MEO dynamics and GNSS disposal strategies

Abstract

In the last years significant understandings in the
knowledge of the dynamics of the MEO satellites were
achieved. Much work was done in the analysis of viable
disposal strategies and technologies for the spacecraft
belonging to the Global Navigation Satellite Systems
(GNSS), with particular emphasis on the European
Galileo system. In the framework of an ESA-ESOC
Contract an extensive numerical simulations of different
long term evolution scenarios, implementing different
disposal strategies were performed. A detailed analysis
of the collision risk and manoeuvres need, related to the
different scenarios, was performed. In terms of the long
term evolution, the scenarios where the orbital
instabilities are exploited to remove the objects from the
operational regions seems favourite. That is, if the focus
is on the long term sustainability of the space
environment, the possibility to dilute the collision risk
and to aim at the re-entry in the atmosphere of a subset of
the disposed GNSS spacecraft is the most attractive. The
most "problematic" constellations are Glonass and
Beidou. This conclusion is driven by the future launch
traffic hypothesized for these constellations and by the
past practices that left already a significant number of
large uncontrolled spacecraft in the constellation orbital
zone, in the case of Glonass. On the other hand, the
Galileo constellation is well detached from the others and
faces the lowest collision risks. The Stable scenarios
seems to minimize the interactions (crossings) with the
operational constellations and, therefore, might be
preferred for operational reasons. In particular, in the
Stable scenarios the inter-constellations interaction is
negligible. Particular care should be devoted to the
efficiency and reliability of the disposal manoeuvers. A
significant share of the collision risk faced by the
operational satellites in every simulated scenario can be
traced back to the "failed'' satellites (the success rate of
the disposal manoeuvers was assumed to be 90 % for all
the constellations).

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Identifiers

ORCID for Hugh G. Lewis: orcid.org/0000-0002-3946-8757

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