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USAF Satellite Launch Vehicles

Over the years, the USAF has developed several types of launch vehicles for the ballistic missile program. These ballistic missile launchers were modified and used to place many USAF and NASA projects into space. The three most important boosters to the United States' unmanned space program were the USAF's Thor, Atlas and Titan rockets. These launch vehicles provided the needed thrust to place into orbit the heavier and more complicated military satellites that the USAF required during the 1960s through the 1980s. In addition to their military applications, civilian agencies such as NASA used USAF-developed boosters for many of their programs as well. Even with the arrival of the Space Shuttle, these launch vehicles and their descendants are stilled used to orbit unmanned spacecraft that cannot be launched by the shuttle. The reliable Titan also was the booster for the first U.S. commercial space launches.

Thor Launch Vehicles
Designed and developed to be an intermediate range ballistic missile (IRBM) launch vehicle, the Thor has become one of the most successful spacecraft boosters ever built. First test flown as an IRBM in 1957 and as a satellite booster in 1958, the Thor has been continuously upgraded to provide more lifting capability. With various upper stages, Thor boosters have provided the USAF and NASA with a reliable and versatile means of placing payloads into space. The basic Thor has undergone numerous modifications through the years, including extending the main propellant tanks and adding from three to nine solid rockets to the base of the first stage. The latter modifications increased the thrust at launch from 150,000 to 971,000 pounds. The Thor with these changes was redesignated the Delta and used into the 1990s by NASA to launch medium weight payloads.

Atlas Launch Vehicles
The Atlas rocket was developed by the U.S. Air Force to be the nation's first Intercontinental Ballistic Missile (ICBM) capable of boosting a nuclear warhead to any target on earth. The program began in the early 1950s with the first successful launch in December 1957. The liquid-fueled Atlas served as one of the primary ballistic missiles until it was phased out of strategic missile service in 1965. It was replaced by the Minuteman ICBM.

The Atlas, however, went on to become one of the nation's most important boosters for Air Force, NASA and Department of Defense orbital payloads. It was first used as a non-strategic missile launcher in December 1958 for Project SCORE (Signal Communications Orbit Relay Equipment). This project provided a first test of a communications system in space and captured world attention by broadcasting a Christmas message by President Dwight D. Eisenhower through an onboard tape recorder.

The Atlas also became the launch vehicle for the Project Mercury manned orbital flights, Project PRIME, the NAVSTAR Global Positioning System, Ranger, Mariner, Pioneer 10, Lunar Orbiter, the Surveyor spacecraft and a variety of other military and civilian projects. To boost most of these payloads into orbit, upper stages had to be added to the Atlas to increase its lifting capacity. The Atlas used three main types of upper stages: the Agena, Centaur and the Burner II.

The Atlas has a unique main engine arrangement often referred to as "stage-and-a-half." Upon launch, all three main engines -- two LR89 boosters and one LR105 sustainer -- ignite and lift the rocket to an altitude of approximately 35 miles. At that point the two outer boosters shut down and were jettisoned along with the engine skirts. The central sustainer engine continues to run until the necessary speed is reached. With design improvements, the thrust of the three main engines (and the two small vernier or maneuvering rockets) was eventually increased from 389,000 pounds to 439,000 pounds at liftoff.

Titan Launch Vehicles
The Titan family of launch vehicles, first conceived in 1955, has become one of the most important launchers of heavy payloads into space. Originally designed and built for the U.S. Air Force to boost nuclear warheads to strategic targets, the Titan I had its first successful flight in January 1959. Titan Is eventually were replaced between 1963 and 1965 by more powerful and redesigned Titan IIs. Titan IIs served as the USAF's most powerful Intercontinental Ballistic Missile (ICBM) until they were withdrawn from service in 1987.

In the early 1960s, NASA selected the Titan II as the only proven rocket that was powerful enough to launch the two-man Gemini series of spacecraft. With small modifications to the basic ICBM-type missile, the Titan II successfully launched every Gemini spacecraft from March 1965 to November 1966.

In the meantime, the Air Force saw the need for more powerful boosters than the Atlas and Thor to launch their newest communications, navigation and reconnaissance satellites. By adding a third stage (the Transtage) to the first two stages of the Titan II, the required thrust to place large satellites in orbit was obtained. Named the Titan III-A, this rocket made its first successful flight in December 1964. The Titan III-A was quickly replaced, however, by the Titan III-B that usually had an Agena D as the third stage. This combination launched numerous Air Force satellites during the 1960s and 1970s.

The biggest change to the Titan series, however, was the addition of two large solid rockets to the main vehicle to increase the available thrust at liftoff from 463,000 to 2,360,000 pounds. These "strap-on" solid rockets would lift the rocket to a certain altitude where the main engines would then ignite. The solid rockets were jettisoned after their propellant was exhausted while the main rocket would continue on its journey. The Titan III-C, the first of the series to have the additional solid rocket boosters, had its first successful test flight in June 1965. All of the succeeding members of the Titan family -- the Titan III-D, III-E, the 34D, and the Titan IV -- have utilized the solid rocket boosters to increase their lifting capability. These solid rockets were so successful that they were adopted as the primary boosters for the Space Shuttle.

The Titan series of launch vehicles have usually used one of four main upper stages -- the Agena, the Transtage, the Boeing Inertial Upper Stage, of the Centaur -- depending on the payload and the mission. The Titan launch vehicles are the most powerful unmanned launchers available to the Department of Defense and civilian agencies. The later Titan versions can place over 10,000 pounds in geosynchronous orbit. (A satellite is said to be in geosynchronous orbit when it is 22,300 miles above the equator where it circles the earth once every 24 hours. Since the orbital period matches earth's rotation, the satellite appears to hang motionless in space.)

Titans have boosted numerous types of payloads into space. These included the Gemini spacecraft, various Air Force reconnaissance, communication, navigation and weather satellites, and many NASA spacecraft such as the Viking 1 and 2 missions to Mars and the interplanetary vehicles Voyager 1 and 2. The Titan program has played an important role in the expansion of the U.S. military and civilian presence in space. It also provided a proven and economical booster for America's first major commercial space launch program.

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