Soyuz-2.1b

Soyuz-2.1b is the more powerful variant of the Russian Soyuz-2 medium-lift expendable launch vehicle, developed and built by the Progress Rocket Space Centre in Samara. It keeps the digital avionics and upgraded booster engines introduced with the Soyuz-2.1a but replaces the third stage RD-0110 engine with the RD-0124, an oxygen-rich staged-combustion engine. The new engine raises specific impulse from 326 to 359 seconds, and although its peak thrust is slightly lower, a longer burn from the same propellant load improves overall performance. From the Baikonur Cosmodrome the payload to low Earth orbit rises from about 7,430 kilograms for the 2.1a to 8,670 kilograms. A Soyuz-2.1b fuelled with naphthyl, a fuel with fewer aromatic compounds than kerosene, flew from Vostochny in October 2022. The first launch is dated 27 December 2006.