#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
09/11/1996	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
15/07/2009	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
01/12/2015	end DORIS/SPOT-5 (2nd generation)		4
23/01/2016	start DORIS/JASON-3 (DGXX)			5
04/04/2016	start DORIS/SENTINEL-3A (DGXX)			6
01/05/2018	start DORIS/SENTINEL-3B (DGXX)			7
03/10/2019	end DORIS/JASON-2 (DGXX)			6
14/09/2020	end DORIS/HY-2A (DGXX)				5
24/09/2020	start DORIS/HY-2C (DGXX)			6
17/12/2020	start DORIS/SENTINEL-6A (DGXX)			7
04/08/2021	start DORIS/HY-2D (DGXX)			8
12/01/2023	start DORIS/SWOT (DGXX)				9
21/11/2025	start DORIS/SENTINEL-6B (DGXX)			10