Satellite remote sensing and non-destructive testing methods for transport infrastructure monitoring: advances, challenges and perspectives

High temporal frequency monitoring of transport infrastructure is crucial to prioritise mainte-nance and prevent major service disruption or structural failures. Ground-based non-destructive testing (NDT) methods have been successfully applied for decades, reaching very high standards for data quality and accuracy. However, routine campaigns and long inspection times are re-quired for data collection and their implementation into reliable infrastructure management systems (IMSs). On the other hand, satellite remote sensing techniques, such as the Mul-ti-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) method, have proven effective in monitoring ground displacements of transport infrastructure (roads, railways and airfields) with a much higher temporal frequency of investigation and the capability to cover wider areas. Nevertheless, the integration of information from i) satellite remote sensing and ii) ground-based NDT methods is still a subject to be fully explored in civil engineering. This paper aims to review significant stand-alone and combined applications in these two areas of endeavour for transport infrastructure monitoring. Recent advances, main challenges and future perspectives arising from their mutual integration are also discussed

Libration Damping System in the Attitude Stabilization of University Microsatellites

In the last twenty years a large impulse in the production of micro and nanosatellites has been recorded all over the world. A number of space university programs started in different countries with the aim to provide students with hands-on training in the field of space technologies. In this field the Gruppo di Astrodinamica dell’Università degli Studi di Roma “La Sapienza” (GAUSS), has been working for more than 15 years with the UNISAT program. Currently, three new educational projects are under development: Unisat-5, EduSAT and UNICubeSAT. Both UNISAT-5 and EduSAT satellites use passive attitude stabilization systems, which permit to keep costs low and to get adequate system reliability. In the paper an overview of EduSAT and UNISAT-5 attitude stabilization systems and an analysis of the main issues related to these topics are given. Moreover the paper deals with the design and sizing of a libration damping system in the attitude stabilization of EduSAT, stabilized by a passive magnetic system, and UNISAT-5, stabilized by a gravity gradient boom. Finally, results of numerical simulations are sketched. Keywords: Satellite, attitude stabilization, gravitational stabilization, magnetic stabilization, magnetic damping, hysteresis rod

Optimal geometry and materials for nanospacecraft magnetic damping systems

A magnetic damping system for nanospacecraft attitude stabilization is proposed, based on the use of thin strips of amorphous Fe-B-Si soft magnetic ribbons. The size, number, and location of the strips is optimized, and a predictive formulation is provided. The main result of ground tests, comparing the performance of several soft magnetic materials, is that suitably heat-treated amorphous ribbons provide the best loss performance in the whole range of magnetic fields expected in orbit

EduSAT: An Italian space agency outreach program

In the 2005, the Italian Space Agency (ASI) proposed a program to launch in orbit an educational satellite named EduSAT, with the main goal to promote space education among high school students and to support scientific careers of PhD and university students. Two years later, the EduSAT project started under the ASI coordination and funding. The EduSAT design, manufacturing, launch and operation in orbit has been committed to the Group of Astrodynamics of the "Sapienza" University of Roma (GAUSS), on the basis of this previous experience, the UNISAT program (University Satellite). In the framework of this Italian university program, four student-built satellites have been launched, respectively in 2000, 2002, 2004 and 2006, from Baykonour Cosmodrome, with DNEPR Space Launch System. The educational activity involving high school students has been committed to IMT srl with the contribution of the University of Roma TorVergata. High school students are provided with 2 satellite models, Basic Satellite Training (DTB) and Advanced Satellite Training (DTS), that form the basis for teaching. Students are also involved in the development of a small payload which will be hosted on board EduSAT. The selected payload is a sun sensor. The EduSAT microsatellite is scheduled to be launched in April 2010 with DNEPR launch vehicle. This paper deals with a project overview, satellite architecture and main subsystems description, high school students payload and educational program organization

Hysteresis rods in the passive magnetic stabilization system for university micro and nano satellites

A passive magnetic attitude stabilization system is simple, easy to realize, cheap and does not require software development and energy consumption. Due to these features the passive magnetic attitude stabilization system is one of the most common attitude stabilization systems implemented on board of small satellites. This system is based on a permanent magnet, which has to provide a restoring torque to align an oriented axis of the satellite with the Earth's magnetic field direction, and a energy dissipation system of the satellite angular motion, which can consist on a set of magnetic hysteresis rods. Despite the simplicity of this attitude stabilization system, predicting performance in orbit and evaluating the obtainable accuracy is not trivial. The main problem is represented by necessity of an accurate modelling of the hysteresis rod magnetization and by the evaluation of the main magnetic parameters of the rods. This paper deals with sizing, choice of the material, manufacturing process, arrangement of a set of hysteresis rods on board small satellites and with the development of an experimental setup to measure hysteresis rod parameters. As an example the dynamics of the EduSAT microsatellite is investigated, by numerical simulations

Permeable rods ground testing system for cubesat angular velocity and residual oscillations damping

Permeable rods have been used in passive magnetic attitude stabilization systems since the beginning of space era, as an efficient means to damp out the satellite angular velocity and residual spacecraft oscillatory motion. A new interest in these kinds of systems has arisen with the nanosatellites coming on the space market and the advent of small university satellites, such as Cubesats. Permeable rods can be interesting for these kinds satellite for two main reasons: when the satellite is passively stabilized, either magnetically, gravitationally or aerodynamically, and when there is a possibility that the angular velocity exceeds its maximum allowed threshold for the on-board attitude control system to work correctly. This last situation is related to the fact that the separation system for these kinds of satellites is typically based on spring release mechanisms, which can give a high angular impulse to the spacecraft. The resulting angular velocity can be very high and, in case the on board sensors sampling rate is too low with respect to the angular rate, the on-board attitude determination algorithms functionality is impaired. A safe measure to recover from these kinds of failures consists in installing a passive energy damping system on-board, to damp out the kinetic energy and slow down the spacecraft rotational motion. Despite its conceptual simplicity, the physical phenomena governing the permeable rods magnetization in orbit are very complex and permeable rods design is not trivial. The design process involves the selection of the right combination of permeable rods material, technological manufacturing process, shape, number and location on board the spacecraft. Approximate analytical models describing the permeable rods magnetic behaviour, based on simplifying assumptions, are available for single, magnetically isolated, permeable rods. This is rarely the case in small spacecraft, in which a number of permeable rods are installed to reach the necessary damping effectiveness. Moreover, a lesson learned from the UNISAT-3 microsatellite in orbit performance is that the permeable rod magnetic parameters strongly depend on the manufacturing process. Therefore permeable rods performance can be assessed only by measurements. In this paper a ground testing system is described, for the measurement of a permeable rod system performance in a 1U-Cubesat volume, including a uniform magnetic field generator, pick-up coils and processing algorithms. This system allows to measure the effect of interactions among the rods and to compare different material and geometric configurations performance, improving the confidence in the predictions of in orbit performance. Copyright ©2010 by the International Astronautical Federation. All rights reserved

Passive magnetic attitude stabilization system of the EduSAT microsatellite

Passive magnetic attitude stabilization systems are simple, easy to realize, cheap, and do not require software development and on-board energy consumption. Owing to these features, passive magnetic attitude stabilization systems were selected for the EduSAT (Educational Satellite) microsatellite, a student-built satellite funded by the Italian Space Agency, scheduled to be launched in the last quarter year of 2010. The passive magnetic attitude stabilization system is based on a permanent magnet, which provides a restoring torque to align an oriented axis of the satellite with the Earth’s magnetic field direction, and an energy dissipation system, which can consist of a set of permeable rods magnetized by the oscillation of the geomagnetic field along their axis. UNISAT-3 attitude determination results after 1 year from its launch demonstrated the necessity of an accurate design and manufacturing process of soft magnetic strips. Predicting system performance in orbit and evaluating the obtainable accuracy are not trivial: the main problem is knowing the effective magnetization of the permeable rods. The paper deals with sizing, choice of material, manufacturing process, and arrangement of a set of permeable rods on board the EduSAT microsatellite on the basis of previous flight experience