Pierluigi Silvestrin

The use of GPS measurements for water vapor determination

Abstract A workshop on the use of Global Positioning System (GPS) measurements in weather and climate with emphasis on water vapor determination, was organized by the National Environmental Research Councils (NERC) Environmental Systems Science Centre (ESSC), at the University of Reading, Reading, United Kingdom, and took place there 29–31 August 2001. This paper gives a broad overview and general background of the use of GPS data for weather and climate. It outlines the objectives of the workshop and presents ongoing national, regional, and international activities both for ground-based and satellite-based systems. This includes work in the United States, China, and Japan, and different European efforts, including activities under European Community programs. Data assimilation of GPS data for weather prediction and climate is discussed as are ways in which to develop GPS-based systems to become an integrated part of the World Weather Watch. This includes ways of systematically using GPS data from the in...

Control and navigation aspects of the new Earth observation missions of the European Space Agency

Abstract Several new space missions are under development within ESAs Earth Observation (EO) programmes. By 2009 the following satellites will be launched: Cryosat (ice altimetry); GOCE (Gravity field and steady-state Ocean Circulation Explorer); SMOS (Soil Moisture and Ocean Salinity); Aeolus (atmospheric winds); Swarm (magnetic field). Other prepared projects include the SPECTRA (Surface Processes and Ecosystem Changes Through Response Analysis) mission. These missions are briefly reviewed, emphasizing control/navigation aspects when instrumental to the novel EO data. Two representative examples, GOCE and SPECTRA, are described in more detail. Relevant sensor and actuator technology aspects are also outlined.

Satellite Formation for a Next Generation Gravimetry Mission

The technique called “Low-Low Satellite-to-Satellite Tracking” makes use of two-satellite loose formations for detecting the Earth’s gravity field and its space/time variations: the effect of the geopotential shows up as a variation of the inter-satellite distance, which is measured by a suitable metrology. Accelerometers are utilized on each satellite for measuring and separating the effect of the non-gravitational forces. Thales Alenia Space Italia (TAS-I) has studied for the European Space Agency a gravimetric mission of this kind, in which the inter-satellite distance variation is measured by a laser interferometer. The reference mission scenario that has been defined and studied consists of two satellites flying along the same circular orbit at 10 km relative distance and 325 km altitude. The formation control for this mission shall be designed to work in synergy with the drag-free control (necessary for providing quiet operational environment to the accelerometers), to not interfere with the scientific measurement and to minimize the use of the thrusters. Another control system is in charge of maintaining the fine pointing of the interferometer laser beam from one satellite to the other. This chapter summarizes the main results of the studies performed by TAS-I and its team on these subjects 1 2 3.

The ESA earth explorer EarthCARE mission

The EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) mission has been recently selected as the 6th ESAs Earth Explorer Mission. The mission objective is to determine, in a radiatively consistent manner, the global distribution of vertical profiles of cloud and aerosol field characteristics. A major innovation of the EarthCARE mission is to include both active and passive instruments on a single platform, which allows for a complete 3-D spatial and temporal picture of the radiative flux field at the top of the atmosphere and the Earths surface to be developed. While the active instruments provide vertical cloud profiles, the passive instruments (mainly the multi-spectral imager) provide supplementary horizontal data to allow for the extrapolation of the 3-D cloud and aerosol characteristics. The EarthCARE payload is composed of four instruments: an Atmospheric backscatter Lidar, a Cloud Profiling Radar, a Multi-Spectral Imager and a Broad Band Radiometer. The mission baseline is a sun-synchronous orbit with an altitude around 450 km. The EarthCARE mission is a cooperative mission with Japan (JAXA and NiCT), which will provide the Cloud Profiling Radar. ESA will provide the ground segment and the rest of the space segment including the lidar, the imager and the broadband radiometer. The launch is planned for 2012.

Robust Attitude Control Design for the BIOMASS Satellite (Earth Explorer Core Mission Candidate)

Abstract The purpose of this paper is to describe the current activities, results to date, and future activities of the European Space Agency (ESA) Robust AOCS technology program in support to the Phase A of BIOMASS, candidate as Earth Explorer Core Mission 7. Due to the specificity of the chosen BIOMASS configuration this activity is driven by the expected interaction between the large flexible reflector antenna structure and its attitude control system. Currently ESA has developed a technology program to enable the capabilities of integrating the structural sizing and control system design in order to avoid interactions problems. The objective is the development of an Integrated Modeling, Control and Analysis framework IMCA: it incorporates uncertainty modeling via LFTs, robustness analysis via the Structured Singular Value μ and various robust control synthesis techniques such as H ∞ and μ methods. This framework results as natural multivariable extensions of the classical Bode frequency domain techniques. It shall be integrated with a structural design loop into an unified computational framework to exploit control structures interactions in order to increase the spacecraft capabilities, such as better pointing stability, and to improve the overall design when compared to the traditional approach. In the execution of this program two parallel activities will be presented, respectively one by Astrium Limited, UK, and the other by ThalesAlenia Space (TAS), Italy.

ESA Earth Explorer Land Surface Processes and Interactions mission

The European Space Agency (ESA) is defining candidate missions for Earth Observation. In the class of the Earth Explorer missions, dedicated to research and pre-operational demonstration, the Land Surface Processes and Interactions Mission (LSPIM) will acquire the accurate quantitative measurements needed to improve our understanding of the nature and evolution of biosphere-atmosphere interactions and to contribute significantly to a solution of the scaling problems for energy, water and carbon fluxes at the Earths surface. The mission is intended to provide detailed observations of the surface of the Earth and to collect data related to ecosystem processes and radiation balance. It is also intended to address a range of issues important for environmental monitoring, renewable resources assessment and climate models. The mission involves a dedicated maneuvering satellite which provides multi-directional observations for systematic measurement of Land Surface BRDF (Bi-Directional Reflectance Distribution Function) of selected sites on Earth. The satellite carries an optical payload: PRISM (Processes Research by an Imaging Space Mission), a multispectral imager providing reasonably high spatial resolution images (50 m over 50 km swath) in the whole optical spectral domain (from 450 nm to 2.35 micrometer with a resolution close to 10 nm, and two thermal bands from 8.1 to 9.1 micrometer). This paper presents the results of the Phase A study awarded by ESA, led by ALCATEL Space Industries and concerning the design of LSPIM.

The ESA Earth Observation Programmes Activities for the Preparation of the Next Generation Gravity Mission

In this paper the main results concerning the preparatory studies of a future ESA Earth Observation gravity mission are presented: the mission will be ultimately devoted to improve our understanding of the Earth’s mass transport phenomena, the temporal variations of the gravity field, at different temporal and spatial scales, being caused by mass changes of ice sheets and ice caps, continental water cycles, ocean masses dynamics and solid-earth deformations. The “Assessment of a Next Generation Gravity Mission for Monitoring the Variations of the Earth’s Gravity” study (concisely: NGGM) consisted of two parallel activities followed by two consortia: each one has involved European universities and academic institutions for scientific support and requirement assessments, in addition to experts in mission analysis and measurement technologies. Several mission concepts have been studied with well-defined science requirements and accurate sub-system designs: in addition to the drivers due to tight propulsion requirements and accelerometer calibration issues, the technical constraints on power and fuel may dictate the choice of orbit. Thus, for each considered constellation type, the different interactions between dragfree and “loose” formation control have been analyzed, together with the design of the relative attitude control, necessary to ensure the laser link for inter-satellite distance measurement all along the mission phases. The latest results concerning the proposed satellite architectures, laser metrology, attitude and orbit control system and formation flying control concepts are presented in the paper, together with the on-going activities for increasing the technological readiness level of the main subsystems. A broad overview is given on the status of the miniaturized RIT and mN-FEEP breadboarding and testing for what concerns the micro-propulsion subsystem, while, concerning the laser metrology, the laser head and the laser stabilization device are described at unit level, with a discussion on the thermal requirements derivation.

PREMIER's imaging IR limb sounder

The Imaging IR Limb Sounder (IRLS) is one of the two instruments planned on board of the candidate Earth Explorer Core Mission PREMIER. PREMIER stands for PRocess Exploration through Measurements of Infrared and Millimetrewave Emitted Radiation and is presently under feasibility study by ESA. Emerging from recent enhanced detector and processing technologies IRLS shall, next to a millimetre-wave limb sounder, explore the benefits of three-dimensional limb sounding with embedded cloud imaging capability. Such 3d imaging technology is expected to open a new era of limb sounding that will allow detailed studies of the link between atmospheric composition and climate, since it will map simultaneously fields of temperature and many trace gases in the mid/upper troposphere and stratosphere across a large vertical and horizontal field of view and with relatively high vertical and horizontal resolution. PREMIER shall fly in tandem formation looking backwards to METOPs swath and thereby explore the benefit of 3-dimensional information for meteorological/environmental analyses and climate forcing investigations. As currently planned and if implemented, IRLS will cover a total horizontal field of about 360 km and observe the limb at altitudes between 4 and 52 km. The vertical spatial sampling distance (SSD) will be well below 1 km. It will be run in two different exclusive modes to address scientific questions about atmospheric dynamics and chemistry at spectral samplings of ~1.2 cm-1 and ~0.2 cm-1, respectively. In such configuration IRLS will be composed of an imaging array with about 1800 macro pixels or sub-samples, thereby allowing cloud imaging and rejection at sufficient spatial resolution. We will present an overview of the instrument requirements as derived from the scientific requirements, the present status of the mission, and we will give an overview of the currently identified technology needs and instrument predevelopments.

Preliminary AOCS Design for Pointing Budget Assessment of the BIOMASS Candidate Earth Explorer Core Mission

Abstract This paper presents the preliminary assessment of the attitude control design and performance for a baseline concept of the Biomass mission, a candidate for ESAs next Earth Explorer Core Missions. This satellite concept, as conceived at the end of the Phase 0 studies, has a 20-meter P-band antenna, for which the impact of high flexibility and uncertainty must be assessed. As a result, a rapid prototyping procedure has been established to assess the feasibility of various performance and robustness requirements at an early stage of the satellites development. This has been done by incorporating a covering uncertainty model to reflect the structural dynamics with associated tolerances. This allows the use of a control design solely based on rigid dynamics, resulting in a low-order control solution, for which coverage is demonstrated by means of multivariable robust performance and stability margins expressed in the structured singular value metrics. Using non-linear simulations, we demonstrate the suitability of the robust design approach to the selected satellite concept.

System, spacecraft, and instrument concepts for the ESA Earth Explorer EarthCARE Mission

The EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) mission has been recently selected as the 6th ESAs Earth Explorer Mission. The mission objective is to determine, in a radiatively consistent manner, the global distribution of vertical profiles of cloud and aerosol field characteristics. A major innovation of the EarthCARE mission is to include both active and passive instruments on a single platform, which allows for a complete 3-D spatial and temporal picture of the radiative flux field at the top of the atmosphere and the Earths surface to be developed. While the active instruments provide vertical cloud profiles, the passive instruments (mainly the multi-spectral imager) provide supplementary horizontal data to allow for the extrapolation of the 3-D cloud and aerosol characteristics. The EarthCARE payload is composed of four instruments: an Atmospheric backscatter Lidar, a Cloud Profiling Radar, a Multi-Spectral Imager and a Broad Band Radiometer. The mission baseline is a sun-synchronous orbit with an altitude around 450 km. The EarthCARE mission is a cooperative mission with Japan (JAXA and NICT), which will provide the Cloud Profiling Radar. ESA will provide the ground segment and the rest of the space segment including the lidar, the imager and the broadband radiometer. The launch is planned for 2012.