Essaim (swarm, in French) was a French military reconnaissance microsatellite constellation. Its main purpose was to collect and map signals intelligence across the world. The DGA described it as a "vacuum cleaner for [radio] waves".
Essaim was a constellation of four 120 kg micro satellites (one of which was a spare) in low earth orbit. They were demonstration models which were supposed to last three years. They flew separated by a few hundreds of kilometers. Missions were designed by the Celar (Centre d'électronique de l'armement) in Bruz, near Rennes and were uploaded from CNES in Toulouse to the constellation. Collected data followed the same path in reverse order.
The constellation was launched from Kourou, in French Guiana, by an Ariane 5 G+ rocket on December 18, 2004. The flight was shared with Helios 2A and two other auxiliary payloads: Parasol and Nanosat.
Individual members of the constellation were Essaim 1 (COSPAR 2004-049C), Essaim 2 (COSPAR 2004-049D), Essaim 3 (COSPAR 2004-049E) and Essaim 4 (COSPAR 2004-049F).
ESSAIM disposal and passivation operations took place in October 2010. The satellites are expected to reenter within 15 to 19 years.