Speaker
Description
The rapid increase of in-orbit payloads in recent years, with mega-constellation exploitation such as Starlink, has made conjunction analyses increasingly critical.
These are typically performed when the spacecraft is in routine and only rarely pre-launch, to assess the first hours after separation. This phase is especially delicate, since the spacecraft typically cannot perform manoeuvres during the deployment of appendages, the initial attitude acquisition, the configuration of the propulsion and AOCS subsystems. That’s why EUMETSAT decided to start performing conjunction assessments pre-launch, for longer trajectories after separation from launcher, and to introduce this in the final procedure leading to selecting the final lift-off time.
The first launches to undergo this process were MTG-S1 (GEO), launched with Falcon 9 on 1st July 2025, and MetOp-SG A1 (LEO), launched with Ariane 6 on 13th August 2025:
• MTG-S1, on a Super-Synchronous-Transfer-Orbit, crossed Starlink altitude shortly before separation but, due to its highly eccentric trajectory, exited the LEO protected quickly and re-entered it one orbit later, without being manoeuvrable beforehand. Moreover, the evolution of the initial uncertainties along a high-elliptical orbit are difficult to model, as linear covariance propagation is not applicable. A relatively wide launch-window (~150minutes) existed: EUMETSAT was to communicate the closed portions of the window, due to high-risk events.
• MetOp-SG A1 was injected at ~800km and remained inside the LEO protected region for the entire period in which the spacecraft was not manoeuvrable. There was no launch window but only a single lift-off time per day. A small lift-off shift was however agreed to be implemented, in case of an anticipated high risk post-separation
With the support of EUSST, EUMETSAT assessed the safety of the post-separation trajectories for both spacecrafts: EUSST screened the ephemerides provided by EUMETSAT versus the SP catalogue of USSF; the resulting conjunction data were then post-processed by EUMETSAT: the main idea was to classify each event according to the potential consequence of a collision, based on secondary object’s size and its status (active/inactive). For instance, a conjunction involving a large active spacecraft entails far more severe consequences (in terms of orbital-environment degradation and in the interaction with another operator) than one involving a small inactive object. This led to the definition of different levels of acceptable risk based on the categories of the classification.
The actual operational experiences for the 2 launches, with the relevant results, will be detailed in this paper.