Molniya
The Molniya, GRAU Index 8K78, was a modification of the well-known R-7 Semyorka rocket and had four stages. The 8K78 resulted from a crash program by the Korolev Bureau to develop a booster for launching planetary probes. A larger third stage was added along with a fourth stage (Blok L) that was designed to fire in-orbit to send the payload out of LEO. The basic R-7 core was also structurally strengthened and given more powerful engines. A rushed development produced multiple malfunctions of the upper stages, which led to its being replaced by the improved Molniya-M.
Missions: 40
Successes: 22
Partial Failures: 1
Failures: 17
Success Streak: 6
Success Rate: 56.2%