Thor-Ablestar

Thor-Ablestar. The Thor-Ablestar was a two-stage expendable launch system used by the United States Air Force during the early 1960s. It was created by mating the proven Thor ballistic missile as a first stage with the Aerojet-built Ablestar upper stage. This vehicle was primarily developed to orbit the United States Navy's Transit series of navigation satellites, which formed the world's first satellite navigation system.

Development and design

The development of this launch vehicle stemmed from a specific military requirement for a reliable rocket to deploy medium-weight payloads into low Earth orbit. The first stage was derived directly from the PGM-17 Thor IRBM, which was originally designed by the Douglas Aircraft Company under contract to the United States Air Force's Ballistic Missile Division. The key innovation was the Ablestar second stage, developed by Aerojet; it was an early example of a restartable upper stage using storable hypergolic propellants, specifically Aerozine 50 fuel and Nitrogen tetroxide oxidizer. This restart capability was crucial for the precise orbital injections required by the Transit program, allowing for orbit circularization and correction maneuvers. The vehicle's design was managed under the oversight of the Space Systems Division and represented a significant collaboration between the United States Navy and the United States Air Force for space launch services.

Operational history

The operational history of the vehicle began with its maiden flight from Cape Canaveral Air Force Station Launch Complex 17 on 13 April 1960, which successfully orbited Transit 1B. This launch marked a major milestone for the United States Navy's Naval Research Laboratory and the Applied Physics Laboratory at Johns Hopkins University. The rocket conducted 19 total launches between 1960 and 1965, with 16 successes and 3 failures. Its primary mission was deploying satellites for the Transit system, including Transit 4A and Transit 4B, but it also launched other significant payloads like the Injun series of spacecraft for the University of Iowa to study radiation belts and the ANNA 1B geodetic satellite for the United States Army, United States Navy, and NASA. The final flight occurred on 13 April 1965, after which it was retired in favor of more capable launch systems like the Thor-Delta.

Launch list

A partial list of notable launches includes the successful deployment of Transit 1B on the inaugural flight and Transit 4A in June 1961. Other significant missions carried Transit 4B in November 1961, the Injun 1 satellite in June 1961, and the ANNA 1B in October 1962. The launch of Transit 5A-1 in December 1962 ended in failure when the second stage malfunctioned. The final mission in April 1965 successfully orbited Transit 9 and Transit 10. All launches were conducted from Cape Canaveral Air Force Station, primarily from Launch Complex 17 pads B and A.

Specifications

The first stage was a standard Thor booster, powered by a single Rocketdyne LR-79 rocket engine burning RP-1 kerosene and liquid oxygen, producing approximately 150,000 pounds of thrust. The second stage was the Ablestar, powered by an Aerojet AJ10-104 engine that generated about 7,800 pounds of thrust using hypergolic Aerozine 50 and Nitrogen tetroxide. The vehicle stood roughly 30 meters tall and had a diameter of 2.44 meters at its first stage. It was capable of placing a 500-pound payload into a 600-mile circular orbit, a performance envelope perfectly suited for the Transit spacecraft. The guidance system for the upper stage was provided by a MIT-designed inertial navigation system.

Category:Thor (rocket family) Category:Expendable launch systems of the United States Category:1960 in spaceflight