1,720,963 research outputs found
Design, Assembly and Verification of the ALMASat-1 Separation System
No full textThis paper presents the activities that led to the assembly and verification of the ALMASat-1 microsatellite separation system carried out at the Microsatellite Laboratory of the University of Bologna, Forlì Campus. ALMASat-1 adapter and separation system was designed according to the requirements imposed by the European launch vehicle VEGA, general mission requirements and additional specific requirements related to ALMASat-1 microsatellite geometry and inertial properties. The analysis of these requirements drove the whole design process. The general architecture selected for the interface is the classical cylindrical
canister adapter with a 2-clamps constraining system. This solution, common for micro- and nano- satellites, has a wide flight heritage, is typically simple and affordable and could be easily implemented for a wide range of launch vehicles. The sizing of the whole
mechanism was carried out by means of theoretical calculations while advanced dynamics simulations based on MATLAB and Nastran code were performed to deeply investigate the transient phenomena characterizing the separation dynamics in the very first tens of milliseconds.
Along with numerical simulations, experimental tests have been performed by means of a separation test-bed, specifically designed to reproduce the correct dynamics of both the separation system and the spacecraft. As part of this experimental activity, the spacecraft angular velocities arising from potential non-symmetric actions of the four DV springs or clamps asynchronous actuation were estimated. This evaluation is extremely important in order to avoid damages to the satellite, other payloads and LV upper stage due to possible collisions. Finally, the structural and topological optimization process performed on the ALMASat-1 Adapter and Separation System will be presented, focusing on the reduction of
the system overall mass which, in turns, determines the launch costs and represents one of the most critical aspects in microsatellite missions
Optimized separation system for small satellites missions
No full textThe launch phase is a critical step in a spacecraft operative life and it is therefore mandatory to provide for a robust and reliable interface between the launch vehicle and the spacecraft, focusing the attention at the same time on both the mechanical aspects and the resulting mass, due to the impact on the overall launch costs.
In this paper the Separation System designed and manufactured by ALMASpace S.r.l. is described, taking into account the FM provided for the ALMASat-1 mission, as interface with the VEGA launch vehicle: concerning the mechanical aspects, the entire design and optimization workflow is presented; in the second half the qualification test campaign performed in order to verify the compliancy with the requirements imposed by the launch vehicle is described.
In particular, since the entire Separation System would like to become a future standard for microsatellite-class spacecrafts, the requirements imposed by the VEGA launch vehicle have been taken into account: the vibration, thermal vacuum and functional tests results will be reported.
The test campaign confirmed the good quality of both the numerical analysis performed on the Separation System and the manufacturing process, allowing the Separation System to achieve the full qualification for the launch
Design and Verification of an Optimized Separation System for Microsatellites: The ALMASat-1 Case Study
No full textThe time of separation of a satellite from its launch vehicle often signs the beginning of its operational life in orbit and this is especially true for micro- and nano-satellites. To preserve the integrity and the efficiency of the spacecraft during launch and perform a correct separation capable to grant safe operations of the spacecraft in orbit, it is necessary to design and manufacture an efficient and reliable interface and separation system from the launch vehicle. The VEGA Qualification Flight has now been postponed till the end of 2010 and several payloads will be released in orbit. First, a scientific payload named LARES will be released along a circular 1450x1450 km orbit, at 71 of inclination. ESA and ASI agreed on embarking a set of secondary payloads which will be released along an elliptic de-orbiting trajectory, after the perigee of the upper stage will be lowered to about 350 km. The 10 secondary payloads include 9 Cubesats and ALMASat-1, the first microsatellite developed, manufactured and assembled by the University of Bologna, Forlì Campus. ALMASat-1 flight opportunity was granted to the University of Bologna under the obligation that the S/C adapter and separation system was part of the ALMASat-1 systems. This paper presents the activities that led to the design, manufacturing, verification and qualification of the ALMASat-1 separation system carried out at the Microsatellite Laboratory of the University of Bologna. The general architecture selected for the interface is the classical cylindrical canister adapter with a 2-clamps constraining system. This solution, common for micro- and nano-satellites, has a wide flight heritage, is typically simple and affordable and could be easily implemented for a wide range of launch vehicles. In order to reduce the power consumption and enhance the system reliability and safety, the release clamps will be retained by Non- Explosive electro-mechanical Actuators (NEA) that allow to preload two couples of springs, one pair for each clamp, until the separation signal is obtained by the LV avionics. Along with numerical simulations, experimental tests have been performed by means of a separation test-bed, specifically designed to reproduce the correct dynamics of both the separation system and the spacecraft. Finally, the structural optimization process performed on the ALMASat-1 Adapter and Separation System will be presented, focusing on the reduction of the system overall mass which, in turns, determines the launch costs and represents one of the most critical aspect in microsatellite missions
ALMASat Microsatellite Structural Analysis: Numerical and Experimental Correlation and Optimization
No full textThe ALMASat Microsatellite is the first educational satellite of Alma Mater Studiorum, University of Bologna. The satellite, designed and built following a general low-cost guideline focused mainly on affordable solutions, modular concepts and COTS components, will be launched in 2008. The initial conceptual design produced a first configuration of the satellite, which has been verified by finite elements analyses, in order to check compatibility with launch vehicle requirements and to reduce structural mass, maintaining at the same time good mechanical properties. An iterative optimization procedure has been performed, involving numerical analyses and subsequent modifications to the structure, in order to reduce material and weight. Moreover, the finite elements model has been improved introducing bolted joints, pre-stresses and increasing the overall accuracy, while optimized modeling methods have been used in order to maintain an acceptable computational time. The results of the analyses have been used to produce a first prototype of the ALMASat structure. In early July 2005, at ENEA Casaccia Laboratory (Rome, Italy), a set of vibration tests has been performed, as verification for the analytical and numerical methods and the optimization procedure. The results of the tests have been compared with numerical data in order to improve the finite elements model for better performances and precision. In particular, the tests stressed the importance of acceleration measurement. The results of numerical spectrum analyses, such as transfer function and PSD nodal response, combined with tests results, have been useful to define the proper mechanical interfaces for devices, on-board systems and payload. In addition, due to non-linear constraint condition, the results correlation has been performed using non-standard techniques based on explicit finite elements codes, which provided the dynamic response of the structure to launch acceleration loads. The time-history post-processing and frequency analysis of the response provided an amplitude/frequency output directly comparable with experimental results. Most of the finite elements simulation techniques, concepts and results herein discussed are suitable for a wide range of small satellites, designed following the same principles of modularity and affordability used for ALMASat
Improvements in Materials Technologies for Low-cost Microsatellites Structures: from Aluminum to Carbon Fiber
No full textLow-cost microsatellites structures represent an extremely interesting challenge and a excellent technology workbench. The contrast between the need of limited weights imposed by launch costs on a hand and the need of a safe satellite structure capable to protect devices and payloads during launch on the other, induces researchers to evaluate a wide range of alternative solution from traditional technologies and material to advanced structures and concepts. The goal is to achieve the best compromise between weight, performances and costs. In this paper will be presented the goals and results of the improvement process which involved the structure of ALMASat-1, the first microsatellite of the University of Bologna. As example the upper plate of the modular structure had been improved. Starting from the analysis of the component, originally realized from a machined aluminum plate, it has been possible to define critical parameters as reference for performance comparison between different technologies and materials. The first frequency of the modal analysis, as well as the overall shape of the plate, have been taken as fixed parameters.
Once defined the new materials and technologies, carbon fiber lamination in this case, it has been possible to determine the total plate thickness, number of layers and their orientation thanks to an iterative analysis procedure. A specific ANSYS code had been developed to modify dynamically the thickness of the plate and execute a series of modal analysis until the first natural frequency calculated was equal to the reference parameter previously set.
In order to verify the dynamic behavior of the plate in launch environment a further Power Spectral Density analysis has been performed evaluating the statistical results in terms of displacements, accelerations, global and layer stresses and frequency response by using advanced post-processing techniques.
As result a new carbon fiber upper plate will be produced and tested in order to correlate numerical and experimental results and confirm the technology improvement success
TEST DI VIBRAZIONE CONDOTTI SUL MICROSATELLITE ALMASAT-1
No full textIl presente articolo illustra e riassume l’attività di qualifica al volo spaziale dei sottosistemi del satellite ALMASat-1 svolta presso il laboratorio per prove di vibrazione della Seconda Facoltà di Ingegneria dell’Università di Bologna, sede di Forlì. Nello specifico, vengono presentati i test di vibrazione condotti sui singoli sottosistemi che compongono il microsatellite universitario, allo scopo di verificare la robustezza dei diversi componenti alle sollecitazioni previste durante il lancio, che avverrà mediante il lanciatore VEGA, a bordo del quale ALMASat-1 sarà alloggiato. Per l’esecuzione dei test sono stati utilizzati uno shaker elettrodinamico Dongling ES-2-150 e la relativa piattaforma di controllo ed acquisizione LMS Test.Lab/SCADAS III forniti da LMS Italiana, in dotazione al laboratorio
Almasat Microsatellite structural analysis: finite element techniques, vibration tests and results correlations
No full textThe ALMASat Microsatellite is the first educational satellite of Alma Mater Studiorum, University of Bologna. The satellite, designed and built following a general low-cost guideline focused mainly on affordable solutions, modular concepts and COTS components, will be launched in 2006 by a Dnepr vehicle.
The initial conceptual design produced a first configuration of the satellite, which has been verified by finite elements analyses, in order to check compatibility with launch vehicle requirements and to reduce structural mass, maintaining at the same time good mechanical properties. An iterative optimization procedure has been performed, involving numerical analyses and subsequent modifications to the structure, in order to reduce material and weight. Moreover, the finite elements model has been improved introducing bolted joints, pre-stresses and increasing the overall accuracy, while optimized modeling methods have been used in order to maintain an acceptable computational time.
The results of the analyses have been used to produce a first prototype of the ALMASat structure. In early July 2005, at ENEA Casaccia Laboratory (Rome, Italy), a set of vibration tests has been performed, as verification for the analytical and numerical methods and the optimization procedure.
The results of the tests have been compared with numerical data in order to improve the finite elements model for better performances and precision. In particular, the tests stressed the importance of acceleration measurement. The high values measured in some critical points for electronics and payloads, forced to modify the local geometry in order to decrease acceleration values in such stressed areas.
The results of numerical spectrum analyses, such as transfer function and PSD nodal response, combined with tests results, have been useful to define the proper mechanical interfaces for devices, on-board systems and payload.
Most of the finite elements simulation techniques, concepts and results herein discussed are suitable for a wide range of small satellites, designed following the same principles of modularity and affordability used for ALMASat
THE ADAPTER AND SEPARATION SYSTEMS SERIES FOR THE VEGA LAUNCH VEHICLE
No full textThe VEGA Maiden Flight represented an important milestones for the ALMASat-1 program. In that frame, ALMASpace has been in charge of the design, manufacturing, testing and qualification for launch of the ALMASat-1 ADapter and Separation System (AD-SS), retaining the spacecraft during the early launch phases and providing the S/C separation when the separation command was received from the on-board avionics.
The ALMASpace AD-SS has been sized and qualified for the launch according to the VEGA requirements, therefore being hitherto the real benchmark for future missions onboard the VEGA flights for satellites up to 35 kg.
In order to extend the AD-SS capabilities to larger spacecraft, ESA has undertaken an activity aimed at the development and qualification of a wider series of products, achieving the goal of supporting satellites missions up to 200 kg, thanks to an overall set of three different AD-SS models.
This paper presents the improvements and the results of the design phases, started in late 2011, aimed at the completion of the second model of ALMASpace AD-SS and its delivery to ESA for the integration on the next VERTA-1 mission, currently scheduled in early 2013
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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