• decadimento orbitale
• deorbiting
• detriti spaziali
• drag sail
• orbital decay
• space debris

The study of deorbiting systems is crucial, because near Earth space is becoming increasingly
crowded, and to mitigate this phenomenon it is necessary to decay satellites at the
end of their operational life. Among the various deorbiting systems there is the drag sail,
a passive method which exploits aerodynamic drag to accelerate re-entry. This thesis
analyzes the decay of a low Earth orbiting-spacecraft equipped with a drag sail. The first
part of the study focuses on the mathematical description of the orbital decay, provided
by Gauss variational equations written in terms of modified equinoctial orbital elements,
and then introducing the perturbative accelerations due to aerodynamic drag and zonal
harmonic J2. Other disturbances, such as due to terrestrial magnetic field, solar radiation
pressure, third-body gravitational pulls, and higher-order zonal harmonics, are neglected.
Afterwards, a MATLAB code capable of integrating the Gauss variational equations
is implemented to derive the decay time. Atmospheric properties are modelled using the
NRL-MSISE-00 model. Then, decays are simulated from various altitudes, for various
values of area-to-mass ratio, and for different solar activity conditions. The results obtained
are almost always in line with the standard and show the strong dependence of
decay time on area-to-mass ratio (as expected), and solar activity.
The main topic of the last part of the thesis is the study of the probability of impact
with space debris, which is of high importance because the spacecraft exposed area significantly
increases when the drag sail is deployed. The first-order analysis using Area-Time
product is improved with a more in-depth study that resulted in an impact probability
value, exploiting data obtained from MASTER software. Finally, the possible effect of a
space debris impact is described, and the calculation of the probability of a catastrophic
collision, which would lead to the creation of more space debris, is introduced.