Zenit 3SL blasts off of Odyssey sea platform
Sea Launch is a joint venture by the United States, Russia, Ukraine and Norway that blasts off especially modified Zenit-3SL rockets with commercial payloads from a floating platform.
Since launches are made from equatorial Pacific Ocean, the service is more cost-effective then land-based space launches. Block DM-SL, the upper, 3rd stage of the Zenit 3SL rocket is designed by Russian state space corporation RKK Energia. In USSR/Russia this upper stage is being used for heavy expendable launch systems, like the N1 rocket, Proton rocket and Zenit rocket. There were plans to use it for some other rockets as well (project Air Launch).
This video shows the 27 launch in the programme that took place on May 21, 2008.