Geosynchronous Orbit Research Articles

A Near‐Zero Index Metamaterial Lens for Reduced Complexity and High‐Performance Active Electronically Scanned Arrays

AbstractA lens consisting of an anisotropic near‐zero index metamaterial (NZIM) is introduced for improving the far‐field performance of active electronically scanned arrays (AESA). Several simulation studies demonstrate how the NZIM lens (metalens) can be functionalized to transform the embedded element pattern of an array from a typical cosinusoidal shape to a flat‐topped pattern, dramatically reducing the gain at wider angles. This corresponds to reductions in scan loss and suppression of grating lobes in the desired field of view (FOV), especially for arrays with large element spacing (i.e., sparse or thinned arrays). The metalens concept is demonstrated through several simulation studies illustrating the beam shaping capability of NZIM materials. A fabricated metalens demonstrates full suppression of grating lobes and minimal scan loss with a ±10° FOV, which is ideally suited for limited FOV applications such as geosynchronous satellite communications.

Comparative Analysis of TPA‐LSTM and Transformer Models for Forecasting GEO Radiation Belt Electron Fluxes

AbstractThe geosynchronous orbit (GEO) is a region filled with energetic electrons and it hosts hundreds of satellites. Electron fluxes at GEO can change sharply within hours, making high‐time‐resolution prediction crucial. In this study, we develop and compare two neural networks for persistent high‐time‐resolution prediction: long short‐term memory with temporal pattern attention (TPA‐LSTM) and Transformer. Unlike most previous models, which only output electron fluxes, our models output the same parameters as the inputs, including magnetic local time, solar wind speed, solar wind dynamic pressure, AE, Kp, Dst, the north‐south component of the interplanetary magnetic field, and electron flux data from GOES‐15. The models are trained on approximately six years of data (2012–2016) and validated using about one year of data (2017–2018). We compare the TPA‐LSTM and Transformer models using 0.8 MeV electron fluxes and find that while the Transformer model performs slightly better, the difference is not statistically significant. Considering the Transformer's higher computational cost, we use the TPA‐LSTM model to develop prediction models for electron fluxes of 275, 475, 0.8 MeV, and 2 MeV with a 5‐min resolution at GEO, up to 3 days. The prediction efficiencies (PE) for 275, 475, 0.8 and 2 MeV electron fluxes based on about one year of test data (2018–2019) are 0.799, 0.831, 0.849, 0.881 (1‐day prediction); and 0.551, 0.618, 0.663 and 0.710 (3‐day prediction), respectively. Our high‐time‐resolution persistent models should be useful for both protecting satellites at GEO and serving as boundary conditions for physics‐based radiation belt models.

Embedded State Estimation for Optimization of Cislunar Space Domain Awareness Constellation Design

The traffic in cislunar space is expected to increase over the coming years, leading to a higher likelihood of conjunction events among active satellites, orbital debris, and noncooperative satellites. This increase necessitates enhanced space domain awareness (SDA) capabilities that include state estimation for targets of interest. Both Earth surface-based and space-based observation platforms in geosynchronous orbit or below face challenges such as range, exclusion, and occlusion that hinder observation. Motivated by the need to place space-based observers in the cislunar space regime to overcome these challenges, this paper proposes a cislunar SDA constellation design and analysis framework that integrates state estimation into an optimization problem for determining the placement of observers for optimal state estimation performance on a set of targets. The proposed multiobserver placement optimization problem samples from a range of possible target orbits. Upon convergence, the optimized constellation is validated against a broader set of targets to assess its effectiveness. Two comparative analyses are presented to evaluate the effects of changes in the sensor tasking procedure and sensor fidelity on the optimized constellation, comparing these to a single observer baseline case. The results demonstrate that the optimized constellations can provide accurate state estimation for various orbit families.

Auroral and Magnetotail Dynamics During Quiet‐Time STEVE and SAID

AbstractAlthough Strong Thermal Emission Velocity Enhancement (STEVE) and subauroral ion drifts (SAID) are often considered in the context of geomagnetically disturbed times, we found that STEVE and SAID can occur even during quiet times. Quiet‐time STEVE has the same properties as substorm‐time STEVE, including its purple/mauve color and occurrence near the equatorward boundary of the pre‐midnight auroral oval. Quiet‐time STEVE and SAID emerged during a non‐substorm auroral intensification at or near the poleward boundary of the auroral oval followed by a streamer. Quiet‐time STEVE only lasted a few minutes but can reappear multiple times, and its latitude was much higher than substorm‐time STEVE due to the contracted auroral oval. The THEMIS satellites in the plasma sheet detected dipolarization fronts and fast flows associated with the auroral intensification, indicating that the transient energy release in the magnetotail was the source of quiet‐time STEVE and SAID. Particle injection was weaker and electron temperature was lower than the events without quiet‐time STEVE. The plasmapause extended beyond the geosynchronous orbit, and the ring current and tail current were weak. The interplanetary magnetic field (IMF) Bz was close to zero, while the IMF Bx was dominant. We suggest that the small energy release in the quiet magnetosphere can significantly impact the flow and field‐aligned current system.

Earth shadow time/accelerometer/GNSS-based geosynchronous transfer orbit determination method for electric propulsion satellite

Autonomous orbital maneuvering of an electric propulsion satellite in geosynchronous transfer orbit (GTO) requires more accurate autonomous orbit determination (OD). Implementing the traditional autonomous OD method for the electric propulsion satellites may result in the accumulation of measurement errors and dynamic errors from orbit extrapolation, which significantly restrict the OD accuracy. Fortunately, an electric propulsion satellite in GTO can sense the transit time in or out of the Earth shadow according to the output power change of the solar array. Therefore, an Earth shadow time/accelerometer/GNSS-based geosynchronous transfer OD method for electric propulsion satellites is proposed in this paper. First, a system state model with dynamics is established for the entire orbit transfer process. Second, measurement models that use the measurement information from the accelerometer, GNSS, and the transit time into or out of the Earth shadow are established. Third, a sequential filtering estimation approach is designed to solve the problem of asynchronous data fusion for autonomous OD. Comparison simulations demonstrate the effectiveness and superiority of the proposed method.

Interplanetary Causes and Impacts of the 2024 May Superstorm on the Geosphere: An Overview

The recent superstorm of 2024 May 10–11 is the second largest geomagnetic storm in the space age and the only one that has simultaneous interplanetary data (there were no interplanetary data for the 1989 March storm). The May superstorm was characterized by a sudden impulse (SI+) amplitude of +88 nT, followed by a three-step storm main-phase development, which had a total duration of ∼9 hr. The cause of the first storm main phase with a peak SYM-H intensity of −183 nT was a fast-forward interplanetary shock (magnetosonic Mach number M ms ∼ 7.2) and an interplanetary sheath with a southward interplanetary magnetic field component B s of ∼40 nT. The cause of the second storm's main phase with an SYM-H intensity of −354 nT was a deepening of the sheath B s to ∼43 nT. A magnetosonic wave (M ms ∼ 0.6) compressed the sheath to a high magnetic field strength of ∼71 nT. Intensified B s of ∼48 nT were the cause of the third and most intense storm main phase, with an SYM-H intensity of −518 nT. Three magnetic cloud events with B s fields of ∼25–40 nT occurred in the storm recovery phase, lengthening the recovery to ∼2.8 days. At geosynchronous orbit, ∼76 keV to ∼1.5 MeV electrons exhibited ∼1–3 orders of magnitude flux decreases following the shock/sheath impingement onto the magnetosphere. The cosmic-ray decreases at Dome C, Antarctica (effective vertical cutoff rigidity <0.01 GV) and Oulu, Finland (rigidity ∼0.8 GV) were ∼17% and ∼11%, respectively, relative to quiet-time values. Strong ionospheric current flows resulted in extreme geomagnetically induced currents of ∼30–40 A in the subauroral region. The storm period is characterized by strong polar-region field-aligned currents, with ∼10 times intensification during the main phase and equatorward expansion down to ∼50° geomagnetic (altitude-adjusted) latitude.

Statistical reliability estimation of space launch vehicles: 2000–2022

This research examines the reliability of space launch vehicles (SLVs) performing commercial, civil, and military space lift missions through trend analysis and a variety of statistical methods. Data sets obtained from the Seradata database are analyzed for trends by examining data subsets including launch date, sector (commercial, civil or military), launch country, intended mission orbit, SLV family, and failed subsystem. Evolving, time-dependent first-level Bayesian success rate analysis is performed to assess SLV reliability and performance trends on 1873 launches occurring during the period 1 January 2000 to 31 December 2022. It was determined that even with a near-exponential increase in launch events in the 2020s, the number of failures is less than 6% each year, with the average success rate being 95% annually. Overall, 56% of launches were sent into low Earth orbit (LEO) and 32% were sent into geosynchronous Earth orbit (GEO) or geostationary Earth orbit (GSO). Although SLVs servicing missions to these orbital regimes featured success rates above 92%, LEO launches accounted for approximately 73% of total launch failures, while GEO-GSO launches accounted for 18% of failures. Specifically looking at U.S. and Russian SLV families, the main subsystem responsible for failure was propulsion, which accounted for 72.3% of 47 reported launch failures. First-level and second-level (using method of moments) Bayesian techniques were performed on 37 launch vehicle families and it was found that vehicles with a high accrual of launches performed with a higher reliability than vehicles with a low number of launches, resulting in first-level success rates of greater than 90%.

PreMevE‐MEO: Predicting Ultra‐Relativistic Electrons Using Observations From GPS Satellites

AbstractUltra‐relativistic electrons with energies greater than or equal to two megaelectron‐volt (MeV) pose a major radiation threat to spaceborne electronics, and thus specifying those highly energetic electrons has a significant meaning to space weather communities. Here we report the latest progress in developing our predictive model for MeV electrons in the outer radiation belt. The new version, primarily driven by electron measurements made along medium‐Earth‐orbits (MEO), is called PREdictive MEV Electron (PreMevE)‐MEO model that nowcasts ultra‐relativistic electron flux distributions across the whole outer belt. Model inputs include &gt;2 MeV electron fluxes observed in MEOs by a fleet of GPS satellites as well as electrons measured by one Los Alamos satellite in the geosynchronous orbit. We developed an innovative Sparse Multi‐Inputs Latent Ensemble NETwork (SmileNet) which combines convolutional neural networks with transformers, and we used long‐term in situ electron data from NASA's Van Allen Probes mission to train, validate, optimize, and test the model. It is shown that PreMevE‐MEO can provide hourly nowcasts with high model performance efficiency and high correlation with observations. This prototype PreMevE‐MEO model demonstrates the feasibility of making high‐fidelity predictions driven by observations from longstanding space infrastructure in MEO, thus has great potential of growing into an invaluable space weather operational warning tool.

Outer Zone Relativistic Electron Response to Mesoscale Periodic Density Structures in the Solar Wind: Van Allen Probes Measurements

AbstractWe investigate the relativistic and the ultra‐relativistic outer radiation belt electron response to the Periodic Density Structures (PDS) in the solar wind. We have studied four intervals between 0000 UT and 1500 UT during 17 January 2013 interplanetary coronal mass ejection (ICME) sheath event following the passage of an interplanetary shock (IP) on 16 January, at 2240 UT. Earlier studies limited to geosynchronous orbit have shown that PDS induce Ultra‐Low‐Frequency (ULF) oscillations in the magnetosphere and modulate energetic electron intensities. Our study shows for the first time, using pitch angle resolved electron intensity measurements, that PDS modulate relativistic and ultra‐relativistic electron intensities in the heart of the radiation belts (L ≈ 4). We find that the modulation of electron intensities occur at frequencies close to those of interplanetary PDS. Furthermore, electron intensity modulations occur over a wide range of energy (≈200 keV to 4 MeV) and pitch angles (≈20–120°). This event study suggests that relativistic and ultra‐relativistic electron intensity modulations driven by PDS may be largely energy and pitch angle independent.

Assessment of Satellite Differential Code Biases and Regional Ionospheric Modeling Using Carrier-Smoothed Code of BDS GEO and IGSO Satellites

The geostationary earth orbit (GEO) represents a distinctive geosynchronous orbit situated in the Earth’s equatorial plane, providing an excellent platform for long-term monitoring of ionospheric total electron content (TEC) at a quasi-invariant ionospheric pierce point (IPP). With GEO satellites having limited dual-frequency coverage, the inclined geosynchronous orbit (IGSO) emerges as a valuable resource for ionospheric modeling across a broad range of latitudes. This article evaluates satellite differential code biases (DCB) of BDS high-orbit satellites (GEO and IGSO) and assesses regional ionospheric modeling utilizing data from international GNSS services through a refined polynomial method. Results from a 48-day observation period show a stability of approximately 2.0 ns in BDS satellite DCBs across various frequency signals, correlating with the available GNSS stations and satellites. A comparative analysis between GEO and IGSO satellites in BDS2 and BDS3 reveals no significant systematic bias in satellite DCB estimations. Furthermore, high-orbit BDS satellites exhibit considerable potential for promptly detecting high-resolution fluctuations in vertical TECs compared to conventional geomagnetic activity indicators like Kp or Dst. This research also offers valuable insights into ionospheric responses over mid-latitude regions during the March 2024 geomagnetic storm, utilizing TEC estimates derived from BDS GEO and IGSO satellites.

Decorrelation rate and daily cycle in sub-daily time series of SAR coherence amplitude

A dataset of sub-daily C-band data, acquired with a ground-based synthetic aperture radar, has been used to study soil and vegetation dynamics during a complete growing season in a controlled agricultural test site. The data have been exploited to analyse the rate and sources of decorrelation in the scene, as well as the consequences of the observation conditions of a sub-daily satellite (with either low, medium or geosynchronous orbit): short revisit times, availability of multiple acquisitions during a single day, and shallow observations at some incidence angles. Repeat-pass coherence is found to be less affected by temporal decorrelation when the primary image is acquired during nighttime or the last hours predawn. Regarding the incidence angle, VV has increased sensitivity to certain phenological stages as the incidence angle increases. Additionally, a periodic oscillation on a sub-daily scale is observed when creating coherence time series with increasing temporal baseline. Factors which strongly contribute to these oscillations are the daily cycles of temperature, soil moisture and vegetation water dynamics.

Evaluation of fengyun geosynchronous orbit and GPM satellites precipitation products over the southeastern Tibetan plateau

ABSTRACT Based on the hourly precipitation data from the observation stations, the accuracy of hourly QPEs from Fengyun geostationary satellites FY-4A, FY-2 H and multi-satellite joint IMERG-Early precipitation products over the southeastern Tibetan Plateau were compared and assessed. And the relationship between the accuracy of various satellites and terrain were discussed. The results show that: (1) The QPEs of FY-4A, FY-2 H and IMERG-Early can reflect the temporal and spatial distribution characteristics of real precipitation; (2) The QPEs of FY-4A and FY-2 H overestimate the precipitation in the researched region, and the overestimation of FY-4A was more obvious, while IMERG-Early QPE underestimates the precipitation. IMERG-Early QPE showed the best overall accuracy performance. (3) All three satellite QPEs were less accurate in July and August. (4) The accuracy of the QPEs of FY-4A and FY −2 H were better than that of IMERG-Early QPE in heavy rainfall. (5) The accuracy of three satellite QPEs increase with the increase of altitude. The results can provide reference for selecting satellite QPEs for operational applications in the southeastern Tibetan Plateau.

Solar Heat Flux Suppression on Optical Antenna of Geosynchronous Earth Orbit Satellite-Borne Lasercom Sensor.

The objective of this article is to examine potential techniques for suppressing solar heat flow on the optical antenna of a laser communication sensor. Firstly, the characteristics of the geosynchronous Earth orbit's (GEO) space radiation environment are analysed, and a combined passive and active thermal control solution is proposed. Secondly, the temperature distribution of the lasercom sensor under extreme operating conditions is simulated utilising IDEAS-TMG (6.8 NX Series) software, which employs Monte Carlo and radiative heat transfer numerical calculation methods. Finally, a strategy for avoiding direct sunlight around midnight is proposed. The simulation results demonstrated that the thermal control solution and solar avoidance strategy proposed in this paper achieved long-term fine-stable control of the temperature field of the optical antenna, which met the thermal permissible communication hours per daily orbit cycle in excess of 14 h per day.

Reducing reentry casualty risk for spacecraft on long-term reentering eccentric inclined geosynchronous (Tundra) disposal orbits

This paper considers disposal of spacecraft and upper stages on eccentric inclined geosynchronous orbits (eccentric IGSOs), specifically the class known as Tundra orbits. The U.S. Government Orbital Debris Mitigation Standard Practices (ODMSP) released in December 2019 include a disposal option to use orbital eccentricity growth for long-term reentry within 200 years that could be used for Tundra orbits. A condition of this disposal option is that reentry casualty risk be limited. An analysis was performed to assess reentry casualty risk for a generic Tundra spacecraft and typical upper stages on Tundra disposal orbits. From propagation sweeps accounting for eccentricity growth of Tundra disposal orbits, several Tundra disposal orbit cases were selected for reentry analysis. A reentry risk analysis for these cases assuming reentry from near-circular orbits was performed. Results show that predicted casualty risk for the generic Tundra spacecraft and typical upper stages well exceed allowable risk limits in the ODMSP. An analysis of reentry from the selected Tundra disposal orbits accounting for the high eccentricity due to eccentricity growth just before reentry was then performed. Results show that the distribution of reentry points on the Earth can be concentrated over ocean in the southern hemisphere where there is less human population. The generic Tundra spacecraft and one of the upper stages considered were then found to be compliant with the limit of 1 in 10,000 expected casualties in the ODMSP. These results indicate promise for wider usage of the long-term re-entry option in the ODMSP.

Probabilistic assessment of disposal orbit lifetime for CubeSat rideshares on resonant decaying geosynchronous transfer orbits

Recent years have seen an increase in CubeSat missions on rideshares to geosynchronous orbit. The typical practice for these missions is to deploy the CubeSat on a geosynchronous transfer orbit (GTO) which results in a perigee altitude that is low enough that atmospheric drag will cause the apogee altitude to decay and eventual reentry. However, for GTOs, demonstrating compliance with limits on orbital lifetime in orbital debris mitigation guidelines is not straightforward due to a solar resonance phenomenon that exists which can cause high variability of the orbital lifetime of the satellite. This paper presents a procedure for determining the likelihood that orbital lifetime of a rideshare CubeSat on a resonant GTO will have an orbital lifetime below a 25-year and 5-year limit. The procedure uses a Monte Carlo analysis in which uncertain parameters are randomly varied, including the launch time/initial RAAN and the drag coefficient. The Aerospace precision propagation tool TRACE is used with a high-fidelity force model to enable precision integration through the atmosphere at perigee. It is shown in the study that there is a systematic variation in likelihood of staying below a 25- and 5-year orbital lifetime limit and that drag enhancement devices may be needed to meet the 5-year limit for CubeSat rideshares. The study also presents findings on a solar radiation pressure induced resonance that was observed for high area-to-mass ratios which suggests that there can be a diminishing return when increasing the area of a drag enhancement device to quicken deorbit.

A multi-satellite survey scheme for addressing open questions on the Earth’s outer radiation belt dynamics

The Earth’s outer radiation belt is highly dynamic, containing relativistic electron fluxes that can increase by several orders of magnitude during magnetospheric disturbances. This greatly increases the likelihood of spacecraft malfunction or failure and significantly influences the solar-terrestrial system’s energy and mass coupling, highlighting the importance of fully understanding the mechanisms governing these dynamics from both theoretical and practical perspectives. Although many theories have been proposed, further research is essential to quantify the specific contributions of different dynamic mechanisms for improving space weather forecasting. To address this, observations of the outer radiation belt with high spatial–temporal resolution to distinguish the spatial and temporal variations are essential. We introduce a 10-CubeSat constellation survey scheme in the geosynchronous transfer orbit (GTO) to achieve this required observation. Three baseline instruments are proposed to be employed: the high energy electron detector (HEED), the search coil wave detector (SCWD), and the magnetometer (MAG). Two groups of physical processes will be investigated: wave-particle interactions involving charged particles interacting with whistler-mode waves, electromagnetic ion cyclotron (EMIC) waves, and ultra-low frequency (ULF) waves; and radial transport encompassing shock-induced injections, substorm injections, storm convection and magnetopause shadowing. The performance parameters of instruments and platform of the constellation are presented. Additionally, aligned with the concept of constellation survey, we outline the COSPAR-coordinated space program, COnstellation of Radiation BElt Survey (CORBES), which will provide a crucial scientific contribution in the absence of the Van Allen Probes. The program’s excellent observational capability enables a comprehensive understanding of the underlying physical mechanisms governing the outer radiation belt dynamics and improved space weather forecasting.

Gravitational Radiation Induced Spiral-in Offsets the Pulsar Pair from its Final Lock-in Position- a New Metric for Relativistic Pulsar Binaries

Author has extensively studied Earth-Moon system, Phobos-Mars system, Deimos-Mars System, Charon-Pluto system and Iapetus-Saturn system and developed Kinematic Model (KM) of tidally interacting binary systems. KM predicts two Geo-synchronous orbits aG1 and aG2 in case of Earth-Moon system and two Clarke’s orbits aG1 and aG2 in case of Phobos-Mars system, Deimos-Mars System, Charon-Pluto system and Iapetus-Saturn system.

Single-Photon Interference over 8.4km Urban Atmosphere: Toward Testing Quantum Effects in Curved Spacetime with Photons.

The emergence of quantum mechanics and general relativity has transformed our understanding of the natural world significantly. However, integrating these two theories presents immense challenges, and their interplay remains untested. Recent theoretical studies suggest that the single-photon interference covering huge space can effectively probe the interface between quantum mechanics and general relativity. We developed an alternative design using unbalanced Michelson interferometers to address this and validated its feasibility over an 8.4km free-space channel. Using a high-brightness single-photon source based on quantum dots, we demonstrated single-photon interference along this long-distance baseline. We achieved a phase measurement precision of 16.2mrad, which satisfied the measurement requirements for a gravitational redshift at the geosynchronous orbit by 5 times the standard deviation. Our results confirm the feasibility of the single-photon version of the Colella-Overhauser-Werner experiment for testing the quantum effects in curved spacetime.

Centimeter-level 2D ultra-small interdigital sensor for ESD detection of spacecraft

The spacecraft in geosynchronous orbit interacts with the space plasma environment, which is prone to electrostatic discharge and affects the safe operation of the spacecraft. In order to realize simple, accurate and reliable electrostatic discharge detection in space environment, based on the energy spectrum characteristics of spacecraft electrostatic discharge electromagnetic radiation electromagnetic pulse and the electromagnetic pulse sensing principle of interdigital electrode, a centimeter-level two-dimensional planar ultra-small interdigital sensor with a size of only 4 cm × 3 cm × 0.01 cm is developed. The impedance matching circuit is established to greatly improve the transmission efficiency of electromagnetic pulse, which is 59.34 % higher than that before the matching circuit is added. Finally, a spacecraft vacuum electrostatic discharge simulation experiment platform is built to test the frequency response characteristics of the sensor. The results show that the frequency response characteristics of the electromagnetic pulse signal perceived by the sensor developed in this paper are consistent with the main frequency characteristics of the spacecraft electrostatic discharge radiation electromagnetic pulse energy spectrum, which can be used for spacecraft electrostatic discharge detection in space environment.

The Distribution of Pc5 Ultralow-frequency Waves at Geostationary Orbit

Using GOES magnetometer data spanning over 30 yr, we study the distribution of Pc5 ultralow-frequency waves at geosynchronous orbit. The CLEAN algorithm was applied to detect narrowband Pc5 waves. This method was first used in astronomical radio interferometry, but has since been applied to many other areas. The algorithm allows for identification of multiple individual peaks within the same power spectral density. We found close to 30,000 events in each magnetic field component in field-aligned coordinates. With some exceptions, results were in agreement with previous studies. Wave occurrence along magnetic local time (MLT) was higher in the 18–23 MLT sector. However, the largest accumulated wave amplitudes were observed on the dayside, peaking close to local noon. As expected, wave amplitudes were larger during more active solar wind conditions. For the radial and parallel components, amplitudes were maximum at the interplanetary magnetic field clock angle of −30° to −45°. The resultant database of Pc5 ultralow-frequency wave events can be used to constrain radiation belt models, while the CLEAN method provides a unique technique to automatically detect narrowband plasma waves in the magnetosphere and beyond.