The Hera Radio Science Experiment at Didymos

Hera represents the European Space Agency's inaugural planetary defence space mission, and plays a pivotal role in the Asteroid Impact and Deflection Assessment international collaboration with NASA DART mission that performed the first asteroid deflection experiment using the kinetic impactor techniques. With the primary objective of conducting a detailed post-impact survey of the Didymos binary asteroid following the DART impact on its small moon called Dimorphos, Hera aims to comprehensively assess and characterize the feasibility of the kinetic impactor technique in asteroid deflection while conducting in-depth investigation of the asteroid binary, including its physical and compositional properties as well as the effect of the impact on the surface and/or shape of Dimorphos. In this work we describe the Hera radio science experiment, which will allow us to precisely estimate key parameters, including the mass, which is required to determine the momentum enhancement resulting from the DART impact, mass distribution, rotational states, relative orbits, and dynamics of the asteroids Didymos and Dimorphos. Through a multi-arc covariance analysis we present the achievable accuracy for these parameters, which consider the full expected asteroid phase and are based on ground radiometric, Hera optical images, and Hera to CubeSats InterSatellite Link radiometric measurements. The expected formal uncertainties for Didymos and Dimorphos GM are better than 0.01% and 0.1%, respectively, while their J2 formal uncertainties are better than 0.1% and 10%, respectively. Regarding their rotational state, the absolute spin pole orientations of the bodies can be recovered to better than 1 degree, and Dimorphos spin rate to better than 10^-3%. Dimorphos reconstructed relative orbit can be estimated at the sub-m level [...

Analisi termiche e progetto di controllo termico per nanosatellite

Con questo elaborato sono stati continuati lo studio e la realizzazione di analisi termiche per nanosatelliti cominciati durante il progetto di tirocinio. In particolare, sono state realizzate analisi per un sottosistema di deorbiting al fine di assicurare il corretto funzionamento di quest'ultimo in qualsiasi configurazione orbitale. La prima fase è stata incentrata sul confronto tra i due modelli esistenti del sottosistema (ARTICA 3U-6U). Nella seconda fase si è passati ad uno studio di dettaglio del nuovo prototipo e sono state realizzate le analisi sul singolo sottosistema e sull'intero modello CubeSat+sottosistema. Le analisi termiche hanno evidenziato la necessità di sistemi di controllo termico per alcune configurazioni orbitali in quanto alcuni componenti fuoriuscivano dai limiti di temperatura operativi. La ricerca è stata finalizzata a sistemi passivi, che sono poi stati implementati nel sottosistema stesso. Sono state ripetute le analisi e i risultati hanno confermato che l'utilizzo di controlli termici permettono di rientrare all'interno dei limiti di temperatura imposti sul sottosistema. Infine sono state eseguite analisi termiche per valutare l'influenza di un emissione di calore interna (internal heat generation) sul sottosistema

Radio Occultation experiments of Venus and Mars: similarities and differences

In the last decades Venus has not been explored as in the early days of interplanetary missions, yet today the interest has increased and different space agencies are preparing proposals for future missions. Venus provides a laboratory next door to our planet to study how rocky planets can form and evolve differently from Earth, even when they start out very similar. Our neighboring planet is the perfect example of what happens in a runaway greenhouse effect, and the state of its atmosphere is interesting in its own right, as it is directly linked to the story of water on the planet and ultimately to the big question of whether life could have arisen beyond Earth. The main purpose of this thesis is the study of the atmosphere of Venus through the radio occultation experiments performed by the Venus Express Mission (VEX), sent by the European Space Agency in 2005. In the frame of this investigation comparisons between the Venus atmosphere and Mars atmosphere are shown, in order to highlight the similarities and differences between the two planets. The conclusions derived from this work can potentially improve our knowledge and highlight new scientific results about the Venus atmosphere

Determination of uncertainty profiles in neutral atmospheric properties measured by radio occultation experiments

Radio occultations are commonly used to assess remotely atmospheric properties of planets or satellites within the solar system. The data processing usually involves the so-called Abel inversion method or the numerical ray-tracing technique. Both are now well established, however, they do not allow to easily determine the uncertainty profiles in atmospheric properties, and this makes results difficult to interpret statistically. Recently, a purely analytical approach based on the time transfer functions formalism was proposed for modeling radio occultation data. Using this formulation, we derive uncertainty relationships between the frequency shift and neutral atmosphere properties such as temperature, pressure, and neutral number density. These expressions are relevant for interpreting previous results from past radio occultation experiments and for deriving the system requirements for future missions in a rigorous manner, and consistently with the scientific requirements about the atmospheric properties retrieval

Analysis of NASA’s DSN Venus Express radio occultation data for year 2014

International audienceThe Venus Express Radio Science Experiment (VeRa) was part of the scientific payload of the Venus Express (VEX) spacecraft and was targeted at the investigation of Venus’ atmosphere, surface, and gravity field as well as the interplanetary medium. This paper describes the methods and the required calibrations applied to VEX-VeRa raw radio occultation data used to retrieve vertical profiles of Venus’ ionosphere and neutral atmosphere. In this work we perform an independent analysis of a set of 25 VEX, single-frequency (X-band), occultations carried out in 2014, recorded in open-loop at the NASA Deep Space Network. Our temperature, pressure and electron density vertical profiles are in agreement with previous studies available in the literature. Furthermore, our analysis shows that Venus’ ionosphere is more influenced by the day/night condition than the latitude variations, while the neutral atmosphere experiences the opposite. Our scientific interpretation of these results is based on two major responsible effects: Venus’ high thermal inertia and the zonal winds. Their presence within Venus’ neutral atmosphere determine why in these regions a latitude dependence is predominant on the day/night condition. On the contrary, at higher altitudes the two aforementioned effects are less important or null, and Venus’ ionosphere shows higher electron density peaks in the probed day-time occultations, regardless of the latitude