Portal:Spaceflight/On This Day/21 May

• 1973 - A Diamant-B fails to launch the D-5A and D-5B satellites.
• 1974 - A Kosmos-3M launches the Kosmos 655 satellite.
• 1975 - A Voskhod launches the Kosmos 731 satellite.
• 1976 - A Soyuz-U launches the Kosmos 820 satellite.
• 1981 - A Soyuz-U launches the Kosmos 1272 satellite.
• 1982 - A Soyuz-U launches the Kosmos 1368 satellite.
• 1986 - A Soyuz-U2 launches the unmanned Soyuz TM-1 test mission.
• 1986 - A Soyuz-U launches the Kosmos 1744 satellite.
• 1987 - A Soyuz-U launches the Kosmos 1846 satellite.
• 1988 - A Proton-K launches three GLONASS satellites.
• 1991 - A Soyuz-U launches a Resurs-F satellite.
• 1993 - A Soyuz-U launches a Resurs-F satellite.
• 2008 - A Zenit-3SL launches the Galaxy 18 satellite.
• 2009 - A Soyuz-2.1a/Fregat places the Meridian 2 satellite into a lower than planned orbit after an upper stage malfunction caused by human error.
• 2010 - An Ariane 5ECA launches the Astra 3B and COMSATBw-2 satellites.