As was typical by all the descendants of the V-2 rocket technology, the turbine is driven by steam generated by catalytic decomposition of H₂O₂.
These are based on a variable sized pellet covered in an aqueous solution of potassium permanganate and sodium.
The RD-107 has an additional two vernier combustion chambers that can thrust vector in a single plane to supply attitude control.
The natural variations in manufacturing between each engine meant that without an active propellant consumption control, each booster could deplete oxygen and fuel at a different rate.
It would generate enormous stress on the structure and cause difficulties in steering due to the mass imbalance.
The mixture ratio control system was developed to ensure the simultaneous consumption of propellant mass among the four R-7 boosters.