Browsing by Autor "J. Baird"

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Nano-Newton electrostatic force actuators for femto-Newton-sensitive measurements: System performance test in the LISA Pathfinder mission
(American Physical Society, 2024) M. Armano; H. Audley; J. Baird; M. Bassan; Pierre Binétruy; M. Born; D. Bortoluzzi; E. Castelli; A. Cavalleri; A. Cesarini
Electrostatic force actuation is a key component of the system of geodesic reference test masses (TM) for the LISA orbiting gravitational wave observatory and in particular for performance at low frequencies, below 1 mHz, where the observatory sensitivity is limited by stray force noise. The system needs to apply forces of order ${10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{N}$ while limiting fluctuations in the measurement band to levels approaching ${10}^{\ensuremath{-}15}\text{ }\text{ }\mathrm{N}/{\mathrm{Hz}}^{1/2}$. We present here the LISA actuation system design, based on audio-frequency voltage carrier signals, and results of its in-flight performance test with the LISA Pathfinder test mission. In LISA, TM force actuation is used to align the otherwise free-falling TM to the spacecraft-mounted optical metrology system, without any forcing along the critical gravitational wave-sensitive interferometry axes. In LISA Pathfinder, on the other hand, the actuation was used also to stabilize the TM along the critical $x$ axis joining the two TM, with the commanded actuation force entering directly into the mission's main differential acceleration science observable. The mission allowed demonstration of the full compatibility of the electrostatic actuation system with the LISA observatory requirements, including dedicated measurement campaigns to amplify, isolate, and quantify the two main force noise contributions from the actuation system, from actuator gain noise and from low frequency ``in band'' voltage fluctuations. These campaigns have shown actuation force noise to be a relevant, but not dominant, noise source in LISA Pathfinder and have allowed performance projections for the conditions expected in the LISA mission.
Tilt-to-length coupling in LISA Pathfinder: Long-term stability
(American Physical Society, 2024) M. Armano; H. Audley; J. Baird; Pierre Binétruy; M. Born; D. Bortoluzzi; E. Castelli; A. Cavalleri; A. Cesarini; A. M. Cruise
The tilt-to-length coupling during the LISA Pathfinder mission has been numerically and analytically modeled for particular time spans. In this work, we investigate the long-term stability of the coupling coefficients of this noise. We show that they drifted slowly (by <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>1</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>μm</a:mi><a:mo>/</a:mo><a:mi>rad</a:mi></a:mrow></a:math> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>6</c:mn><c:mo>×</c:mo><c:msup><c:mn>10</c:mn><c:mrow><c:mo>−</c:mo><c:mn>6</c:mn></c:mrow></c:msup></c:math> in 100 days) and were strongly correlated to temperature changes within the satellite (<e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mn>8</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>μm</e:mi><e:mo>/</e:mo><e:mi>rad</e:mi><e:mo>/</e:mo><e:mi mathvariant="normal">K</e:mi></e:mrow></e:math> and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mrow><h:mn>30</h:mn><h:mo>×</h:mo><h:msup><h:mrow><h:mn>10</h:mn></h:mrow><h:mrow><h:mo>−</h:mo><h:mn>6</h:mn></h:mrow></h:msup><h:mo>/</h:mo><h:mi mathvariant="normal">K</h:mi></h:mrow></h:math>). Based on analytical tilt-to-length coupling models, we attribute the temperature-driven coupling changes to rotations of the test masses and small distortions in the optical setup. Particularly, our findings lead to the conclusion that LISA Pathfinder’s optical baseplate was bent during the cooldown experiment, which started in late 2016 and lasted several months. Published by the American Physical Society 2024