In this paper the enhancement of the sensitivity and of the duty-cycle of a double stage suspended torsion pendulum are described. The increase in sensitivity, both for force and torque measurements, ...was obtained rearranging the pendulum mechanics, reducing the value of the suspended masses and moments of inertia and by adopting additional read-outs based on optical levers. The improvement of the duty-cycle was obtained by controlling the suspension point of the pendulum to reduce the effect of seismic noise on the translation resonances of the system. The reduction of these motions allowed continuous operation for three weeks, in high sensitivity regime of the read-out electronics, resulting in a force sensitivity of and a torque sensitivity of around 10 mHz.
A torsion pendulum with 2 soft degrees of freedom (DOFs), realized by off-axis cascading two torsion fibers, has been built and operated. This instrument helps characterize the geodesic motion of a ...test mass for LISA Pathfinder or any other free-fall space mission, providing information on cross talk and other effects that cannot be detected when monitoring a single DOF. We show that it is possible to simultaneously measure both the residual force and the residual torque acting on a quasifree test mass. As an example of the investigations that a double pendulum allows, we report the measurement of the force-to-torque cross talk, i.e., the amount of actuation signal, produced by applying a force on the suspended test mass, that leaks into the rotational DOF, detected by measuring the corresponding (unwanted) torque.
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We report J, H, and K photometry of 86 stars in 40 fields in the Northern Hemisphere. The fields are smaller than or comparable to a 4- x 4-arcmin FOV and are roughly uniformly distributed over the ...sky, making them suitable for a homogeneous broadband calibration network for NIR panoramic detectors. K magnitudes range from 8.5 to 14 and J-K colors, from -0.2 to 1.2. The photometry is derived from a total of 3899 reduced images; each star has been measured, on average, 26.0 times per filter on 5.5 nights. Typical errors on the photometry are about 0.012 mag. (Author)
In this paper we report the observations of HD189733b, Kepler-41b, Kepler-42b, GJ 436b, WASP-77ab, HAT-P-32b and EPIC 211818569 as measured at the Osservatorio Polifunzionale del Chianti, a new ...astro-nomical site in Italy. Commissioning observing runs have been done in order to test capabilities, systematics and limits of the system and to improve its accuracy. For this purpose, a software algorithm has been developed to estimate the differential photometric error of any transit observation, so that the integration time can be chosen to reach optimal signal-to-noise ratios, and to obtain a picture of what kind of transits this setup can reveal. Currently, the system is able to reach an accuracy of about 1 mmag and so it is ready for the much needed exoplanetary transit follow-up.
We report on a double torsion pendulum, where motion along two degrees of freedom (DoFs) is almost free. The Test Mass (TM) is enclosed in a replica of the LISA-Pathfinder electrostatic readout and ...actuation system. This apparatus is designed to perform extensive ground testing of undesired effects such as leakage of the readout noise from one DoF to another, or actuation cross talks with closed feedback loop. Such investigation is relevant to the noise budget of LISA and LISA-Pathfinder missions, as the TM will be sensitive to weak forces along all 6 degrees of freedom (DoFs). The instrument being developed in Firenze is capable of measuring the forces and stiffnesses acting simultaneously along the 2 soft DoFs. We have completed an upgrade of the apparatus to a definitive configuration and we report on both advances in the commissioning tests and on measurements of residual charge, with the first DoF released.
Ground testing with torsion pendulums played a key role in the development and characterization of the Gravitational Reference Sensor (GRS) of LISA-Pathfinder (LPF). We report on a torsion pendulum ...facility with 2 soft degrees of freedom (DOF), realized by off-axis cascading two torsion fibers. This instrument, developed for testing on two DOFs the LPF GRS, allows simultaneous measurement of force and torque acting on the suspended test mass (TM), approaching free-fall condition on two DOFs down to a few mHz. We will report on the results of some measurement campaigns devoted in particular to the characterization of force to torque and torque to force actuation cross-talks (CT).
Heliospheric influences on LISA Grimani, C; Fabi, M; Finetti, N ...
Classical and quantum gravity,
05/2009, Volume:
26, Issue:
9
Journal Article, Conference Proceeding
Peer reviewed
Laser interferometer space antenna (LISA) is the first interferometer devoted to the detection of low frequency gravitational waves in space. Control of the environment and the study of the effects ...of energetic particles traversing the LISA apparatus are mandatory for this experiment to be fully successful. Telescopes for solar and cosmic-ray particle monitoring will be placed on board LISA and its precursor mission LISA Pathfinder (LISA-PF). In particular, proton, helium and electron detection is recommended on LISA. In this paper, we report expected incident galactic proton and helium fluxes at the time of LISA and LISA-PF missions. The number of solar events with the fluence ranging between 106 and 1011 protons cm-2 above 30 MeV occurring during the LISA missions is estimated as well. Finally, we discuss the importance of electron detection on LISA to forecast upcoming solar energetic protons.
The LISA Test-Mass (TM) is sensitive to weak forces along all 6 Degrees of Freedom (DoFs). Extensive ground testing is required in order to evaluate the influence of crosstalks of various read-outs ...and actuators operating on different DoFs. To this purpose, and to better represent the flight conditions, we are developing a facility with 2 soft DoFs which consists of two stage roto-translational pendulum. This facility will measure the forces and stiffnesses simultaneously acting on the Test Mass along 2 different soft DoFs. The advantages with respect to a single DoF test bench are a more effective identification and debug of spurious effects between the TM and the capacitive position sensor surrounding it and the possibility to test actuation crosstalk with closed feedback loop. In particular, it allows us to measure the residual disturbance along one DoF when we close the control loop on the other one.
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