Earth Observation Space Research Articles

Smaller Satellites, Larger Constellations: Trends and Design Issues for Earth Observation Systems

The importance of earth observation (EO) from space is felt today more than ever in many different fields of human activity. Governments, international organizations, military bodies, private industry, and even individuals benefit every day of the products of spaceborne remote sensing technology. In this paper, we present a brief overview of some of the main trends in the EO scenario, focusing on the emergence of a new paradigm for EO space systems namely: the ongoing, disruptive shift from large satellites to constellations of small spacecraft, fueled by the recent introduction of several key technologies, such as for instance electric propulsion. We present the outline of a tool specifically conceived to assist the system architect in the early design phase of an EO constellation of microsatellites equipped with electric thrusters. A case study is presented for the application of a multisegmented constellation, with visual, thermal infrared, and radar components to remotely monitor a national railway network. We conclude that, in spite of the complexity of modern small satellite constellations, preliminary design can be successfully performed in a simplified and effective way.

Optimal design and robust analysis of a net of active devices for micro-vibration control of an on-orbit large space antenna

Large deployable antennas are required for the advancement of space communications, Earth observation, radio astronomy and deep space exploration. Most contemporary space antennas have exceeded the size of launching vehicles, leading to the necessity of stowed concepts to overcome the limitation. Many structural models have been investigated by different organizations. Generally, mesh deployable reflectors are currently more mature compared to other foldable solutions. This will be the topic of this paper. Orbital disturbances, perturbations originated by on-board sources and thermal deformations affecting the deployed configuration can deteriorate the accuracy of the communications system. Undesired dynamic behaviour of structural components has to be predicted and counteracted. Therefore, vibration control is a key technology to correct the distortions altering the proper functioning of the system. An intelligent active structure is introduced as a structure configured with distributed actuators and sensors and guided by a controller to modify the dynamic response of the system. In this paper, the supporting structure of a very large mesh reflector is described. A FEM formulation is adopted to assemble the frame and it is validated by comparing it with commercial codes. According to the adopted model, the active elements can be embedded in the middle of the truss elements. Of course, active control of all the devices at the same time requires a control effort which could be not affordable in space applications. However, the effectiveness is not the same for all the actuators. In this study, two cascade optimization procedures are performed to assess the best positioning and velocity feedback gains of the actuators that must be controlled to damp vibrations. In particular, a gradient-based technique is used after both a Genetic Algorithm and a Reinforcement Learning methodology to find the best set of gains for the controller. The objective function is set as a weighted sum of power consumption of the actuators. As a study case, the spacecraft implements a velocity feedback strategy when performing a generic attitude manoeuvre to coordinate the simultaneous action of the devices to ensure the damping performance of the system is enhanced. In addition, the impact of damaged actuators and uncertainties on the mechanical properties of the passive structure has been discussed and analysed.

Building the Appropriate Capacity for Enabling Space Programs in Africa: The Nigerian Experience

This paper x-rays the two-decade gradual yet steady strides made by Nigeria in building the capacity of its workforce in space science and technology. Information concerning the technical training modules on earth observation satellites (EOS), communication satellites, space transport and propulsion systems, and space systems application software is provided. Details are also provided of the locations for these training, the number of personnel involved and the associated cost implication for some of the capacity building programs. This review concludes that despite the funding challenges, global legal bottlenecks and the security implications associated with undertaking and executing a national space program, a continual investment in space capacity building programs is necessary, crucial and essential. This is because the immediate and long-term national benefits of these capacity building programs are immense and the spin-offs have trans-generational impacts.

THE ROLE OF VENEZUELAN SPACE TECHNOLOGY IN PROMOTING DEVELOPMENT IN LATIN AMERICA

Abstract. Space technology and resources are used around the world to address societal challenges. Space provides valuable satellite services, unique scientific discoveries, surprising technology applications and new economic opportunities. Venezuela formally recognizes the advantages of space resources and pursues national level activity to harness them. Venezuela space cooperation has grown in the past several years, contributing to debates over Venezuela’s rising influence in the Latin America. This paper summarizes the establishment and current development of space activities in the Bolivarian Republic of Venezuela, these activities are focused on the areas of telecommunications, Earth observation, research and development space and has as a primary goal the satisfaction of social needs. This analysis offers the elements most important of the Venezuelan space policy: technological transfer, capacity building and human training and international cooperation including the new participation of Venezuela in the international charter on space and major disasters. Our analysis shows that Venezuela has the potential to become a space leadership country, promoting the social welfare, integration, and sustainable development of Latin American countries.

Analysis and experiment on dynamic stiffness of clearance hinge in large circular truss antenna

Large space structures (LSS) composed of trusses, cables and meshes deployed on orbit, serves as the large antenna for different space missions. Deployable structures which are employed as large space supporting structures of space-borne antennas are widely used in earth observation space missions due to their large stiffness, small folding volume, light weight and easy extensibility. The dynamic research on deployable structures is great importance for the design, analysis, and capacity improvement of such structures. Each LSS contains many joints to combine the substructures, which contain clearance inevitably. The existence of the clearance causes the complicated dynamic characteristics of the LSS. It is necessary to estimate the influence of clearance on the structure. Hinge stiffness is an important factor in determining the dynamic characteristics of articulated structure, this paper will analyze the dynamic characteristics of radial connection part of the plane rotary hinge on large space deployable circular truss antenna structure, the radial kinetic model of hinges is established, the influence of hinge clearance, external excitation and displacement amplitude are discussed. The results indicate that the effect of clearance on the dynamic stiffness of the hinge is significant. On the exciting frequency and natural frequency in the hinge, when the ratio of radial vibration amplitude and the hinge clearance is constant, dynamic stiffness coefficient with the increase of external excitation is reduced. Dynamic stiffness coefficient with the frequency increases with increasing hinge. On the gap size and the hinge vibration amplitude, fixed frequency ratio, with the increase of the gap, the dynamic stiffness coefficient has a decreasing trend with the increase of the amplitude of the hinge, and with the decrease of the gap, the dynamic change of stiffness coefficient is not obvious, when the gap becomes larger, the dynamic stiffness coefficient increases significantly. When the clearance increases, the dynamic stiffness coefficient decreases. The validity of the theoretical calculation is verified by experiments.

Performance evaluation of linear time-series ionospheric Total Electron Content model over low latitude Indian GPS stations

Precise modeling of the ionospheric Total Electron Content (TEC) is a critical aspect of Positioning, Navigation, and Timing (PNT) services intended for the Global Navigation Satellite Systems (GNSS) applications as well as Earth Observation System (EOS), satellite communication, and space weather forecasting applications. In this paper, linear time series modeling has been carried out on ionospheric TEC at two different locations at Koneru Lakshmaiah University (KLU), Guntur (geographic 16.44°N, 80.62°E; geomagnetic 7.55°N) and Bangalore (geographic 12.97°N, 77.59°E; geomagnetic 4.53°N) at the northern low-latitude region, for the year 2013 in the 24th solar cycle. The impact of the solar and geomagnetic activity on periodic oscillations of TEC has been investigated. Results confirm that the correlation coefficient of the estimated TEC from the linear model TEC and the observed GPS-TEC is around 93%. Solar activity is the key component that influences ionospheric daily averaged TEC while periodic component reveals the seasonal dependency of TEC. Furthermore, it is observed that the influence of geomagnetic activity component on TEC is different at both the latitudes. The accuracy of the model has been assessed by comparing the International Reference Ionosphere (IRI) 2012 model TEC and TEC measurements. Moreover, the absence of winter anomaly is remarkable, as determined by the Root Mean Square Error (RMSE) between the linear model TEC and GPS-TEC. On the contrary, the IRI2012 model TEC evidently failed to predict the absence of winter anomaly in the Equatorial Ionization Anomaly(EIA) crest region. The outcome of this work will be useful for improving the ionospheric now-casting models under various geophysical conditions.

Power Processing Unit Activities in Airbus DS Space Equipments

This paper presents the Power Processing Units in Airbus DS Space Equipment.Electric propulsion has (EP) become a reality in the commercial market, and therefore is not anymore a niche market for earth observation and/or deep space missions. Major players worldwide for Commercial satellite manufacturers are targeting in their current programs, electric satellites solutions for orbit raising (OR) and station keeping (SK) maneuvers. Several EP technologies are competing against each other, in particular Hall Effect Thruster (HET), Gridded Ion Engine (GIE) technology (including Kaufmann and Radio Frequency technologies) and High Efficiency Multistage Plasma (HEMP). The main two parameters used to trade-off the main EP technologies are Thrust/Power ratio and Specific Impulse (ISP). Currently the market is mainly thrust driven, and therefore the dominant technology is HET. HET is the most efficient technology for the Thrust/Power ratio parameter.Airbus DS Space Equipment include in our portfolio PPU solutions for high Thrust ratio and high ISP solutions.

An analytical approach for the design of carbon-fibre-reinforced polymer laminates with minimised thermal expansion

The potential of carbon-fibre-reinforced polymers (CFRP) for the design of structures with extremely small coefficients of thermal expansion (CTE) is commonly known. Such structures play an important role in space applications, like earth observation satellites and space telescopes. But they also have a high potential for earthbound applications, for example, for precise mechanical and optical measurement devices. This paper demonstrates that orthotropic and quasi-isotropic laminates are most suitable for the design of laminates with minimised CTE. The derivation of a shortcut equation to the tensor calculations of the classical lamination theory is presented. Its purpose is to assist engineers in the selection of suitable carbon fibres and matrix polymers for the design of a laminate with high thermomechanical stability. The application of the equation is discussed and demonstrated on examples with practical relevance.

Large deployable antennas

It is an honour and a great pleasure for us to present this special issue of the CEAS Space Journal devoted to the development of large deployable antennas and related technologies. Large deployable antennas for space applications have been under development worldwide for several decades, driven by both mission performance enhancement goals as well as mission enabling goals. Developments in ESA started already in the 80s with a 5-m metal-mesh reflector built by MBB/ERNO in Germany, continued later with a 10-m inflatable reflector built by Contraves in Switzerland and more recently a 12-m antenna built by Thales Alenia Space in Italy. However, for various reasons all these developments did not result in a final available European antenna reflector product. As a matter of fact, today there is no European antenna reflector product larger than 4 m aperture available, forcing European spacecraft developers to procure large reflectors from non-European sources. Three years ago, an ESA Working Group on large reflector antennas was set up with the mandate to define recommendations on how to proceed with new large reflector developments in Europe. Several spacecraft missions in need of antenna reflectors were identified, including well-established telecommunication markets such as fixed and broadcasting satellite services, mobile interactive/broadcast services, broadband services, but also new applications such as air traffic management and emergency communications. These missions cover the frequency spectrum up to Ka-band. Synergies with Earth Observation, Navigation and Scientific deep space missions were also identified. One of the main conclusions of the Working Group was that near-term effort should be devoted to the development of technologies for reflectors with scalability and/or modularity features to cover sizes above 4 m and up to 25 m for frequency bands ranging from P to Ka. It was understood that many of the technologies were in fact available or within reach, and the missing task of coordination and industrial implementation was considered achievable. In October 2012, the first Large Deployable Antenna Workshop took place at ESA/ESTEC, The Netherlands, with a significant participation from European industry and research organisations. During this workshop, several recent technology developments for large antenna reflectors were presented and discussed together with a new reflector deployment demonstration. The workshop addressed as well developments for inflight reconfigurability of space antennas using reflector reshaping that is finally becoming technically feasible after many years of trials. Reflect-arrays and lenses were also addressed, as well as radio frequency testing, especially relevant due to the challenges ahead of us for the development of test facilities required for large apertures. This special issue of the CEAS Space Journal is intended to present the key technologies addressed in this workshop. A second edition of the workshop is under preparation for 2014 with the objective to report on the major developments performed over the last 2 years. T. K. Henriksen (&) Structures and Mechanisms Division, ESA/ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, ZH, The Netherlands e-mail: Torben.Henriksen@esa.int

The hydrogen value chain: applying the automotive role model of the hydrogen economy in the aerospace sector to increase performance and reduce costs

Hydrogen will assume a key role in Europe's effort to adopt its energy dependent society to satisfy its needs without releasing vast amounts of greenhouse gases. The paradigm shift is so paramount that one speaks of the “Hydrogen Economy”, as the energy in this new and ecological type of economy is to be distributed by hydrogen. However, H2 is not a primary energy source but rather an energy carrier, a means of storing, transporting and distributing energy, which has to be generated by other means.Various H2 storage methods are possible; however industries' favourite is the storage of gaseous hydrogen in high pressure tanks. The biggest promoter of this storage methodology is the automotive industry, which is currently preparing for the generation change from the fossil fuel internal combustion engines to hydrogen based fuel cells. The current roadmaps foresee a market roll-out by 2015, when the hydrogen supply infrastructure is expected to have reached a critical mass. The hydrogen economy is about to take off as being demonstrated by various national mobility strategies, which foresee several millions of electric cars driving on the road in 2020.Fuel cell cars are only one type of “electric car”, battery electric as well as hybrid cars – all featuring electric drive trains – are the others. Which type of technology is chosen for a specific application depends primarily on the involved energy storage and power requirements. These considerations are very similar to the ones in the aerospace sector, which had introduced the fuel cell already in the 1960s. The automotive sector followed only recently, but has succeeded in moving forward the technology to a level, where the aerospace sector is starting considering to spin-in terrestrial hydrogen technologies into its technology portfolio. Target areas are again high power/high energy applications like aviation, manned spaceflight and exploration missions, as well as future generation high power telecommunication satellites. Similar trends can be expected in the future for RADAR Earth Observation satellites and space infrastructure concepts of great scale.This paper examines current activities along the hydrogen value chain, both in the terrestrial and the aerospace sector. A general assessment of the synergy potential is complemented by a thorough analysis of specific applications serving as role models like a lunar manned base or pressurised rover, an aircraft APU or a high power telecommunications satellite. Potential performance improvements and cost savings serve as key performance indicators in these comparisons and trade-offs.

Recent changes of the Earth’s core derived from satellite observations of magnetic and gravity fields

To understand the dynamics of the Earth's fluid, iron-rich outer core, only indirect observations are available. The Earth's magnetic field, originating mainly within the core, and its temporal variations can be used to infer the fluid motion at the top of the core, on a decadal and subdecadal time-scale. Gravity variations resulting from changes in the mass distribution within the Earth may also occur on the same time-scales. Such variations include the signature of the flow inside the core, though they are largely dominated by the water cycle contributions. Our study is based on 8 y of high-resolution, high-accuracy magnetic and gravity satellite data, provided by the CHAMP and GRACE missions. From the newly derived geomagnetic models we have computed the core magnetic field, its temporal variations, and the core flow evolution. From the GRACE CNES/GRGS series of time variable geoid models, we have obtained interannual gravity models by using specifically designed postprocessing techniques. A correlation analysis between the magnetic and gravity series has demonstrated that the interannual changes in the second time derivative of the core magnetic field under a region from the Atlantic to Indian Ocean coincide in phase with changes in the gravity field. The order of magnitude of these changes and proposed correlation are plausible, compatible with a core origin; however, a complete theoretical model remains to be built. Our new results and their broad geophysical significance could be considered when planning new Earth observation space missions and devising more sophisticated Earth's interior models.

PLEIADES-HR SYSTEM PRODUCTS PERFORMANCE AFTER IN-ORBIT COMMISSIONING PHASE

Abstract. Launched on 2011, December 16th by the second Soyuz operated in French Guiana, PLEIADES-HR acquired its first high resolution images 3 days after. The PLEIADES program is a space Earth Observation system led by the French Space Agency (CNES), it provides the first european high resolution satellite which will simultaneously acquire in Panchromatic and Multi- Spectral modes 20 km wide images with a 70 cm nadir resolution. Imaging capabilities have been highly optimized in order to acquire, in the same pass, along-track mosaics, stereo pairs and triplets, and multi-targets. Ground segment processes automatically data to ensure operational requirements and quick access to images for the users. Since ground processing capabilities have been taken into account very early in the mission development, it has been possible to relax some costly on-board components requirements, in order to achieve a cost effective on-board/ground compromise. Starting from the PLEIADES system and on board characteristics, this paper first presents an overview of ground segment functional breakdown. Then it focuses more precisely on the different levels of products and associated processing performances. Finally the paper shows how appropriate ground processing systems allowed CNES Image Quality team to assess radiometric and geometric performances during the 6 first months of PLEIADES 1A.

PLEIADES SYSTEM ARCHITECTURE AND MAIN PERFORMANCES

Abstract. France, under the leadership of the French Space Agency (CNES), has set up a cooperative program with Austria, Belgium, Spain, Sweden, in order to develop a space Earth Observation system called PLEIADES. PLEIADES is a dual system, this means that it is intended to fulfill an extended panel of both civilian and Defense user’s needs.. This paper reports the status of the satellite after its launch and the in orbit commissioning, the PLEIADES satellite first model has been launched at the end of year 2011, the second model will be launched about 12 months later. It describes the main mission characteristics and performances status. It exposes how the system, satellite and ground segment have been designed in order to be compliant with a dual exploitation between civilian and defense partners. The system is based on the use of a set of newly European developed technologies to feature the satellite. In order to maximize the agility of the satellite, weight and inertia have been reduced using a compact hexagonal shape for the satellite bus. The optical mission consists in Earth optical observation composed of 0.7 m nadir resolution for the panchromatic band and 2.8 m nadir resolution for the four multi-spectral bands. The image swath is about 20 km. PLEIADES delivers optical high resolution products consisting in a Panchromatic image, into which is merged a four multispectral bands image, orthorectified on a Digital Terrain Model (DTM). Thanks to the huge satellite agility obtained with control momentum gyros as actuators, the optical system delivers as well instantaneous stereo images, under different stereoscopic conditions and mosaic images, issued from along the track thus enlarging the field of view. The ground segment is composed of a dual ground center located in CNES Toulouse premises in charge of preparing the dual mission command plan and of the real time contacts with the satellite through a control center. The dual ground center interfaces with several mission centers : one center is built for each Defense partner (France, Spain …), one center is set up for the Civilian Operator. Each mission center is in charge of managing the programming requests, then, receiving the mission telemetry, processing the data to feed a catalog and an archive, to generate the system products and distribute them to the final user. System reactivity has been optimized with a chronology based on three mission planning activations per day. The mission plan is uploaded to the satellite just before flyby over East Asia , Europe and North America. In addition a Direct Tasking mode is available for commercial Image Receiving Stations.

Long-term Preservation of Earth Observation Data and Knowledge in ESA through CASPAR

ESA-ESRIN, the European Space Agency Centre for Earth Observation (EO), is the largest European EO data provider and operates as the reference European centre for EO payload data exploitation. EO Space Missions provide global coverage of the Earth across both space and time generating on a routine continuous basis huge amounts of data (from a variety of sensors) that need to be acquired, processed, elaborated, appraised and archived by dedicated systems. Long-term Preservation of these data and of the ability to discover, access and process them is a fundamental issue and a major challenge at programmatic, technological and operational levels.Moreover these data are essential for scientists needing broad series of data covering long time periods and from many sources. They are used for many types of investigations including ones of international importance such as the study of the Global Change and the Global Monitoring for Environment and Security (GMES) Program. Therefore it is of primary importance not only to guarantee easy accessibility of historical data but also to ensure users are able to understand and use them; in fact data interpretation can be even more complicated given the fact that scientists may not have (or may not have access to) the right knowledge to interpret these data correctly.To satisfy these requirements, the European Space Agency (ESA), in addition to other internal initiatives, is participating in several EU-funded projects such as CASPAR (Cultural, Artistic, and Scientific knowledge for Preservation, Access and Retrieval), which is building a framework to support the end-to-end preservation lifecycle for digital information, based on the OAIS reference model, with a strong focus on the preservation of the knowledge associated with data.In the CASPAR Project ESA plays the role of both user and infrastructure provider for one of the scientific testbeds, putting into effect dedicated scenarios with the aim of validating the CASPAR solutions in the Earth Science domain. The other testbeds are in the domains of Cultural Heritage and of Contemporary Performing Arts; together they provide a severe test of preservation tools and techniques.In the context of the current ESA overall strategies carried out in collaboration with European EO data owners/providers, entities and institutions which have the objective of guaranteeing long-term preservation of EO data and knowledge, this paper will focus on the ESA participation and contribution to the CASPAR Project, describing in detail the implementation of the ESA scientific testbed.

The future ESA Earth-Observation strategy and ESA's ‘Living Planet’ programme

The European Space Agency future strategy for marks a big departure with the past. Following the series, ERS1, ERS2, Envisat, which have established no doubt of Europe's technical capability, the new programme will focus on smaller but more frequent spacecraft. Individual missions will be much more focused for both scientific purpose and applications. Information from space Earth Observation is an essential element in Europe's strategic armoury to meet the environmental and economic challenges of the next century. For the space community, the challenge will be to show that the small focussed approach really can meet the requirements for a much-reduced budget.

A new generation of satellite sensors for Earth observation: The German MOMS-2P on the MIR-station

More and more useful spectral information has been supplied to geoscientists from sophisticated space sensors with increasing detecting ability. Because the quality of spectral information depends on its sensor characteristics, sensor development is the key to remote sensing techniques. As an Earth observation space sensor the German MOMS-2P (Modular Optoelectronic Multispectral Stereo Scanner) was launched May 1996 aboard the PRIRODA Module docked on the Russian MIR Space Station in a preoperational mission for about three year duration. Technical features of the Sensor are three-line along-track stereo imaging, high spatial and spectral resolution, optimized multispectral and panchromatic bands and combination of stereo and multispectral imaging. The advanced sensor on the MIR-station can receive data covering the earth surface from N51.6° to S51.6°. This paper gives a critical review of the new generation of optical satellite sensors for earth observation, with special emphasis on the technical development of the sensor MOMS-2P and demonstrates newly acquired MOMS images that can be applied to many fields of thematic investigations.