Titan is a U.S. launch
vehicle. Titan I (1959Ð62) used nonstorable liquid oxygen and kerosene propellants. The next version,
Titan II, used storable NMOy and aerozine-50 propellants. The two first-stage engines each developed a thrust of 956,000 newtons (98,000 kg/216,000 lb), the single second-stage engine a thrust of 445,000 newtons (45,500 kg/100,300 lb).From 1963 to 1981, Titan II was the largest of the nation's intercontinental ballistic missiles, or ICBMs. It stood 31.4 m (103 ft) tall and had a diameter of 3.05 m (10 ft). The liftoff weight was about 149,690 kg (330,000 lb), the top range was 15,000 km (9,320 mi), and the single reentry
vehicle usually carried a thermonuclear warhead of 5 to 10 megatons' yield (see rockets, missiles, and space launch vehicles). The ICBMs were stored in underground silos at bases in Arizona, Kansas, and Arkansas. One Arizona silo is now the Titan Missile Museum.A modified Titan II was employed in the Gemini program, and later versions continue to be used. Titan IIIC consists of a Titan II core, a restartable transstage, and two strap-on
boosters. Heavy payloads are launched by Titan IIID, with two Titan core stages and two strap-on solid-propellant boosters. Titan 34D, used for military launches, is still more powerful. Titan IIIE, combining the technology of Titan IIIC with a Centaur stage, launched Viking and Voyager probes. Launches of the Titan IVA, another heavy-lift version making use of a Centaur upper stage, came to an end in August 1998 with a failed, explosive liftoff of the rocket from Cape Canaveral. Titan IVB, with a liquid core vehicle and two strap-on solid-propellant boosters, was first tested in 1997. It is the most powerful such vehicle since the old Saturn V.