Filippo Graziani

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.

Use of weak stability boundary trajectories for planetary capture

The consideration of transfers to the Weak Stability Boundary region represents one of the most advanced concepts when trying to reduce the propellant requirements to obtain an interplanetary goal. Deimos Space, under ESA contract, has developed a tool to simulate such transfers to inner planets, giant planets and natural moons of giant planets. The method is based on a three-step approach consisting on: selection of strategy, generation of initial solutions and numerical optimisation. The feasibility of building WSB transfer trajectories to Mercury, Venus and Mars has been proven. Instead of ∆V saving, the greatest advantage results from the increased flexibility in the selection of the final orbit with no ∆V penalty in most cases. The use of the Sun/Planet WSB region for the problem of giant planets capture does not introduce significant profit since the penalty in transfer time makes the mission unrealistic. Feasible missions to Jupiter and Saturn are obtained when using a double flyby strategy in Ganymede and Titan respectively. The capture by a natural moon of a giant planet incorporates a phase of energy reduction by moon flybys using resonant orbits linking at the end with the WSB region of the moon to achieve a ballistic capture.

Soft Magnets for Passive Attitude Stabilization of Small Satellites

The spinning and oscillatory motions of small orbiting satellites can be damped exploiting the magnetic energy dissipation occurring in onboard soft magnetic strips, cyclically excited by the oscillation of the earth field component along their axis. In this paper we investigate the role played by the intrinsic magnetic properties of the material, the aspect ratio of the strips, and their mutual arrangement in achieving maximum energy dissipation under typical spacecraft working conditions. Grain-oriented Fe-Si, mumetal, and Fe-based amorphous alloys, all endowed with near-rectangular hysteresis loops, are considered. Their energy loss behaviour is calculated when, either as single strip samples or arranged into an array of strips, they are subjected to a slowly oscillating magnetic field of defined peak value, emulating the action of the earth magnetic field on the travelling satellite. The strip size and array layout leading to maximum energy loss are predicted. Amorphous alloys, combining high saturation magnetization with flexible hysteresis loop properties, are shown to lead to the best damping behaviour under both oscillating and spinning satellite motions. In the latter case the Fe-Si strips appear to provide comparably high damping effects, while inferior behaviour is always predicted with mumetal samples.

Elastic waves propagation in bounded periodic structures

Abstract Large space structures are mostly designed and constructed by repetitive lattice grids. Continuum models have been proposed in the literature as a simple means for the structural analysis of lattices. However continuum models hide some typical properties of the modular structures, such as their filtering effects. This paper investigates the differences between continuum and periodic models of a modular structure from the point of view of the elastic wave propagation. The analysis reveals that only for small wave numbers the models are equivalent, otherwise the dispersive behavior strongly differs and the continuum models become no longer effective.

Debris cloud evolution: Mathematical modelling and application to satellite constellation design☆

Abstract Orbital break-ups produce a large number of fragments, which constitute an obvious hazard for other satellites in nearby orbits. Of these fragments, many are too small to be detected by ground-based facilities: this leads to the need for mathematical modelling as a tool for adequate risk analysis. In this paper an average spatial density model is presented. It is based on the Gauss analogy and, for unperturbed Keplerian orbits, it matches the asymptotic density model developed by other authors. Risk analysis for satellite constellations is an interesting application of debris cloud evolution models: the survivability of a constellation as a whole following the break-up of one of its satellites is obviously of primary concern in the constellation design. Risk analysis is conducted over a number of traditional configurations in order to achieve an additional constraint on the design parameters. Results indicate the remarkable influence of the fragmentation point position along the orbit; moreover, the higher risk for low orbit and the advantage of placing more satellites on a limited number of planes are assessed.

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.