arXiv subjects

P. Tortora

Publications and source records attributed to P. Tortora.

3 recordsLinked to original sources

arXiv2024

Characterization of avalanche photodiodes (APDs) for the CUbesat Solar Polarimeter (CUSP) mission

The CUbesat Solar Polarimeter (CUSP) project is a CubeSat mission orbiting the Earth aimed to measure the linear polarization of solar flares in the hard X-ray band by means of a Compton scattering polarimeter. CUSP will allow the study of the magnetic reconnection and particle acceleration in the flaring magnetic structures of our star. CUSP is a project in the framework of the Alcor Program of the Italian Space Agency aimed at developing new CubeSat missions. It is approved for a Phase B study. In this work, we report on the characterization of the Avalanche Photodiodes (APDs) that will be used as readout sensors of the absorption stage of the Compton polarimeter. We assessed the APDs gain and energy resolution as a function of temperature by irradiating the sensor with a \textsuperscript{55}Fe radioactive source. Moreover, the APDs were also characterized as being coupled to a GAGG scintillator.

astro-ph.IM↗

arXiv2023

Combining astrometry and JUICE -- Europa Clipper radio science to improve the ephemerides of the Galilean moons

The upcoming JUICE and Europa Clipper missions to Jupiter's Galilean satellites will provide radio science tracking measurements of both spacecraft. Such data are expected to significantly help estimating the moons' ephemerides and related dynamical parameters. However, the two missions will yield an imbalanced dataset, with no flybys planned at Io, condensed over less than six years. Current ephemerides' solutions for the Galilean moons, on the other hand, rely on ground-based astrometry collected over more than a century which, while being less accurate, bring very valuable constraints on the long-term dynamics of the system. An improved solution for the Galilean satellites' complex dynamics could however be achieved by exploiting the existing synergies between these different observation sets. To quantify this, we merged simulated JUICE and Clipper radio science data with existing ground-based astrometric and radar observations, and performed the inversion. Our study specifically focusses on the resulting formal uncertainties in the moons' states, as well as Io's and Jupiter's tidal dissipation parameters. Adding astrometry stabilises the moons' state solution, especially beyond the missions' timelines. It furthermore reduces the uncertainties in $1/Q$ (inverse of the tidal quality factor) by a factor two to four for Jupiter, and about 30-35\% for Io. Among all data types, classical astrometry data prior to 1960 proved particularly beneficial. We also show that ground observations of Io add the most to the solution, confirming that ground observations can fill the lack of radio science data for this specific moon. We obtained a noticeable solution improvement when exploiting the complementarity between all different observation sets. These promising simulation results thus motivate future efforts to achieve a global solution from actual JUICE and Clipper radio science data.

astro-ph.EP↗

arXiv2020

Relativistic modeling of atmospheric occultations with time transfer functions

Context: Occultation experiments represent unique opportunities for probing remotely physical properties of atmospheres. The data processing requires one to properly account for refractivity while modeling the time/frequency transfers of an electromagnetic signal. On theoretical grounds, little work have been done concerning the elaboration of a covariant approach for modeling occultation data. Aims: We present an original method allowing one to derive up to the appropriate order fully analytical expressions for the covariant description of time/frequency transfers during an atmospheric occultation experiment. Methods: We make use of two independent powerful relativistic theoretical tools, namely the optical spacetime metric, and the time transfer functions formalism. The first one allows us to consider refractivity as spacetime curvature while the second one is used to determine the time/frequency transfers occurring in a curved spacetime. Results: We provide the integral form of the time transfer function up to any post-Minkowskian order. We specify the discussion to a stationary optical spacetime describing an occultation by a steady rotating and spherically symmetric atmosphere. Explicit analytical expressions for the time/frequency transfers are provided at the first post-Minkowskian order and their accuracy is assessed by comparing them to results of a numerical integration of the equations for optical rays. Conclusions: The method accurately describes vertical temperature gradients and properly accounts for light-dragging effect due to the motion of the optical medium. It can be pushed further in order to derive the explicit form of the time transfer function at higher order and beyond the spherical symmetry assumption.

gr-qc↗