High-altitude Satellites Research Articles

Study on radiation characteristics of multi-phase plumes containing ice crystals in orbit-control engines

In order to obtain the radiation characteristics of the multiphase plume containing ice crystals in the high-altitude orbit control engine and analyze its influence on the telemetry effect, this paper deduces the radiation characteristics parameters of gases based on Einstein radiation theory and radiation transfer equation. Based on the latest HITRAN2020 spectral line library solving gas radiation and the Mie theory of particle scattering solving particle radiation, the radiation characteristic parameters of the multi-phase plume containing ice crystals in the high-altitude orbital control engine and the radiation intensity distribution in the near-infrared and mid-long wave infrared bands are simulated, and the main influencing factors of the radiation are analyzed. The results show that, in general, the main radiation of the engine plume includes the scattered light in the near infrared band and the thermal radiation in the middle long wave infrared band. In the near-infrared band, considering solar background radiation, the total radiation amount in the calculation domain is about 10 −6 W/sr, and the thermal radiation is dominant within the axial distance of 0.5 m, while the ice crystal scattering is dominant beyond the axial distance of 0.5 m . In the mid-long wave infrared band, the total radiation amount in the calculation domain is about 10 W/sr, and the thermal radiation of gas dominates within 1 m axial distance, while the thermal radiation of ice crystal dominates beyond 1 m axial distance.

EDT demonstration for keeping low altitude orbit using carbon nanotube tether

This paper describes an electrodynamic tether system (EDT). Conductive tethers are used to overcome atmospheric resistance in low orbit and extend orbit life using EDT propulsion. First, based on the conceptual design, the feasibility of the EDT system has been evaluated through simulation. Especially, the induced electromotive force of the conductive tether has been clarified, the amount of current required to keep the orbital altitude, and the requirements for each device. Then, feasibilities of the key mission devices have been evaluated experimentally. Those are the conductive tether, the electron emission device, and the tether extension control mechanism. The conductive tether is planned to be made of carbon nanotubes, which are attracting attention as a new material, and its properties are evaluated. The electron-emitting device has been evaluated as a device that can be mounted on a micro/nano satellite. Tether extension mechanism was developed in our past project, then it should be evaluated with the purpose of adapting to conductive tether systems. Based on the evaluation, the orbital demonstration mission plan using a micro/nano satellite has been introduced. The mission is as follows. The conductive tether is extended and stabilized by the gravity gradient. By emitting electrons from an electron emitter mounted on a high-altitude satellite and collecting electrons on bare tether at low-altitude end, a current is generated from the high-altitude side to the low-altitude side. According to Fleming's law, the Lorentz force is generated in the direction of the orbiting accelerated, so it can be propelled in the upward direction of the orbit.

Space-Based Passive Orbital Maneuver Detection Algorithm for High-Altitude Situational Awareness

Orbital maneuver detection for non-cooperative targets in space is a key task in space situational awareness. This study develops a passive maneuver detection algorithm using line-of-sight angles measured by a space-based optical sensor, especially for targets in high-altitude orbit. Emphasis is placed on constructing a new characterization for maneuvers as well as the corresponding detection method. First, the concept of relative angular momentum is introduced to characterize the orbital maneuver of the target quantitatively, and the sensitivity of the proposed characterization is analyzed mathematically. Second, a maneuver detection algorithm based on the new characterization is designed in which sliding windows and correlations are utilized to determine the mutation of the maneuver characterization. Subsequently, a numerical simulation system composed of error models, reference missions and trajectories, and computation models for estimating errors is established. Then, the proposed algorithm is verified through numerical simulations for both long-range and close-range targets. The results indicate that the proposed algorithm is effective. Additionally, the sensitivity of the proposed algorithm to the width of the sliding window, accuracy of the optical sensor, magnitude and number of maneuvers, and different relative orbit types is analyzed, and the sensitivity of the new characterization is verified using simulations.

RIS-aided double beamforming optimization algorithm for improving secrecy rate in space–ground integrated networks

The high-frequency band, crucial for supporting the 5G/6G system, faces challenges of signal obstruction by obstacles. This is attributed to significant path loss resulting from radio straightness and short radio distance. To address these challenges, there is a growing interest in leveraging non-terrestrial networks (NTNs) and reconfigurable intelligent surfaces (RISs), utilizing high-altitude satellites as base stations or terminals. Within a three-dimensional NTN system, the vulnerability of wireless signals to eavesdropping due to the open nature of the environment is a notable drawback. To mitigate this vulnerability, this paper introduces an algorithm designed to maximize the secrecy rate. The proposed algorithm optimizes security performance by fine-tuning the base station and RIS beamforming vectors. This optimization is achieved through successive convex approximation and minorization–maximization algorithms. Simulation results affirm the superiority of the proposed algorithm in terms of secrecy rate over existing techniques.

Orbital Facility Location Problem for Satellite Constellation Servicing Depots

This work proposes an adaptation of the facility location problem for the optimal placement of on-orbit servicing depots for satellite constellations in high-altitude orbit. The high-altitude regime, such as medium Earth orbit, is a unique dynamic environment where low-thrust propulsion systems can provide the necessary thrust to conduct plane-change maneuvers between the various orbital planes of the constellation. As such, on-orbit servicing architectures involving servicer spacecraft that conduct roundtrips between servicing depots and the client satellites of the constellation may be conceived. To this end, a new orbital facility location problem formulation is proposed based on binary linear programming, in which the costs of operating and allocating the facility(ies) to satellites are optimized in terms of the sum of the effective mass to low Earth orbit (EMLEO). The low-thrust transfers between the facilities and the clients are computed using a parallel implementation of a Lyapunov feedback controller. The total launch cost of the depot, along with its servicers, propellant, and payload, is taken into account as the cost to establish a given depot. The proposed approach is applied to designing an on-orbit servicing depot architecture for the Galileo and the GPS constellations.

Autonomous navigation of an asteroid orbiter enhanced by a beacon satellite in a high-altitude orbit

Autonomous navigation of an asteroid orbiter enhanced by a beacon satellite in a high-altitude orbit

LR Aerial Photo Categorization by Cross-Resolution Perceptual Knowledge Propagation.

There are hundreds of high-and low-altitude earth observation satellites that asynchronously capture massive-scale aerial photographs every day. Generally, high-altitude satellites take low-resolution (LR) aerial pictures, each covering a considerably large area. In contrast, low-altitude satellites capture high-resolution (HR) aerial photos, each depicting a relatively small area. Accurately discovering the semantics of LR aerial photos is an indispensable technique in computer vision. Nevertheless, it is also a challenging task due to: 1) the difficulty to characterize human hierarchical visual perception and 2) the intolerable human resources to label sufficient training data. To handle these problems, a novel cross-resolution perceptual knowledge propagation (CPKP) framework is proposed, focusing on adapting the visual perceptual experiences deeply learned from HR aerial photos to categorize LR ones. Specifically, by mimicking the human vision system, a novel low-rank model is designed to decompose each LR aerial photo into multiple visually/semantically salient foreground regions coupled with the background nonsalient regions. This model can: 1) produce a gaze-shifting path (GSP) simulating human gaze behavior and 2) engineer the deep feature for each GSP. Afterward, a kernel-induced feature selection (FS) algorithm is formulated to obtain a succinct set of deep GSP features discriminative across LR and HR aerial photos. Based on the selected features, the labels from LR and HR aerial photos are collaboratively utilized to train a linear classifier for categorizing LR ones. It is worth emphasizing that, such a CPKP mechanism can effectively optimize the linear classifier training, as labels of HR aerial photos are acquired more conveniently in practice. Comprehensive visualization results and comparative study have validated the superiority of our approach.

Study on mission planning algorithm for multi-target passive tracking based on satellite formation

Mission planning for Space Situational Awareness (SSA) is challenging when only passive optical sensors are available to observe the targets. In this study, a mission-planning algorithm using a passive optical sensor for multi-target tracking in high altitude orbits based on microsatellite formation was developed, and a two-layer iterative consensus-based auction algorithm was designed to solve the optimization problem with requirements and constraints. First, orbit estimation was formulated using the perturbed dynamics and the line-of-sight angle measurement model. Second, distributed multi-target tracking tasks, including tasking metrics and observation constraints, were constructed for planning. Then, a two-layer iterative consensus-based auction algorithm was developed to solve the mission planning and conflict problem of multi-target tracking using multiple satellites. The only requirement for the algorithm was information exchange between neighboring observers, which encompasses the limitations of centralized planning and facilitates the execution of tasks more efficiently and flexibly. In addition, an event-triggered collaborative filtering approach suitable for this scenario was proposed to solve the distributed estimation problem of measurement asynchrony in epoch and frequency from different observers. Finally, numerical simulations were conducted under different conditions to verify the feasibility of the proposed method.

Sunflower mission concept for high-altitude earth observation in LEO via nanosatellite with pyramidal solar sail

Solar sails are an attractive technology for propellant-free propulsion, especially in small satellites with tight power and mass budgets. Several recent missions have shown promising applications of solar sails for nanosatellite orbital control in low Earth orbit (LEO). They enable easier access to and removal from high-altitude orbits. Since solar radiation pressure produces torques in addition to forces, a solar sail can also be used for low-power attitude control. Few missions have exploited this effect. In response, this paper proposes a new nanosatellite mission concept, only achievable by combined orbit-attitude control via solar sail: the sunflower mission, for high-altitude wide-area Earth observation. A realistic sail design meeting the mission requirements is obtained via parametric analysis and comprehensive review of past missions. A pyramid-shaped sail is proposed for the mission, and its advantages and drawbacks are analysed. The dynamics are evaluated using a high-fidelity numerical simulator with all relevant physical perturbations in LEO. The imaging objectives are successfully achieved over a multi-year duration. The sail also provides propellant-free orbit insertion from a low-altitude launch orbit, and fast de-orbit at end-of-life. It uses less power and has a smaller stowed size than several competitor technologies for orbit-attitude control of LEO nanosatellites.

The LARES 2 satellite, general relativity and fundamental physics

LARES 2, successfully launched on July 13, 2022, is a new generation laser-ranged satellite. LARES is an acronym for LAser RElativity Satellite. The first LARES satellite was successfully launched on February 13, 2012 with the ESA-ASI-AVIO launch vehicle VEGA. LARES 2 was injected with extremely high precision onto a high-altitude orbit at about 5900 km altitude with the new ESA-ASI-AVIO launch vehicle VEGA C. Laser-ranged satellites have many applications, including to test Einstein’s theory of general relativity. The main general relativistic phenomenon that LARES 2 will test with high accuracy is the dragging of inertial frames, or frame-dragging. It will also test other aspects and principles of fundamental physics and general relativity, such as the weak equivalence principle at the foundation of viable gravitational theories. Frame-dragging is the name Einstein himself gave in 1913 to an intriguing phenomenon of general relativity which implies that a current of mass-energy, such as the rotation of a body, will generate spacetime curvature. Frame-dragging has a key role in high energy astrophysics, e.g., in the generation of gravitational waves by the collision of two black holes to form a rotating black hole. Frame-dragging by the rotating Earth was measured to a few percent accuracy by combining the data of the satellites LARES, LAGEOS and LAGEOS 2 (Ciufolini et al. in Eur Phys J C 79:872, 2019). LARES 2, thanks to its extremely high injection precision, is projected to improve the test of frame-dragging by at least an order of magnitude. LARES 2 has also relevant applications in space geodesy and geodynamics, e.g., in the study of the shape of the Earth and in the determination of the International Terrestrial Reference Frame (ITRF) by improving the determination of the Earth center of mass and by contributing to a better determination of its rotation axis.

Simulation Analysis of LEO Constellation Augmented GNSS (LeGNSS) Zenith Troposphere Delay and Gradients Estimation

Compared with current GNSS, which consists of medium- and high-altitude orbit satellites, Low Earth Orbit (LEO) satellites move faster and can greatly improve the observing geometry. In this contribution, LEO constellation augmented GNSS (LeGNSS) troposphere estimation is investigated, and the impacts of relevant factors are analyzed in detail. When the temporal resolutions of zenith troposphere delay (ZTD) and horizontal gradients are 1 h and 2 h, while standard deviations (STDs) of phase and pseudorange observations at the zenith direction are 0.005 m and 0.5 m, the accuracies of ZTD, north gradient, and east gradient augmented by LEO constellation improve by 15.7%, 29.6%, and 16.4%, respectively, compared with GNSS solution. The results of troposphere estimation under obstructed environment and using low-cost dual frequency receivers also become more robust after adding LEO observations. Most importantly, analysis results during periods with rapid varying troposphere parameters suggest that the contribution of LEO constellation becomes even bigger with increasing temporal resolutions of ZTD and horizontal gradients, indicating that LeGNSS can be used to extract tropospheric parameters with improved accuracies at high temporal resolution. Thus, the capability in rapidly capturing severe weather events can be improved by LeGNSS observations, and the performance can become even better with increasing number of LEO satellites. All these results suggest that LeGNSS might be an important tool in improving the performance of troposphere estimation, and would promote GNSS application in water vapor monitoring.

High-altitude satellites range scheduling for urgent request utilizing reinforcement learning

Abstract High-altitude satellites are visible to more ground station antennas for longer periods of time, its requests often specify an antenna set and optional service windows, consequently leaving huge scheduling search space. The exploitation of reinforcement learning techniques provides a novel approach to the problem of high-altitude orbit satellite range scheduling. Upper sliding bound of request pass was calculated, combining customized scheduling strategy with overall antenna effectiveness, a frame of satellite range scheduling for urgent request using reinforcement learning was proposed. Simulations based on practical circumstances demonstrate the validity of the proposed method.

Contribution of Etalon Observation to Earth Rotation Parameters under a New Observation Scenario

The standard products of the International Laser Ranging Service (ILRS) are mainly based on the two laser geodynamics satellites (LAGEOS) due to the sparse observations of the Etalon satellites. With improvements in the ability to track high-altitude satellites, ILRS conducted a 3-month Etalon tracking campaign. In this paper, we study the contribution of more Etalon observations in the new observation scenario to weekly ILRS products, such as station coordinates, Earth rotation parameters (ERPs) and satellite orbit. We compare the ILRS products estimated from LAGEOS-only solutions and LAGEOS+Etalon solutions. In the new observation scenario of 2019, the numbers of observations of Etalon satellites are 1.4 and 1.7 times larger than those in 2018. It is shown that the quality of station coordinates, and the satellite orbit of LAGESOS satellites are only slightly affected by the increase in Etalon observations of the campaign. However, for station 1868, which is dedicated to high-altitude satellites, the root mean square (RMS) values of the residuals in the N, E, and U components are improved by 3.1 cm, 2.1 cm and 2.3 cm, respectively. The internal precision of orbit for Etalon-1/2 satellites in tangle and normal directions are improved by 1.5 cm and 2.9 cm, respectively. Most remarkably, the standard deviations for Xp, Yp and LOD can be improved by 6.9%, 14.3% and 5.1%, respectively, compared with the International Earth Rotation System (IERS)-14-C04 series. With our research, the ILRS could increase efforts on Etalon satellite tracking without affecting the routine observations of LAGEOS satellites.

Development of a computational and experimental method for assessment of the interference effects of lightning discharge radio emissions on the functioning of ground-based receiving stations of high-altitude satellite networks using domestic geoinformation systems

Problem statement . In the spring/summer season, operation of high-altitude satellite systems (HASS) is periodically hindered by disturbances in reception of information from space vehicles (SV), resulting from the interference effects produced by the electromagnetic emissions of lightning discharges (LD) on the receiving channels of ground-based stations (GBS), occurring due to thunderstorm activity. It is necessary to reliably assess the degree of influence such natural phenomena have upon functioning of HASS according to their intended purpose, with quantitative estimates made, and determine practicable ways to parry those phenomena. Objective . To develop a method for assessing LD radio emission effects, resulting from thunderstorm activity, for the purpose of making qualitative and quantitative estimates of the degree of their interference effect on the functioning of HASS’s GBS. Results . The paper proposes a computational and experimental method for assessing LD radio emission effects on the functioning of HASS’s GBS using a software complex for computation of electromagnetic field (EMF) and EMC parameters of communications electronics, developed on the basis of a domestic geoinformation system (GIS). Practical usefulness . A qualitative and quantitative estimate is drawn up as to the degree of interference effect produced by LD on the receiving lines of HASS’s GBS, and a method is proposed for compensation of losses in information reception by using spatially diverse GBS.

Analytical simulations of the effect of satellite constellations on optical and near-infrared observations

Context. The number of satellites in low-Earth orbit is increasing rapidly and many tens of thousands of satellites are expected to be launched in the coming years. There is a strong concern among the astronomical community about the contamination of optical and near-infrared observations by satellite trails, what has led to several initial investigations of the impact of large satellite constellations. Aims. We expand the impact analysis of such constellations on ground-based optical and near-infrared astronomical observations in a more rigorous and quantitative way, using updated constellation information and considering imagers and spectrographs and their very different characteristics. Methods. We introduce an analytical method that allows us to rapidly and accurately evaluate the effect of a very large number of satellites, accounting for their magnitudes and the effect of trailing of the satellite image during the exposure. We use this to evaluate the impact on a series of representative instruments, including imagers (traditional narrow field instruments, wide-field survey cameras, and astro-photographic cameras) and spectrographs (long-slit and fibre-fed), taking their limiting magnitude into account. Results. Confirming earlier findings, the effect of satellite trails is more damaging for high-altitude satellites, on wide-field instruments, or essentially during the first and last hours of the night. Thanks to their brighter limiting magnitudes, low- and mid-resolution spectrographs will be less affected, but the contamination will be at about the same level as that of the science signal, introducing additional challenges. High-resolution spectrographs will essentially be immune. We propose a series of mitigating measures, including one that uses the described simulation method to optimise the scheduling of the observations. We conclude that no single mitigation measure will solve the problem of satellite trails for all instruments and all science cases.

Moving Target Localization in Sports Image Sequence Based on Optimized Particle Filter Hybrid Tracking Algorithm

This paper proposes a fusion stadium positioning algorithm, which uses self-optimizing particle filter to integrate the improved athlete dead reckoning and WiFi position fingerprint algorithm for stadium positioning. In order to determine the initial absolute position of the stadium positioning, for athletes entering the stadium from the outside, a seamless switching algorithm outside the stadium is proposed, using the characteristics of high-altitude satellite GPS to find a suitable switching point as the initial absolute position. If in the stadium, WiFi static positioning determines the initial absolute position. Then, aiming at the problem that the poorly diversified particles cannot be better integrated and localized, a self-optimized particle filter algorithm is proposed. After resampling and retaining high-weight particles, the characteristics of low-weight particles are embedded in the copied high-weight particles. This can improve diversity, and we finally carry out fusion positioning. The target tracking algorithm based on Mean Shift has a fixed-scale tracking window, and the tracking effect of variable-size targets is not ideal. In this paper, an affine transformation algorithm is introduced to improve it. First, we iterate the adjacent image frames in reverse Mean Shift to determine the center position of the target and then use the corner matching method to perform template matching on the target to adjust the size of the tracking window. Through simulation verification, it is proved that the optimized particle filter hybrid tracking algorithm can achieve the ideal result when the target size changes. For the image sequence S1, the tracking window of the 20th frame and the 40th frame has a small offset, but the optimal position can be quickly found by Mean Shift iteration. For the image sequence S2, between the 40th frame and the 60th frame, the target occlusion causes the accuracy of the target template to decrease, and the Bhattacharyya coefficient is at a relatively low value. For the image sequence S3, the tracking effect of the optimized particle filter hybrid tracking algorithm meets the requirements.

Circulating, eccentric periodic orbits at the Moon

Loosely captured orbits with circulating and pulsating eccentricity vectors have a variety of attractive mission design properties, including low insertion costs, near-circular and highly eccentric phases, mid- to high inclinations, long-term stability, and spatially distributed close approaches. Such orbits are the known result of averaging third-body perturbations over the spacecraft and system motions. Unfortunately, the doubly averaged model does not match long-term unaveraged motion well at high altitudes. Singly averaged dynamics are accurate for orbits with much higher semimajor axis values, providing a mechanism to predict and characterize high-altitude motion in the unaveraged model. In this work, singly averaged circulating, eccentric orbits are surveyed in the specific context of the dimensioned Earth–Moon system, where high-altitude orbits are expected to have the most useful applications. A global search is performed over non-impacting system resonances, and families of periodic orbits are used as a framework to map the feasible space. The resulting database of periodic orbits is provided as an online supplement. The singly averaged families are shown to provide a reliable bridge between the analytic results of the doubly averaged system and initial guesses that converge to periodic orbits in the unaveraged model. Non-impacting circulating, eccentric orbits are demonstrated to maintain their structure for multiple years in a high-fidelity force model. These circulating, eccentric, lunar orbits may be useful for human-crewed space stations, dedicated science orbits, extended missions, loitering orbits, or transfers between the Lagrange points and low-lunar orbits.

Sulfur Transfer Melt Infiltration for High‐Power Carbon Nanotube Sheets in Lithium‐Sulfur Pouch Cells

AbstractAmong next‐generation battery systems, the lithium‐sulfur (Li−S) technology is attracting increasing attention driven by the low active material costs, high theoretical specific energy, and promising progress made in terms of its technology readiness level (TRL) in the recent years. However, the power density, especially in prototype cells, is an often neglected parameter being crucial for future application sectors. In this work, the cathode is redesigned by introducing a scalable, non‐toxic, and homogeneous sulfur impregnation process for free‐standing carbon scaffolds and tailorable sulfur areal loading. This novel sulfur transfer melt infiltration is exemplarily applied to process carbon nanotube (CNT)‐based Li−S cathode structures, but as a generic and scalable methodology is highly versatile. We demonstrate the development for CNT Buckypaper (BP) and CNT powder‐based dry transfer electrodes (DryFilm) as cathode host structures with the highly polysulfide (PS) solvating electrolyte system DME/DOL. In order to evaluate the practicability for high power application, the redesigned CNT BP cathode system with varying sulfur contents is employed in multi‐layered pouch cell format with 4 μL mgS−1 for reduced electrolyte conditions. Additionally, first pouch cells with circular perforated aluminum current collector enable 80 % weight savings of passive cathode material without compromising cell performance for free‐standing thin‐film cathodes. This study is an important step towards the development of lightweight Li−S cells for high power applications, such as drones or high altitude satellites.

Regularized luni-solar gravity dynamics on resident space objects

Resident space object population in highly elliptical high perigee altitude (> 600 km) orbits is significantly affected by luni-solar gravity. Using regularization, an analytical orbit theory with luni-solar gravity effects as third-body perturbations in terms of Kustaanheimo-Stiefel regular elements is developed. Numerical tests with different cases resulted in good accuracy for both short- and long-term orbit propagations. It is observed that the luni-solar perturbations affect the accuracy of the analytical solution seasonally. The analytical theory is tested with the observed orbital parameters of the few objects in highly elliptical orbits. The analytical evolution of osculating perigee altitude is found to be concurrent with observed data. Solar perturbation, when compared with lunar perturbation, is established to be dominant over such orbits.

The benefits of very low earth orbit for earth observation missions

Very low Earth orbits (VLEO), typically classified as orbits below approximately 450 km in altitude, have the potential to provide significant benefits to spacecraft over those that operate in higher altitude orbits. This paper provides a comprehensive review and analysis of these benefits to spacecraft operations in VLEO, with parametric investigation of those which apply specifically to Earth observation missions. The most significant benefit for optical imaging systems is that a reduction in orbital altitude improves spatial resolution for a similar payload specification. Alternatively mass and volume savings can be made whilst maintaining a given performance. Similarly, for radar and lidar systems, the signal-to-noise ratio can be improved. Additional benefits include improved geospatial position accuracy, improvements in communications link-budgets, and greater launch vehicle insertion capability. The collision risk with orbital debris and radiation environment can be shown to be improved in lower altitude orbits, whilst compliance with IADC guidelines for spacecraft post-mission lifetime and deorbit is also assisted. Finally, VLEO offers opportunities to exploit novel atmosphere-breathing electric propulsion systems and aerodynamic attitude and orbit control methods.However, key challenges associated with our understanding of the lower thermosphere, aerodynamic drag, the requirement to provide a meaningful orbital lifetime whilst minimising spacecraft mass and complexity, and atomic oxygen erosion still require further research. Given the scope for significant commercial, societal, and environmental impact which can be realised with higher performing Earth observation platforms, renewed research efforts to address the challenges associated with VLEO operations are required.