LEO Satellite Research Articles

Machine Learning-Based Resource Allocation in Satellite Networks Supporting Internet of Remote Things

Satellite networks have been regarded as a promising architecture for supporting the Internet of remote things (IoRT) due to their advantages of wide coverage and high communication capacity in remote areas, which further promotes the development of the satellites for IoRT networks (SIoRTNs). The effectiveness of multi-dimensional resource collaboration has significant impacts on the IoRT data downloading performance. However, the environment ’ s dynamics, e.g., channel conditions and solar infeed process, are unknown in practical scenarios, which poses daunting challenges in making efficient utilization of multi-dimensional resources. Motivated by this fact, we model the joint resource scheduling and IoRT data scheduling problem with the aim of maximizing the amount of the IoRT data of the overall network by applying the model-free reinforcement learning framework. To overcome the limitations of traditional reinforcement learning algorithms, we propose several feature functions by investigating the natural attributes of the multi-dimensional resources of the SIoRTNs, and further exploit the concept of function approximation to approximate the expected downloaded IoRT data given the network state. Furthermore, we propose a state-action-reward-state-action (SARSA) based actor-critic reinforcement learning (SACRL) resource allocation strategy to achieve the optimal resource allocation and IoRT data scheduling with casual information at LEO satellites. Simulations validate the convergence property and the effectiveness of the proposed SACRL algorithm in terms of the amount of the downloaded IoRT data. Particularly, we investigate the impact of typical network parameters on network performance to further provide guidance for future SIoRTN system design.

Retrieval of Raindrop Size Distribution Using Dual-Polarized Microwave Signals from LEO Satellites: A Feasibility Study through Simulations.

In this paper, a novel approach for raindrop size distribution retrieval using dual-polarized microwave signals from low Earth orbit satellites is proposed. The feasibility of this approach is studied through modelling and simulating the retrieval system which includes multiple ground receivers equipped with signal-to-noise ratio estimators and a low Earth orbit satellite communicating with the receivers using both vertically and horizontally polarized signals. Our analysis suggests that the dual-polarized links offer the opportunity to estimate two independent raindrop size distribution parameters. To achieve that, the vertical and horizontal polarization attenuations need to be measured at low elevation angles where the difference between them is more distinct. Two synthetic rain fields are generated to test the performance of the retrieval. Simulation results suggest that the specific attenuations for both link types can be retrieved through a least-squares algorithm. They also confirm that the specific attenuation ratio of vertically to horizontally polarized signals can be used to retrieve the slope and intercept parameters of raindrop size distribution.

Lagrange Point Missions: The Key to next Generation Integrated Earth Observations. DSCOVR Innovation

A new perspective for studying Earth processes has been soundly demonstrated by the Deep Space Climate Observatory (DSCOVR) mission. For the past 6 years, the first Earth-observing satellite orbiting at the Lagrange 1 (L1) point, the DSCOVR satellite has been viewing the planet in a fundamentally different way compared to all other satellites. It is providing unique simultaneous observations of nearly the entire sunlit face of the Earth at a relatively high temporal resolution. This capability enables detailed coverage of evolving atmospheric and surface systems over meso- and large-scale domains, both individually and as a whole, from sunrise to sunset, under continuously changing illumination and viewing conditions. DSCOVR’s view also contains polar regions that are only partially seen from geostationary satellites (GEOs). To exploit this unique perspective, DSCOVR instruments provide multispectral imagery and measurements of the Earth’s reflected and emitted radiances from 0.2 to 100 µm. Data from these sensors have been and continue to be utilized for a great variety of research involving retrievals of atmospheric composition, aerosols, clouds, ocean, and vegetation properties; estimates of surface radiation and the top-of-atmosphere radiation budget; and determining exoplanet signatures. DSCOVR’s synoptic and high temporal resolution data encompass the areas observed during the day from low Earth orbiting satellites (LEOs) and GEOs along with occasional views of the Moon. Because the LEO and GEO measurements can be easily matched with simultaneous DSCOVR data, multiangle, multispectral datasets can be developed by integrating DSCOVR, LEO, and GEO data along with surface and airborne observations, when available. Such datasets can open the door for global application of algorithms heretofore limited to specific LEO satellites and development of new scientific tools for Earth sciences. The utility of the integrated datasets relies on accurate intercalibration of the observations, a process that can be facilitated by the DSCOVR views of the Moon, which serves as a stable reference. Because of their full-disc views, observatories at one or more Lagrange points can play a key role in next-generation integrated Earth observing systems.

Inter-satellite load balancing routing algorithm for LEO satellite constellation based on regional-traffic-detour

Inter-satellite load balancing routing algorithm for LEO satellite constellation based on regional-traffic-detour

The new generation of attitude determination sensor for LEO satellite based on Induced electric field

Abstract For carrying out their missions, many satellites use closed-loop attitude control. For closing the control loop, they use several sensors, such as sun sensors, magnetometer, and star tracker. Sun sensors are not operational during the eclipse; therefore, one of the observed vectors is lost. For this reason, attitude determination in eclipse can be a challenging issue for control engineers. This paper presents a novel idea for producing a new generation of sensors that can measure the induced electric field vector not only in eclipse but also in the whole orbit. This electric field comes from the high velocity of the spacecraft in the magnetic field of the Earth. This vector is always perpendicular to the magnetic field; thus, it is never aligned with the magnetic vector and never causes singularity and accuracy decreasing. The induced electric field is measured by three RC circuits that are actuated by sinusoidal voltage. The dielectrics of the capacitors are made of ferroelectric materials; therefore, the induced voltage affects the permittivity and voltage of the capacitor. By measuring and calibrating this effect in three perpendicular axes can measure the three components of the electric field vector. The theory of the proposed sensor has been developed, and simulation studies validate the results.

The future of data communication in Aviation 4.0 environment

Currently experienced the dawn of the Aviation 4.0 era is transforming the contemporary technological environment, throughout the whole aeronautical industry, by creating cyber-physical systems. Following the evolutionary path, incorporating advanced automated and first autonomy systems, the applications involved are becoming increasingly data- oriented. The need for progressive data analytics, massive adoption and operation of IoT devices, delivering advanced monitoring and machine learning opportunities, building the core structure for artificial intelligence, will put a significant pressure on data communication and connectivity itself. In the near future, the problems may especially arise in datalink used in civil aviation. This research paper briefly studies the contemporary systems used for datalink, determines dominant aspects of Aviation 4.0 and their overall impact on the performance requirements of the data communications network, and proposes the possible solution to the problematics, with newly emerging LEO satellite mega-constellations providing Internet connectivity. The conclusion of this paper highlights the requirements for future data communication systems and determines whether the existing and proposed datalink subnetwork technologies are capable of meeting the demands established by Aviation 4.0.

Vehicle detection base on Road Segmentation for surveillance satellites video

With the development of data acquisition ability, the LEO satellites can work with a surveillance camera on board by focusing a particular area for dozens of seconds, so it drives us to develop some applications based on this data. In this paper, a data preparation method named DERS (Density Estimation based Road Segmentation) is proposed to divide the road from background to reduce the worse impact from relative-motion and then improve the precession and recall for vehicles for surveillance satellite video sequence. DERS has three main steps: frame difference, morphology, pyramid iteration, segmentation. Our experiments with the satellite videos from SkySat-1, and compared between Gaussian Mixture Model (GMM) and GMM with Ders shows that the precision rate and recall has improved of the traditional method with Ders, the precision of GMM with Ders has been improved from 64.42% to 88.71, the recall of GMM with Ders is from 76.21% to 74.16%, and the F-Score has been improved from 69.82% to 80.79%.

A satellite-based quantum key distribution using decoy-state protocol

An ideal QKD implementation that provides the promising unconditional security using single photon laser source is not practically easy, also sending these photons over a fiber channel affects the maximum distance of link up to few hundreds of kilometers because of the receiver’s detectors losses. Therefore, the achievement of a global quantum network is not easy, and the need to use LEO satellites [1,2] for establishing quantum links makes the job easier as quantum free space link provides much less losses to the link than fiber links. Nowadays, a quantum communication link can be established by satellites through free space. in this paper, we propose an implementation [3] of a satellite-based quantum key distribution using decoy-state protocol [4], we then compare this protocol with the BB-84 protocol [3] against security and the key length of the generated shared key.

An efficient link-building strategy for cross seam in LEO satellite network

An efficient link-building strategy for cross seam in LEO satellite network

Modular Impulsive Green Monopropellant Propulsion System (MIMPS-G): For CubeSats in LEO and to the Moon

Green propellants are currently considered as enabling technology that is revolutionizing the development of high-performance space propulsion, especially for small-sized spacecraft. Modern space missions, either in LEO or interplanetary, require relatively high-thrust and impulsive capabilities to provide better control on the spacecraft, and to overcome the growing challenges, particularly related to overcrowded LEOs, and to modern space application orbital maneuver requirements. Green monopropellants are gaining momentum in the design and development of small and modular liquid propulsion systems, especially for CubeSats, due to their favorable thermophysical properties and relatively high performance when compared to gaseous propellants, and perhaps simpler management when compared to bipropellants. Accordingly, a novel high-thrust modular impulsive green monopropellant propulsion system with a micro electric pump feed cycle is proposed. MIMPS-G500mN is designed to be capable of delivering 0.5 N thrust and offers theoretical total impulse Itot from 850 to 1350 N s per 1U and >3000 N s per 2U depending on the burnt monopropellant, which makes it a candidate for various LEO satellites as well as future Moon missions. Green monopropellant ASCENT (formerly AF-M315E), as well as HAN and ADN-based alternatives (i.e., HNP225 and LMP-103S) were proposed in the preliminary design and system analysis. The article will present state-of-the-art green monopropellants in the (EIL) Energetic Ionic Liquid class and a trade-off study for proposed propellants. System analysis and design of MIMPS-G500mN will be discussed in detail, and the article will conclude with a market survey on small satellites green monopropellant propulsion systems and commercial off-the-shelf thrusters.

A multi-constraint optimal routing algorithm in LEO satellite networks

A multi-constraint optimal routing algorithm in LEO satellite networks

Assessment of Total Attenuation and Adaptive Scheme for Quality of Service Enhancement in Tropical Weather for Satellite Networks and 5G Applications in Nigeria

The dynamic weather condition is a major concern for optimum channel utilization in recent times, especially at higher frequencies with larger bandwidth for 5G applications. Over the years, rain-induced attenuation among the hydrometeors has been linked as the major cause of signal impairment especially at the frequency, f ≥ 10 GHz. However, when f > 18 GHz, the significant impact of other hydrometeors; cloud/fog, and scintillation increases tremendously, especially for Low Earth Orbit, LEO satellites. LEO satellites find applications in fibre optics technology, scientific research, remote sensing, surveillance, meteorology, satellite imaging, and other applications. In this paper, the assessment of combined impairments based on 5-year (2012-2016) data has been carried out and a dynamic adaptive intelligent scheme (DAIS) has been adopted to achieve a good quality of service along the satellite channels operating at Ku-V band frequencies over five stations representing different climatic regions in Nigeria namely: Port Harcourt (PH), Akure, Ilorin, Zaria, and Kano. The proposed DAIS based on fuzzy logic was able to achieve a significant reduction in the transmitting power by about 70% and SNR by 50% across the frequencies considered without altering the information content of the downlink parameters, thereby improving the QoS significantly and adhere to Customer Service Level Agreements (CSLAs) irrespective of the weather dynamics. The overall results show that the adaptive intelligent techniques can effectively fix signal links under the dynamic weather conditions for both satellite and wireless networks in this region. Information from the results is timely because it will serve as the bedrock for the newly launched transformation to the digital video broadcasting (DVB) system in Nigeria for effective service delivery.

Design of a high-stability heterogeneous clock system for small satellites in LEO

We describe our investigation into the performance of low-power heterogeneous timing systems for small satellites, using real GPS observables from the GRACE Follow-On mission. Small satellites have become capable platforms for a wide range of commercial, scientific and defense missions, but they are still unable to meet the needs of missions that require precise timing, on the order of a few nanoseconds. Improved low-power onboard clocks would make small satellites a viable option for even more missions, enabling radio aperture interferometry, improved radio occultation measurements, high altitude GPS navigation, and GPS augmentation missions, among others. One approach for providing improved small satellite timekeeping is to combine a heterogeneous group of oscillators, each of which provides the best stability over a different time frame. A hardware architecture that uses a single-crystal oscillator, one or more Chip Scale Atomic Clocks (CSACs) and the reference time from a GPS receiver is presented. The clocks each contribute stability over a subset of timeframes, resulting in excellent overall system stability for timeframes ranging from less than a second to several days. A Kalman filter is used to estimate the long-term errors of the CSACs based on the CSAC-GPS time difference, and the improved CSAC time is used to discipline the crystal oscillator, which provides the high-stability reference clock for the small satellite. Simulations using GRACE-FO observations show time error standard deviations for the system range from 2.3 ns down to 1.3 ns for the clock system, depending on how many CSACs are used. The results provide insight into the timing performance which could be achieved on small LEO spacecraft by a low power timing system.

A novel adaptive code block group hybrid automatic repeat request scheme for low earth orbit satellite networks

SummaryLow earth orbit (LEO) satellite networks provide important support to expand 5G‐and‐beyond networks to realize global coverage. Hybrid automatic repeat requests (HARQs) can greatly improve the reliability of transmission through dynamic satellite channels. Due to the large propagation delay in LEO satellite channels, the biggest challenges of HARQ in satellite networks are the delayed channel state information (CSI) and overflow of receiver memory. In this paper, we propose a novel adaptive code block group HARQ (ACBG‐HARQ) scheme that achieves lower retransmission rates with reliable data receiving. First, we build a new channel state model (CSM) to describe the relationship between the packet error rate (PER) and global channel degradation. Three states of receiver memory allocation for HARQ are designed with respect to the channel state and memory occupation: idle state, non‐full state, and full state. Then, we propose an optimal HARQ scheme for LEO satellite networks with the Markov decision process (MDP) based on the fuzzy Q‐learning (FQL) algorithm to improve the accuracy of ACBG‐HARQ state transfer, which contributes to adaptive selection of the HARQ code block group size. Simulation results show that the ACBG‐HARQ scheme can achieve a maximum spectrum efficiency gain of 10% and that the probability of receiver memory overflow is reduced by 1%∼6%.

Downlink aware data scheduling with delay guarantees in resource-limited leo satellite networks

In recent years, data scheduling in satellite networks has drawn much attention. The nodes in the satellite network change dynamically, and there is no continuous connectivity between nodes. Due to the intermittent connection between satellites, data transmission is based on a storage-carry-forward mode. In such a network, it will inevitably result in transmission delay. It is challenging to schedule a large amount of observation data with delay guarantees in resource-limited satellite networks. In this paper, we propose a downlink aware data scheduling algorithm based on a decomposition strategy of rolling horizon mechanism. The data flows with deadlines are allocated to ground stations orderly through feasible routes during each sliding horizon. Considering the issues of time-varying node centrality and downlink capacity, a link metric is provided to solve the problem of downlink contact conflict. Then a heuristic routing algorithm is exploited to design inter-satellite link contact. Further simulation results demonstrate the effectiveness of the proposed algorithms in network profit improvement while ensuring the transmission delay demand.

Passive magnetic detumbling to enable Active Debris Removal of non-operational satellites in Low Earth Orbit

Under the umbrella of the Clean Space Initiative, ESA has promoted activities in the area of Active Debris Removal (ADR). One of the main challenges driving the complexity of the rendezvous and capture of debris is its tumbling motion. It is highly desirable that kinetic energy dissipation devices damp the angular rates of debris in advance. Unfortunately, Eddy currents in conductive structures only provide a very slow detumbling. A potentially faster solution proposed by ESA (patent pending Ref EP19182205) consists in short-circuiting the satellite Magnetic Torquers already on board LEO satellites. The tumbling motion of the satellite within the Earth magnetic field results in the induction of currents in the Magnetic Torquers coils, dissipating energy by Joule heating. With a spin rate around 1 rpm, the Gravity Gradient torques create a slow precession of the satellite angular momentum around the orbit normal while the magnetic torques generated by a potential satellite residual dipole command a perpendicular precession around the North Pole. In parallel, the short-circuited Magnetic Torquers create damping and tilting magnetic torques. The spin axis re-orientation and the reduction of the angular rates are analytically predicted. A reduced set of driving parameters (debris inertias, altitude, spin axis orientation, and Magnetic Torquers characteristics) are identified that estimate the detumbling durations. ESA aims to further study and implement this concept with industry during the procurement phase of the new Copernicus Expansion Sentinels kicked off in autumn 2020, with first launches in 2025. The increased definition of the six satellites will permit to consider the positive contribution of Eddy currents in the metallic structures as well as the detrimental impact of the Solar Radiation pressure on tumbling Solar Arrays.

The influence of LEO satellite Doppler effect on LoRa modulation and its solutio

In order to explore the adaptability of LoRa technology in low Earth orbit satellite communications, this paper studies the influence of the Doppler effect on LoRa modulation in satellite-to-Earth radio channel, and finds that the larger the LoRa modulation spreading factor, the more vulnerable to the Doppler-Rate. The LoRa technology did not estimate and compensate the Doppler-Rate when it was designed. Therefore, this paper proposes a Doppler-Rate estimation algorithm that can better adapt the LoRa technology to low Earth orbit satellite communications.

A Joint Optimization Scheme for Hybrid MAC Layer in LEO Satellite Supported IoT

The Internet of Things (IoT) aims to interconnect and converge the physical world and cyberspace. It represents the future of networking, and leads the wave of the third industrial revolution. As IoT applications evolve, more and more regions lacking infrastructures are also experiencing an urgent need to deploy and connect IoT devices into the network. Low earth orbit satellites, due to its wide coverage and relatively low latency, can provide network access for IoT system. In this article, we propose a low-latency heterogeneous network MAC approach for space-earth integrated IoT network, which can significantly reduce network latency, improve system scalability and balance total system load. Specifically, we design a geographic priority time slot allocation strategy which ensures optimal load and latency, besides, we also design a continuous forward time slot allocation strategy, which guarantees data timeliness while reducing the utilization of satellite resources. Then we design three algorithms based on above strategies, which can effectively reduce network latency and balance the satellite resources. The simulation experimental results are consistent with the theoretical results, which embodies the effectiveness of the algorithm.

Studying the change in inclination and semi-major axis of the satellites for low earth orbits

The main point of this paper is to evaluate the change in the inclination (i) and semi-major axis (a) due to tidal perturbation in orbital elements of a low Earth orbiting satellite LEO's. The orbital elements in the sense of Keplerian motion are affect perturbation in a satellite motion and change in the orbital elements must be employed to study the perturbations of the tidal effect on these satellites. These elements remain constant in the absence of perturbation where perturbed equation of motion was numerically integrated using Lagrange’s formulas where numerical analysis is the most suitable method to analyze disturbances. The findings demonstrate that the tidal disruption of the orbital elements relies on the satellite's inclination the variation in the ratio (∆i/i) and (∆a/a) decreases with increasing the inclination of satellite, while it increases with increasing the time and the difference in inclination reduces as the satellite's inclination rises, and the difference in semi major axis increases as time increases.

Studying the change in inclination and semi-major axis of the satellites for low earth orbits

The main point of this paper is to evaluate the change in the inclination (i) and semi-major axis (a) due to tidal perturbation in orbital elements of a low Earth orbiting satellite LEO's. The orbital elements in the sense of Keplerian motion are affect perturbation in a satellite motion and change in the orbital elements must be employed to study the perturbations of the tidal effect on these satellites. These elements remain constant in the absence of perturbation where perturbed equation of motion was numerically integrated using Lagrange’s formulas where numerical analysis is the most suitable method to analyze disturbances. The findings demonstrate that the tidal disruption of the orbital elements relies on the satellite's inclination the variation in the ratio (∆i/i) and (∆a/a) decreases with increasing the inclination of satellite, while it increases with increasing the time and the difference in inclination reduces as the satellite's inclination rises, and the difference in semi major axis increases as time increases.