Titan I and Titan II
Simultaneously with the development of Polaris and then Minute – man, the air force continued work on two liquid-propellant missiles, the Titans I and II. The Titan II introduced storable propellants into the missile inventory and laid the groundwork for the core portion of the Titans III and IV space-launch vehicles. Titan I began as essentially insurance for Atlas in case the earlier missile’s technology proved unworkable. The major new feature of the first of the Titans was demonstration of the ability to start a large second-stage engine at a high altitude.93 The WAC Corporal had proved the viability of the basic process involved, and Vanguard would develop it further (after Titan I was started). But in 1955, using a full second stage on a ballistic missile and igniting it only after the first-stage engines had exhausted their propellants seemed risky.
The air force approved development of Titan I on May 2, 1955. Meanwhile, the Western Development Division had awarded a 44 contract on January 14, 1955, to Aerojet for engines burning liq – Chapter 1 uid oxygen and a hydrocarbon fuel for possible use on Atlas. These soon evolved into engines for the two-stage missile. Even though the Aerojet engines burned the same propellants as Atlas, there were problems with development, showing that rocket engineers
still did not have the process of design “down to a science." Despite the change in propellants, the Titan II used a highly similar design for its engines, making Aerojet’s development for that missile less problematic than it might otherwise have been (although still not without difficulties), with technology then carrying over into the Titans III and IV core launch vehicles. Meanwhile, the air force deployed the Titan Is in 1962. They quickly deactivated in 1965 with the deployment of Minuteman I and Titan II, but Titan I did provide an interim deterrent force.94
The history of the transition from Titan I to Titan II is complicated. One major factor stimulating the change was the 15 minutes or so it took to raise Titan I from its silo, load the propellants, and launch it. Another was the difficulty of handling Titan I’s extremely cold liquid oxygen used in Titan I inside a missile silo. One solution to the twin problems would have been conversion to solid propellants like those used in Polaris and Minuteman, but another was storable propellants. Under a navy contract in 1951, Aerojet had begun studying hydrazine as a rocket propellant. It had good performance but could detonate. Aerojet came up with a compromise solution, an equal mixture of hydrazine and unsymmetrical dimethyl hydrazine, which it called Aerozine 50. With nitrogen tetroxide as an oxidizer, this fuel mixture ignited hypergolically (upon contact with the oxidizer, without the need for an ignition device), offering a much quicker response time than for Titan I.95 As a result of this and other issues and developments, in November 1959 the Department of Defense authorized the air force to develop the Titan II. The new missile would use storable propellants, in-silo launch, and an all-inertial guidance system.96
On April 30, 1960, the Air Force Ballistic Missile Division’s development plan for Titan II called for it to be 103 feet long (compared to 97.4 feet for Titan I), have a uniform diameter of 10 feet (whereas Titan I’s second stage was only 8 feet across), and have increased thrust over its predecessor. This higher performance would increase the range with the Mark 4 reentry vehicle from about 5,500 nautical miles for Titan I to 8,400. With the new Mark 6 reentry vehicle, which had about twice the weight and more than twice the yield of the Mark 4, the range would remain about 5,500 nautical miles. Because of the larger nuclear warhead it could carry, the Titan II served a different and complementary function to Minuteman I’s in the strategy of the air force, convincing Congress to fund them both. It was a credible counterforce weapon, whereas Minuteman I served primarily as a countercity missile, offering deterrence rather than the ability to destroy enemy weapons in silos.97
In May 1960, the air force signed a letter contract with the Martin Company to develop, produce, and test the Titan II. It followed this with a contract to General Electric to design the Mark 6 reentry vehicle. In April 1959, AC Spark Plug had contracted to build an inertial guidance system for a Titan missile, although it was not clear at the time that this would be the Titan II.98
Although the Titan II engines were based on those for Titan I, the new propellants and the requirements in the April 30 plan necessitated considerable redesign. Because the new designs did not always work as anticipated, the engineers had to resort to empirical solutions until they found the combinations that provided the necessary performance. Even with other changes to the Titan I engine designs, the Titan II propulsion system had significantly fewer parts than its Titan I predecessor, reducing chances for failure during operation. Despite the greater simplicity, the engines had higher thrust and higher performance, as planned.99
Flight testing of the Titan II had its problems, complicated by plans to use the missile as a launch vehicle for NASA’s Project Gemini, leading to the Project Apollo Moon flights. However, the last 13 flights in the research-and-development series were successful, giving the air force the confidence to declare the missile fully operational on the final day of 1963. Between October and December 1963, the Strategic Air Command deployed six squadrons of nine Titan IIs apiece. They remained a part of the strategic defense of the United States until deactivated between 1984 and 1987. By that time, fleet ballistic missiles and smaller land-based, solid-propellant ballistic missiles could deliver (admittedly smaller) warheads much more accurately than could the Titan IIs. Deactivation left the former operational Titan II missiles available for refurbishment as space – launch vehicles.100
Development of Titan I and Titan II did not require a lot of new technology. Instead, it adapted technologies developed either earlier or simultaneously for other missile or launch-vehicle programs. Nevertheless, the process of adaptation for the designs of the two Titan missiles generated problems requiring engineers to use their fund of knowledge to find solutions. These did work, and Titan II became the nation’s longest-lasting liquid-propellant missile with the greatest throw weight of any vehicle in the U. S. inventory.