January 6, 2020


CAESAR (Conjunction Analysis and Evaluation Service, Alerts and Recommendations) is a trial public service provided by CNES for the French SSA Centre (Space Surveillance Awareness). The French SSA Centre is known by the acronym GNOSE (Groupement National Opérationnel de Surveillance de l'Espace – National operational group for space monitoring), and it constitutes the pooling under the same name of the operational capacity of the space surveillance division (DSE) of the CDAOA, which is to become COSMOS (Centre Opérationnel de Surveillance Militaire des Objets Spatiaux – operational centre for military surveillance of space objects), and of the CNES operational orbit tracking centre (Centre d'Orbitographie Opérationnel – COO).

CAESAR opened as a trial public service in mid-2012. CAESAR subscribers are required to sign a contract with CNES.

The United States Strategic Command (USSTRATCOM) is currently the only organisation in the world which monitors all trackable objects and provides the international community with data: since July 2010, USSTRATCOM has been distributing “Conjunction Messages” for each approach detected. The first format used by USSTRATCOM for the “Conjunction Messages” is the CSM (Conjunction Summary Message). The CSM format is a complete set of data for analysis of a conjunction. The next format will be the CDM (Conjunction Data Message), a standard format for messages being prepared by the CCSDS (Consultative Committee for Space Data Systems).

Nonetheless, for each conjunction, it must be permanently possible to analyse the available data, evaluate the risk level and trigger an alert in the Control Centre whenever avoidance action needs to be considered. CAESAR meets this need. CAESAR was first of all designed to provide a “middle-man” service for all the satellites controlled at CNES (between 15 and 20) before being extended as a trial public service in mid-2012.


Figure 1
Schematic representation of the “Middle-man” role between the JSpOC and the Operators (O/O), where HIE stands for "High Interest Event"

For more information on the CAESAR service, visit https://spod.cnes.fr