Launch of the Transit 1A satellite on a Thor-Able II
|Function||Expendable launch system
|Country of origin||United States|
|Height||26.9 metres (88 ft) - 27.8 metres (91 ft)|
|Diameter||2.44 metres (8 ft 0 in)|
|Mass||51,608 kilograms (113,776 lb)|
|Payload to 640km LEO||120 kilograms (260 lb)|
|Launch sites||LC-17A, Canaveral|
|First flight||24 April 1958|
|Last flight||1 April 1960|
|First stage - Thor|
|Thrust||758.71 kilonewtons (170,560 lbf)|
|Specific impulse||282 sec|
|Burn time||165 seconds|
|Second stage - Able|
|Thrust||34.69 kilonewtons (7,800 lbf)|
|Specific impulse||270 sec|
|Burn time||115 seconds|
|Third stage (optional) - Altair|
|Thrust||12.45 kilonewtons (2,800 lbf)|
|Specific impulse||256 sec|
|Burn time||38 seconds|
The Thor-Able was an American expendable launch system and sounding rocket used for a series of re-entry vehicle tests and satellite launches between 1958 and 1960. It was a two stage rocket, consisting of a Thor IRBM as a first stage, and a Vanguard-derived Able second stage. On some flights, an Altair solid rocket motor was added as a third stage. It was a member of the Thor family, and an early predecessor of the Delta.
Sixteen Thor-Ables were launched, nine on sub-orbital re-entry vehicle test flights, and seven on orbital satellite launch attempts. Six launches resulted in failures, in which three of those failures were the result of an Altair upper stage added to the rocket to allow it to launch the spacecraft onto a trans-lunar trajectory. All sixteen launches occurred from Cape Canaveral Air Force Station Launch Complex 17A.
The Thor-Able vehicle had a stronger airframe than the standard Thor IRBM and had the inertial guidance system replaced by a radio guidance package mounted on the Able stages. It saw its first test on April 24, 1958 when Vehicle 116 was launched with dummy upper stages. 146 seconds after liftoff, it exploded from a turbopump failure. The second and third tests on July 10 and 23 were successful, after which Vehicle 127 was prepared for launch with the world's first lunar probe. This flight, broadcast live on television, took place on August 17 but ended embarrassingly when the Thor exploded 77 seconds into the launch due to another turbopump malfunction. After an Atlas missile test a month later also failed due to the turbopumps, the Air Force Ballistic Missile Division quickly replaced the pumps in all of their missiles and this problem did not repeat itself again.
On October 10, Pioneer 1 was launched on Thor 130. The second stage shut down too early and the probe did not have sufficient velocity to escape Earth's orbit. It reentered the atmosphere and burned up 43 hours after launch.
Pioneer 2 was launched November 8 and reentered the atmosphere less than an hour after launch when the third stage failed to ignite.
The next six Thor-Able flights were suborbital tests for the Air Force (January 23, February 28, March 21, April 8, May 20, and June 11, 1959). All of these were successful except the first one, which failed to stage due to an electrical problem and fell into the Atlantic Ocean.
On August 7, Explorer 6 (a scientific satellite) was launched on Vehicle 134 and successfully orbited.
On September 17, Transit 1A failed to orbit due to the third stage again failing to ignite.
On November 3, Pioneer 5 was successfully launched. Intended originally as a Venus probe, technical delays caused it to be launched after the 1959 Venus window had closed so that it was instead sent into heliocentric orbit.
The final Thor-Able launch orbited Tiros 1 on April 4, 1960.
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