Space Tracking Research Articles

Step-barrier dynamical system

The step-barrier dynamical system is discussed in detail. The behavior of particles captured in the barrier bucket remarkably varies depending on their initial conditions. The intrinsic nature of motion observed in the fully normalized area-preserving mapping simulations is simply clarified by a value of energy or momentum of particle at the initial stage. A rational initial value of y in the normalized phase space (x, y) at beginning leads to the periodic solution. Meanwhile, an irrational value of y gives the oscillation in amplitude with multi-frequency, resulting in broad tracks in the phase space. Effectively, the barrier bucket size is reduced due to these broad tracks. We arrive at the concept of effective stable region, which is defined by the contour of the averaged step-barrier Hamiltonian and useful in actual applications.

Discovery of the Magellanic Stellar Stream Out to 100 kpc

The Magellanic Stream (MS)—an enormous ribbon of gas spanning 140° of the southern sky trailing the Magellanic Clouds—has been exquisitely mapped in the five decades since its discovery. However, despite concerted efforts, no stellar counterpart to the MS has been conclusively identified. This stellar stream would reveal the distance and 6D kinematics of the MS, constraining its formation and the past orbital history of the Clouds. We have been conducting a spectroscopic survey of the most distant and luminous red giant stars in the Galactic outskirts. From this data set, we have discovered a prominent population of 13 stars matching the extreme angular momentum of the Clouds, spanning up to 100° along the MS at distances of 60–120 kpc. Furthermore, these kinematically selected stars lie along an [α/Fe]-deficient track in chemical space from −2.5 < [Fe/H] <− 0.5, consistent with their formation in the Clouds themselves. We identify these stars as high-confidence members of the Magellanic Stellar Stream. Half of these stars are metal-rich and closely follow the gaseous MS, whereas the other half are more scattered and metal-poor. We argue that the metal-rich stream is the recently formed tidal counterpart to the MS, and we speculate that the metal-poor population was thrown out of the SMC outskirts during an earlier interaction between the Clouds. The Magellanic Stellar Stream provides a strong set of constraints—distances, 6D kinematics, and birth locations—that will guide future simulations toward unveiling the detailed history of the Clouds.

A strategy for human safety monitoring in high-temperature environments by 3D-printed heat-resistant TENG sensors

Flexible wearable devices based on triboelectric nanogenerators (TENGs) can be used to track many parameters around the human body, including signals from motions, gestures, and contacts, to perform a variety of tasks. However, it is still a challenge to achieve wide working temperature and multi-parameter body motion sensing with TENG sensors. To address that, this work reports a facile 3D printing-based strategy for preparing functionalized heat-resistant TENG sensors. In detail, a printable heat-resistant ink and multiple 3D printing-based assembly methods are proposed. The as-fabricated ink, which could maintain up to 200 ℃, then serves as multiple components in the TENG sensors through patterning. Functionalized TENG sensors and human–machine interfaces are printed and subsequently networked on a human body to sense comprehensive motion information. The results indicate six typical motions can be recognized with 94.85% accuracy based on neural network algorithms. A simple digital twin for motion capture and trace tracking in virtual space is furthermore implemented. Combining the proposed TENG sensors with virtual reality (VR) platforms opens up a new road for human safety monitoring in high-temperature environments.

Understanding the Effect of Substrate Preheating Temperature and Track Spacing on Laser Assisted Cold Spraying of Ti6Al4V

In this study, laser-assisted cold spray (LACS) of titanium alloy Ti6Al4V onto Ti6Al4V substrates has been investigated in two phases: (i) single-track deposits on substrates preheated to 400 °C, 600 °C, and 800 °C, respectively, and (ii) single-layer (multi-track) deposits on substrates preheated to 600 °C with three different track spacings (1 mm, 2 mm, and 3 mm). Cross-sectional microstructures of the single-track deposits showed intimate contact at the interfaces, especially extensive interfacial mixing for specimens with substrate preheating at 600 °C and 800 °C. Cross-sectional area porosity content in single layer LACS coatings was found to be around 0.4%, which is significantly lower than the standard or conventional cold spray (CS) process having ~2.3% porosity. The microstructure reveals that the LACS process has improved the adhesion and cohesion of the deposits, in addition to the other advantages of the CS process. The average microhardness values of LACS deposits were found to be in the range of 388–403 HV (the highest hardness with the lowest track spacing), which is approximately 6–10% lower than that of the CS deposits without laser substrate preheating. Tensile residual stresses were found in all three LACS coatings, which was due to elevated process gas temperature along with high heat input during laser preheating of the substrate. It was observed that the higher the track spacing, the higher the stress magnitude, i.e., 31 MPa, 135 MPa, and 191 MPa in the longitudinal direction when deposited with 1 mm, 2 mm, and 3 mm track spacings, respectively. Heat treatments induced varied microstructures in LACS coatings, encompassing fully equiaxed or lamellar α-phase within the β-phase, or a bimodal microstructure, with characteristics linked to track spacing variations. Key contributions of this study include enhanced coating-substrate adhesion through extensive interfacial mixing, a substantial reduction in cross-sectional area porosity compared to CS, insights into the effects of residual stresses, and, ultimately, advancing the comprehension of LACS and its potential advantages over conventional CS process.

Performance analysis of a time difference of arrival sensors network for LEO satellites orbit determination

The rising interest for space activities within the so-called “New Space Economy” has led in the past few years to a substantial increase of satellites launches, making space more and more populated, especially in the LEO region, where most of the newly conceived missions are supposed to operate. This phenomenon is imposing the need of an improvement and augmentation of the current space surveillance systems, possibly implementing high-capacity and passive methodologies capable of exploiting standard satellite radio-frequency transmissions. This paper describes and analyzes the performances of a satellite orbit determination method based on Time Difference of Arrival (TDOA) measurements, collected by means of a radio stations network. The analysis is aimed at assessing the influence of a variety of parameters on the orbit estimate accuracy, in order to determine whether this method can be used effectively to support and contribute to current space tracking techniques.

Mechanisms underlying pathological cortical bursts during metabolic depletion

Cortical activity depends upon a continuous supply of oxygen and other metabolic resources. Perinatal disruption of oxygen availability is a common clinical scenario in neonatal intensive care units, and a leading cause of lifelong disability. Pathological patterns of brain activity including burst suppression and seizures are a hallmark of the recovery period, yet the mechanisms by which these patterns arise remain poorly understood. Here, we use computational modeling of coupled metabolic-neuronal activity to explore the mechanisms by which oxygen depletion generates pathological brain activity. We find that restricting oxygen supply drives transitions from normal activity to several pathological activity patterns (isoelectric, burst suppression, and seizures), depending on the potassium supply. Trajectories through parameter space track key features of clinical electrophysiology recordings and reveal how infants with good recovery outcomes track toward normal parameter values, whereas the parameter values for infants with poor outcomes dwell around the pathological values. These findings open avenues for studying and monitoring the metabolically challenged infant brain, and deepen our understanding of the link between neuronal and metabolic activity.

Feature-Based Electromagnetic Tracking Registration Using Bioelectric Sensing

Catheter tracking is essential during minimally invasive endovascular procedures, and Electromagnetic (EM) tracking is a widely used technology for this purpose. When preoperative patient images are available, they can be used to guide EM-tracked interventions. However, a registration step between preoperative images and intraoperative EM tracking space is usually required. Most existing solutions for this registration process require manual interactions, which can add additional steps to the workflow. In this paper, a novel automatic feature-based registration method is proposed, based on electric sensing of vascular geometry by the catheter, also known as Bioelectric sensing. The technique employs the Bioelectric sensing capabilities of the catheter to identify vascular features, such as bifurcations, aneurysms, or stenosis. The known EM position of these features is then utilized to register the EM tracking space and the preoperative images. The registration is refined using iterative closest point (ICP) registration algorithms. Unlike existing solutions, the proposed method does not require external markers, interventional imaging, or additional surgeon actions, and hence does not impact the interventional workflow.

A-contrario detection and tracking from optical telescope data

The precipitous growth of the Anthropogenic Space Object population demands new approaches to high-volume detection and measurement for orbital analyses and conjunction assessment. Optical sensors, which can be smaller and more cost-effective than other mechanisms such as radar sensors, have potential for rapid network expansion, community-driven data acquisition, and space-based sensing. However, traditional detection methods of source extraction and track filtering require high-fidelity a-priori assumptions of data content and are limited by extensive calibration requirements costing time, resources, and expert knowledge of particular detection pipelines. Machine learning methods mitigate a-priori assumptions but require extensive training data which is costly to manually label and restricts applicable use cases. We instead consider a new approach to optical Space Surveillance and Tracking based on a-contrario analysis, detecting features which cannot be attributed to noise from the hardware, atmosphere, or background celestial environment. In such an approach, we reduce epistemic uncertainty by recursive conditioning and inference of data structures. This approach is implemented and assessed on data from the ASTRIANet telescope network of The University of Texas at Austin, and we demonstrate the capacity for orbit determination by quantifying detection rates for actively tracked objects, discussing applicability to sidereal tracking and object discovery, and evaluating the resulting orbit estimates.

Deep Space Navigation by Optical Pulsars

Nowadays, deep-space navigation strongly depends on ground segments, e.g., ESA’s European Space Tracking and NASA’s Deep Space Network. However, the positioning accuracy of ground-based navigation systems decreases with the distance from the Earth, significantly increasing the positioning uncertainty for interplanetary missions. Furthermore, ground-based navigation systems require extensive ground operations, and their limited bandwidth could lead to a point of full utilization in the future. The aim of this work is to introduce—for the first time—the concept of space navigation by optical pulsars, a novel technology that aims at overcoming the limits of ground-based navigation systems. This paper presents, first, an introduction to satellite navigation by using pulsars, discussing on the physical and timing properties of optical pulsars. Then, it investigates on the timing techniques allowing to reconstruct, process, and make use of a pulsar signal, leading to a position estimation. Finally, it reports the results of a clock error estimation performed on ground with real pulsar data and a first estimation of the achievable positioning accuracy in a simulated highly elliptical orbit around the Earth.

A stochastic reaction–diffusion modeling investigation of FLASH ultra-high dose rate response in different tissues

Purpose: The aim of the study was to propose a theory based on topology and geometry of diffusion channels in tissue to contribute to the mechanistic understanding of normal tissue sparing at ultra-high dose rates (UHDRs) and explore an interplay between intra- and inter-track radical recombination through a reaction–diffusion mechanism.Methods: We calculate the time evolution of particle track structures using a system of coupled reaction–diffusion equations on a random network designed for molecular transport in porous and disordered media. The network is representative of the intra- and inter-cellular diffusion channels in tissues. Spatial cellular heterogeneities over the scale of track spacing are constructed by incorporating random fluctuations in the connectivity between network sites, resembling molecular mass and charge heterogeneities at the cellular level.Results: We demonstrate the occurrence of phase separation among the tracks as the complexity in intra- and inter-cellular structure increases. At the strong limit of structural disorder, tracks evolve individually like isolated islands with negligible inter-track as they propagate like localized waves in space, analogous to the Anderson localization in quantum mechanics. In contrast, at the limit of weak disorder in a homogeneous medium, such as water, the neighboring tracks melt into each other and form a percolated network of non-reactive species. Thus, the spatiotemporal correlation among chemically active domains vanishes as the inter-cellular complexity of the tissue increases from normal tissue structure to fractal-type malignancy.Conclusion: Differential FLASH normal tissue sparing may result from the interplay of the proximity of tracks over the intra- and inter-cellular landscape, a transition in the spatial distribution of chemical reactivity, and molecular crowding. In this context, insensitivities in the radiobiological responses of the tumors to FLASH-UHDR are interpreted via a lack of geometrical correlation among isolated tracks. The structural and geometrical complexities of cancerous cells prevent the clustering of tracks over a timescale, in which inter-track chemical reactivities presumably prevail in normal tissues. A series of systematic experiments on radiolysis-induced diffusivity and reactivity in actual normal and cancerous tissues must be performed to classify the tissues potentially spared by FLASH-UHDRs and verify our theory.

Enhancing the radar system simulator tool suite to allow the simulation of sensor networks

The number of human-made objects orbiting the Earth is growing steadily. This trend is further accelerating during recent years due to increasing commercialization in the field of satellite operations and an increasing launch rate. Concerning the area of space surveillance and tracking (SST), this leads to higher demands with respect to object observation capabilities. In order to ensure the safe usability of the different Earth orbits for all spacecraft operators, it is of great importance to continuously observe and catalog as many of the human-made objects as possible. This is especially true for inactive and uncontrollable objects, i.e. space debris. Only by maintaining accurate catalogs of the space debris environment, involuntary collisions can be avoided and risks of losing a spacecraft kept low. While the number of space debris objects can only be expected to further increase, it is not trivial to increase the number of observation sites, such as telescopes and radars, or their capabilities to counter this. One way to increase the observation capabilities without constructing new observation sites is to search for possibilities to improve the efficiency with which the existing sensors observe objects.With the goal to study and analyze single sensors, sensor networks, and how they can be used in the most efficient way, a sensor network simulator tool suite has been developed at the Institute of Space Systems of the Technical University of Braunschweig. Originally, the tool suite was developed as a radar system simulator concentrating on the different radar system configurations, such as reflector antennas or phased arrays that are used in a mono- or bistatic mode. Additionally, the corresponding radar performance model is able to simulate a tracking as well as a scanning mode. Building upon this tool suite, it is now extended to include an optical performance model and the possibility to simulate not only ground-based but also space-based sensors. Within this work, the preliminary results obtained with the newly implemented optical performance model are shown.Using the enhanced version of this sensor network simulator tool suite, thorough analyses can now be made using the radar and optical performance models. Sensor networks consisting of radars and telescopes being both ground- or space-based can be studied in different configurations. Thereby, different aspects, such as observation strategies, sensor tasking, or choosing the right location and sensor to reach a certain goal can be investigated.

The vowel system of Qatari Arabic: Evidence for peripheral/non-peripheral distinction between long and short vowels

Arabic has a vowel system with three long and three short monophthongs. One of the parameters that accounts for qualitative differences between long and short vowels across languages is tenseness/laxness of vowels located on the peripheral/non-peripheral tracks in the vowel space. The present study investigates acoustical cues (F1, F2, and duration) of vowels using the data obtained from 21 speakers of Qatari Arabic. The vowels were produced in four phonetic contexts: labial, alveolar, uvular, and pharyngeal. The results revealed considerable qualitative differences between long and short vowels. The long vowels were articulated at the periphery of vowel space; the short vowels occupied more centralized positions. The co-articulatory effect of the preceding consonant was more prominent in short vowels. Short high vowels /i u/ were lowered toward the mid position; short low /a/ was fronted; long low /aː/ was retracted and raised. The findings suggest that short vowels in Qatari Arabic are lax and non-peripheral.

Robust State/Output-Feedback Control of Robotic Manipulators: An Adaptive Fuzzy-Logic-Based Approach With Self-Organized Membership Functions

This article aims to design a joint space tracking controller for robotic manipulators having uncertainties in their mathematical representations under the additional constraint that joint velocity sensing not being available. A two-part design is followed where in the first part, the modeling uncertainties are dealt with a self-organized adaptive fuzzy-logic (AFL)-based controller where full-state feedback (FSFB) is assumed. The stability analysis yields semiglobally uniformly ultimately bounded tracking results. In the second part, a high-gain joint velocity observer is designed followed by replacing error vectors in the FSFB controller with their saturated versions obtained from the observer design to arrive at a self-organized AFL-based robust output-feedback controller. The stability analysis is performed via a multiple-step Lyapunov-type method where the semiglobal uniform ultimate boundedness of the tracking error is ensured. Comparative experiment results obtained from a planar robotic manipulator are presented to demonstrate the efficacy of the proposed control methodology.

Evaluation of different satellite navigation methods for the Moon in the future exploration age

Numerous lunar missions are planned for the next decade and the current deep space tracking system could not be sufficient to support all of them, since it has inherent limits in terms of complexity, availability, costs and user capacity. Consequently, new semi-autonomous or autonomous navigation systems are under study for the Moon, using satellites deployed in lunar orbit.In this work, a general and modular architecture for a satellite based navigation system, compatible with the state-of-the-art recommendations, is defined and three different localization methods, exploiting One-Way and Two-Way ranging, are proposed. The Two-Way ranging is proposed with two different implementation techniques: Earth based and user based round trip delay. These solutions were evaluated for two types of constellations that are, at the moment, the most promising for a future lunar navigation system, the Halo and ELFO constellations, by the use of the Cramer–Rao Lower Bound. Moreover, models for measurement errors affecting the lunar navigation system are proposed.The results show that Two-Way localization has slightly better accuracy and availability w.r.t. the One-Way localization, but it has also some limits in terms of capacity and latency. In the author’s opinion, the two methods might coexist for different user requirements and services in a future lunar navigation system.

A Constant Elevation Search Method for Narrow Beam Radar to Capture Space Targets

Position prediction is the basis of guiding radar to seek, capture, and track space targets, although there’s a risk of insufficient accuracy for narrow beam radar due to the influence of orbit determination and propagation error. Since the along-track error is the main factor that affects the accuracy of position prediction, this paper proposed a Constant Elevation Search (CES) method for narrow beam radar, based on the idea of along-track error compensation, to seek and capture transit targets. With along-track error estimation, all possible positions on a specified elevation can be observed, thus the success rate of capturing transit targets will be improved. Simulation shows that when the position prediction method fails, the CES method still works.

Payload Camera Breadboard for Space Surveillance—Part I: Breadboard Design and Implementation

The rapid increase of space debris poses a risk to space activities, so it is vital to develop countermeasures in terms of space surveillance to prevent possible threats. The current Space Surveillance Network is majorly composed of radar and optical telescopes that regularly observe and track space objects. However, these measures are limited by size, being able to detect only a tiny amount of debris. Hence, alternative solutions are essential for securing the future of space activities. Therefore, this paper proposes the design of a payload camera breadboard for space surveillance to increase the information on debris, particularly for the under-catalogued ones. The device was designed with similar characteristics to star trackers of small satellites and CubeSats. Star trackers are attitude devices usually used in satellites for attitude determination and, therefore, have a wide potential role as a major tool for space debris detection. The breadboard was built with commercial off-the-shelf components, representing the current space-camera resolution and field of view. The image sensor was characterized to compute the sensitivity of the camera and evaluate the detectability performance in several simulated positions. Furthermore, the payload camera concept was tested by taking images of the night sky using satellites as proxies of space debris, and a photometric analysis was performed to validate the simulated detectability performance.

MANEUVERS: OPERATIONAL PERFORMANCE OF SUGARCANE HARVESTERS

Sugarcane is among the main crops that compose Brazilian’s agribusiness. Therefore, cropping has a significant economic and social role, as production increases yearly. Currently, in Brazil, the mechanized harvest of sugarcane is growing fast in most of the country. The improvement in the harvester’s performance allows for fewer expenses and a higher operating yield. This study aimed to analyze the correlation between fuel consumption and maneuvering time of sugarcane harvesters in three different areas (W1 &gt; 20 ha, 10 ha &lt; W2&lt; 20 ha, and W3 &lt; 10 ha). Were calculated fuel consumption per maneuver in each area and analyzed how this value can change due to the tracks' spatial variability combined with the machine's hourly consumption. Based on the variable maneuvering time results and consumption per maneuver, the treatment W3 was the one that obtained the lowest fuel consumption with the T maneuver, due to the shorter mean maneuvering time, besides the more significant available track space to perform them. So that is the best configuration that aims at more significant savings in production cost.

Barriers and Gateways to Cleaning Up Earth Orbit: The Legal, Economic, and Political Dimensions of Debris Remediation

The preponderance of human-made debris in Earth orbit has long been recognized as a significant threat to continued safe operations in space. National space agencies and private space companies are paying considerable attention to the technical questions surrounding the active removal of debris (ADR). Nonetheless there are still significant legal, economic, and geopolitical questions that need to be addressed before any meaningful and sustained industry around the removal of debris can be established. This discussion will focus on identifying the legal issues of responsibility, jurisdiction and liability and proposing possible solutions within the current nexus of international agreements. Yet these must be considered alongside the economic roadblocks to funding ADR; the challenges for states looking to collaborate in current geopolitical circumstances; and the often overlooked ‘data deficit’ in respect of the space surveillance and tracking (SST) capabilities needed to enable the safe removal of debris. It is contended that any system for managing ADR, Debris Mitigation and general protection of the space environment should not emerge in isolation. A coherent system of managing and coordinating the orbital environment needs to be developed. This article will argue that it is for individual nations to show political leadership and an economic commitment to properly manage the delicate extraterrestrial environment. Failure to do so will represent a missed opportunity and leave a troubling legacy for future generations. Active Debris Removal, Astropolitics, Space Law, Dual use technology, Space Environment

Recent glacier and lake elevation changes in the western Kunlun Mountains (Tibetan Plateau) revealed by CryoSat-2 satellite altimetry data

Mountain glaciers and alpine lakes are significant indicators of regional climate change. The temperature rise has resulted in the retreat of glaciers, further influencing the ecological cycle and the water balance. The present work mainly focuses on recent glacier and lake elevation changes in the western Kunlun Mountains. The CryoSat-2 satellite altimetry with relatively dense ground track spacing can measure more elevation samples for small glaciers and lakes surrounded by complex topography. The CryoSat-2 data with various algorithms were employed to monitor the water levels of the three typical lakes and the surface elevation changes of their supplying glaciers. The glacier surface elevations showed a slightly increasing trend and remarkable spatial heterogeneity from 2010 to 2021. Meanwhile, the Bangda Lake and Aksayqin Lake displayed clear and strong increasing trends over the observation period with an annual change rate of +0.65 and +0.20 m / yr, respectively. Surprisingly, Gozha Lake exhibited a decreasing trend with the rate of −0.04 m / yr. Regional climate warming led to more melt-water from the glaciers and permafrost flowing into the three typical lakes. The increase in precipitation played a leading role in lake expansion over the western Kunlun Mountains. The present work demonstrated that the satellite altimetry data provide important supplementary data to help us perform the cryosphere research in the data-scarce northern Tibetan Plateau depopulated zone.

Early cataloguing of fragments from break-up events

Break-up events represent the dominant source of objects in space catalogues, surpassing half of the overall population. These not so uncommon events include explosions, collisions or anomalous events resulting in fragmentations and their number is estimated to be higher than 630. The early cataloguing of the fragments generated during these events poses a complex challenge for space objects catalogue build-up and maintenance processes. The provision of Space Surveillance and Tracking products and services during the few first days after a break-up event can be crucial to avoid collisions between the fragments and other space objects, particularly in highly congested regimes, such as Low Earth Orbit. In this regard, reducing the time required to accurately estimate the trajectories of the fragments may enable the execution of collision avoidance manoeuvres, in the case of operational space objects with manoeuvre capabilities, and analyse potential collision cascade events, which may endanger the space environment. This paper studies the whole cataloguing process after a break-up event, starting from a catalogue with no fragments from the fragmentation under-analysis, and until a well-established orbit is obtained for all fragments, using a ground-based sensor network. First, the observations enter a multi-sensor multi-target track-to-track association algorithm in charge of grouping observations belonging to the same objects. To resolve the ambiguity, particularly shortly after the event, hypotheses about tracks belonging to the same fragment are generated, scored, pruned, and promoted, only when there is enough confidence, leading to the initialisation of new objects in the catalogue. As soon as the catalogue is populated, a track-to-orbit correlation algorithm is responsible for the correlation of observations and already catalogued orbits. This alleviates the track-to-track association and enables the update of the orbital estimates, required for maintaining the catalogue.