Operational Satellite Research Articles

Questions of fault liability: A case study analysis of in-orbit collisions with debris

In 1972, the international community established a regime of liability for damages occurring in outer space based on ‘fault’. Fifty years later, the congested and polluted reality of the space environment has limited dramatically its effectiveness. Only in very few instances, filing a claim under such regime can reasonably ensure compensation to an injured satellite operator. The present paper describes different study cases where resorting to a fault-based liability claim appears problematic. Based on real conjunction assessment alerts, the authors look into various hypothetical scenarios from the perspective of a fictitious satellite operator, whose spacecraft was damaged by an accidental collision in orbit. The aim is to analyse the effective observability over orbital collisions involving small satellites and space debris (attributable or not) and to evaluate the real chances of obtaining compensation, from the operational and legal points of view. At the centre of this study, therefore, is the evaluation, in fact and in law, of the solidity of a potential claim against the perpetrator of the harm. To that end, the discourse takes into consideration the legal difficulties that are generally connected to fault-based liabilities in international law.The definitional vagueness of the term ‘fault’, the necessity to identify a fault-standard, the proof of failure in the performance of a duty of care, are all elements to consider for filing a claim under the liability regime of 1972.However, next to them, the space environment poses additional hurdles with regard to facts and evidence. Satellite operators do not always have the technological instruments to retrieve all the information related to orbital events, such as collisions. Moreover, a complete observability over in-orbit events can be hard to reach for several classes of spacecraft (e.g. small, nano- or pico-satellites). This is especially troublesome for establishing one of the essential elements of ‘fault’: the so-called “chain of causation”. The authors will present their views on how the uncertainties posed by the liability regime of 1972 can be dealt with from a legal and from a technical perspective. In addition, several possible legal solutions and recommendations for the upcoming years of in-orbit operations and space traffic management will be proposed at the end.

Multifidelity Framework for Small Satellite Thermal Analysis

Anomalies, unexpected events, and model inaccuracies have detrimental effects on satellite operations. High-fidelity models are required, but these models quickly become large and expensive. Cheap or low-fidelity models speed up computation but lack accuracy. To compromise these requirements, this study proposes a multifidelity framework based on cokriging. The proposed multifidelity framework is compared against three other standard methods often used in satellite simulations: a standalone gated recurrent unit, Gaussian process regression, and the autoregressive integrated moving average with explanatory variables model. The robustness of high-fidelity data point placement is also examined. Moreover, the real-time aspect of the simulation is considered by applying the sliding window technique. This multifidelity framework is demonstrated using temperature data obtained from thermal vacuum testing of Small Demonstration Satellite 4: a 50-kg-class satellite. The multifidelity framework provided higher accuracy and robustness than the other methods, however, having a higher computational cost as compared to a purely low-fidelity model. Up to 92% reduction of the error was achieved by the proposed framework.

A Color Matching Method for Mosaic HY-1 Satellite Images in Antarctica

Antarctic mapping with satellite images is an important basic task for polar environmental monitoring. Since the first Chinese marine satellite was launched in 2002, China has formed three series of more than 10 marine satellites in orbit. As global operational monitoring satellites of ocean color series, HY-1C and HY-1D have good coverage characteristics and imaging performance in polar regions, and they provide an effective tool for Antarctic monitoring and mapping. In this paper, Antarctic images acquired by the HY-1 satellite Coastal Zone Imager (CZI) sensor were used to study color matching in the mosaic process. According to the CZI characteristics for Antarctic imaging, experiments were carried out on the illuminance nonuniformity of a single image and color registration of multiple images. A gray-level segmentation color-matching method is proposed to solve the problem of image overstretching in the Antarctic image color-matching process. The results and statistical analysis show that the proposed method can effectively eliminate the color deviation between HY-1 Antarctic images, and the mosaic results have a good effect.

Investigating the Interhemispheric Asymmetry in Joule Heating During the 2013 St. Patrick's Day Geomagnetic Storm

AbstractSudden changes in energy input from the magnetosphere during geomagnetic storms could drive extreme variability in the ionosphere‐thermosphere system, which in turn affect satellite operations and other modern infrastructure. Joule heating is the main form of magnetospheric energy dissipation in the ionosphere‐thermosphere system, so it is important to know when and where Joule heating will occur. While Joule heating occurs all the time, it can increase rapidly during geomagnetic storms. We investigated the Joule heating profile of the 2013 St Patrick's day storm using the University of Michigan Global Ionosphere‐Thermosphere Model (GITM). Using empirical and data‐assimilated drivers we analyzed when and where intense Joule heating occurred. The timing, location, and sources of interhemispheric asymmetry during this geomagnetic storm are of key interest due to near equinox conditions. Hemispheric comparisons are made between parameters, including solar insolation, total electron content profiles, and Pedersen and Hall conductance profiles, obtained from GITM driven with empirical driven input, versus those driven with data‐assimilated patterns. Further comparisons are made during periods of peak hemispheric Joule heating asymmetry in an effort to investigate their potential sources. Additionally, we compare the consistency of the interhemispheric asymmetry between empirical‐ and data‐assimilated driven simulations to further analyze the role of data‐assimilated drivers on the IT system.

Operational Considerations for Crew Fatality on the International Space Station.

BACKGROUND: While catastrophic spaceflight events resulting in crew loss have occurred, human spaceflight has never suffered an on-orbit fatality with survival of other crewmembers on board. Historical plans for management of an on-orbit fatality have included some consideration for forensic documentation and sample collection, human remains containment, and disposition of remains; however, such plans have not included granular detailing of crew or ground controller actions. The NASA Johnson Space Center Contingency Medical Operations Group, under authority from the Space and Occupational Medicine Branch, the Space Medicine Operations Division, and the Human Health and Performance Directorate, undertook the development of a comprehensive plan, including an integrated Mission Control Center response for flight control teams and Flight Surgeons for a single on-orbit crew fatality on the International Space Station (ISS) and subsequent events. Here we detail the operational considerations for a crew fatality should it occur during spaceflight onboard the ISS, including forensic and timeline constraints, behavioral health factors, and considerations for final disposition of decedent remains. Future considerations for differential survival and crewmember fatality outside of low-Earth orbit operations will additionally be discussed, including consideration of factors unique to planetary and surface operations and disposition limitations in exploration spaceflight. While the efforts detailed herein were developed within the constraints of the ISS concept of operations, future platforms may benefit from the procedural validation and product verifications steps described. Ultimately, any response to spaceflight fatality must preserve the goal of handling decedent remains and disposition with dignity, honor, and respect.Stepaniak PC, Blue RS, Gilmore S, Beven GE, Chough NG, Tsung A, McMonigal KA, Mazuchowski EL II, Bytheway JA, Lindgren KN, Barratt MR. Operational considerations for crew fatality on the International Space Station. Aerosp Med Hum Perform. 2023; 94(9):705-714.

Thermal Performance of Perovskite‐Based Photovoltaics for Operation in Low Earth Orbit

Perovskite‐based photovoltaics are attractive for applications in space. The space environment is harsh with ionizing radiation, atomic oxygen, UV radiation, extreme temperatures, and thermal cycling. Herein, the thermal performance of perovskite active layer and perovskite photovoltaic devices in low earth orbit is analyzed. A 1 μm silicon oxide layer coupled with 500 nm zirconia thin film aid in cell thermal management is determined. The residual stresses between various layers in a device are modeled and it is proved that thermally induced mechanical failure of the perovskite (time years) is unlikely during operating lifetime of any mission. Target power conversion efficiencies are also shared to manage maximum operating temperature of a perovskite‐based device.

Two‐Line Elements Based Thermospheric Mass Density Specification From Parameter Optimization of a Physics‐Based Model

AbstractAccurately estimating the mass density of the thermosphere can assist satellite operators in planning missions and optimizing satellite orbits, reducing the risk of collisions. The newly developed GOFT (Global Observation‐based Forecast for the Thermosphere) model specifies thermospheric mass density by optimizing uncertainty parameters in a physics‐based model based on model errors. This study extends the model to specify thermospheric mass density based on Two‐Line Elements (TLEs) from numerous space objects. The resulting mass density is validated against accelerometer‐derived mass density from different satellites. The comparison results revealed that assimilating TLEs into the GOFT model significantly improved the accuracy of the thermospheric mass density. In addition, the GOFT model also improved the accuracy of the electron density in the ionosphere, indicating that the assimilation capability of GOFT allows simultaneous specification of coupled ionosphere and thermosphere in future applications.

Anomaly Detection for Agile Satellite Attitude Control System Using Hybrid Deep-Learning Technique

Agile low-Earth-orbit (LEO) observation satellites need a robust attitude control and determination system. It is a critical satellite subsystem, which stabilizes the satellite to different desired orientations during its mission using different actuators. The detection of satellite misorientation is a highly challenging problem because it requires continuous monitoring of data from hundreds of satellite sensors to guarantee healthy operability. In this paper, the authors propose a data-driven deep-learning framework for detecting satellite misorientation by analyzing attitude control subsystem telemetry data. The proposed approach combines a hybrid predictive deep-learning model that consists of long short-term memory and convolutional neural networks in two parallel paths to predict telemetry data and a robust isolation forest classifier for anomaly detection purposes that can classify output residuals as normal or anomalous. The hybrid model was optimized by the particle swarm optimization algorithm to ensure faster fitness function convergence with optimal model hyperparameters. The suggested data-driven model was validated using real telemetry datasets, including real anomalous case studies. The experimental results proved the suggested approach’s superiority for identifying satellite misorientation as well as helping satellite operators monitor the system’s health and deduce the causes of anomalies to aid in decision-making.

Hardware-in-the-loop based ground test system for space berthing and docking mechanism of small spacecraft

Ground test for space berthing and docking mechanism plays crucial roles in their stable operation in orbit. In this paper, a hardware-in-the-loop based ground test system is presented for economic reliability test for space berthing and docking mechanism of small spacecraft. In the system, the support and adapter unit is employed to fix the active part of the berthing and docking mechanism, and the end-effector of the manipulator connects the passive part. The manipulator is driven according to the relative motion calculated by the hardware-in-the-loop model after gravity compensation, to simulate motion of space berthing and docking mechanism in space. A Smith predictor is introduced for control system delays compensation. A berthing and docking mechanism was employed in the experiment to evaluate the performance of the test system. The results validated the effectiveness of the test system. Since only one manipulator is exploited in the test system, compared with existing systems using two manipulators, the system cost can be greatly decreased.

Predictors of Intraoperative Difficulty and Postoperative Examination Abnormalities in 164 Orbital Operations

Although orbital fractures are common, prediction of outcomes in orbital surgery can be quite challenging. We aim to identify predictors of intraoperative difficulty, operating time, and postoperative examination abnormalities in subjects undergoing post-traumatic orbital reconstructions. This is a retrospective cohort study of all consecutive orbital operations performed at a private, Level 1 trauma center in Portland, Oregon, USA over an 82-month period. All subjects that underwent exploration of the internal orbit for traumatic indications during the study period were included in the cohort. Four plating styles, surgical approach (transorbital vs transantral), days from injury to first surgery, fracture size (approximated as a rectangle using linear measurements from computed tomography scans), anteroposterior fracture position, and medial wall involvement were examined. The primary outcome variable was intraoperative difficulty (defined as requiring revision after intraoperative imaging or return to the operating room). Secondary outcome variables included operating time and postoperative examination abnormalities. Age and sex were included. χ2 and Regression analyses were performed using a significance level of P<.05. One hundred and sixty four orbital operations were performed (90 isolated injuries and 74 combined orbital/midface injuries) on 155 subjects (73% male, mean age 39.8years, standard deviation 16.7). In subjects with isolated orbital fractures, medial wall involvement was associated with intraoperative difficulty (P=.01). When using a transantral approach, intraoperative difficulty was more likely in more anterior fractures (P=.02). Plating style was associated with operating time (P=.03), with median times from 81 to 105minutes (range 21 to 248minutes). Postoperative examination abnormalities were more likely in the transorbital approach group (P=.01). Neither days to first surgery nor intraoperative difficulty were associated with postoperative examination abnormalities. Postoperative eyelid changes were seen in 13.6% of transorbital approaches and 0% of transantral approaches. Correction of gaze restriction and enophthalmos were more likely than correction of diplopia (P<.01). Medial wall involvement is associated with intraoperative difficulty in orbital surgery. Anteriorly positioned fractures are better treated transorbitally, while posterior fractures may be amenable to transantral repair, thus avoiding risk of lower eyelid changes.

High-Density Pixel Imaging Sensor Readout Electronics for Space Applications: A Design Overview

With the specialization of VLSI ASICs for front-end signal processing electronics, the customization of the control back-end electronics (BEE) has become critical to fully deploy the ASIC performance. In the context of space operations, with typical constraints on power and reliability, the design and qualification of such integrated systems present significant challenges. In this paper, we review the design and performance of the BEE systems after two years of operations in low Earth orbit (LEO); these systems read out the custom ASICs inside the gas pixel detectors, which are located at the heart of the imaging X-ray polarimetry explorer (IXPE), a NASA-ASI small explorer mission designed to measure X-ray polarization in the 2–8 keV energy range.

Solving dynamic satellite image data downlink scheduling problem via an adaptive bi-objective optimization algorithm

The satellite image data downlink scheduling problem (SIDSP) plays a critical role in the mission planning operation of earth observation satellites. However, with recent developments in satellite technology, the traditional SIDSP is poorly effective for modern satellites. To offer additional modeling flexibility and renewed capabilities, a dynamic SIDSP (DSIDSP), which combines two interlinked operations of image data segmentation and image data downlink dynamically, was introduced. We have formulated the DSIDSP as a bi-objective problem of optimizing the image data transmission rate and the service-balance degree. Harnessing the power of an adaptive large neighborhood search (ALNS) algorithm with a nondominated sorting genetic algorithm II (NSGA-II), an adaptive bi-objective memetic algorithm, NSGA2ALNS, is developed to solve DSIDSP. Results of extensive computational experiments carried out using benchmark instances are also presented. Our experimental results reveal that the NSGA2ALNS algorithm is an effective and efficient method of solving DSIDSP based on various performance metrics. In addition, new benchmark instances are also provided for DSIDSP that could be used in future research.

Satellite uplink interference measurements in the 437 MHz UHF amateur radio band onboard LUME-1

Satellite operators struggle to communicate with their satellites over Europe in the UHF amateur band (430–440 MHz) due to high power in-orbit interference. Statistical characterisation of the interference beyond average interference levels using in-orbit measurements is useful for the design of suitable countermeasures. Some recent studies have started to investigate both the frequency and time behaviour of the interference, but more measurements are needed to cover the whole UHF amateur band. In this paper, we use the Local Mean Envelope (LME) method to analyse the time and frequency characteristics of in-orbit radio interference from the LUME-1 satellite, measured in the 437 MHz band. Satellite measurements were performed on a TOTEM Software-Defined Radio (SDR), in orbit over Europe and Antarctica and the results were downloaded for analysis on the ground. The average power spectrum and the variability of the LME for different time windows in the 437 MHz band are presented. The data analysis also includes the coefficient of variation of the LME to study the dispersion of the interference. The results are compared to previous measurements in the 435 MHz band using the same method. The new results are found to differ compared with previous measurements on the 435 MHz band. The bandwidth of the band-limited signals measured at 435 MHz was found to be 300 kHz, and at 437 MHz, 200 kHz wide for this dataset. Also, the interference power was found to be higher for 437 MHz. In both cases the interference behaviour is highly non-Gaussian, suggesting that typical communication countermeasures will not be sufficient. Although more measurements are needed for better spatial resolution, our findings may contribute to explaining why satellite operations are difficult on these bands. A better knowledge of the time and frequency variability of the interference can indicate which mitigation techniques are required and are efficient to improve satellite communication in that band.

Machine learning methods for nonlinear dimensionality reduction of the thermospheric density field

Accurate prediction of the thermospheric density field has recently been gaining a lot of attention, due to an outstanding increase in space operations in Low-Earth Orbit, in the context of the NewSpace. In order to model such high-dimensional, non-Gaussian systems, Reduced-Order Models (ROMs) have been developed against existing physics-based density models. In general, the data-driven reconstruction of dynamical systems usually consists of two steps of compression and prediction. In this paper, we focus on the compression step and assess state-of-the-art order reduction methodologies such as autoencoders, linear, and nonlinear Principal Component Analysis (PCA). We show that Kernel-based PCA, a nonlinear generalization of PCA, can perform better than Neural Networks in representing the model in low-dimensional space in terms of accuracy, computational time, and energy consumption for both the Lorenz system, a chaotic dynamical system developed in the context of atmospheric modeling, and the thermospheric density.

How useful are mispointing phase SARAL/AltiKa geophysical products for ocean applications?

SARAL/AltiKa, the first microwave altimeter operating at Ka-band frequency, recently completed nine years of operations in orbit. During these years, it has catered to many applications related to operational oceanography, climate sciences, hydrology and cryosphere. More specifically, in oceanography, SARAL has contributed immensely to operational wave and circulation modelling, eddy detection/tracking, ocean current generation and many more. However, since Feb 2019, SARAL has moved from the drifting phase (DP) to the mispointing phase (MP) due to the malfunctioning of the star sensor of the spacecraft. In this study, we analyse the instrument’s performance and its waveforms during its ongoing MP. We find out that during the MP, significant wave height (SWH) measurements are anomalously high between 18 and 24 m, and wind speed measurements are between 16 and 19 m/s. In sea surface height anomaly (SSHA), there is a steady rise in negative values during the MP. In the return waveform, ∼15% degradation in Brown-type waveforms in the open ocean region is noticed. These changes significantly impact the SARAL applications. Two important applications of wave forecast and eddy detection are discussed here as examples. Following this, we also recommend using provided quality flags so that the data can be further explored for various ocean applications.

Mechanism of capture section affecting an intake for atmosphere-breathing electric propulsion

Atmosphere-Breathing Electric Propulsion (ABEP) can compensate for lost momentum of spacecraft operating in Very Low Earth Orbit (VLEO) which has been widely concerned due to its excellent commercial potential. It is a key technology to improve the capture efficiency of intakes, which collect and compress the atmosphere for ABEP. In this paper, the mechanism of the capture section affecting capture efficiency is investigated by Test Particle Monte Carlo (TPMC) simulations with 3D intake models. The inner surface smoothness and average collision number are determined to be key factors affecting capture efficiency, and a negative effect growth model is accordingly established. When the inner surface smoothness is less than 0.2, the highest capture efficiency and its corresponding average collision number interval are independent of the capture section’s geometry and its mesh size. When the inner surface smoothness is higher than 0.2, the capture efficiency will decrease by installing any capture section. Based on the present results, the manufacturing process and material selection are suggested to be prioritized during the intake geometry design in engineering projects. Then, the highest capture efficiency can be achieved by adjusting the length and mesh size of the capture section.

Investigation of long-term storage of space materials for future constellation missions: study of Braycote® 601 EF lubricant

The long-term storage (LTS) of space materials is becoming more and more critical for the next missions. For instance, for MTG (Meteosat Third Generation) mission, 5-year assemble, integration and testing (AIT) time on ground, up to 17.5-year storage for recurring models plus at least 8.5 years in orbit operation are planned. Hence, a good understanding of materials’ aging properties is desirable to ensure that materials’ specifications are still suitable after LTS, and, eventually, to anticipate the potential non-conformities. For this purpose, the European Space Research and Technology Centre (ESTEC) is investigating these problematics thanks to its wide capabilities from aging with environmental, climatic and vacuum chambers up to physico-chemical characterizations by numerous instruments such as microscopes, spectroscopes, thermal, mechanical or electrical analyzers. An overview is presented herein through the study of a fluorinated based grease lubricant named Braycote® 601EF widely used in mechanisms in space sector such as the US space shuttles actuator or the basic end effectors of The European Robotic Arm.

Annealing effects on Al/polyimide adhesion in flexible optical solar reflectors

Flexible optical solar reflectors are made of single and multi-layered metal thin films on polymer substrates and will encounter around 6000 thermal cycles exceeding +/-100°C during one year of operation in low earth orbit. The candidate thin film system of Inconel/silver (Ag)/Teflon (FEP) recently demonstrated early damage formation (cracks and voids) after only a few thermal cycles, most likely due to the poor interfacial properties between Ag and FEP. An alternative material system that could be used is colourless polyimide, Tormed, instead of FEP. Additionally, aluminium (Al) has demonstrated very good interfacial properties with polyimide even after thermal cycling and has suitable optical properties. The adhesion of the Al/Tormed and Ag/Tormed interfaces were evaluated with tensile induced delamination. Generally, Al/Tormed has a much higher interface adhesion energy compared to Ag/Tormed, and there is no significant degradation after bake-out in vacuum (200°C, 10-6 mbar) for 10 and 24 hrs. Thus, the Al/Tormed system could be a more robust coating system for future flexible solar reflectors.

Full Velocities and Propagation Directions of Coronal Mass Ejections Inferred from Simultaneous Full-disk Imaging and Sun-as-a-star Spectroscopic Observations

Coronal mass ejections (CMEs) are violent ejections of magnetized plasma from the Sun that can trigger geomagnetic storms, endanger satellite operations, and destroy electrical infrastructures on the Earth. After systematically searching Sun-as-a-star spectra observed by the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory (SDO) from 2010 May to 2022 May, we identified eight CMEs associated with flares and filament eruptions by analyzing the blue-wing asymmetry of the O iii 52.58 nm line profiles. Combined with images simultaneously taken by the 30.4 nm channel of the Atmospheric Imaging Assembly on board SDO, the full velocity and propagation direction for each of the eight CMEs are derived. We find a strong correlation between geomagnetic indices (Kp and Dst) and the angle between the CME propagation direction and the Sun–Earth line, suggesting that Sun-as-a-star spectroscopic observations at extreme-ultraviolet wavelengths can potentially help to improve the prediction accuracy of the geoeffectiveness of CMEs. Moreover, an analysis of synthesized long-exposure Sun-as-a-star spectra implies that it is possible to detect CMEs from other stars through blue-wing asymmetries or blueshifts of spectral lines.

Optimized Controller Provisioning in Software-Defined LEO Satellite Networks

The controller provisioning, which adjusts the number, locations, and members of satellite controllers adaptive to the dynamic network load and topology, fundamentally impacts the performance of software-defined satellite networks (SDSNs). An ideal provisioning strategy should achieve a low total control overhead throughout the entire satellite operation period, which is extremely challenging since the network load can only be predicted in a short time scale. Existing methods can hardly achieve this goal for they greedily configure controllers in each time slot, where switches have to frequently migrate from one controller to another. In this paper, we focus on achieving globally optimized strategies with only current network load information. We firstly propose a comprehensive control overhead model and formulate the Controller Provisioning Problem (CPP) in SDSNs as a non-convex integer programming problem. To solve the problem, we propose an approximate algorithm named AROA by introducing a regularization framework and based on randomized rounding. We theoretically derive its competitive ratio. To produce strategies in time for future large satellite constellations, we further propose a more efficient heuristic algorithm HROA. Evaluations on our built simulation system show that our proposed methods significantly outperform related schemes in control overhead, latency, and scalability.