Simulation of optical observables for space missions to small bodies

The navigation of deep space spacecraft requires accurate measurement of the probe’s state and attitude with respect to a body whose ephemerides may not be known with good accuracy. The heliocentric state of the spacecraft is estimated through radiometric techniques (ranging, Doppler, and Delta-DOR), while optical observables can be introduced to improve the uncertainty in the relative position and attitude with respect to the target body. In this study, we analyze how simulated optical observables affect the estimation of parameters in an orbit determination problem, considering the case of the ESA’s Hera mission towards the binary asteroid system composed of Didymos and Dimorphos. To this extent, a shape model and a photometric function are used to create synthetic onboard camera images. Then, using a stereophotoclinometry technique on some of the simulated images, we create a database of maplets that describe the 3D geometry of the surface around a set of landmarks. The matching of maplets with the simulated images provides the optical observables, expressed as pixel coordinates in the camera frame, which are fed to an orbit determination filter to estimate a certain number of solve-for parameters. The noise introduced in the output optical observables by the image processing can be quantified using as a metric the quality of the residuals, which is used to fine-tune the maplet-matching parameters. In particular, the best results are obtained when using small maplets, with high correlation coefficients and occupation factors.

Characterization of Mars rotational dynamics from Doppler tracking of the InSight lander

In the last decades the evolution of radio science has made it possible to infer the atmosphere composition, the surface and the internal structure of the planets. Since the arrival of the first landers on Mars it was possible to make accurate measurements of the dynamics of this planet; in this thesis we will focus on InSight, considering the data disclosed by the JPL relative to the period from November 26th, 2018 to August 15th, 2021. In particular, the Doppler and Range measurements conducted by the RISE (Rotation and Interior Structure Experiment) will be analyzed. Since the accuracy of these measurements was improved significantly the effects due to the atmosphere of Mars might be measured so it should thus be possible to obtain a better estimate of the parameters characterizing the rotational dynamic of Mars. A large part of this study will therefore be dedicated to the study, modeling, implementation and analysis of the atmosphere of Mars, in both its components: troposphere and ionosphere. Once the complete model of Mars had been built, i.e. including the atmosphere, it was then possible to analyze the residuals, obtained between the data of the measurements carried out and the values predicted by the developed model, in order to obtain an estimate of the rotational dynamic of Mars.