Sun-Earth System Research Articles

An assessment of different relay network topologies to improve Earth–Mars communications

The future of deep space communications encompasses a challenging situation where the current facilities used to communicate with different spacecraft may become saturated as a result of an increasing number of missions and their complexity. From this forecast, the present study intends to provide a solution to saturation problems through strategically-located upgradable relays for Earth–Mars communications. The foremost goal of this paper is to quantitatively uncover the potential enhancements coming from relay placement in strategic orbits between Earth and Mars. Herein, two relay configurations – a.k.a. network topologies – are analyzed: the Lagrange-relays network topology and a circular, homogeneously-distributed satellite constellation, acknowledged here as pearl constellation. The first uses the Earth–Sun system Lagrange points L3, L4 and L5 as potential locations for the relays, whilst the second defines an optimized orbit between Earth and Mars with 3 or 4 relay satellites.To aid in the analysis, the authors developed an open-sourced piece of software that obtains the link availability as well as the data rate at which two nodes may communicate, taking as a reference the Deep Space Network (DSN) for Earth, and the Mars Reconnaissance Orbiter for Mars. For complex topologies with more than two communicating nodes, the software outputs the end-to-end bit rate and optimal communication route at each time step. Moreover, this product is extensible to analyze and optimize any network topology and could be adapted to be used for contact management and mission planning in the future.The results show that the network-topology proposals are an advantageous option to significantly increase the link availability of Earth–Mars communications. Nevertheless, the Direct-To-Earth (DTE) link always outperforms the multi-hop path due to the limited telecommunication system’s capabilities of both the spacecraft and the relays. As a result of this, the study includes an analysis on the requirements of the relay’s design in order to make the constellation a beneficial and comparable alternative to the DTE link. This way, the proposed network topologies become a suitable option whom to share with the DSN communications workload, providing enhanced bit rates and data volumes as well as higher availability of the communication.

The behavior of a satellite trajectory near the equilibrium points of sun-earth system and its control

In this paper, the behavior of a satellite trajectory near the equilibrium points of the Sun-Earth system is studied. The equations describing the motion of the satellite in the circular restricted three body problem for the Sun-Earth system, are discussed for their ordinary differential equations form, and Lagrange points are determined. Then, the stability is studied at each Lagrange point. The trajectories of a satellite starting its motion near Lagrange points are illustrated, showing the stability and instability behavior. Finally, the unstable trajectory is controlled by using ??2-method at ??1 as an example.

Algorithm theoretical basis for ozone and sulfur dioxide retrievals from DSCOVR EPIC

Abstract. On board the Deep Space Climate Observatory (DSCOVR), the first Earth-observing satellite at the L1 point (the first Lagrangian point in the Earth–Sun system), the Earth Polychromatic Imaging Camera (EPIC) continuously observes the entire sunlit face of the Earth. EPIC measures the solar backscattered and reflected radiances in 10 discrete spectral channels, four of which are in the ultraviolet (UV) range. These UV bands are selected primarily for total ozone (O3) and aerosol retrievals based on heritage algorithms developed for the series of Total Ozone Mapping Spectrometers (TOMS). These UV measurements also provide sensitive detection of sulfur dioxide (SO2) and volcanic ash, both of which may be episodically injected into the atmosphere during explosive volcanic eruptions. This paper presents the theoretical basis and mathematical procedures for the direct vertical column fitting (DVCF) algorithm used for retrieving total vertical columns of O3 and SO2 from DSCOVR EPIC. This paper describes algorithm advances, including an improved O3 profile representation that enables profile adjustments from multiple spectral measurements and the spatial optimal estimation (SOE) scheme that reduces O3 artifacts resulting from EPIC's band-to-band misregistrations. Furthermore, this paper discusses detailed error analyses and presents intercomparisons with correlative data to validate O3 and SO2 retrievals from EPIC.

Magnetic Signatures of Large-Scale Electric Currents in the Earth’s Environment at Middle and Low Latitudes

The purpose of space weather is the systemic study of the Sun–Earth system, in order to determine the impact of solar events on the electromagnetic environment of the Earth. This article proposes a new transdisciplinary approach of the Sun–Earth system based on the universal physical process of the dynamo. The dynamo process is based on two important parameters of the different plasmas of the Sun–Earth system, the motion and the magnetic field. There are four permanent dynamos in the Sun–Earth system: the solar dynamo, the Earth dynamo, the solar wind-magnetosphere dynamo, and the ionospheric dynamo. These four permanent dynamos are part of different scientific disciplines. This transdisciplinary approach links all of these dynamos in order to understand the variations in the Earth’s magnetic field. During a magnetic disturbed period, other dynamos exist. We focused on the ionospheric disturbed dynamo generated by Joule energy dissipated in the high latitude ionosphere during magnetic storms. Joule heating disrupts the circulation of thermospheric winds and in turn generates disturbances in the Earth’s magnetic field. This systemic approach makes it possible to understand magnetic disturbances previously not well understood.

Design of the On-Board Data Compression for the Bolometer Data of LiteBIRD

LiteBIRD is a space-borne experiment dedicated to detecting large-scale $B$-mode anisotropies in the linear polarization of the Cosmic Microwave Background (CMB) predicted by the theory of inflation. It is planned to be launched in the late 2020s to the second Lagrange point (L2) of the Sun-Earth system. LiteBIRD will map the sky in 15 frequency bands. In comparison to $\it{Planck}$ HFI, the previous low-temperature bolometer-based satellite for CMB observations, the number of detector has increased by two orders of magnitude, up to $\sim$5000 detectors in total. The data rate is 19 Hz from each detector. The bandpass to the ground is limited to 10 Mbps using the X-band for a few hours per day. These require the data to be compressed by more than 50 %. The exact value depends on how much information entropy is contained in the real data. We have thus evaluated the compression by simulating the time-ordered data of polarization sensitive bolometers. The foreground emission, detector noise, cosmic ray glitches, leakage from the CMB intensity to polarization, etc. are simulated. We investigated several algorithms and demonstrated that the required compression ratio can be achieved by some of them. We describe the details of this evaluation and propose algorithms that can be employed in the on-board digital electronics of LiteBIRD.

A Synergic Strategy to Characterize the Habitability Conditions of Exoplanets Hosted by Solar-Type Stars

We present a new synergic strategy that merges the potential of asteroseismology with solar space weather/climate techniques in order to characterize solar-like stars and their interaction with hosted exoplanets. The method is based on the use of seismic data obtained by the space missions Kepler/K2 and TESS Transiting Exoplanet Survey Satellite, coupled with stellar activity estimates deduced from ground-based campaigns (e.g., Mount Wilson Observatory HK Project). Our investigation allows us to determine not only highly accurate fundamental parameters of the mother star and its orbiting planet, but also to study the stellar magnetic activity and the star-planet interaction: in analogy to the Sun-Earth system, it is possible to infer the mean stellar wind acting on the exoplanet in order to define the conditions of the exoplanetary environment and the erosion of its atmosphere with an impact on the habitability of the planet.

Stability Analysis of Earth Co-orbital Objects

In this paper, we investigate the stability of Earth co-orbital objects (ECOs) based on the torus structure. The Hamiltonian value is an index to evaluate co-orbital stability. According to topological characters of tadpole (TP), horseshoe (HS), quasi-satellite (QS), and critical compound surfaces in the torus space, the co-orbital area is divided into several regions in detail. We select 221 potential ECOs as representative samples. Numerical integration in the Sun–Earth system illustrates that most of objects above the collision line are short- or long-term stable ECOs in the QS–HS and QS–TP motions, and most of objects in the unstable region are unstable ones, which is in agreement with our semi-analytical conclusions. The stability of an ECO with a larger Hamiltonian value could be stronger. An efficient method to determine the long-term co-orbital stability of a potential ECO is proposed without long-term numerical integration. Numerical integration in the multiplanet model demonstrates that our stability analysis is still applicable for the real solar system. As an application of our stability analysis, two well-determined QS–HS ECOs above the collision line are identified and analyzed for the first time. For instance, the QS–HS state of 2019 VL5 can be sustained for more than 3000 yr, and its current HS state will be sustained for at least 800 yr.

Semantics of visual models in space research

Objectives. The aim of the study is to develop a methodology for assessing the semantics of weakly structured or morphologically complex visual information models. In order to achieve the goal, a criterion for classifying visual models as complex and an algorithm for obtaining a gradient image with several levels of density were introduced. The gradient image is not binary, thus increasing the reliability of finding boundaries or contours. An auxiliary structural visual model was introduced, and a series of images of different densities was used in processing. Next, the concept of a conditional image coordinate system was introduced. This allows for information to be transferred from different visual models to a synthetic resulting visual model.Methods. Using gradient image processing and constructing a new intermediate structural model allows models with different densities to be linked. A system of conditional image coordinates was introduced and a series of models with different densities to obtain a synthetic image was processed.Results. The visual models obtained from satellite images with poor visibility of objects were processed in the Sun– Earth–Moon system. The Sun–Earth system was chosen as the basis. A characteristic of space images is the fact that the bright light of the Sun “clogs” the images of other objects with large phase angles. The use of the contouring technique allows for the visibility of images of low brightness and high brightness to be equalised. The shift of the frequency response after detection of all objects enabled the formation of a clear visual model.Conclusions. In primary visual models, low brightness images were not visible. They appeared when exposure was increased, while high-density objects merged into one. Because of this, it is fundamentally impossible to obtain a high-quality image of all objects, or the complete semantics of a visual model from a single high, medium, or lowdensity image. In order to obtain the complete semantics of the visual model, a series of images need to be processed with the transfer of images to a common synthetic image. The proposed technique allowed for such problems to be resolved. A comparison of the results obtained using the methods of processing a single image proved the reliability and high information content of the method.

Local time dependence of earthquakes occurrence and its possible connection with geomagnetic diurnal variations

ABSTRACT Occurrence of earthquakes is not only controlled by internal processes such as the tectonic processes, but also by external ones as Sun-Earth system processes. The aim of the current study is to examine the distribution of earthquakes occurrence at some active seismic regions in order to determine the dominant period of earthquakes occurrence with respect to local time and its possible connection with geomagnetic diurnal variations. Analyzing long-term datasets from 1986 to 2020 demonstrated that the occurrence of earthquakes at the studied regions is strongly depending on local time where earthquakes tend to occur more often during noon local time. This behavior is in somehow similar to the pattern of geomagnetic diurnal variations. Therefore, the study was extended to investigate the probable correlation between both of them. Diurnal variation of North-South geomagnetic component (X-component) was examined and compared with the local time distribution of earthquakes at each region. Data analysis revealed a significant correlation between the geomagnetic diurnal variations and earthquakes occurrence. Thus, the results support the idea of existence a dominating time interval of earthquakes occurrence and also a relationship between local time dependence of earthquakes and geomagnetic diurnal variations that may help in earthquakes prediction in the future.

High-resolution imaging of a black hole shadow with Millimetron orbit around lagrange point l2

ABSTRACT Imaging of the shadow around supermassive black hole (SMBH) horizon with a very long baseline interferometry (VLBI) is recognised recently as a powerful tool for experimental testing of Einstein’s General relativity. The Event Horizon Telescope (EHT) has demonstrated that an Earth-extended VLBI with the maximum long base (D = 10 700 km) can provide a sufficient angular resolution θ ∼ 20 μas at λ = 1.3 mm (ν = 230 GHz) for imaging the shadow around SMBH located in the galaxy M87*. However, the accuracy of critically important characteristics, such as the asymmetry of the crescent-shaped bright structure around the shadow and the sharpness of a transition zone between the shadow floor and the bright crescent silhouette, both of order Δθ ∼ 4 μas, is still to be improved. In our previous paper, we have shown that Space-Earth VLBI observation within a joint Millimetron and EHT configuration at the near-Earth high elliptical orbit can considerably improve the image quality. Even more solid grounds for firm experimental validation of General relativity can be obtained with a higher resolution available within the joint Millimetron and EHT program at the Lagrangian point L2 in the Sun-Earth system with an expected imaging resolution at 230 GHz of Δθ ∼ 5 μas. In this paper, we argue that in spite of limitations of L2 orbit, an adequate sparse (u, v) coverage can be achieved and the imaging of the shadows around Sgr A* and M87* can be performed with a reasonable quality.

Halo Orbit Maintenance around L1 Point of the Sun-Earth System Using Optimal Control and Lyapunov Stability Theory

AbstractThis paper addresses the maintenance of a halo orbit around the L1 point of the Sun-Earth system in a circular restricted three-body problem. To this effect, a trajectory tracking problem i...

Predictability of variable solar–terrestrial coupling

Abstract. In October 2017, the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) Bureau established a committee for the design of SCOSTEP's Next Scientific Programme (NSP). The NSP committee members and authors of this paper decided from the very beginning of their deliberations that the predictability of the Sun–Earth System from a few hours to centuries is a timely scientific topic, combining the interests of different topical communities in a relevant way. Accordingly, the NSP was christened PRESTO – PREdictability of the variable Solar–Terrestrial cOupling. This paper presents a detailed account of PRESTO; we show the key milestones of the PRESTO roadmap for the next 5 years, review the current state of the art and discuss future studies required for the most effective development of solar–terrestrial physics.

SRG X-ray orbital observatory

The orbital observatory Spectrum-Roentgen-Gamma (SRG), equipped with the grazing-incidence X-ray telescopes Mikhail Pavlinsky ART-XC and eROSITA, was launched by Roscosmos to the Lagrange L2 point of the Sun–Earth system on July 13, 2019. The launch was carried out from the Baikonur Cosmodrome by a Proton-M rocket with a DM-03 upper stage. The German telescope eROSITA was installed on SRG under an agreement between Roskosmos and the DLR, the German Aerospace Agency. In December 2019, SRG started to perform its main scientific task: scanning the celestial sphere to obtain X-ray maps of the entire sky in several energy ranges (from 0.2 to 8 keV with eROSITA, and from 4 to 30 keV with ART-XC). By mid-June 2021, the third six-month all-sky survey had been completed. Over a period of four years, it is planned to obtain eight independent maps of the entire sky in each of the energy ranges. The sum of these maps will provide high sensitivity and reveal more than three million quasars and over one hundred thousand massive galaxy clusters and galaxy groups. The availability of eight sky maps will enable monitoring of long-term variability (every six months) of a huge number of extragalactic and Galactic X-ray sources, including hundreds of thousands of stars with hot coronae. In addition, the rotation of the satellite around the axis directed toward the Sun with a period of four hours enables tracking the faster variability of bright X-ray sources during one day every half year. The chosen strategy of scanning the sky leads to the formation of deep survey zones near both ecliptic poles. The paper presents sky maps obtained by the telescopes on board SRG during the first survey of the entire sky and a number of results of deep observations performed during the flight to the L2 point in the frame of the performance verification program, demonstrating the capabilities of the observatory in imaging, spectroscopy, and timing of X-ray sources. It is planned that in December 2023, the observatory will for at least two years switch to observations of the most interesting sources in the sky in triaxial orientation mode and deep scanning of selected celestial fields with an area of up to 150 square degrees. These modes of operation were tested during the performance verification phase. Every day, data from the SRG observatory are dumped onto the largest antennas of the Russian Deep Space Network in Bear Lakes and near Ussuriysk.

The Second Earth Trojan 2020 XL5

Abstract The Earth Trojans are coorbitals librating around the Lagrange points L 4 or L 5 of the Sun–Earth system. Although many numerical studies suggest that they can maintain their dynamical status and be stable on timescales up to a few tens of thousands of years or even longer, they remain an elusive population. Thus far only one transient member (2010 TK7) has been discovered serendipitously. Here, we present a dynamical study of asteroid 2020 XL5. With our meticulous follow-up astrometric observations of the object, we confirmed that it is a new Earth Trojan. However, its eccentric orbit brings it close encounters with Venus on a frequent basis. Based on our N-body integration, we found that the asteroid was captured into the current Earth Trojan status in the fifteenth century, and then it has a likelihood of 99.5% to leave the L 4 region within the next ∼10 kyr. Therefore, it is most likely that 2020 XL5 is dynamically unstable over this timescale.

Dynamical Evolution of an Active-region Filament Driven by Magnetic Reconnection

Abstract Studying solar filament dynamical evolutions is an important approach to reveal the driving mechanism of solar eruptions, which seriously impact on the Sun–Earth system and could cause disastrous space weather. To better understand the evolution process of solar filaments, here we investigate an active-region filament by employing observations from the New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory, and Interface Region Imaging Spectrograph. The high-resolution NVST Hα images show that the northern footpoint of the filament gradually moved northward. Near the northern footpoint, there is an arch filament system (AFS). Between adjacent footpoints of the filament and the AFS, transient brightening, underlying magnetic cancellation, and bidirectional flows were detected, which jointly imply that it could be the magnetic reconnection between the filament and the AFS that changes the connection of filament threads and drives its footpoint to move northward. In addition, during the footpoint evolution, the filament with highly twisted structure underwent several untwisting motions. Meanwhile, transient brightenings were also observed and appeared as bright knots around several positions where filament threads might braid with each other. And some bright blobs were also detected to propagate outward from the brightening region. These observations suggest that magnetic reconnection might be responsible for the untwisting motion. This work exposes us to a dynamical scenario of the filament evolution driven by magnetic reconnection, which will promote our understanding of the formation and eruption of the filaments.

Predicting the CME arrival time based on the recommendation algorithm

CME is one of the important events in the sun-earth system as it can induce geomagnetic disturbance and an associated space environment effect. It is of special significance to predict whether CME will reach the Earth and when it will arrive. In this paper, we firstly built a new multiple association list for 215 different events with 18 characteristics including CME features, eruption region coordinates and solar wind parameters. Based on the CME list, we designed a novel model based on the principle of the recommendation algorithm to predict the arrival time of CMEs. According to the two commonly used calculation methods in the recommendation system, cosine distance and Euclidean distance, a controlled trial was carried out respectively. Every feature has been found to have its own appropriate weight. The error analysis indicates the result using the Euclidean distance similarity is much better than that using cosine distance similarity. The mean absolute error and root mean square error of test data in the Euclidean distance are 11.78 and 13.77 h, close to the average level of other CME models issued in the CME scoreboard, which verifies the effectiveness of the recommendation algorithm. This work gives a new endeavor using the recommendation algorithm, and is expected to induce other applications in space weather prediction.

Analysis of nominal halo orbits in the Sun–Earth system

Analysis of nominal halo orbits in the Sun–Earth system

Strategies to capture asteroids to distant retrograde orbits in the Sun–Earth system

Capturing near-Earth asteroids would be of great significance for future space missions. Due to its stability, distant retrograde orbit (DRO) around the Earth has the potential to be an ideal destination for the captured asteroids. In this paper, we propose three strategies to capture asteroids to DROs in the model of the circular restricted three-body problem in the Sun–Earth system. In the manifold-assisted strategy, Lyapunov orbits that are tangential to DROs are calculated, and then stable manifolds are employed to design transfers for capturing asteroids. The non-coplanar Hohmann transfer is used to guess the total cost of capturing an asteroid, and candidate asteroids are thus selected. The second strategy of asteroid capture is defined as direct capture to increase opportunities of capturing asteroids with low cost. The captured asteroid can be inserted into the target DRO with a maneuver at any position along the DRO. Then optimal results are obtained after analyzing the capture conditions. Finally, a strategy of using a flyby of the Earth is proposed as the power Earth-flyby capture, and an additional maneuver is imposed on an asteroid at the perigee of the transfer trajectory. Results show that the direct and powered Earth-flyby asteroid capture strategies potentially need fewer velocity increments than the manifold-assist strategy. Furthermore, 2020SO can be captured into DROs with lower energy than the other candidate asteroids in three capture strategies, and the minimum cost is approximately 189.93 m/s.

Transmission Spectroscopy of the Earth–Sun System to Inform the Search for Extrasolar Life

Abstract Upcoming NASA astrophysics missions such as the James Webb Space Telescope will search for signs of life on planets transiting nearby stars. Doing so will require coadding dozens of transmission spectra to build up sufficient signal to noise while simultaneously accounting for challenging systematic effects such as surface/weather variability, atmospheric refraction, and stellar activity. To determine the magnitude and impacts of both stellar and planet variability on measured transmission spectra, we must assess the feasibility of stacking multiple transmission spectra of exo-Earths around their host stars. Using our own solar system, we can determine if current methodologies are sufficient to detect signs of life in Earth’s atmosphere and measure the abundance of habitability indicators, such as H2O and CO2, and biosignature pairs, such as O2 and CH4. We assess the impact on transmission spectra of Earth transiting across the Sun from solar and planetary variability and identify remaining unknowns for understanding exoplanet transmission spectra. We conclude that a satellite observing Earth transits across the Sun from beyond L2 is necessary to address these long-standing concerns about the reliability of coadding planet spectra at UV, optical, and infrared wavelengths from multiple transits in the face of relatively large astrophysical systematics.

Enhanced simulations on the Athena/Wide Field Imager instrumental background

The Wide Field Imager (WFI) is one of two focal plane instruments of the Advanced Telescope for High-Energy Astrophysics (Athena), ESA’s next large x-ray observatory, planned for launch in the early 2030s. The current baseline halo orbit is around L2, and the second Lagrangian point of the Sun-Earth system L1 is under consideration. For both potential halo orbits, the radiation environment, solar and cosmic protons, electrons, and He-ions will affect the performance of the instruments. A further critical contribution to the instrument background arises from the unfocused cosmic hard x-ray background. It is important to understand and estimate the expected instrumental background and to investigate measures, such as design modifications or analysis methods, which could improve the expected background level to achieve the challenging scientific requirement (<5 × 10 − 3 counts / cm2 / keV / s at 2 to 7 keV). Previous WFI background simulations done in Geant4 have been improved by taking into account new information about the proton flux at L2. In addition, the simulation model of the WFI instrument and its surroundings employed in Geant4 simulations has been refined to follow the technological development of the WFI camera.