Delta rockets are a family of
vehicles by which a wide variety of satellites have been launched as part of U.S. and international
space programs. NASA placed the original contract with the Douglas Aircraft Company in April 1959. The early three-stage vehicle had an overall length of 26.8 m (88 ft), and the rocket's liftoff weight was 51,480 kg (113,500 lb). The modified Thor first stage had a thrust of about 756,000 newtons (77,100 kg/170,000 lb). On May 13, 1960, the first Delta did not achieve orbit, but later
vehicles proved very reliable.Modifications since the first Deltas include strap-on solid rocket
boosters, increased main-stage thrust, larger propellant tankage, and improved guidance. The most powerful version thus far is Delta 3920/PAM-D (Payload Assist Module-Delta class), first used in 1982, which has nine strap-on boosters. Its three stages have an overall height of 41.6 m (136.5 ft), its launch weight is 193,593 kg (426,800 lb), and total thrust is 452,367 kg (997,300 lb). A delay in Delta launchings followed the forced destruction of a rocket in May 1986 when it failed during launch. The program resumed in February 1989 when a NAVSTAR satellite was launched by a modified vehicle called Delta II, which also uses nine strap-on boosters. In 1996 the Mars Global Surveyor and the Mars Pathfinder were sent on their way toward Mars by two Delta II vehicles. A new version of the rocket, Delta III, exploded in August 1998 during an attempted launch of a communications satellite from Cape Canaveral.