Cosmopolis XXI was a late 2000s Russian concept launch vehicle billed as a space tourism vehicle, similar to Mojave Aerospace's Tier One program.
Designed and built by the Myasishchev Design Bureau, it would use the M-55X launch aircraft (derived from Myasishchev M-55), and the proposed C-21 spaceplane or its successor the Explorer.
It would be a TSTSO (Two-Stage to SubOrbit) launch platform.
It is to be air-launched by carrier aircraft from a Space Adventures spaceport.
Space Adventures abandoned the Explorer project in 2010 because "it got too expensive.