Also, the four Buran liquid rocket boosters were designed to also function as the first stage of a smaller launch vehicle, Zenit. At one point, Zenit was set t

Also, the four Buran liquid rocket boosters were designed to also function as the first stage of a smaller launch vehicle, Zenit. At one point, Zenit was set to replace many of the existing Soviet launchers -- that never quite happened, mostly because Zenit is built in the Ukraine, but it has still been a reasonably successful rocket (and although it hasn't launched yet this year, I believe a few more launches are still planned). The RD170 engine family developed for Zenit has been very successful. A half-sized version (RD180) powers Atlas V, and a quarter-sized version (RD191) powers the first-stage modules of Russia's new Angara rocket family.