022 is also presented. These results represent almost ten years of experience in nine missions hosting different technologies in orbit. [ABSTRACT FROM AUTHOR]

Discussions about space security have long focused on Earth orbit, where satellites are extensively used to support military activities on the surface of the planet, and where that use makes satellites themselves potentially attractive targets. This is about to change, as the US military prepares to expand its activities into the vast region between Earth geosynchronous orbit and the moon, an area otherwise known as "cis-lunar space." If it does, the militaries of other countries will surely follow. But it does not need to be this way. The demarcation of Earth orbit and cis-lunar space provides a clear line upon which a demilitarization commitment could be based. We can still develop the moon and the region around it, but as we have learned from decades of activity in Earth orbit, developing space in a sustainable way requires foresight, planning, and cooperation. Space must be recognized as an environment that is worth preserving, and as one in which fast-paced alterations can have unintended consequences. [ABSTRACT FROM AUTHOR]

Based on the speckle observations of the wide double star ADS 15571 with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences in 2014, we have confirmed the existence of a close companion to component A that was previously detected from astrometric observations at the Pulkovo Observatory. An extension of the BTA observations from 2014 to 2022 has allowed 28 positions of the companion relative to the primary star to be obtained. From this series we have constructed the relative orbit of the companion and determined the sum of the masses of subsystem A ( ). A comparison of this orbit with the orbit of the photocenter of component A constructed from Pulkovo photographic observations has also allowed the mass ratio of the primary star and the companion and their individual masses to be estimated: and . Based on the estimates of the magnitude difference between the two stars of the system ADS 15571A, we have estimated the spectral types of the components: ADS 15571Aa—F8V; ADS 15571Ab—K5V–K5.5V. The speckle observations of component B have shown that it has no resolvable companions. [ABSTRACT FROM AUTHOR]

In the traditional X-ray pulsar Doppler velocimetry approach, a single pulsar only provides the velocity information of spacecraft in the line-of-sight (LOS) direction of a pulsar. Theoretically, we prove that the spacecraft velocity error in any direction can distort the X-ray pulsar profile in orbit around Jupiter. Moreover, using singular value decomposition (SVD), we find that the observability of velocities in both the maximal and middle singular directions is far better than that of the minimal one. Based on theoretical analysis results, we propose a two-dimensional Doppler velocimetry approach using a single X-ray pulsar to provide more velocity information for spacecraft. Firstly, we use SVD to give two well-observable singular directions for velocity estimation. And then, to eliminate duplicate computations in the accumulative process of X-ray pulsar signals, we build the piecewise complete dictionary of accumulated pulsar profiles, which has no identical accumulated pulsar profile. Finally, using the chi-square value of X-ray pulsar sup-profiles as an evaluation standard, we develop the two-level velocity estimation based on dictionary folding (DF) to measure the two-dimensional Doppler velocity. Experimental results demonstrate that compared with the traditional one-dimensional pulsar velocimetry approach, the two-dimensional Doppler velocimetry approach using a single X-ray pulsar provides more velocity information and is more robust to the initial velocity error. The accuracies of velocities in both two singular directions reach 0.3 m/s. In addition, compared with the traditional epoch folding, the elapsed time of the DF reduce by more than 70% and gets 4 min. • We develop a new idea that provides two-dimensional Doppler velocity for spacecraft. • We prove the propagation property of velocity error in the orbit around a planet. • Two directions for Doppler velocity are calculated by singular value decomposition. • We build the piecewise complete dictionary to remove numerous duplicate computations. • We propose dictionary folding to substitute for epoch folding and improve real-time. [ABSTRACT FROM AUTHOR]

Periodic orbit families that exist around the asteroid (101955) Bennu were computed and analyzed to gain insight into the dynamical environment about the asteroid. A constant-density polyhedron model was used to generate the families. The planar direct and retrograde families, and families emanating from equilibria, were computed. Ten distinct families were identified in this set, and many of the orbit structures were similar (e.g., the vertical families emanating from the equilibria behaved in similar ways), and several of these structures were connected to each other. We identified 12 distinct families emanating from bifurcation points in the initial families. These 12 families could be classified into four types. Even though the model of Bennu had no exact symmetry, many nearly symmetric structures were identified. There were also many similarities to structures identified using simplified models like the homogeneous rotating gravitating triaxial ellipsoid. The behavior of the identified families also provided insight into the evolution of the dynamical environment around the asteroid. We expect the qualitative behavior of the families we identified to be similar to the families that would exist around other asteroids that are nearly spherical. [ABSTRACT FROM AUTHOR]

Small satellites in low-Earth orbit (LEO) attract much attention from both industry and academia. The latest production and launch technologies constantly drive the development of LEO constellations. However, wideband signals, except text messages or voice in a few Kbps, cannot be transmitted directly from a LEO satellite to a standard mobile cellular phone due to the insufficient link budget. The current LEO constellation network has to use an extra ground device to receive the signal from the satellite first and then forward the signal to the user equipment (UE). To achieve direct network communications between LEO satellites and UE, in this article, we propose a novel distributed beamforming technology based on the superposition of electromagnetic (EM) waves radiated from multiple satellites that can significantly enhance the link budget. EM full-wave simulation and Monte Carlo simulation results are provided to verify the effectiveness of the proposed method. The simulation results show a nearly 6-dB enhancement using two radiation sources and an almost 12-dB enhancement using four sources. The received power enhancement could be doubled compared to the diversity gain in multiple-input, single-output (MISO). Furthermore, other practical application challenges, such as synchronization and the Doppler effect, are also presented. [ABSTRACT FROM AUTHOR]

Let j be a fixed integer. Let { x n } be a sequence of complex numbers and let Δ x j = x j + 1 - x j. Let 0 < α < 1 , first, it is shown that (a) | x n | = O (e ϵ n α ) , as n → ∞ for all ϵ > 0 , and (b) | Δ n x j | 1 n → 0 as n → ∞ , if and only if there exists a positive constant R such that ‖ Δ n x j ‖ ≤ R n n n (1 - 1 α). Second, we present an extended version of our result [3], where the condition on the growth of the sequence is replaced by the same condition on the Cesàro means M n (x n) and retaining the conclusion. Applications to the orbits of operators are given. This helps to elucidate and improve former results of Mbekhta–Zemánek, Atzmon and others. [ABSTRACT FROM AUTHOR]