INTEGRAL dancing with the Moon 'till the Earth's atmosphere
The orbit of the INTEGRAL mission belongs to the class of Highly
Elliptical Orbits (HEOs). These orbits are characterised by relatively
low pericentre altitudes and extremely high apocentre altitudes. For
this reason, HEO missions offer a privileged position for astrophysics
and astronomy operations as the spacecraft spends most of its time at an
altitude above the Earth's radiation belts, offering a radiation-free
environment for the scientific observations. Specifically, INTEGRAL is
currently on an orbit whose lowest point is 2000 kilometres and its
highest point near 150000 kilometres.
Given its peculiar shape, the orbit of INTEGRAL is not only influenced
by Earth's gravity and the atmospheric drag, but also by the
gravitational attraction of the Moon and by the Solar Radiation Pressure
(SRP). These additional forces can drastically influence the trajectory
of the spacecraft, leading to different predictions about its future.
INTEGRAL is a large spacecraft, five metres tall and more than 4 tonnes
in weight. Its disposal will be performed via a re-entry in Earth's
atmosphere and given its size, it is important to predict its re-entry
and its demise in the atmosphere to ensure the safety of people and
properties on the ground.
Given INTEGRAL's orbit and the little fuel left on-board, the re-entry
of the spacecraft is only possible after several years from the
manoeuvre; therefore, its predicted entry is not trivial. A study funded
by the European Research Council COMPASS (
http://www.compass.polimi.it)
combines the long-term prediction of INTEGRAL's orbit with re-entry
dynamics (the concept of overshoot boundary) to help improve the
re-entry predictions of HEO satellites and study their demisability. By
performing a sensitivity analysis on the disposal manoeuvre of INTEGRAL,
the variability of the re-entry scenarios could be studied and the
difference with approaches that were neglecting the re-entry dynamics be
highlighted (by directly targeting a very low pericentre radius).
The left graph shows the predicted entry trajectories, highlighting in
colour the Liquid Mass Fraction (LMF) that is the portion of the
spacecraft mass that is predicted to demise during re-entry. In black,
instead, the entry trajectory for a fixed targeted entry interface.
The middle graph and right graph show the evolution of the mechanical
and thermal loads, respectively, on the spacecraft during the different
entry trajectories. The colours highlight the value of the peak
acceleration and heat flux, respectively.
From the analysis, it is clear that when one predicts the re-entry, one
needs to consider an array of possible solutions and understand the
sensitivity to the initial conditions, as even small differences in the
manoeuvre can lead to largely different trajectories and
thermomechanical loads on the spacecraft, which in turn affect its demise.
Credits:
"Interface between the long-term propagation and the destructive re-entry phases exploiting the overshoot boundary",
Fusaro C., Trisolini M., Colombo C.,
Journal of Space Safety Engineering, 2022, In Press, DOI:
https://doi.org/10.1016/j.jsse.2022.02.008
"Re-entry prediction and demisability analysis for the atmospheric disposal of geosynchronous satellites",
Trisolini M., Colombo C.,
Advances in Space Research, 2021, Vol. 68, Issue 11, pp. 4321-4335,
https://doi.org/10.1016/j.asr.2021.09.024
"End-of-life earth re-entry for highly elliptical orbits: the INTEGRAL mission",
Colombo, C., Letizia, F., Alessi, E. M., and Landgraf, M. (2014a).
in Proceedings of the 24th AAS/AIAA Space Flight Mechanics Meeting (Santa Fe: AAS 14-325)
