Titan IIIE

--HISTORY--
In the 1960s, with its massive pre- Moon landing budget, NASA intended to fly the Atlas-Centaur booster until a reusable heavy lift system (AKA the Space Shuttle) could be developed. However, the Vietnam war caused Congress to cut the civilan space program's budget. This introduced delays on the Space Shuttle program, and made many missions that required heavy lifting impossible.

In 1967, NASA began considering the use of a Centaur upper stage on a Titan booster. Together with two mandatory strap-on solid rocket motors, it had enough performance to launch 15t to LEO. While not ideal, this solution was a good-enough stopgap until more capable systems arrived. For some time, it was the largest launch system available to NASA for scientific missions, only eclipsed by the Moon rockets. That's why it was the rocket of choice for some of the most famous scientific missions - the two Voyagers, two Vikings and two Helios space probes.

--LAUNCHES--

Feb 11, 1974 - FAILIURE
Sphinx satellite, Viking Dynamic Simulator

Dec 10, 1974 - SUCCESS
Helios 1 space probe

Aug 20, 1975 - SUCCESS
Viking 1 orbiter and lander

Sep 9, 1975 - SUCCESS
Viking 2 orbiter and lander

Jan 15, 1976 - SUCCESS
Helios 2 space probe

Aug 20, 1977 - SUCCESS
Voyager 2 space probe

Sep 5, 1977 - SUCCESS
Voyager 1 space probe

Success rate - 86% (6/7)