#evolution of the DORIS constellation
Date		Event								Number of satellites
31/03/1990	start DORIS/SPOT-2 (1st generation)		1
25/09/1992	start DORIS/TOPEX (1st generation)		2
01/02/1994	start DORIS/SPOT-3 (1st generation)		3
13/11/1996	end DORIS/SPOT-3 (1st generation)		2
01/05/1998	start DORIS/SPOT-4 (1st generation)		3
15/01/2002	start DORIS/JASON-1 (2nd generation)		4
11/06/2002	start DORIS/SPOT-5 (2nd generation)		5
13/06/2002	start DORIS/ENVISAT (2nd generation)		6
01/11/2004	end DORIS/TOPEX (1st generation)			5
12/07/2008	start DORIS/JASON-2 (DGXX)				6
14/07/2009	end DORIS/SPOT-2 (1st generation)		5
30/05/2010	start DORIS/CRYOSAT-2 (DGXX)			6
01/10/2011	start DORIS/HY-2A (DGXX)				7
08/04/2012	end DORIS/ENVISAT (2nd generation)		6
14/03/2013	start DORIS/SARAL (DGXX)				7
21/06/2013	end DORIS/JASON-1 (2nd generation)		6
24/06/2013	end DORIS/SPOT-4 (1st generation)		5
22/12/2015	end DORIS/SPOT-5 (2nd generation)		4
17/01/2016	start DORIS/JASON-3 (DGXX)				5
16/02/2016	start DORIS/SENTINEL-3A (DGXX)				6