The Laser Interferometer Space Antenna (LISA) mission, that will provide the first dedicated space-based gravitational wave observatory, is based on laser interferometry between free-flying test masses enclosed in three drag-free spacecraft. Each test mass is firstly retained and then released by the Grabbing, Positioning and Release Mechanism (GPRM) to be then set into a purely geodesic trajectory. Upon the test masses release tests of LISA Pathfinder mission, it was found out that the test mass release velocities were up to ten times higher than the ones expected. Despite the electrostatic suspension actuation, managed by a robust sliding mode controller, was finally able to deal with the dynamics of each free-floating test mass, for LISA mission a further investigation is necessary. This thesis will focus on the on-board software used for the electrostatic control of a free-falling test mass upon its release and, in particular, on the development of a new test mass controller for the accelerometer mode of the Drag-Free Attitude Control System (DFACS). Starting from the promising results on the test mass actuation algorithm and control law based on a DC electrostatic actuation with no duty cycle, a new control law will be designed, with the aim of reducing the capturing time of the test mass and exploiting the whole available actuation authority given by the Gravitational Reference Sensor (GRS) hardware, for coping with critical test mass release conditions. Different electrostatic actuation schemes (both DC and AC actuation, with and without duty cycle) will be used for testing the obtained control law for different design scenarios, comparing the time-simulation results to the ones of the already existing accelerometer mode controllers. Finally, the maximum capabilities of each control architecture, i.e. combination of control law and actuation scheme, will be investigated, firstly finding the maximum controllable test mass release velocity and then deriving a new proposal for the test mass release requirements. The obtained results will provide a useful baseline for improving the GRS hardware surrounding each test mass.
La missione Laser Interferometer Space Antenna (LISA) costituirà il primo osservatorio spaziale di onde gravitazionali ed è basata sull'interferometria laser tra due masse di prova in caduta libera racchiuse dentro tre satelliti dotati di un sistema di sospensione drag-free. Ogni massa di prova è prima vincolata e in seguito rilasciata dal meccanismo di cattura, posizionamento e rilascio (GPRM) per venire immessa su una traiettoria geodetica. Durante i rilasci di prova della missione LISA Pathfinder, le velocità di rilascio sono state fino a dieci volte maggiori di quelle previste. Nonostante l'azione elettrostatica usata per controllare le masse di prova, governata da un controllore sliding mode, sia stata infine in grado di controllare la dinamica delle masse in caduta libera, sono necessarie ulteriori analisi in vista della missione LISA. Questa tesi si concentrerà sullo studio del software di bordo usato per il controllo elettrostatico delle masse di prova al momento del loro rilascio e, in particolare, sullo sviluppo di un nuovo controllore facente parte della modalità accelerometer mode del sistema Drag-Free Attitude Control System (DFACS). Partendo dai risultati promettenti ottenuti nell'algoritmo di conversione da forze/coppie a tensioni e nella legge di controllo delle masse di prova, verrà progettata una nuova legge di controllo che riduca il tempo necessario alla cattura di ciascuna massa di prova e sfrutti tutta l'autorità di controllo data dal sensore inerziale (GRS). Verranno utilizzati diversi sistemi di controllo elettrostatico (sia a corrente continua che alternata, con e senza duty cycle) per mettere alla prova la nuova legge di controllo e i risultati delle simulazioni verranno confrontati con quelli delle leggi di controllo già esistenti per l'accelerometer mode. Infine, i limiti di ciascuna architettura di controllo verranno analizzati, dapprima trovando la massima velocità di rilascio che può essere correttamente controllata e in seguito derivando una nuova proposta per i requisiti di rilascio delle masse di prova. I risultati ottenuti forniranno un utile punto di partenza per migliorare il GRS.
Time-optimal electrostatic control and capture of a free-falling test mass
Gioia, Andrea
2019/2020
Abstract
The Laser Interferometer Space Antenna (LISA) mission, that will provide the first dedicated space-based gravitational wave observatory, is based on laser interferometry between free-flying test masses enclosed in three drag-free spacecraft. Each test mass is firstly retained and then released by the Grabbing, Positioning and Release Mechanism (GPRM) to be then set into a purely geodesic trajectory. Upon the test masses release tests of LISA Pathfinder mission, it was found out that the test mass release velocities were up to ten times higher than the ones expected. Despite the electrostatic suspension actuation, managed by a robust sliding mode controller, was finally able to deal with the dynamics of each free-floating test mass, for LISA mission a further investigation is necessary. This thesis will focus on the on-board software used for the electrostatic control of a free-falling test mass upon its release and, in particular, on the development of a new test mass controller for the accelerometer mode of the Drag-Free Attitude Control System (DFACS). Starting from the promising results on the test mass actuation algorithm and control law based on a DC electrostatic actuation with no duty cycle, a new control law will be designed, with the aim of reducing the capturing time of the test mass and exploiting the whole available actuation authority given by the Gravitational Reference Sensor (GRS) hardware, for coping with critical test mass release conditions. Different electrostatic actuation schemes (both DC and AC actuation, with and without duty cycle) will be used for testing the obtained control law for different design scenarios, comparing the time-simulation results to the ones of the already existing accelerometer mode controllers. Finally, the maximum capabilities of each control architecture, i.e. combination of control law and actuation scheme, will be investigated, firstly finding the maximum controllable test mass release velocity and then deriving a new proposal for the test mass release requirements. The obtained results will provide a useful baseline for improving the GRS hardware surrounding each test mass.| File | Dimensione | Formato | |
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2020_12_Gioia.pdf
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https://hdl.handle.net/10589/175041