In-flight testing of the injection of the LISA Pathfinder test mass into a geodesic |
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| Authors: | D. Bortoluzzi D. Vignotto A. Zambotti M. Armano H. Audley J. Baird P. Binetruy M. Born E. Castelli A. Cavalleri A. Cesarini A.M. Cruise K. Danzmann M. de Deus Silva I. Diepholz G. Dixon R. Dolesi L. Ferraioli Carlo Zanoni |
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| Affiliation: | 1. Department of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, Italy;2. Trento Institute of Fundamental Physics and Applications, Italian Institute of Nuclear Physics (INFN), Via Sommarive 14, 38123 Trento, Italy;3. European Space Technology Centre, European Space Agency Keplerlaan 1, 2200 AG Noordwijk, the Netherlands;4. Albert-Einstein-Institut, Max-Planck-Institut für Gravitationsphysik und Leibniz Universität Hannover, Callinstraße 38, 30167 Hannover, Germany;5. APC, Univ Paris Diderot, CNRS/IN2P3, CEA/lrfu, Obs de Paris, Sorbonne Paris Cité, France;6. Dipartimento di Fisica, Università di Trento and Trento Institute for Fundamental Physics and Application/ INFN, 38123 Povo, Trento, Italy;7. Istituto di Fotonica e Nanotecnologie, CNR-Fondazione Bruno Kessler, I-38123 Povo, Trento, Italy;8. DISPEA, Università di Urbino “Carlo Bo”, Via S. Chiara, 27, 61029 Urbino/INFN, Italy;9. The School of Physics and Astronomy, University of Birmingham, Birmingham, UK;10. European Space Astronomy Centre, European Space Agency, Villanueva de la Cañada, 28692 Madrid, Spain;11. Institut für Geophysik, ETH Zürich, Sonneggstrasse 5, CH-8092 Zürich, Switzerland;12. The UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK;13. Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Cerdanyola del Vallès, Spain;14. Institut d’Estudis Espacials de Catalunya (IEEC), C/ Gran Capità 2-4, 08034 Barcelona, Spain;15. isardSAT SL, Marie Curie 8-14, 08042 Barcelona, Catalonia, Spain;p. European Space Operations Centre, European Space Agency, 64293 Darmstadt, Germany;q. High Energy Physics Group, Physics Department, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2BW, UK;r. Department of Mechanical and Aerospace Engineering, MAE-A, P.O. Box 116250, University of Florida, Gainesville, FL 32611, USA;s. Physik Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland;t. SUPA, Institute for Gravitational Research, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK;u. Observatoire de la Côte d’Azur, Boulevard de l’Observatoire CS 34229, F 06304 Nice, France;v. Department d’Enginyeria Electrònica, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain;w. Gravitational Astrophysics Lab, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 USA |
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| Abstract: | LISA Pathfinder is a technology demonstrator space mission, aimed at testing key technologies for detecting gravitational waves in space. The mission is the precursor of LISA, the first space gravitational waves observatory, whose launch is scheduled for 2034. The LISA Pathfinder scientific payload includes two gravitational reference sensors (GRSs), each one containing a test mass (TM), which is the sensing body of the experiment. A mission critical task is to set each TM into a pure geodesic motion, i.e. guaranteeing an extremely low acceleration noise in the sub-Hertz frequency bandwidth. The grabbing positioning and release mechanism (GPRM), responsible for the injection of the TM into a geodesic trajectory, was widely tested on ground, with the limitations imposed by the 1-g environment. The experiments showed that the mechanism, working in its nominal conditions, is capable of releasing the TM into free-fall fulfilling the very strict constraint imposed on the TM residual velocity, in order to allow its capture on behalf of the electrostatic actuation.However, the first in-flight releases produced unexpected residual velocity components, for both the TMs. Moreover, all the residual velocity components were greater than maximum value set by the requirements. The main suspect is that unexpected contacts took place between the TM and the surroundings bodies. As a consequence, ad hoc manual release procedures had to be adopted for the few following injections performed during the nominal mission. These procedures still resulted in non compliant TM states which were captured only after impacts. However, such procedures seem not practicable for LISA, both for the limited repeatability of the system and for the unmanageable time lag of the telemetry/telecommand signals (about 4400 s). For this reason, at the end of the mission, the GPRM was deeply tested in-flight, performing a large number of releases, according to different strategies. The tests were carried out in order to understand the unexpected dynamics and limit its effects on the final injection. Some risk mitigation maneuvers have been tested aimed at minimizing the vibration of the system at the release and improving the alignment between the mechanism and the TM. However, no overall optimal release strategy to be implemented in LISA could be found, because the two GPRMs behaved differently. |
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| Keywords: | LISA Pathfinder Injection into geodesic motion Space mechanism in-flight testing Impulse measurement |
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