Speaker
Description
Spacecraft that survive their nominal mission lifetime are generally proposed for a mission extension in order to maximize their return on investment, to validate new technologies or to have a higher flexibility in the replenishment of a constellation.
However, a life extension has some limits and threats, especially when satellites units are operated well beyond their qualified lifetime: the performance may be degraded and the probability of having unexpected behaviors may increase over time. This may lead to an unsuccessful End of Life (EoL) disposal.
In fact, a low success rate of the disposal manoeuvers is currently observed in LEO, despite the requirements dictated by the international Space Debris Mitigation (SDM) standards. The main reasons have been often linked to:
- being old satellites not designed to be disposed and passivated;
- a disposal decision based mainly on the remaining propellant mass;
- a not-attempted start of the EoL manoeuvres or a too late decision, after the occurrence of major failures.
It is therefore clear that satellite design, reliability models and decision-making process have to be improved in order to dispose satellites in a safe manner and at the right time, before completely losing the disposal capability.
In order to address these challenges a new reliability model is proposed where systems engineering aspects, innovative reliability approaches including Risk Assessment, real operating conditions and events observed by satellite operators are taken into account to support the decision on how and when the satellite has to be disposed.
A new short-term reliability criterion is also proposed in addition to the current one based on consumables. The disposal success rate and the reference duration are currently being chosen in order to decide for a disposal initiation only when a too high risk of losing the satellite exists, avoiding to interrupt a mission that could be extended.
This reliability criterion will be even more important for future missions since the post mission disposal of constellations is the major contributor to the future presence of debris in LEO, and because the propellant mass criterion could become less adequate or at least useful to decide when to dispose the satellite with future on-orbit refueling and servicing missions (space tug).
In conclusion, the final goals are to have satellite designs fully compliant to SDM requirements and to be able to dispose the satellite at EoL in a safe and reliable manner and therefore limit the proliferation of space debris in already crowded LEO and GEO orbits.
