Launch of a Thor-Ablestar 2 with a Transit satellite
|Function||Orbital carrier rocket|
|Country of origin||United States|
|Height||29 metres (95 ft)|
|Diameter||2.44 metres (8 ft 0 in)|
|Mass||53,000 kilograms (117,000 lb)|
|Payload to 1100km LEO||150 kilograms (330 lb)|
|Launch sites|| LC-17, Canaveral |
|First flight||13 April 1960|
|Last flight||13 August 1965|
|First stage – Thor|
|Thrust||760.64 kilonewtons (171,000 lbf)|
|Specific impulse||285 sec|
|Burn time||164 seconds|
|Second stage – Ablestar|
|Thrust||36.02 kilonewtons (8,100 lbf)|
|Specific impulse||280 sec|
|Burn time||296 seconds|
The Thor-Ablestar, or Thor Able-Star, also known as Thor-Epsilonwas an early American expendable launch system consisting of a PGM-17 Thor missile, with an Ablestar upper stage. It was a member of the Thor family of rockets, and was derived from the Thor-Able.
An expendable launch system is a launch vehicle that can be launched only once, after which its components are either destroyed during reentry or discarded in space. ELVs typically consist of several rocket stages that are discarded sequentially as their fuel is exhausted and the vehicle gains altitude and speed. Most satellites and human spacecraft are currently launched on ELVs. ELVs are simpler in design than reusable launch systems and therefore may have a lower production cost. Furthermore, an ELV can use its entire fuel supply to accelerate its payload, offering greater fuel efficiency. ELVs are proven technology in wide-use for many decades. ELVs are usable only once, and therefore have a significantly higher per-launch cost than reusable vehicles. New reusable launch systems under development by private companies such as SpaceX and Blue Origin have the potential to obsolete many existing ELVs due to the lower per-launch costs of reusable rockets.
The PGM-17A Thor was the first operational ballistic missile of the U.S. Air Force (USAF). Named after the Norse god of thunder, it was deployed in the United Kingdom between 1959 and September 1963 as an intermediate-range ballistic missile (IRBM) with thermonuclear warheads. Thor was 65 feet (20 m) in height and 8 feet (2.4 m) in diameter. It was later augmented in the U.S. IRBM arsenal by the Jupiter.
Thor was a US space launch vehicle derived from the PGM-17 Thor intermediate-range ballistic missile. The Thor rocket was the first member of the Delta rocket family of space launch vehicles. The last launch of a direct derivative of the Thor missile occurred in 2018 as the first stage of the final Delta II.
The Ablestar second stage was an enlarged version of the Able, which gave the Thor-Ablestar a greater payload capacity compared to the Thor-Able. It also incorporated restart capabilities, allowing a multiple-burn trajectory to be flown, further increasing payload, or allowing the rocket to reach different orbits. It was the first rocket to be developed with such a capability and development of the stage took a mere eight months.
The Able rocket stage was a rocket stage manufactured in the United States by Aerojet as the second of three stages of the Vanguard rocket used in the Vanguard project from 1957 to 1959. The rocket engine used nitric acid and UDMH as rocket propellants. The Able rocket stage was discontinued in 1960. The improved Ablestar version was used as the upper stage of the Thor-Ablestar two stage launcher. The Ablestar second stage was an enlarged version of the Able rocket stage, which gave the Thor-Ablestar a greater payload capacity compared to the earlier Thor-Able. It also incorporated restart capabilities, allowing a multiple-burn trajectory to be flown, further increasing payload, or allowing the rocket to reach different orbits. It was the first rocket to be developed with such a capability and development of the stage took a mere eight months.
Nineteen Thor-Ablestars were launched between 1960–65, of which four failed, and a fifth resulted in a partial failure, as only one of two payloads separated from the upper stage.
The first failure was the launch of Courier 1A, an experimental communications satellite, on 19 August 1960 when the first stage shut down 30 seconds earlier than planned and was destroyed by the Range Safety officer. On 30 November, another launch involving a Transit satellite failed in practically identical fashion. This episode nearly created an international incident as parts of the Thor landed in Cuba. Cuban leader Fidel Castro subsequently sold off the Thor's engine to the Soviets and the Chinese received its thrust vectors, which ended up proving valuable to the latter's development of a ballistic missile capability. To prevent this from happening again, future Thor Ablestar launches had their flight paths modified to avoid passing over Cuba.
Cuba, officially the Republic of Cuba, is a country comprising the island of Cuba as well as Isla de la Juventud and several minor archipelagos. Cuba is located in the northern Caribbean where the Caribbean Sea, Gulf of Mexico and Atlantic Ocean meet. It is east of the Yucatán Peninsula (Mexico), south of both the U.S. state of Florida and the Bahamas, west of Haiti and north of both Jamaica and the Cayman Islands. Havana is the largest city and capital; other major cities include Santiago de Cuba and Camagüey. The area of the Republic of Cuba is 110,860 square kilometers (42,800 sq mi). The island of Cuba is the largest island in Cuba and in the Caribbean, with an area of 105,006 square kilometers (40,543 sq mi), and the second-most populous after Hispaniola, with over 11 million inhabitants.
Fidel Alejandro Castro Ruz was a Cuban communist revolutionary and politician who governed the Republic of Cuba as Prime Minister from 1959 to 1976 and then as President from 1976 to 2008. A Marxist–Leninist and Cuban nationalist, Castro also served as the First Secretary of the Communist Party of Cuba from 1961 until 2011. Under his administration, Cuba became a one-party communist state, while industry and business were nationalized and state socialist reforms were implemented throughout society.
The launch of a Transit satellite on 22 February 1961 was successful, but its companion Lofti satellite failed to separate from the second stage.
The third failure was the launch of several piggybacked satellites on 24 January 1962 when the second stage produced insufficient thrust to achieve orbital velocity.The fourth and final failure was the launch of an Anna geodetic satellite on 10 May 1962 when the second stage completely failed to ignite.
Two versions were built; the Thor-Ablestar 1, with a DM-21 Thor, and an AJ-10-104 second stage engine, and the Thor-Ablestar 2, which had a DSV-2A Thor first stage, and an uprated AJ-10-104D engine on the second stage.Thor-Ablestar 1 launches occurred from LC-17 at Cape Canaveral, and Thor-Ablestar 2 rockets were launched from LC-75-1 at Point Arguello, which has since become part of Vandenberg Air Force Base and is now designated SLC-2.
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