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Introduction: Current and future astronauts will endure prolonged exposure to spaceflight hazards and environmental stressors that could compromise cognitive functioning, yet cognitive performance in current missions to the International Space Station remains critically under-characterized. We systematically assessed cognitive performance across 10 cognitive domains in astronauts on 6-month missions to the ISS. Methods: Twenty-five professional astronauts were administered the Cognition Battery as part of National Aeronautics and Space Administration (NASA) Human Research Program Standard Measures Cross-Cutting Project. Cognitive performance data were collected at five mission phases: pre-flight, early flight, late flight, early post-flight, and late post-flight. We calculated speed and accuracy scores, corrected for practice effects, and derived z-scores to represent deviations in cognitive performance across mission phases from the sample's mean baseline (i.e., pre-flight) performance. Linear mixed models with random subject intercepts and pairwise comparisons examined the relationships between mission phase and cognitive performance. Results: Cognitive performance was generally stable over time with some differences observed across mission phases for specific subtests. There was slowed performance observed in early flight on tasks of processing speed, visual working memory, and sustained attention. We observed a decrease in risk-taking propensity during late flight and post-flight mission phases. Beyond examining group differences, we inspected scores that represented a significant shift from the sample's mean baseline score, revealing that 11.8% of all flight and post-flight scores were at or below 1.5 standard deviations below the sample's baseline mean. Finally, exploratory analyses yielded no clear pattern of associations between cognitive performance and either sleep or ratings of alertness. Conclusion: There was no evidence for a systematic decline in cognitive performance for astronauts on a 6-month missions to the ISS. Some differences were observed for specific subtests at specific mission phases, suggesting that processing speed, visual working memory, sustained attention, and risk-taking propensity may be the cognitive domains most susceptible to change in Low Earth Orbit for high performing, professional astronauts. We provide descriptive statistics of pre-flight cognitive performance from 25 astronauts, the largest published preliminary normative database of its kind to date, to help identify significant performance decrements in future samples. [ABSTRACT FROM AUTHOR]

Atmosphere-breathing electric propulsion systems provide a competitive advantage for the lower orbit altitudes since the propellant is collected directly from the atmosphere. The effectiveness of this technology depends on crucial aspects such as the collection and compression performance characterization, as well as the drag estimation and compensation. In the first part of this study, the lower Mars and Earth atmospheric characterization is derived based on current models and mission data. This characterization is a reliable dataset for the boundary conditions for the simulations carried out in the second part of this study. The proposed computational framework based on the Direct Simulation Monte Carlo method aims to investigate the collection and compression performances and to estimate the drag. The numerical comparison with a literature case validates the numerical setup presented in this study. The effect of different gas-surface interaction models is investigated by comparing the results yielded by the Maxwellian model (fully specular and partially diffuse reflection) and the Cercignani-Lampis-Lord model. Since the intermolecular collisions can become more relevant at the inlet of the ionization stage, both the variable hard and variable soft sphere models are briefly examined, as well as the inclusion of gas-phase reactions. Finally, the simulation results of the two cases for the low Mars orbit (150 and 140 km) are compared to the Earth case (180 km). [ABSTRACT FROM AUTHOR]

Space solar power (SSP), envisioned for decades as a solution for continuous, stable, and dynamically dispatchable clean energy, has seen tremendous interest and a number of experimental demonstrations in the last few years. A practical implementation has been elusive to date, owing to the high launch costs associated with heavy, rigid photovoltaic and wireless power transfer (WPT) arrays. Lightweight and flexible solutions for WPT have been demonstrated terrestrially but, to date, have not been deployed and tested in space. In this paper, we present an experimental space demonstration of a lightweight, flexible WPT array powered by custom radio-frequency integrated circuits. The transmit arrays, receive arrays, and the rest of the system were operated and tested for eight months in Low Earth Orbit (LEO). Results from these experiments, including pointing of the array's beam to Earth and its detection by a ground station, are presented and discussed in detail. Observations and results from this mission uncover existing strengths and weaknesses that inform future steps towards realizing SSP. • First demonstration of wireless power transfer in space. • Use of novel, custom, flexible phased array for wireless power transfer. • Pointing of in-space payload towards Earth and detection of power using custom ground station. • Presentation of short- and long-term performance degradation. [ABSTRACT FROM AUTHOR]

Summary: Free space optical communication has emerged as a promising technology for high‐speed and secure data transmission between ground stations on Earth and orbiting satellites. However, this communication technology suffers from signal attenuation due to atmospheric turbulence and beam alignment precision. Low Earth orbit satellites play a pivotal role in optical communication due to their low altitude over the Earth surface, which mitigates the atmospheric precipitation effects. This paper introduces a novel data path control law for satellite optical communication exploiting artificial intelligence‐based predictive weather forecasting and a node selection mechanism based on reinforcement learning. Extensive simulations on three case studies demonstrate that the proposed control technique achieves remarkable gains in terms of link availability with respect to other state‐of‐the‐art solutions. [ABSTRACT FROM AUTHOR]

The growing amount of space debris in the low Earth orbit poses a danger to manned as well as uncrewed missions. Additionally, the new business model of providing internet from space is emerging among new space players, making low Earth orbit more crowded. These factors have encouraged the space community to focus on sustainability in space. Satellite manufacturers typically have the capability to perform complete life cycle analysis (LCA) on their own products based on the manufacturing data. However, there is a lack of a method for non-manufacturers such as environmentalists and the general public to predict the carbon footprint of satellite manufacturing using a subsystem-level mass budget. Hence, this paper presents a method to quantify environmental pollution caused by the production of satellite constellations. Starlink is taken as a case study in this paper, and mass budget is predicted based on space systems engineering budget estimation techniques, the parametric method, and Federal Communication Commission orbital data. With the budget table used as an input, space-specific life cycle assessment is performed based on European Space Agency's life cycle inventory database. Finally, the single score for Starlink constellation version 1 was found to be 76 kilo points. This signifies the annual environmental load. These results could be helpful in obtaining an overview of the environmental effects of the production phase of satellite constellations. Further, the results could act as a foundation for further research on implementing more circular approach practices on Earth as well as in space. [ABSTRACT FROM AUTHOR]

Making use of the geomagnetic field and the electron density data from the ionosphere observed by the three Swarm satellites that were recorded through 2020, 303 days before and 62 days after the Samos earthquake were investigated, which occurred at 11:51 UTC on Oct 30, 2020, happened in an offshore location around 60 km southwest of Izmir, western Turkey, and 16 km north of Samos Island, Greece 37.897°N 26.784°E. Magnetic and electron density data abnormalities were examined using the Analysis of Magnetic Swarm (AMSW) and the Analysis of Electron Density Swarm (AEDSW) algorithms. The quiet time abnormalities during nighttime within the Dobrovisky region showed exciting results. It showed an enhancement in the cumulative number of tracks (acceleration) approximately 150 days before the mainshock of the earthquake in the magnetic and electron density data. In addition, magnetic and electron density data results matched the ground-based observatory data recorded within the same period and the Dobrovisky region. [ABSTRACT FROM AUTHOR]

In this paper, expressions for high-precision simulation of multi-GNSS observations received in low Earth orbit are given. Based on this observation model, the real spacecraft orbit was refined. Based on real data from the GRACE space project, the results were compared with simulated measurements from foreign software. The average deviation in determining the spacecraft location was 18 mm, which confirms the correctness of the described observation model. [ABSTRACT FROM AUTHOR]

Atomic oxygen (AO) in low Earth orbit (LEO) can cause severe progressive damage to spacecraft orbiting at hypervelocities over 7 km/s; therefore, all space-graded materials need to be qualified for protection against these high energy impacts. Instead of treating AO as a threat, can we use these atomic impacts, which have enough energy to cause material failure, to generate power? Despite its potential, no attempt has yet been made to utilize the hypervelocity impact energy of AO. Thus, we propose a piezoelectric energy harvesting method through the hypervelocity AO impact in LEO. In this study, energy harvesting with various configurations was experimentally demonstrated using a conventional lead zirconate titanate (PZT) ceramic plate under oxygen plasma exposure to simulate AO impact. The average output power density was 4 W/m2 under 1.43 × 1016 atoms/cm2s effective AO flux conditions. Our study provides a new method for generating energy in a space environment with limited energy sources. [Display omitted] • Energy harvested from hypervelocity atomic oxygen impact in low Earth orbit. • Piezoelectric energy harvesting at atomic level in simulated space environment. • Output power density of approximately 4 W/m2 from PZT-5A under oxygen plasma. • Challenges and potential of atomic oxygen as a space energy source discussed. [ABSTRACT FROM AUTHOR]

This paper outlines the development phases of a wave-driven Helicon Plasma Thruster for cutting-edge Low Earth Orbit (LEO) constellations. The two-stage ambipolar electric propulsion (EP) system combines the efficient ionization of an ultra-compact helicon reactor with plasma acceleration based on an ambipolar electric field provided by a magnetic nozzle. This paper reveals maturation challenges associated with an emerging EP system in the hundreds-watt class, followed by outlook strategies. A 3 cm diameter helicon reactor was operated using argon gas under a time-modulated RF power envelope ranging from 250 W to 500 W with a fixed magnetic field strength of 400 G. Magnetically enhanced inductively coupled plasma reactor characteristics based on half-wavelength right helical and Nagoya Type III antennas under capacitive (E-mode), inductive (W-mode), and wave coupling (W-mode) were systematically investigated based on Optical Emission Spectroscopy. The operation characteristics of a wave-heated reactor based on helicon configuration were investigated as a function of different operating parameters. This work demonstrates the ability of two-stage HPT using a compact helicon reactor and a cusped magnetic field to outperform today's LEO spacecraft propulsion. [ABSTRACT FROM AUTHOR]

Real-time precise orbits of low earth orbit (LEO) satellites are becoming indispensable with the rapid development of real-time Earth observation application and LEO enhanced precise point positioning. Currently, GNSS-based precise orbit determination is a widely used method for LEO onboard navigation. However, the real-time LEO satellite orbits are usually obtained by ambiguity-float solution even when the GNSS augmentation corrections are considered. In this study, we perform LEO ambiguity-fixed multi-GNSS real-time precise orbit determination (RTPOD) based on square root information filter. One month of onboard GPS + Galileo observations from Sentinel-6A and real-time products of the Centre National d’Etudes Spatiales (CNES) are used to investigate the contribution of integer ambiguity resolution (IAR). The benefit of dual-system combination on LEO RTPOD is firstly evaluated. The combination of GPS and Galileo dual-system contributes to more visible GNSS satellites and better observation geometry for LEO RTPOD, which results in an evident accuracy improvement of 19% over GPS and a convergence time reduction of 43% and 41% compared to the GPS and Galileo solutions respectively. Considering the short arc of onboard GNSS observations and imperfections in GNSS real-time products, we propose a strict IAR quality control method to avoid fixing the ambiguity to the wrong values. The results indicate that the IAR quality control method we used can effectively reduce the wrong fixing risk and increase the robustness of the IAR solution. Using onboard GPS and Galileo observations, the 3D orbit accuracy of the ambiguity-fixed solution is significantly improved from 5.17 to 3.61cm, by 30%, compared to the ambiguity-float solution. Furthermore, the application of IAR also achieves a faster convergence to the centimeter-level orbit. [ABSTRACT FROM AUTHOR]

Un-differenced (UD) ambiguity resolution (AR) is widely applied since it can avoid wrong-fixing and fix the most of ambiguities. However, in the precise orbit determination (POD) solution using ground network only, the accuracy of float estimates is not sufficient for a direct UD AR, and thus double-differenced (DD) AR must be conducted first. It is demonstrated that integrating low-Earth orbit (LEO) satellites improves the accuracy of ambiguity-float solutions and consequently the improved ambiguity estimates enable successful UD AR. With more and more LEO satellites receiving Global Positioning System (GPS) observations, it is important to investigate the effect of different LEO configurations for LEO-augmented GPS UD AR. In this study, about 100 stations of the International GNSS Service (IGS), and eight LEO satellites with five orbital configurations, including two GRACE-FO, three SWARM, two SENTINEL-3, and one SENTINEL-6 satellites, are used for integrated processing of LEO satellites and ground network. The influence of different numbers of LEO satellites and orbital configurations on the performance of UD POD is investigated by analyzing the POD results of the ground network together with 35 different LEO-satellite schemes. We demonstrate that the performance of POD, in terms of GPS orbit accuracy and unsuccessful fixing in the UD AR solution, depends on the accuracy of float estimates. The number of unsuccessful fixings can be reduced by the increasing number of LEO satellites and orbital configurations. Moreover, including LEO satellites from more orbital configurations is more efficient for a given number of LEO satellites. [ABSTRACT FROM AUTHOR]

Ionospheric tomography offers three-dimensional (3D) description of the electron density distribution, enabling the direct incorporation of electron density data into the slant total electron content (STEC) computation. As a result, STEC derived from tomography helps mitigate the ionospheric delay experienced in the line of sight between global navigation satellite systems (GNSS) and satellites positioned in low Earth orbits (LEO). Tomography can therefore be effectively employed to correct single-frequency GNSS observations and allow enhanced positioning of spaceborne platforms. We demonstrate the accuracy and performance of a global-scale ionospheric tomography method for determining satellite orbits, utilizing single-frequency GNSS measurements combined with a precise point positioning (PPP) algorithm. We compare the tomographic outcomes against orbit determination derived from the GRoup and PHase ionospheric correction (GRAPHIC) observable and based on an ionospheric climatological model. Near the peak of solar cycle 24, the overall accuracy achieved with tomography was around 3.8 m. notably, compared to the background climatological model, tomography demonstrated improvements ranging from 15 to 20%. The GRAPHIC method outperformed tomography, achieving an accuracy of 0.7 m, whereas we obtained around 7 m accuracy when no ionospheric model is employed. Although the developed ionospheric tomography has yet to match the precision of GRAPHIC, our results bring us relatively closer to this objective. [ABSTRACT FROM AUTHOR]

Traditional polyimides have highly conjugated structures, causing significant coloration under visible light. Fluorinated colorless polyimides, known for their light weight and excellent optical properties, are considered ideal for future aerospace optical lenses. However, their lifespan in low Earth orbit is severely limited by high-density atomic oxygen (AO) erosion, and the degradation behavior of fluorinated polyimides under AO exposure is not well understood. This study uses reactive molecular dynamics simulations to model two fluorinated polyimides, PMDA-TFMB and 6FDA-TFMB, with different fluorine contents, to explore their degradation mechanisms under varying AO concentrations. The results indicate that 6FDA-TFMB has slightly better resistance to erosion than PMDA-TFMB, mainly due to the enhanced chemical stability from its -CF3 groups. As AO concentration increases, widespread degradation of the polyimides occurs, with AO-induced cleavage and temperature-driven pyrolysis happening simultaneously, producing CO and OH as the main degradation products. This study uncovers the molecular-level degradation mechanisms of fluorinated polyimides, offering new insights for the design of AO erosion protection systems. [ABSTRACT FROM AUTHOR]

This paper presents a large vacuum facility (6-ft-diameter, 10-ft-long chamber) equipped with a magnetic filter-type low Earth orbit plasma source. A recommended operating envelope for the plasma source was established through single-point measurements by varying the discharge currents of the plasma source and the gas flow rates. A three-axis translation stage was fabricated and tested with 2D and 3D scans of the simulated plasma environment. The measured plasma density during this study was between 1.63×1012-3.1×1012m-3 for the electrons and 7.54×1013m-3 for the ions, whereas the electron and ion temperatures ranged from 0.55 to 2.06 eV and 1 to 3 eV, respectively. The simulated plasma environment compares well with orbital equivalents, specifically the F layers of the ionosphere. [ABSTRACT FROM AUTHOR]

Summary: This paper presents low Earth orbit (LEO) satellite constellation configuration based on the performance of Doppler effect in laser intersatellite links (LISLs). It studies the impact of the LEO constellation's parameters on the performance of the Doppler effect in LISLs. The paper aims to develop LEO satellite constellation configurations that evolve LISLs with minimal Doppler shift. It evaluates the impact of the variation of the relative distance, the inclination angle of the LEO constellation orbital planes, the orbital planes number in the LEO constellation, and the altitude on the performance of Doppler wavelength shift (DWS) in LISLs, for different operating laser wavelengths (OLWs) with respect to two possible intersatellite links (ISL) connection modes within the constellation, straight ISL (n‐to‐n) and inclined ISL (n‐to‐n − 1). n is the order of the satellite in the orbital plane. Simulations are conducted to evaluate the performance of these configurations in terms of altitude, OLW, inclination angle, and the number of orbital planes. In addition, both OneWeb and Starlink constellations are studied to evaluate DWS performance. The study demonstrates that DWS decreases either with the diminution of the relative distance between linked LEO satellites, the inclination of LEO constellation, and the OLW, or with the augmentation of the orbital planes number and altitude. Moreover, the overall DWS between two LEO satellites in the proposed constellation is at least 50% lower than the constellation configuration in other literature. The paper proposes the LEO constellation's configurations that perform LISLs with less possible Doppler effect by optimizing the LEO constellation parameters that impact the Doppler effect. The result of this study helps in the early stage of LEO satellite constellation designing in terms of payload simplicity and cost. [ABSTRACT FROM AUTHOR]

Doppler positioning, as an early form of positioning, has regained significant research interest in the context of Low Earth Orbit (LEO) satellites.Given the LEO mega-constellation scenario, the objective function of Doppler positioning manifests significant nonlinearity, leading to ill-conditioning challenges for prevalent algorithms like iterative least squares (LS) estimation, especially in cases where inappropriate initial values are selected. In this study, we investigate the causes of ill-posed problems from two perspectives. Firstly, we analyze the linearization errors of the Doppler observation equations in relation to satellite orbital altitude and initial value errors, revealing instances where traditional algorithms may fail to converge. Secondly, from an optimization theory perspective, we demonstrate the occurrence of convergence to locally non-unique solutions for Doppler positioning. Subsequently, to address these ill-conditioning issues, we introduce Tikhonov regularization terms in the objective function to constrain algorithm divergence, with a fitted model for the regularization coefficient. Finally, we conduct comprehensive simulation experiments in both dynamic and static scenarios to validate the performance of the proposed algorithm. On the one hand, when the initial values are set to 0, our algorithm achieves high-precision positioning, whereas the iterative LS fails to converge. On the other hand, in certain simulation scenarios, the iterative LS converges to locally non-unique solutions, resulting in positioning errors exceeding 50 km in the north and east directions, several hundred kilometers in the vertical direction, and velocity errors surpassing 120 m/s. In contrast, our algorithm demonstrates typical errors of a position error of 6.8462 m, velocity error of 0.0137 m/s, and clock drift error of 8.3746 × 10 − 6 s/s. This work provides an effective solution to the sensitivity issue of initial points in Doppler positioning and can serve as a reference for the algorithm design of Doppler positioning receivers with LEO mega-constellations. [ABSTRACT FROM AUTHOR]

The combination of satellite laser ranging (SLR) observations to various low earth orbit (LEO) satellites can enhance the accuracy and robustness of SLR-derived geodetic parameters, benefiting the realization of the International terrestrial reference frames. Observation stochastic models play a critical role in the integrated processing of SLR observations to multiple LEO satellites. The consideration of precision in heterogeneous SLR observations from various satellites is essential. In this study, we aim to improve the combination of multi-LEO SLR observations for geodetic parameters determination by optimizing the stochastic model using variance component estimation (VCE). We perform weekly estimates of the geodetic parameters, including station coordinates, Earth rotation parameters, and geocenter coordinates (GCC), using three years of SLR observations to seven LEO satellites at different orbits. The satellite-dependent, station-dependent, and satellite–station-dependent variance components are separately estimated through VCE processing to refine the stochastic models. Given the fact that the precision of SLR observations significantly differs in satellites and stations, the multiple LEO combination can be significantly improved with the implementation of VCE. Satellite–station-pair-dependent variance components are more suitable to the SLR VCE and the accuracy of station coordinates, pole coordinates, and length of day can be averagely improved by 8.4, 22.6, and 21.9%, respectively, compared to the equal-weight solution. Our result also indicates that the observation insufficiency for some stations may result in an unreliable VCE estimation, and eventually leads to an accuracy degradation for station coordinates. To overcome this deficiency, we adopt the variance components derived from the monthly solutions to build the stochastic model in the weekly solutions. The application of monthly weights can effectively mitigate the accuracy deterioration of station coordinates, improving the repeatability of the station coordinates by 15.9, 14.6, and 9.2% with respect to the equal-weight solution in E, N, and U components. The global geodetic parameters also benefit from this processing. The import of monthly weight decreases the outliers in the GCC series, especially in the X and Y components. [ABSTRACT FROM AUTHOR]

This paper delves into the recent advancements in phased-array antenna systems, focusing on their application in low earth orbit (LEO) satellite systems and their implications for high-speed, low-latency communication networks. The escalating demand for high-speed data transfer and responsive communication has spurred the exploration of novel antenna technology solutions. In light of meeting these needs, phased-array antenna systems are now giving the prospect of offering something that conventional antenna systems cannot: the capacity to steer building and pathway beams in numerous and precise means to make the most of signal intersection. Realized by the directing and molding strategies, this capability reduces the signal transmission time, which enhances the low latency process in the network hence increases its responsiveness. In addition, the design of phased-array antennas allows increased data rates as it increases network capacity and allows for multiplication of transmission beams to provide faster data processing. The paper also looks into the interaction of these advancements with the LEO satellites, satellites that orbit close to the Earth and move from point to point quite frequently. The issues that arise when implementing LEO systems such as target mobility and communicating with multiple targets, overcoming interference in crowded orbits can be resolved by adopting phased-array antenna systems for resilient infrastructure. [ABSTRACT FROM AUTHOR]

IntroductionCurrent and future astronauts will endure prolonged exposure to spaceflight hazards and environmental stressors that could compromise cognitive functioning, yet cognitive performance in current missions to the International Space Station remains critically under-characterized. We systematically assessed cognitive performance across 10 cognitive domains in astronauts on 6-month missions to the ISS.MethodsTwenty-five professional astronauts were administered the Cognition Battery as part of National Aeronautics and Space Administration (NASA) Human Research Program Standard Measures Cross-Cutting Project. Cognitive performance data were collected at five mission phases: pre-flight, early flight, late flight, early post-flight, and late post-flight. We calculated speed and accuracy scores, corrected for practice effects, and derived z-scores to represent deviations in cognitive performance across mission phases from the sample’s mean baseline (i.e., pre-flight) performance. Linear mixed models with random subject intercepts and pairwise comparisons examined the relationships between mission phase and cognitive performance.ResultsCognitive performance was generally stable over time with some differences observed across mission phases for specific subtests. There was slowed performance observed in early flight on tasks of processing speed, visual working memory, and sustained attention. We observed a decrease in risk-taking propensity during late flight and post-flight mission phases. Beyond examining group differences, we inspected scores that represented a significant shift from the sample’s mean baseline score, revealing that 11.8% of all flight and post-flight scores were at or below 1.5 standard deviations below the sample’s baseline mean. Finally, exploratory analyses yielded no clear pattern of associations between cognitive performance and either sleep or ratings of alertness.ConclusionThere was no evidence for a systematic decline in cognitive performance for astronauts on a 6-month missions to the ISS. Some differences were observed for specific subtests at specific mission phases, suggesting that processing speed, visual working memory, sustained attention, and risk-taking propensity may be the cognitive domains most susceptible to change in Low Earth Orbit for high performing, professional astronauts. We provide descriptive statistics of pre-flight cognitive performance from 25 astronauts, the largest published preliminary normative database of its kind to date, to help identify significant performance decrements in future samples.

We statistically evaluate the global distribution and energy spectrum of electron precipitation at low‐Earth‐orbit, using unprecedented pitch‐angle and energy resolved data from the Electron Losses and Fields INvestigation CubeSats. Our statistical results indicate that during active conditions, the ∼63 keV electron precipitation ratio peaks at L > 6 at midnight, whereas the spatial distribution of precipitating energy flux peaks between the dawn and noon sectors. ∼1 MeV electron precipitation ratio peaks near midnight at L > ∼6 but is enhanced near dusk during active times. The energy spectrum of the precipitation ratio shows reversal points indicating energy dispersion as a function of L shell in both the slot region and at L > ∼6, consistent with hiss‐driven precipitation and current sheet scattering, respectively. Our findings provide accurate quantification of electron precipitation at various energies in a broad region of the Earth's magnetosphere, which is critical for magnetosphere‐ionosphere coupling. Plain Language Summary: Precipitation into the Earth's upper atmosphere is an important loss process of radiation belt electrons and can change the ionospheric conductance and atmospheric chemistry. Electrons can be moved into the loss cone through either wave‐particle interactions or due to special magnetic field geometries, such as current sheet scattering (CSS). To determine the relative contribution of wave‐particle interactions and CSS, it is crucial to investigate the global distribution and energy spectra of the electron precipitation rate. Previous measurements of energetic electron precipitation at low‐Earth‐orbit either had low resolution in pitch angle and energy or were contaminated by ions and penetrating particles. In this study, we used data from the twin Electron Losses and Fields INvestigation CubeSats, which do not suffer from similar deficiencies, to statistically analyze the dependence of energetic electron precipitation rates on geomagnetic activity, with high resolution in both pitch angle and energy. These findings cast new light on the physical mechanisms that determine the precipitation rate from the magnetosphere into the atmosphere and may have implications for future studies of the ionospheric conductivity and atmospheric chemistry. Key Points: A global survey of electron precipitation is performed using the pitch angle and energy resolved data from Electron Losses and Fields INvestigation CubeSatsAt ∼1 MeV, electron precipitation is strongest at L > ∼6 near midnight and is enhanced near dusk during active timesThe energy spectrum of the precipitation ratio shows reversal points indicating energy dispersion in L shells in the slot region and L > ∼6 [ABSTRACT FROM AUTHOR]

Due to its small mass and eccentricity, the motion of a piece of debris in low Earth orbit (LEO) may be chaotic. This paper demonstrates that ultra-chaos widely exists in the case of a square thin plate in LEO with a center of mass (COM) that is initially displaced from the axis of symmetry. Chaotic systems are well-known for their sensitive dependence on initial conditions, though their statistical properties are usually insensitive to small disturbances. However, a recent concept called ultra-chaos has been introduced to describe chaotic systems whose statistics are sensitive to even tiny disturbances. This paper demonstrates that ultra-chaos is widely exists in a square thin plate in LEO with a displaced COM from the axis of symmetry. The results show that an ultra-chaotic plate trajectory exhibits higher disorder than that of a normal plate, with a position deviation that can be two orders of magnitude larger than that of a normal-chaotic subsystem. Distinct from earlier findings concerning ultra-chaotic systems, the present study uncovers the manifestation of ultra-chaos in a physically constrained system devoid of periodic boundaries. Prior investigations of ultra-chaotic systems have featured at least one periodic boundary or lacked a physical boundary. The new concept of ultra chaos provides a plausible explanation as to why space debris can spread to a vast area, as most pieces of debris have a displaced COM. [ABSTRACT FROM AUTHOR]

The deployment of megaconstellations in low Earth orbit (LEO) poses significant collision risks with space debris. This paper focuses on analyzing the short-term and long-term collision probabilities of megaconstellations to assess their collision risk. Firstly, a short-term collision risk evolution model is developed to accurately address rendezvous collisions. Secondly, a long-term collision risk evolution model is established by considering space object density, space debris attenuation, space target disintegration, and the distribution of disintegration targets. Through simulations conducted on the Starlink Phase I constellation, the results demonstrate a 30–40% increase in short-term collision probability within the constellation shell, a 70.2% probability of at least one collision during the constellation's lifetime, and a 25.3% increase in secondary collisions following a collision event. This study provides a reference and application for analyzing the orbital safety of LEO megaconstellations and for promoting the sustainable development and utilization of space resources. [ABSTRACT FROM AUTHOR]

The protection of satellites from the harsh space environment is heavily reliant on external spacecraft materials. These materials undergo continuous changes in their physical, chemical, and optical properties due to exposure to solar radiation and aggressive chemical species present in Earth's upper atmosphere. By gaining a thorough understanding of how these material properties evolve over the planned lifetime of a mission, the reliability of spacecraft can be enhanced. Additionally, the establishment of correlation factors between actual space exposure and accelerated space weather experiments performed in ground facilities allows for the precise prediction of on-orbit material performance based on laboratory-based testing. This paper presents an assessment of the radiation effects of the low Earth orbit environment, including exposure to high-energy electrons, atomic oxygen, and vacuum ultraviolet, on the material properties of a prospective spacecraft polymer, Mylar® M021. The study is part of the 16th Materials International Space Station Experiment (MISSE), which our team conducted from 08/31/22 to 02/23/23. An overview of the MISSE project is provided, including details on the materials used, results of ground experiments, and preliminary findings from the orbital phase of the study. [ABSTRACT FROM AUTHOR]

Low Earth orbit satellites face challenges from Earth's magnetic field, causing attitude disturbances. Attaining a magnetic-dipole-free satellite is crucial. Layout optimization and in-orbit dipole compensation are common methods, but layout optimization can be impractical. In contrast, in-orbit dipole compensation struggles with rapidly changing magnetic dipoles like those from reaction wheel motors. This research proposes an alternative solution using Mu-metal, known for shielding against magnetic exposure. This shield can be applied to trap the magnetic field generated by the motors. Ground tests evaluated this approach. First, it determined the minimum distance between the magnetometer and the shield for accurate measurements with minimal interference, with the result of 10 cm as the least affected distance, particularly important for small satellite layout design. Second, it assessed the shield's effectiveness in trapping the motor-generated magnetic field. Tests showed a significant reduction in magnetic field magnitude and up to a 95% reduction in field fluctuations when the motor is activated. This research offers a practical solution for small satellite layout design, addressing the challenges posed by their compact dimensions. Mu-metal shielding proves effective for mitigating rapidly changing magnetic dipoles and enhancing magnetic cleanliness in low Earth orbit.

The study of navigation solutions other than GNSS is becoming increasingly important due to growing concerns about the vulnerability of GNSS to interference. The use of existing LEO satellite signals is a promising option in this respect. This study analyzes the accuracy of Doppler shift measurements for three satellite systems: Iridium-next, Orbcomm, and NOAA, based on actual signal acquisition, and evaluates the potential of their combination in positioning. The study takes advantage of Orbcomm’s dual frequency capability to reduce Doppler shift measurement noise, while highlighting the irrelevance of the ionosphere-free combination with Orbcomm. It proposes a method for obtaining unambiguous Doppler shifts from NOAA’s FM-AM signal, and introduces a smoothing technique to further improve Doppler shift measurement accuracy of LEO satellites. The positioning results show that positioning with three constellations is more accurate than positioning with one or two constellations, and that the effectiveness of passively combining several LEO systems for positioning is limited by the disparity between satellite constellations and the measurement quality inherent in each system.

In order to find a simpler method to simulate the charging of spacecraft surface and further analyze the characteristics of the charging reaction of low-orbit spacecraft surface materials, this paper uses COMSOL to perform finite element analysis on the charging of low-orbit spacecraft surface materials at an altitude of 300–400 km. First, the surface charging potential is established using the particle transport equation. By calculating the thermal diffusion movement of particles, the adsorption, secondary electron emission and backscattering effects of the material surface are evaluated to simulate the charging potential of the spacecraft surface. The results show that COMSOL based on the plasma module can replace SPIS to simulate the charged properties of spacecraft surface materials, indicating that different physical properties of the material surface are attached with different magnitudes of potential and small potential differences; In addition, based on the particle transport equation, this paper obtains the surface charging results of the Kapton connector between the solar panel and the spacecraft body, which is prone to charging. This research content provides a simplified method and new direction for the simulation study of spacecraft surface charging.

Carbon fiber reinforced polymers (CFRPs) offer exceptional properties that make them highly relevant in the aerospace industry, such as high thermal conductivity and an outstanding strength‐to‐weight ratio. Advances in additive manufacturing have expanded the aerospace applications of CFRPs, even allowing for in‐space fabrication of complex structures. Understanding the stability of CFRPs in the harsh conditions of low Earth orbit (LEO) is crucial. LEO exposes materials to extreme environmental factors, such as vacuum, radiation, atomic oxygen, and temperature fluctuations, which can accelerate degradation. To investigate the space‐environment effect on material, changes in properties of 3D‐printed CFRPs are compared with CFRPs made through forging and conventional compression molding. Surface analyses examine morphological, chemical, and matrix composition changes, along with an evaluation of mechanical integrity. Remarkably, the naked 3D printed CFRPs withstood 8 months of LEO exposure similar to the compression molded CFRP samples, with changes in chemical properties limited to the sample's outer surface. Further, despite no protective coatings are used, limited surface erosion and no variation in mechanical strength are observed. These results provide relevant information for the development and deployment of novel 3D printed CFRPs materials for a wide spectrum of terrestrial and space applications. [ABSTRACT FROM AUTHOR]

In space application, hybrid pixel detectors of the Timepix family have been considered mainly for the measurement of radiation levels and dosimetry in low earth orbits. Using the example of the Space Application of Timepix Radiation Monitor (SATRAM), we demonstrate the unique capabilities of Timepix-based miniaturized radiation detectors for particle separation. We present the incident proton energy spectrum in the geographic location of SAA obtained by using Bayesian unfolding of the stopping power spectrum measured with a single-layer Timepix. We assess the measurement stability and the resiliency of the detector to the space environment, thereby demonstrating that even though degradation is observed, data quality has not been affected significantly over more than 10 years. Based on the SATRAM heritage and the capabilities of the latest-generation Timepix series chips, we discuss their applicability for use in a compact magnetic spectrometer for a deep space mission or in the Jupiter radiation belts, as well as their capability for use as single-layer X- and γ -ray polarimeters. The latter was supported by the measurement of the polarization of scattered radiation in a laboratory experiment, where a modulation of 80% was found. [ABSTRACT FROM AUTHOR]

We consider optimal intellectual property (IP) policy when (1) firms embed 'constellations' of IP—patented, secret/non-patentable, and patentable-but-secret innovations—into products such as communication satellites operating in low Earth orbit and (2) an innovation may improve both product performance and ambient environmental quality. For instance, a materials science innovation by SpaceX that is shared via patent licensing could raise the technical performance of all satellites in low Earth orbit and at the same time reduce orbital debris. Traditional IP policy helps innovators monetize spillover technological benefits by combining patent licensing rights with the right of competitors to reverse engineer patentable-but-secret innovations. However, we show that when disclosure of an innovation also creates spillover environmental improvements, licensing policies that address only the technological knowledge spillover are inefficiently weak. We characterize the conditions under which private firms will hold secret more patentable innovations than are socially optimal. We then suggest implementable IP policies for jointly promoting technical innovation and environmental quality improvements. [ABSTRACT FROM AUTHOR]

Colorless and transparent polyimide (CPI) films with good atomic oxygen (AO) resistance and high thermal endurance are highly required in low earth orbit (LEO) space exploration. Conventional CPI films based on fluoro-containing 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) have been widely used in space applications. However, the AO erosion yields and glass transition temperatures (Tg) of the 6FDA-based CPI films have to be modified in order to meet the severe serving environments. In the current work, novel CPI films based on a multi-ring fluoro-containing 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylicdianhydride (6FCDA) monomer were developed. In order to enhance the AO resistance of the derived CPI film, a phosphorus-containing aromatic diamine, 2,5-bis[(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO) was used to polymerize with the dianhydride to create the organo-soluble resin. Then, two phosphorus-containing CPI films (PPI), including PPI-1 (6FDA-BADPO) and PPI-2 (6FCDA-BADPO) were prepared by thermally curing of the PPI solutions at elevated temperatures. The PPI films maintained good optical transparency with transmittance values over 80% at a wavelength of 450 nm. PPI-2 exhibited a Tg value of 311.0 °C by differential scanning calorimetry (DSC) measurement, which was 46.7 °C higher than that of the PPI-1 counterpart (Tg = 264.3 °C). In addition, the PPI-2 film showed a coefficient of linear thermal expansion (CTE) value of 41.7 × 10−6/K in the range of 50~250 °C, which was apparently lower than that of the PPI-1 sample (CTE = 49.2 × 10−6/K). Lastly, both of the two PPI films exhibited good AO resistance with the erosion yields (Ey) of 6.99 × 10−25 cm3/atom for PPI-1 and 7.23 × 10−25 cm3/atom for PPI-2 at an exposure flux of 5.0 × 1020 atoms/cm2. The Ey values of the current PPI films were obviously lower than that of the standard polyimide (PI) film based on pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) (Ey = 3.0 × 10−24 cm3/atom). [ABSTRACT FROM AUTHOR]

Abstract—Spore-forming bacteria have a unique resistance to negative environmental conditions, including aggressive space factors, and are an excellent model for studying adaptation mechanisms and survival strategies at the molecular level. The study analyzed the genome of Bacillus velezensis, which remained viable after a 2-year exposure in outer space on the outer surface of the ISS as part of the Test space experiment. A comparative analysis of the draft genomes of the exhibit strain and the ground control did not reveal significant changes; the average nucleotide identity was 99.98%, which indicates the ability of microorganisms to maintain genome stability in space conditions, due to both increased stress resistance of bacterial spores and efficient operation of the system of repair of accumulated changes. The study of a single nucleotide polymorphism in the genome of B. velezensis revealed nine point substitutions, three of which are in intergenic regions, six in protein-coding genes, three of them are missense mutations, two nucleotide deletions leading to a shift in the reading frame, and one synonymous substitution. The profiles of the housekeeping genes were determined during MLST typing and it was found that the allelic profiles obtained for B. velezensis T15.2 and 924 strains do not correspond to any of the previously described sequence types.The presented results indicate the ability of B. velezensis bacteria to maintain the viability of spores and the integrity of the genome for a long time under extreme conditions of outer space, which is important for the problem of planetary protection, as well as the potential possibility of performing biotechnological processes based on B. velezensis during space exploration. [ABSTRACT FROM AUTHOR]

Eighty-three percent of all operational satellites are deployed in Low Earth Orbit (LEO), where Starlink is the largest mega-constellation with 5 233 satellites in working phase (data available for June 2024) (Planet4589, 2023). To date, SpaceX has launched the first 6 505 Starlink satellites out of 11 908 units planned (with a possible supplement of 22 488 units). One of the failed satellites was the Starlink-1353 (2020-025G) unit, for which the controlled decay above Hokkaido Island, on February 21, 2023, was in the field-of-view of one telescope from Kitasubaru Astronomical Observatory. Luckily, in that moment the telescope was performing observations on the Orion Nebula region, in a live streaming session (Kitasubaru, 2024). The major break-up was captured by the video camera of the telescope and based on the frame-by-frame image analysis, we identified 15 fragments after the atmospheric re-entry. According to our analysis based on Debris Assessment Software (DAS) (NASA), the major breakup occurred at 64.4 km above the sea level and some fragments were spread over an area of 15.13 m2. The paper presents hypothesis about the composition of the fragments that crossed the sky above Japan and if these can reach the sea level. In order to study the dynamical behaviour of Starlink-1353, before the moment of planned re-entry maneuvers, the observation recorded by Berthelot Observatory (IAU Code L54) were used. Orbital evolution of the satellite is presented using numerical integration for the available Two Line Elements (TLE) values. Using the last TLE, published five hours before re-entry, an estimated time 10:46 UTC, February 21, 2023 was computed. [ABSTRACT FROM AUTHOR]

Low Earth Orbit (LEO) satellite communication systems typically achieve identity authentication through the encryption and decryption of two-way information, which requires complex key management systems. In contrast, the integration of navigation and communication (NavCom) signals provides novel opportunities for physical observation and authentication solutions due to its measurement functions. This paper introduces a novel signal authentication scheme based on twice two-way satellite time transfer (TWSTT) for LEO satellite systems. It leverages the non-mutated nature of the clock difference to ascertain the legitimacy of the signal by measuring the clock difference of signals at different instances. Unlike traditional authentication methods, this approach directly exploits the temporal and spatial characteristics of the signal, negating the necessity for intricate authorization key systems. Additionally, it adeptly tackles the challenges posed by spoofing interference. The performance analysis indicates that this scheme can achieve a high detection probability for the repeater spoofing signal in the low carrier-to-noise ratio conditions. [ABSTRACT FROM AUTHOR]

Low Earth orbit satellites face challenges from Earth's magnetic field, causing attitude disturbances. Attaining a magnetic-dipole-free satellite is crucial. Layout optimization and in-orbit dipole compensation are common methods, but layout optimization can be impractical. In contrast, inorbit dipole compensation struggles with rapidly changing magnetic dipoles like those from reaction wheel motors. This research proposes an alternative solution using Mu-metal, known for shielding against magnetic exposure. This shield can be applied to trap the magnetic field generated by the motors. Ground tests evaluated this approach. First, it determined the minimum distance between the magnetometer and the shield for accurate measurements with minimal interference, with the result of 10 cm as the least affected distance, particularly important for small satellite layout design. Second, it assessed the shield's effectiveness in trapping the motor-generated magnetic field. Tests showed a significant reduction in magnetic field magnitude and up to a 95% reduction in field fluctuations when the motor is activated. This research offers a practical solution for small satellite layout design, addressing the challenges posed by their compact dimensions. Mu-metal shielding proves effective for mitigating rapidly changing magnetic dipoles and enhancing magnetic cleanliness in low Earth orbit. [ABSTRACT FROM AUTHOR]

Remote sensing of the Earth is now widely used in various fields. One of the challenges of remote sensing is the creation of inexpensive satellite systems operating in polar circular orbits. These systems require the development of a receptiontransmission system that allows tens of gigabits of video information to be transmitted to an earth receiving station within ten minutes. That is, there is a need to create a communication system that provides high speed data transmission from small satellites weighing up to 50 kg. Objective. The aim of the work is to study the features of digital signal formation in modern satellite communication lines and to develop a communication system with a high data transfer rate (usually 300 Mbit/s), which can be applied to small Earth Observation satellites. Method. Proposed concept for building a high-speed data transmitter from a remote sensing earth satellite using commercially available off-the-shelf technology. Calculations of the power flow density created at the input of the receiving earth station were performed to find out the possible power of the on-board transmitter. Results. A diagram of a communication system based on the DVB-S standard using the technology of commercially available off-the-shelf products has been developed. The high-speed data transmitter is implemented on a Xilinx® Zynq Ultrascale+ ™ MPSoC FPGA microchip, which is located on an Enclustra Mercury XU8 module with a high-performance dual 16-bit AD9174 DAC. The on-board transmitter with a power of up to 2 W meets the requirements of the ITU Radio Regulations for the power flux density on the surface of the Earth, which is created by the radiation of the space station EESS in the range 8025–8400 MHz. It is shown that the energy reserve of the communication line of 3 dB is achieved for various commands for coding and modulation changes with an increase in the elevation angle, which allows to increase the speed of information transmission. Conclusions. An original receiving-transmitting system was developed for use in small satellites for remote sensing of the Earth. It is shown that the function of adaptive modeling of ACM of the DVB-S standard allows you to automatically change the transmission parameters in real time depending on the changing conditions of the channel, providing opportunities for more flexible and effective data transmission in various conditions, which will allow to increase the volumes of information transmitted by communication session. The proposed system operates in the X-band and is built using commercially available off-the-shelf products. An antenna with double circular polarization is used as the emitter. Two physical channels represent two polarization modes: right circular polarization and left circular polarization, each of which has three frequency channels. [ABSTRACT FROM AUTHOR]

Abstract We statistically evaluate the global distribution and energy spectrum of electron precipitation at low‐Earth‐orbit, using unprecedented pitch‐angle and energy resolved data from the Electron Losses and Fields INvestigation CubeSats. Our statistical results indicate that during active conditions, the ∼63 keV electron precipitation ratio peaks at L > 6 at midnight, whereas the spatial distribution of precipitating energy flux peaks between the dawn and noon sectors. ∼1 MeV electron precipitation ratio peaks near midnight at L > ∼6 but is enhanced near dusk during active times. The energy spectrum of the precipitation ratio shows reversal points indicating energy dispersion as a function of L shell in both the slot region and at L > ∼6, consistent with hiss‐driven precipitation and current sheet scattering, respectively. Our findings provide accurate quantification of electron precipitation at various energies in a broad region of the Earth's magnetosphere, which is critical for magnetosphere‐ionosphere coupling.

Thermal control of small satellites in low earth orbit (LEO) is not easy due to the intermittent heating conditions. The satellites in LEO are sometimes present in the illumination zone and other times in the eclipse zone, which imposes difficulties keeping their temperatures within the safe range. The present study investigates a thermal energy storage panel (TESP) integrated with phase change materials (PCM) to control the temperatures of satellite subsystems. The TESP was made of aluminium with outer dimensions of 100 mm long, 71 mm wide, and 25 mm high. The PCMs used were organic-based materials, which were RT 12, RT 22, and RT 31. The TESP was tested under two thermal powers of 11 W and 14 W. These powers are typical of satellite subsystems. The finite volume method was adopted for thermal analysis of the TESP. The significance of this study is that it provides a detailed computational analysis of the TESP for microsatellites' temperature management under typical LEO conditions. The research outcomes show a significant advancement in the thermal managing performance of PCM-based TESP. RT 22 could reduce the highest temperature by 4.7 % and raise the lowest by 9.5 %. It was observed from the analysis that the PCM with intermediary melting temperature provided better thermal control efficiency. RT 12 reported a lower extreme temperature difference (ETD) and could decrease it by 63.9 % relative to the case with no PCM. At the same time, RT 22 reported an ETD of 23 min and could reduce it by 63 % relative to the case with no PCM at 14 W. The present study concluded that PCMs show great potential as a viable approach for effectively thermally managing devices that experience cyclic thermal fluctuations, such as the subsystems of satellites operating in LEO.

This paper outlines the development phases of a wave-driven Helicon Plasma Thruster for cutting-edge Low Earth Orbit (LEO) constellations. The two-stage ambipolar electric propulsion (EP) system combines the efficient ionization of an ultra-compact helicon reactor with plasma acceleration based on an ambipolar electric field provided by a magnetic nozzle. This paper reveals maturation challenges associated with an emerging EP system in the hundreds-watt class, followed by outlook strategies. A 3 cm diameter helicon reactor was operated using argon gas under a time-modulated RF power envelope ranging from 250 W to 500 W with a fixed magnetic field strength of 400 G. Magnetically enhanced inductively coupled plasma reactor characteristics based on half-wavelength right helical and Nagoya Type III antennas under capacitive (E-mode), inductive (W-mode), and wave coupling (W-mode) were systematically investigated based on Optical Emission Spectroscopy. The operation characteristics of a wave-heated reactor based on helicon configuration were investigated as a function of different operating parameters. This work demonstrates the ability of two-stage HPT using a compact helicon reactor and a cusped magnetic field to outperform today’s LEO spacecraft propulsion.

Traditional polyimides have highly conjugated structures, causing significant coloration under visible light. Fluorinated colorless polyimides, known for their light weight and excellent optical properties, are considered ideal for future aerospace optical lenses. However, their lifespan in low Earth orbit is severely limited by high-density atomic oxygen (AO) erosion, and the degradation behavior of fluorinated polyimides under AO exposure is not well understood. This study uses reactive molecular dynamics simulations to model two fluorinated polyimides, PMDA-TFMB and 6FDA-TFMB, with different fluorine contents, to explore their degradation mechanisms under varying AO concentrations. The results indicate that 6FDA-TFMB has slightly better resistance to erosion than PMDA-TFMB, mainly due to the enhanced chemical stability from its -CF3 groups. As AO concentration increases, widespread degradation of the polyimides occurs, with AO-induced cleavage and temperature-driven pyrolysis happening simultaneously, producing CO and OH as the main degradation products. This study uncovers the molecular-level degradation mechanisms of fluorinated polyimides, offering new insights for the design of AO erosion protection systems.

Doppler positioning, as an early form of positioning, has regained significant research interest in the context of Low Earth Orbit (LEO) satellites.Given the LEO mega-constellation scenario, the objective function of Doppler positioning manifests significant nonlinearity, leading to ill-conditioning challenges for prevalent algorithms like iterative least squares (LS) estimation, especially in cases where inappropriate initial values are selected. In this study, we investigate the causes of ill-posed problems from two perspectives. Firstly, we analyze the linearization errors of the Doppler observation equations in relation to satellite orbital altitude and initial value errors, revealing instances where traditional algorithms may fail to converge. Secondly, from an optimization theory perspective, we demonstrate the occurrence of convergence to locally non-unique solutions for Doppler positioning. Subsequently, to address these ill-conditioning issues, we introduce Tikhonov regularization terms in the objective function to constrain algorithm divergence, with a fitted model for the regularization coefficient. Finally, we conduct comprehensive simulation experiments in both dynamic and static scenarios to validate the performance of the proposed algorithm. On the one hand, when the initial values are set to 0, our algorithm achieves high-precision positioning, whereas the iterative LS fails to converge. On the other hand, in certain simulation scenarios, the iterative LS converges to locally non-unique solutions, resulting in positioning errors exceeding 50 km in the north and east directions, several hundred kilometers in the vertical direction, and velocity errors surpassing 120 m/s. In contrast, our algorithm demonstrates typical errors of a position error of 6.8462 m, velocity error of 0.0137 m/s, and clock drift error of 8.3746 × 10−6 s/s. This work provides an effective solution to the sensitivity issue of initial points in Doppler positioning and can serve as a reference for the algorithm design of Doppler positioning receivers with LEO mega-constellations.

In this study, a dual-mode waveguide circularly polarized antenna for TC&R (telemetry, command, and ranging) was proposed for the communication between a low-orbit satellite and a ground station. The proposed antenna required both a wide −10 dB bandwidth and axial ratio bandwidth of 7.1–7.3 GHz and 8.0–8.4 GHz. The antenna was designed with a stepped septum inside a square waveguide to obtain circular polarization and the axial ratio wide bandwidth. Next, a dual-mode synthesis method was adopted for link budgeting by combining square and circular waveguides. The requirement was that the co-polarization level with a symmetric −3 dB beamwidth of 39° must be −5 dBic or higher at ±76.5°, and the cross-polarization level must average −15 dBic or lower at ±76.5°. Finally, the corrugate structure attached to the outside of the extended circular waveguide was offset in multiple steps to suppress the back lobe of the cross-polarization As a result, the axial ratio maintained an average of 1.8 dB at 0° within each band of the required frequency. In addition, the co-polarization obtained an average of −4.52 dBic in the 7.2 GHz band and −5.31 dBic in the 8.2 GHz band at ±76.5°. Finally, in the case of the cross-polarization pattern, the back lobe level was suppressed by 9.89 dB at 7.2 GHz by the corrugate structure, and an average value of −19.9 dBic or less was obtained at ±76.5°. The proposed antenna was confirmed to be effective as a Korean low-orbit satellite TC&R antenna with a radiation pattern of a symmetric beamwidth.

Thermal control of small satellites in low earth orbit (LEO) is not easy due to the intermittent heating conditions. The satellites in LEO are sometimes present in the illumination zone and other times in the eclipse zone, which imposes difficulties keeping their temperatures within the safe range. The present study investigates a thermal energy storage panel (TESP) integrated with phase change materials (PCM) to control the temperatures of satellite subsystems. The TESP was made of aluminium with outer dimensions of 100 mm long, 71 mm wide, and 25 mm high. The PCMs used were organic-based materials, which were RT 12, RT 22, and RT 31. The TESP was tested under two thermal powers of 11 W and 14 W. These powers are typical of satellite subsystems. The finite volume method was adopted for thermal analysis of the TESP. The significance of this study is that it provides a detailed computational analysis of the TESP for microsatellites' temperature management under typical LEO conditions. The research outcomes show a significant advancement in the thermal managing performance of PCM-based TESP. RT 22 could reduce the highest temperature by 4.7 % and raise the lowest by 9.5 %. It was observed from the analysis that the PCM with intermediary melting temperature provided better thermal control efficiency. RT 12 reported a lower extreme temperature difference (ETD) and could decrease it by 63.9 % relative to the case with no PCM. At the same time, RT 22 reported an ETD of 23 min and could reduce it by 63 % relative to the case with no PCM at 14 W. The present study concluded that PCMs show great potential as a viable approach for effectively thermally managing devices that experience cyclic thermal fluctuations, such as the subsystems of satellites operating in LEO. [ABSTRACT FROM AUTHOR]

While global navigation satellite system (GNSS) technologies have always been the go-to solution for localization problems, they may not be the best choice for some Internet-of-Things (IoT) applications due to the incurred power consumption and cost. In this paper, we present an alternative satellite-based localization method exploiting the signature of Doppler shifts and angle-of-arrival measurements as seen by a low-Earth-orbit (LEO) satellite. We first derive the joint likelihood function of the measurements, which is represented as a combination of three Gaussian distributions. Then, we show that the maximum likelihood problem reduces to a more-efficient mean squared error minimization in the Gaussian case as inferred from real measurements we collected from low-Earth-orbit satellite using a tracking ground station. Thus, we propose utilizing a stochastic optimizer to search for the global minimum of the mean squared error, which represents the location of the ground IoT device as estimated by the satellite platform. The emulated results show that the IoT device localization, in such a realistic model, can be performed with sufficient accuracy for IoT applications. [ABSTRACT FROM AUTHOR]

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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 >460$\textrm{ } > 460$ 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. [ABSTRACT FROM AUTHOR]

With the continuous construction of large-scale Low Earth Orbit (LEO) constellations, their potential for Global Navigation Satellite System (GNSS) applications has been emphasized. This study aims to derive an optimal positioning configuration formula based on the ratio of high-elevation and low-elevation satellites, which can improve the positioning accuracy and overcome the accuracy loss due to signal occlusion. A genetic algorithm is used to solve the optimal positioning configuration problem for large-scale satellite selection. Through a simulation using Starlink satellites currently in orbit, it is verified that the traditional recursive algorithm cannot be applied to satellite selection for large-scale constellations. The proposed formula has a similar accuracy to the Quasi-Optimal algorithm when there is no signal occlusion and the satellites are uniformly selected. However, the accuracy of the latter deteriorates significantly under signal occlusion. Our algorithm can effectively overcome this problem. Moreover, we discuss the effect of different types of obstructions on the accuracy loss. We find that the Quasi-Optimal algorithm is more sensitive to a single large-angle obstruction than multiple small-angle obstructions. Our proposed formula can reduce the localization accuracy degradation caused by signal occlusions in both scenarios. [ABSTRACT FROM AUTHOR]

In recent years atomic oxygen (AO) has become a major challenge for the space community. AO is the most dominant species of the residual atmosphere in low Earth orbit (LEO). In addition, AO was found at the top of the Venusian and Martian atmospheres. As a result of exposure to AO, organic space-facing materials erode, leading to changes in their roughness, thermo-optical properties, and mass loss. In the past years, there has been a growing interest in very low Earth orbit missions, below an altitude of 350 km, where AO density and thus, AO flux, are extremely high. At these low altitudes, material degradation by AO erosion poses a great risk to the integrity of any space-facing material, unless well protected. As such, measuring the AO flux and the consequential material erosion by AO, in real-time while under actual space conditions, are of great interest to the space community. Thus, in this work we present real-time AO material erosion measurements that were conducted, for the first-time in LEO, using the on-orbit material degradation detector (ORMADD). The ORMADD is a low-cost and simple to operate detector, comprised of photovoltaic cells coated with semi-transparent AO sensitive coatings. Two ORMADDs were integrated on TAUSAT-1, a 3U CubeSat, deployed into LEO from the international space station. The first ORMADD was coated with a thin amorphous-carbon coating and the second was covered with a thick pyrolytic Kapton film. Using ORMADD, we were able to follow the erosion of the coatings in real-time conditions and calculate the AO flux in TAUSAT-1 orbit. The average in-orbit flux, derived from ORMADD data, was found to be comparable to the theoretical average AO flux calculated by the space environment information system (SPENVIS) software. This work demonstrates the abilities of ORMADD as a space environment detector, as well as a space material degradation research instrument. • Atomic oxygen measurements were done by the on-orbit material degradation detector. • The on-orbit material degradation detector is based on coated photovoltaic cells. • The erosion of the coating was measured and the atomic oxygen flux was derived. • Atomic oxygen flux was also simulated by the SPENVIS simulation software. • Space measured atomic oxygen flux is comparable to the flux simulated by SPENVIS. [ABSTRACT FROM AUTHOR]

This research investigates the performance of a space-based laser system to remove debris objects with size smaller than 10 cm. The laser system is placed in a 800 km Sun Synchronous Orbit and consists of a 20 kW laser that shoots 300 J energy pulses with a repetition frequency of 66.66 Hz. The system is able to detect and track debris objects in situ using a 2.0 m mirror from 800 km distance. From a distance of about 500 km, the laser fluence on the targets is sufficiently high to trigger ablation, which decelerates the debris objects and reduces their lifetime. The feasibility of the concept is tested in scenarios where the laser system targets the debris objects from a different orbiting altitude and from varying azimuth angles. For many geometries, the laser is capable of significantly reducing the lifetime of the debris object. Extrapolating to longer periods of operation, the laser can be expected to provide a significant reduction of the population of small debris objects in LEO. [ABSTRACT FROM AUTHOR]

Abstract The Low Earth Orbit (LEO) satellites can be used to effectively speed up Precise Point Positioning (PPP) convergence. In this study, 180 LEO satellites with a global distribution are simulated to evaluate their contribution to the PPP convergence. LEO satellites can give more redundant observations and improve satellite geometric distributions, particularly for a single Global Navigation Satellite System (GNSS). The convergence speed of the PPP float solution using the Global Positioning System (GPS, G) or BeiDou Navigation Satellite System (BDS, C) single system as well as the G/C/Galileo navigation satellite system (Galileo, E)/GLObal NAvigation Satellite System (GLONASS, R) combined system with LEO satellites added is improved by 90.0%, 91.0%, and 90.7%, respectively, with respect to the system without LEO satellites added. We introduced LEO observations to assist GNSS in PPP-AR (Ambiguity Resolution) and PPP-RTK (Real Time Kinematic). The success fix rate of a single system is significantly improved, and the Time-To-First-Fix (TTFF) of G and G/C/E is reduced by 86.4% and 82.8%, respectively, for the PPP-AR solution. We analyzed the positioning performance of LEO satellite assisted G/C/E PPP-RTK in the reference networks of different scales, namely different atmospheric delay interpolation accuracies. The success fix rate of the G/C/E combined system is improved from 86.8 to 94.9%, and the TTFF is reduced by 36.8%, with the addition of LEO satellites in the 57 km reference network. In the 110 km reference network, the success fix rate of the G/C/E combined system is improved from 64.0 to 88.6%, and the TTFF is reduced by 32.1%. GNSS PPP-RTK with adding the LEO satellites in the reference networks of different scales shows obvious improvement because the atmospheric correlation decreases with increasing distance from the reference networks.