Earth Observation Space Research Articles

Spacecraft formation flying orbital control for earth observation mission

Synthetic Aperture Radar (SAR) sensors have gained much attention for multiple civil use cases, where NewSpace startups have launched and planning to launch sensors to orbit to harvest the unique capabilities of SAR for the Earth Observation (EO) market. Unlike optical, SAR can capture images in all lighting conditions and penetrate cloud cover, generating exceptional use cases, which makes SAR the most reliable sensor. For example, monitoring soil deformation with millimeter accuracy, oil spills, crop lodging, and typical EO use cases of optical sensors that are unable to penetrate the clouds or see at night. However, SAR is still limited in civil use cases because it is tough to interpret. In addition, unlike government users who can consume the SAR data directly, most civil end-users need analytics on top of the data. To unlock the potential civil use cases, many experts believe that optical EO data should be fused with SAR at the EO upstream, thus suggesting optical and SAR sensors fly in formation. Spacecraft Formation Flying (SFF) is one of the key technology enablers for space exploration and EO space missions. This paper presents an SFF EO mission (SAR and Optical) design considering orbit requirements to maximize user objectives inspired by OptiSAR™ Constellation.

Accurate extrinsic calibration for the invisible-light 1D laser rangefinder and camera

Abstract A combined sensor, comprising a camera and a one-dimensional laser rangefinder (1D LRF), has wide application across engineering sectors, notably in aerospace. This combined sensor is pivotal for earth observation and deep space exploration. To achieve precise and stable external parameters for this combined sensor, an accurate external calibration method is proposed. Initially, a technique for localized registration of laser spots is introduced to ensure precise determination of their positions, addressing the challenge of laser invisibility in a 1D LRF. Subsequently, a data evaluation criterion known as the data synthesis criterion is presented, addressing the issue of limited constraints in traditional calibration methods. This criterion evaluates relative errors encompassing 1D LRF ranging values, camera external parameters, and laser spot positions. Finally, based on the proposed criteria, a robust extrinsic calibration method is introduced that automatically filters observation data with significant errors and utilizes the growth rate of camera spatial resolution as the termination condition. The efficacy of the proposed method is confirmed through simulation experiments and real-world data experiments.

Space Activities and the Simultaneous Development of the Economy in Türkiye

As space technologies have become an integral part of our daily lives, they have profoundly influenced the course of human civilization since 1957. These technologies have provided humanity with many remarkable insights. Therefore, they have an important role in modern society. Satellite technology is not only vital for military and defence but also for civil applications such as transportation, communication, disaster management, agriculture planning, land, and urban planning. These applications make the space sector an engine of economic growth having advanced and the state-of-the art technology. Technological advances in space continuously benefit the citizens of developed countries. The space economy is defined as all the actions and resources that produce value and benefit to people through exploration, research, knowledge, management, and utility of space. Through satellite communications, navigation systems, earth observation missions, space science and technology research, employment is created, economic growth is achieved, and many industries become more competitive in worldwide economic market. Spinoff companies are born from space activities. In 1994, the Türkiye had its first communication satellite TURKSAT 1B built by Aerospatiale; thus, Türkiye entered the space field being an operator in its region. After millennium, the Turkish space industry has ramped-up by developing its dedicated communication and observation satellites, and their subsystems and creating a launcher system for microsatellites. Türkiye is now developing space technology more comprehensively. This article describes recent developments of space activities and future work in Türkiye. In the article, the strategies in other countries in space technologies are also discussed and suggestions are made for space technology education, development of space economy and regulation of space activities for Türkiye.

Research on proton displacement damage effects in charge-domain accumulation type TDI CMOS image sensors

TDI CMOS image sensors are the most widely used photodetectors in space earth observation and multispectral imaging. The displacement damage caused by high-energy proton irradiation in the space environment leads to the continuous degradation of TDI CMOS image sensor parameters, seriously affecting its performance, reliability, and service life. This paper focuses on a space-based TDI CMOS image sensor chip and carries out 3 MeV proton irradiation tests and post-irradiation annealing tests to obtain the change rules of optical and electrical parameters. The degradation mechanism of sensitive parameters of TDI CMOS image sensors caused by proton irradiation is analyzed, and the sensitive region of proton displacement damage are discussed. The study demonstrates that after proton irradiation, the parameters especially full well capacity and temporal dark noise of the device degrade less, with small sensitivity to proton irradiation. However, the dark current, CTE, and pixel column FPN significantly degrade, and the degree of degradation is linearly related to the proton irradiation dose. In addition, the test also obtained the short-term and long-term annealing changes of sensitive parameters after proton irradiation of TDI CMOS image sensors, providing scientific advice for TDI CMOS image sensors space proton radiation effect tests and evaluations. The research results of this paper provide important references for the evaluation of radiation effects, on-orbit performance estimation, and radiation resistance reinforcement of space-based TDI CMOS image sensors.

Evaluation of the thermo-elastic response of space telescopes using uncertainty assessment

The aerospace sector is evolving due to reduced launch costs and standardization of small satellite platforms. This research, aligned with European Guidelines for Thermo-Elastic Verification, addresses the pointing precision gap in small satellites by assessing space telescope performance using uncertainty propagation in thermo-elastic models. The methodology will be directly applied to an Earth observation space telescope, VINIS, currently under development by the Instituto de Astrofísica de Canarias (IAC). This procedure helps to identify key design elements impacting its functionality. Thirteen elements were identified as main contributors to the deformations in the optical bench. Due to the bench's crucial role in the telescope's performance, this paper also explores how results vary with different sandwich panel modelling techniques and the enhancements from design modifications. While the focus is on space telescopes, this approach has broader applicability to thermo-elastic analysis of various space instruments.

Micro-vibration control of spaceborne payload with smart parallel struts

Currently, the observation resolution of Earth observation satellites and space telescopes is progressively increasing. However, vibrations induced by solar panel vibrations, control torque gyroscopic reaction forces, and internal satellite noise significantly impede the observation accuracy of space-borne precision optical payloads. To mitigate the impact of vibrations on precision payload, it is necessary to incorporate isolation devices into the transmission path between the payload and spacecraft bus. This paper aims to design a six-degree-of-freedom parallel struts for active control of vibration in sensitive payloads. An optical payload isolation system is constructed using a Gough-Stewart parallel configuration with flexible hinges. The dynamic model of the system is established by the Newton-Euler method. The dynamic characteristics and response of the isolation system are analyzed. Then the active controller is designed based on the Fuzzy Auto-Disturbance Rejection Control strategy, and the effectiveness of the controller is simulated and compared with the fuzzy Proportion Integration Differentiation (PID) control algorithm. The results show that the active parallel struts exhibit excellent vibration isolation performance and possess strong robustness, which provides a theoretical reference for further space applications.

Synthesis and Networking of Spaceborne Deployable Prismatic Antenna Mechanisms Based on Graph Theory

Spaceborne deployable cylindrical antennas have broad application prospects in the fields of space earth observation and remote-sensing detection because of their significant advantages of ultralong aperture, high gain, and flexible beam scanning. As application requirements rapidly develop, a new type of spaceborne deployable cylindrical antenna mechanism with a large diameter and deployability is urgently needed. This paper presents an innovative design for a cylindrical deployable antenna mechanism based on 18R triangular prism elements based on graph theory. The correctness of the configuration is verified by developing a prototype. First, four kinds of nonoverconstrained 12-bar triangular prism-stabilized truss structure configurations and their corresponding topological diagrams are constructed. Second, based on graph theory, three types of 102 triangular prism-stabilized truss mechanism configurations that can be folded into linear mechanisms are derived. Third, the kinematic pair configuration is established to achieve a single-degree-of-freedom 7R2U9S triangular prism deployable unit. Fourth, combined with the geometric topology characteristics of the unit network, a triangular prism unit networking method is proposed, and a cylindrical network mechanism configuration based on 18R triangular prism units is obtained. A prototype was fabricated by 3D printing, and an expansion and retraction function test was conducted, which verified the correctness of the theoretical analysis in this paper. Finally, a new concept configuration for a parabolic cylindrical antenna is proposed. This paper provides a reference for the configuration of large-scale folding truss structures with unit expansion.

Microvibration analysis methods review

It is known that today the problem of microvibration in spacecraft structures is relevant and widely researched. On- orbit operation of modern spacecrafts such as geodetic satellites, Earth observation satellites or space telescopes is associated with the use of onboard equipment sensitive to micro- vibration. In most cases, the conditions for the normal functioning of precision spacecraft equipment are provided by the operation of electromechanical devices, which in turn are sources of vibration. This article attempts to highlight the main approaches to the microvibration analysis that are known today. In this regard, the analysis of both native and foreign sources, in which the central problem is the analysis of microvibration, is carried out. This paper takes formulation of the microvibration problem and its role in the creation of modern spacecraft process. It also gives a literature review on methods and approaches to the microvibration analysis of spacecraft. Based on the analysis of publications on a similar topic, here one can find the tasks to solve in the process of the spacecraft microvibration analysis. The advantages, disadvantages and limitations of existing approaches and methods are revealed.

Stable Spinning Deployment Control of a Triangle Tethered Formation System.

The tethered formation system has been widely studied due to its extensive use in aerospace engineering, such as Earth observation, orbital location, and deep space exploration. The deployment of such a multitethered system is a problem because of the oscillations and complex formation maintenance caused by the space tether's elasticity and flexibility. In this article, a triangle tethered formation system is modeled, and an exact stable condition for the system's maintaining is carefully analyzed, which is given as the desired trajectories; then, a new control scheme is designed for its spinning deployment and stable maintenance. In the proposed scheme, a novel second-order sliding mode controller is given with a designed nonsingular sliding-variable. Based on the theoretical proof, the addressed sliding variable from the arbitrary initial condition can converge to the manifold in finite time, and then sliding to the equilibrium in finite time as well. The simulation results show that compared with classic second sliding-mode control, the proposed scheme can speed up the convergence of the states and sliding variables.

Advances in fine line-of-sight control for large space flexible structures

The increased need in pointing performance for Earth observation and science Space missions together with the use of lighter and flexible structures directly come with the need of a robust pointing performance budget from the very beginning of the mission design. An extensive understanding of the system physics and its uncertainties is then necessary in order to push control design to the limits of performance and constrains the choice of the set of sensors and actuators. A multi-body framework, the Two Input Two Output Ports approach, is used to build all the elementary flexible bodies and mechanisms involved in a fine pointing mission. This framework allows the authors to easily include all system dynamics with an analytical dependency on varying and uncertain mechanical parameters in a unique Linear Fractional Transformation (LFT) model. This approach opens the doors to modern robust control techniques that robustly guarantee the expected fine pointing requirements. In particular, a novel control architecture is proposed to reduce the microvibrations induced both by reaction wheel imbalances and Solar Array Drive Mechanism driving signal, by letting them work during the imaging phase. Thanks to a set of accelerometers placed at the isolated base of the payload and in correspondence of the mirrors with the largest size in a Space telescope (typically the primary and secondary ones), it is possible to estimate the line-of-sight error at the payload level by hybridizing them with the low-frequency measurements of the camera. While a classical Fast Steering Mirror in front of the camera can compensate for a large amount of microvibration, an innovative architecture with a set of six Proof-Mass Actuators installed at the payload isolator level can further improve the pointing performance. In particular, it is shown how the proposed architecture is able to robustly guarantee an absolute performance error of 10 arcsec in face of system parametric uncertainties at low frequency (≈ 1rad/s) with a progressive reduction of the jitter down to 40 marcsec for higher frequencies where micro-vibration sources act.

The development and prospect of China's space earth observation technology

The development and prospect of China's space earth observation technology

On-Going European Space Agency Activities on Measuring the Benefits of Earth Observations to Society: Challenges, Achievements and Next Steps

Understanding the Earth system and its physical and societal processes is crucial for helping humankind develop in a sustainable way, and for designing effective policies across a wide range of applications that include mitigating the effects of climate change, the sustainable management of natural resources, food security and public health. Earth observation (EO) satellites provide regular and accurate observations of the entire planet that can greatly support improvements in such understanding. The European Space Agency (ESA) is committed to supporting international efforts to decipher the processes and phenomena that regulate life on Earth, by building world class EO space missions and making data available to scientists and citizens across the world. How successful is ESA in this endeavour? Given the variable and dynamic nature of EO data use, it is difficult to answer the question through established figures. Yet, it is crucial that ESA be able to discriminate and assess the benefits brought by the use of its EO missions, in order to demonstrate its achievements, to keep improving its systems, to better design and plan future missions, and to promote further uptake. In this article, after recalling its commitments in support of Earth system sciences, ESA’s attempts to conduct valuations of the impact of its own space missions are described. In particular, the challenges encountered in measuring such impacts and the solutions pursued by the Agency to improve its assessment capabilities are detailed, together with the open issues and the current lines of work.

Remote Sensing Object Tracking With Deep Reinforcement Learning Under Occlusion

Object tracking is an important research direction of space Earth observation in the field of remote sensing. Although the existing correlation filter-based and deep learning (DL)-based object tracking algorithms have achieved great success, they are still unsatisfactory for the problem of object occlusion. The occlusion caused by the complex change in background, and the deviation of the tracking lens, causes object information to go missing, which leads to the omission of detection. Traditionally, most methods for object tracking under occlusion adopt a complex network model, which redetects the occluded object. To address this issue, we propose a novel object tracking approach. First, an action decision-occlusion handling network (AD-OHNet) based on deep reinforcement learning (DRL) is built to achieve low computational complexity for object tracking under occlusion. Second, the temporal and spatial context, the object appearance model, and the motion vector are adopted to provide the occlusion information, which drives actions in reinforcement learning under complete occlusion and contributes to improving the accuracy of tracking while maintaining speed. Finally, the proposed AD-OHNet is evaluated on three remote sensing video datasets of Bogota, Hong Kong, and San Diego taken from Jilin-1 commercial remote sensing satellites. The video datasets all shared problems of low spatial resolution, background clutter, and small objects. Experimental results on the three video datasets validate the effectiveness and efficiency of the proposed tracker.

Investigation of tape flexures for space borne deployable structures

Space exploration arises the demand for launching large size structures to satisfy the need of high bandwidth telecommunication, earth observation and deep space interplanetary missions. Launching of these monolithic structures of sizes 3 m or more are not feasible due to limited launch fairing space of state-of-the-art launch vehicles. Therefore, the development of innovative deployment mechanisms is need of the hour. Deployment process of space borne deployable systems is the process of transition from mechanism to structure which is one of the unreliable stage due to existence of many conventional rotary joints which causes loss of energy due to backlash, friction and misalignment. An investigation study is presented in this paper for churning out a solution of flexible hinges using tape springs in state-of-the-art space deployable configurations which eliminates the factors causing loss of energy. Analytical and experimental methods are evaluated for investigating the bending behaviour of tape flexures. Tape flexures demonstrate to be a suitable candidate for compliant deployable configuration. The proposed configuration with combination of two tape flexures mounted in such a way that concave curve of each tape faces each other are structurally analysed for desired rotation angle. A comparison study is carried out for various material options of single and double layered tape flexures proposed for a flexure hinge. Practical feasibility of the proposed configuration is also demonstrated successfully on space borne deployable structures.

Satellite X-band SAR data exploitation trends in the framework of ASI’s COSMO-SkyMed Open Call initiative

Abstract COSMO-SkyMed (Constellation of Small satellites for Mediterranean basin Observation) is an Italian Earth Observation (EO) and Dual-Use (Civilian and Defense) Space System conceived with the aim to establish a worldwide service providing Synthetic Aperture Radar (SAR) data, products and services compliant with well-established international standards and relevant to a wide range of applications, such as emergency and risk management, scientific and commercial applications and defense Applications. Starting from 2007, the Italian Space Agency (ASI) has promoted the COSMO-SkyMed SAR data exploitation through several initiatives such as “Announcement of Opportunity”, “Open Call for Science” and “Open Call for National Small and Medium Enterprises (SMEs)”. This paper is focused on the trends and results observed in the context of the “Open Call for Science”, an initiative completely addressed to the national and international scientific community since 2015. In particular, in this framework, the observed trend and advances in science and applications of SAR imagery and Interferometric SAR (InSAR) are summarized and assessed, also in light of the scientific evidence published in the recent literature by scientific users of ASI’s “Open Call for Science”.

Spectral Analysis of Stationary Signals Based on Two Simplified Arrangements of Chirp Transform Spectrometer

The classical two-channel push-pull chirp transform spectrometer (CTS) has been widely applied in satellite-borne remote sensing systems for earth observation and deep space exploration. In this paper, we present two simplified structures with single M(l)-C(s) CTS arrangements for the spectral analysis of stationary signals. A simplified CTS system with a single M(l)-C(s) arrangement and a time delay line was firstly developed. Another simplified structure of CTS with a M(l)-C(s) arrangement and a frequency conversion channel was also developed for spectral analysis of stationary signals. Simulation and experiment results demonstrate that the two simplified arrangements can both realize spectrum measurement for the stationary signals and obtain the same frequency resolution, amplitude accuracy and system sensitivity as that of the classical two-channel push–pull CTS system. Compared to the classical CTS structure, the two simplified arrangements require fewer devices, save power consumption and have reduced mass. The matching problem between the two channels can be avoided in the two simplified arrangements. The simplified CTS arrangements may have potential application in the spectrum measurement of stationary signals in the field of aviation and spaceflight.

Mission and system architecture for an operational network of earth observation satellite nodes

Nowadays, constellations and distributed networks of satellites are emerging as clear development trends in the space system market to enable augmentation, enhancement, and possibilities of new applications for future Earth Observation (EO) missions. While the adoption of these satellite architectures is gaining momentum for the attaining of ever more stringent application requirements and stakeholder needs, the efforts to analyze their benefits and suitability, and to assess their impact for future programmes remains as an open challenge to the EO community. In this context, this paper presents the mission and system architecture conceived during the Horizon 2020 ONION project, a European Union research activity that proposes a systematic approach to the optimization of EO space infrastructures. In particular, ONION addressed the design of complementary assets that progressively supplement current programs and took part in the exploration of needs and implementation of architectures for the Copernicus Space Component for EO.Among several use cases considered, the ONION project focused on proposing system architectures to provide improved revisit time, data latency and image resolution for a demanding application scenario of interest: Marine Weather Forecast (MWF).A set of promising system architectures has been subject of a comprehensive assessment, based on mission analysis expertise and detailed simulation for evaluating several key parameters such as revisit time and data latency of each measurement of interest, on-board memory evolution and power budget of each satellite of the constellation, ground station contacts and inter-satellite links. The architectures are built with several heterogeneous satellite nodes distributed in different orbital planes. Each platform can embark different instrument sets, which provide the required measurements for each use case.A detailed mission analysis has then been performed to the selected architecture for the MWF use case, including a refined data flow analysis to optimize system resources; a refined power budget analysis; a delta-V and a fuel budget analysis considering all the possible phases of the mission. This includes from the correction of launcher injection errors and acquisition of nominal satellite position inside the constellation, orbit maintenance to control altitude, collision avoidance to avoid collision with space debris objects and end-of-life (EOL) disposal to comply with EOL guidelines.The relevance of the system architecture selected for the MWF has been evaluated for three use cases of interest (Arctic sea-ice monitoring, maritime fishery pressure and aquaculture, agricultural hydric stress) to show the versatility and the feasibility of the chosen architecture to be adapted for other EO applications.

Microlens testing on back-illuminated image sensors for space applications.

The optoelectronic properties of image sensors, among which are the photosensitivity and resolution, are key to the quality factors for imaging as well as spectrometry in Earth observation and scientific space exploration missions. Microlens arrays (MLAs) further improve state-of-the-art CMOS image sensors (CIS) by redirecting more photons into the photosensitive surface/volume of each pixel. This paper reports the design, deposition, optical characterization, and reliability assessment of such an MLA made from a UV-curable hybrid polymer and replicated on a packaged back-illuminated CIS having a pixel pitch of 15.5 µm. We find that such MLAs are highly stable to temperature variations, exposure to humidity, mechanical shocks and vibrations, as well as irradiation by gamma rays, while improving the parasitic light sensitivity by a factor of 1.8. Such MLAs can be applied on a large variety of image sensors, back-illuminated but mostly front-illuminated, with pixel pitches ranging from a few to several hundreds of micrometers, making them suitable for most specifications of the space industry.

Mission planning and scheduling for Earth observation space system

Mission planning and scheduling for Earth observation space system

Mission planning and scheduling for Earth observation space system

Planning and scheduling systems are needed to manage Earth observing satellites for satisfying the optimum usage of the constellation's resources. This is a combinatorial optimisation NP-hard problem which is solved in this paper using the constraint programming technique. The proposed system can deal with a heterogeneous constellation that consists of satellites with different manoeuvrability, placed in different orbits, and loaded with different payloads. The system's user can choose one of six optimisation objectives, three of them were not used before, for constructing the satellites' mission plan. Searching within the system is performed using one of five different search algorithms. The system produces plans with different planning horizons ranging from one track to more than one month. The obtained results depict that the proposed system behaves, comparatively, in a perfect manner even when dealing with a complicated case study consisting of three satellites, 2,500 targets, and one month planning horizon.