Astrophysics
A visualization of the reconstructed S/C orientation is supplied by the following image.
Space Science
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In the framework of LISA Pathfinder satellite mission I am involved in two independent research activities. The LISA Pathfinder (LPF) differential accelerometer performance is limited by random force noise acting on the free-falling test masses. Since at least one of the two test-masses requires control forces along the sensitive x measurement axis, TM acceleration noise is produced by any instability in the electrostatic actuation forces and contributes to the overall acceleration noise limit of $3 \times 10^{-14}\,\mathrm{m}/ \mathrm{s}^2/ \mathrm{Hz}^{1/2}}$ at $1\,\mathrm{mHz}$. This is likely to be the dominant instrumental limitation for measurements below $3\,\mathrm{mHz}$. I am involved in modeling and testing the acceleration noise arising from actuation fluctuation and to identify and constraint its different components and uncertainty by analyzing laboratory measurements. Such a modeling will be also employed in order to identify the best suspension loop configuration to minimize the overall amount of electronic force noise. Furthermore, I am attempting to utilize the LPF radio tracking observables in order to provide an independent estimate of the LISA Technology package (LTP) at very low-frequency characterizing the residual self-gravity between the spacecraft and the proof test-masses TMs.
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Orbiting around the first Sun-Earth Lagrangian point (L1), LISA Pathfinder (LPF) carries on the most sensitive inertial sensor ever flown. S/C-to-dfTM mutual gravitational attraction has been optimally constrained by design approach via CAD/CAM technology and very accurate investigations about residual electrostatic forces acting on the dfTM will be carried out during LPF operation. However, a very-low-frequency independent characterization of any residual acceleration contribution would contribute to better identify the overall performance of the LPF proposed technology in the very-low-frequency range. The extraordinary complexity of the LPF attitude control system (ACS), which acts at very-low frequencies ( $<\!10^{-4}\,\mathrm{Hz}$), and the Drag-Free Attitude Control System (DFACS), acting in the $10^{-4}-10^{-2}\,\mathrm{Hz}$ frequency range, encumbers the efforts for precision orbit determination (POD) w.r.t. the on-board drag-free proof Test-Mass (dfTM). The gravitational pull exerted between the S/C and the dfTM can be quantified by comparing simulated and actual orbits. We will simulate the dfTM orbit in a pure Keplerian motion around L1 for known initial state (PVA) and ephemeris time (ET). Traditionally, radio science range and Doppler tracking observables allow to extract S/C distance and radial velocity which, in turn, are utilized for orbit determination. Then, chaining ground-based measurements with dfTM to S/C antenna Centre-of-Phase (CoP), we will determine the dfTM orbit. The determination process will account for periodic electrostatic actuations and the relative position w.r.t. the S/C barycentre of the dfTM.
