Several rockets were analyzed to launch the Kliper spacecraft, the Soyuz rocket, the Zenith-2SLB, an improved version of the Zenit-2, and the Angara-3A rocket. The purpose of this study is to reuse an existing launcher, even if it needs few modifications, to minimize development costs.
Very fast the choice concerned a Soyuz type rocket especially since the project of Soyuz to Kourou (French Guiana), signed on November 7th, 2003, let foresee a partnership between the ESA and Roskosmos for the launch of Klipers.
Onega launcher, Soyuz
The modified version of Soyuz was called in the initial reports Soyouz 2-3 then Onega (Onega is the name of a lake not far from St-Petersburg). Very few informations were delivered on this subject. Its capacity in low earth orbit is 10t. Another more powerful version is presented in Moscow on June 10th, 2005 Soyouz 3, its payload capacity is increased to 14t. All the engines are changed, the central body uses NK-33 (modification of the N1 lunar rocket engine), whereas the side boosters use RD-120.10F (modified engine coming from the central body of Energia), finally the third stage is propelled by a RD-0146E. The first two stage use some oxygen and some fuel while the last stage works with cryogenic fuels.
Presumably Soyouz 2-3 would have been able to launch the Kliper without wings and without the service module (working with the module Parom), whereas Soyouz 3 would have been used for the winged and autonomous heavier version (capable of docking to the station by its own).
