Fabrizio Piergentili

Determination of disposed-upper-stage attitude motion by ground-based optical observations

The results of an observation campaign devoted to the determination of the rotational state of uncontrolled disposed upper stages by ground-based optical observations are presented. The photometric analysis is performed to extract light curves from photographs obtained by a camera based on charge-coupled devices. The rotation-axis direction and rotation period are determined comparing measurements with theoretical predictions obtained in the simplifying assumption of cylindrical diffusely reflecting cylinders. The angular speed is evaluated by the light-curve period. The direction of rotation axis is evaluated by measuring the difference between the maximum and minimum apparent magnitude of disposed upper stages. This evaluation can be performed from a single observing site by combining measurements collected during a suitable observation time span. The results achieved for two orbiting objects are reported showing a good agreement between determinations obtained in completely different observation geomet...

Analysis of the UNISAT-3 solar array in-orbit performance

DOI: 10.2514/1.32392 A technological experiment to assess the in-orbit performance of non-space-rated solar arrays is onboard the microsatellite UNISAT-3. These include terrestrial-technology monocrystalline silicon and low-efficiency triplejunction solar arrays, assembled using commercial off-the-shelf materials and following conventional non-spacerated procedures. A space-rated monocrystalline silicon solar array is also onboard, used for comparison of the achieved results. The manufacturing process is described andthe solararray performance is evaluated based on the data collected in the first two-and-a-half years of operation in orbit. For both terrestrial-technology and lowefficiencytriple-junctionsolararrays,theobservedsolararraydegradationisveryfastinthe firsthalf-year,inwhich approximately one-fourth of the initial efficiency is lost. Then degradation stabilizes, showing a long-term decaying rate with a time constant of ten years, which makes the suggested technology suitable for small scientific and educational low-Earth-orbit spacecraft.

Passive magnetic attitude stabilization system of the EduSAT microsatellite

Abstract 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 Earths 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.

Designing, manufacturing, and testing a self-contained and autonomous nanospacecraft attitude control system

AbstractThis paper describes the development of a three-axis attitude control system for nanosatellites and CubeSats, based on commercial electronics and capable to work autonomously for attitude stabilization or controlled from Earth to perform real-time orientation maneuvers. The system contains three microreaction wheels and related drivers, three magnetorquers with their control circuits, three magnetometers, and control electronics. The system is completely independent from the host spacecraft, with all systems included in its structure. For autonomous attitude control, an external sensor is required, providing the orientation of a reference source, such as the sun, eventually evaluated based on solar array outputs, Earth, or stars. The communication interface is based on a serial link and can be used to transfer commands, parameters, and housekeeping data. Miniaturization of the system components and of the whole assembly are among the main innovations introduced with respect to traditional attitude...

Attitude Determination of Orbiting Objects from Lightcurve Measurements

This paper describes a method based on virtual reality tools to achieve the attitude determination of an orbiting object using lightcurve measurements. A virtual model of the orbiting object is propagated in order to reproduce its lightcurve. The differences between the real and simulated lightcurves are used as the cost function to be minimized through a multiobjective genetic algorithm. Lightcurve measurements in different spectral bands, both with monostatic and multistatic optical observations can be used. The method is applied to the real measurements taken from Cerro Tololo and Flagstaff Observatory of the spacecraft GSAT3. A set of attitude parameters compatible with the measured lightcurves is identified and discussed.

Efficient Fast Open-Loop Attitude Control Strategy for Earth Imaging Nanospacecraft

AbstractThis paper proposes a computationally efficient attitude control strategy for nanospacecraft fast reorientation maneuvers. The paper considers a 3U CubeSat for visual Earth observation miss...

Design, Manufacturing, and Ground Testing of a Control-Moment Gyro for Agile Microsatellites

AbstractA recently emerged driving requirement for microsatellites is a precise and fast attitude maneuvering capability. Agility enhances the operational efficiency of missions requiring a high le...

Spacecraft Recognition in Co-Located Satellites Cluster Through Optical Measures

The optical orbit determination is one of the most important ways for noncooperative object tracking. One of the main problems with noncooperative object tracking is its recognition through different nights. In this study, the conditions that ensure the recognition of a geostationary satellite inside a cluster were assessed through a hard real case study. This study was developed through a three-phase approach. The first phase was the observation campaign for the images acquisition. The second phase was the images astrometric reduction for the data collection and the third phase was the orbit determination and data analyses. To evaluate the recognition ability, the residuals between the celestial coordinates obtained from the propagated orbit, which was carried out from the fitting between first night data and the environment gravity model through a least squares approach, and the measures collected during the second night were assessed. This approach, which is totally independent from the satellite cooperation actions, can be extended to the space debris recognition during different nights.

Design of a Small Educational Satellite for the Italian High School Students: The EduSAT Project

This chapter deals with the design of the EduSAT microsatellite: a small educational satellite developed by the Group of Astrodynamics of University of Roma “Sapienza” (GAUSS), on the basis of its previous experience. The UNISAT program (UNIversity SATellite) started at School of Aerospace Engineering of Roma in the early nineties. The EduSAT Project is funded and coordinated by Italian Space Agency with the aim to promote space education among high school students and to support the qualification and scientific careers of young people (university students, PhD students and young researchers). Another target of this program is to develop a small space mission for low cost scientific experiments and technological tests in orbit. The launch of EduSAT microsatellite is scheduled in 2010: a cluster launch in Low Earth Orbit, performed by Russian-Ukrainian DNEPR Launch Vehicle. This chapter synthesizes project motivations, program organization and describes system architecture and satellite main subsystems design.