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Thor was the United States's first operational ballistic missile. It was deployed with thermonuclear warheads in the U.K. between 1959 and 1963. It went on to spawn a string of space launch vehicles. Its descendants fly to this day as the Delta series of rockets.
Fearful that the Soviet Union would deploy a long-range ballistic missile before the United States, in January 1956 the Air Force began developing the Thor, a 1,500 mile (2,400 km) intermediate-range ballistic missile (IRBM). The Thor program unfolded with amazing speed, and within 3-years of the program?s inception the first Thor squadron became operational in Great Britain. The Thor was a stop-gap measure, however, and once the first generation of ICBMs based in the United States became operational, the Thor missiles were quickly retired. The last of the missiles was withdrawn from operational alert in 1963.
All sixty of the Thor missiles deployed in Great Britain were based at above-ground launch sites. The missiles were stored horizontally on transporter-erector trailers and covered by a retractable missile shelter. To fire the weapon, the crew electronically rolled back the missile shelter and then, using a powerful hydraulic launcher-erector, lifted the missile to an upright position. Once it was standing on the launch mount, the missile was fueled and fired. The entire launch sequence took about 15 minutes. When the launch control officer pressed the firing button, the main engine ignited with a roar. It burned for almost 2l/2 minutes, boosting the missile to a speed of 14,400 ft/s (4.4 km/s). Ten minutes into its flight the missile reached an altitude of 280 miles (450 km), close to the apogee of its elliptical flight path. At that point the reentry vehicle separated from the fuselage and began its descent down toward the target. Total flight time from launch to impact: 18 minutes.
Development of the Thor was initiated by the US Air Force in 1954 as a Tactical Ballistic Missile. The goal was a missile system that could deliver a nuclear warhead over a distance of 1150 to 2300 miles (1900 to 3700 km) with a CEP of 2 miles (3 km). This range would allow Moscow to be hit from a launch site in the U.K.
The initial design studies were headed by Cmdr. Robert Truax (US. Navy) and Dr. Adolph K. Thiel (Ramo-Wooldridge Corp, formerly Redstone Arsenal). They refined the specs to an IRBM with:
On November 30, 1955 three companies were given one week to bid on the project: Douglas, Lockheed, and North American Aviation. They were asked to create "a management team that could pull together existing technology, skills, abilities, and techniques in 'an unprecedented time.'" On December 27, 1955 Douglas Aircraft Corporation was awarded the prime contract for the airframe and integration. The Rocketdyne division of North American Aviation was awarded the engine contract, AC Spark Plug the primary inertial guidance system, Bell Labs the backup radio guidance system, and General Electric the nose cone/reentry vehicle.
Douglas further refined the design by choosing bolted tank bulkheads (as opposed to the initially suggested welded ones) and a tapered fuel tank for improved aerodynamics. The engine was developed as a direct descendant of the Atlas MA-3 booster engine. Changes involved removal of one thrust chamber and a rerouting of the plumbing to allow the engine to fit within the smaller Thor boat-tail. Engine tests where being performed as of March 1956. The first engineering model engine was available in June, followed by the first flight engine in September. Engine development was complicated by serious turbopump problems. Early Thor engines suffered from what was known as "Bearing Walking', whereby the turbopump bearings rotate axially within their housing, causing it to wear out and the bearings to seize.
Thor test launches were to be from LC17 at Cape Canaveral. The development schedule was so compressed that plans for the Atlas bunker were used to allow the completion of the facility in time. Nevertheless pad LC17-B was just ready for the first test flight.
The first flight of the Thor IRBM was on 25 January 1957. The first airframe, number 101 was delivered in October of the previous year. The vehicle reached a apogee of 6 in (150 mm) whereupon contamination destroyed a LOX supply valve causing the engine to lose thrust. The Thor slid backwards through the launch ring and exploded on contact with the thrust deflector. Serious pad damage occurred.
The second Thor flight (102) lasted 35 seconds after an April 1957 launch. It was ended by a range safety officer who acted on faulty data from a readout which showed the missile heading inland over Florida.
Thor vehicle 103 (May 1957) exploded on the pad during tanking due to a faulty main fuel valve resulting in tank overpressurization leading to tank rupture.
Thor vehicle 104 (Aug 1957) broke up after 92 seconds due to a loss of guidance.
Thor vehicle 105 (20 September 1957), 21 months after the start of construction, flew 1100 miles (1,800 km) downrange. Estimated range without the extra load of the R&D instrumentation was 1500 miles (2,400 km).
1957 saw five more flights, the longest of which covered 2700 miles (4,300 km).
Thor was deployed to the UK starting in August 1958.
All sixty of the Thor missiles deployed in Great Britain were based at above-ground launch sites. The missiles were stored horizontally on transporter-erector trailers and covered by a retractable missile shelter. To fire the weapon, the crew electronically rolled back the missile shelter and then, using a powerful hydraulic launcher-erector, lifted the missile to an upright position. Once it was standing on the launch mount, the missile was fueled and fired. The entire launch sequence took about 15 minutes. When the launch control officer pressed the firing button, the main engine ignited with a roar. It burned for almost 2.5 minutes, boosting the missile to a speed of 14,400 ft/s ( 4.4 km/s). . Ten minutes into its flight the missile reached an altitude of 280 miles (450 km), close to the apogee of its elliptical flight path. At that point the reentry vehicle separated from the fuselage and began its descent down toward the target. Total flight time from launch to impact was about 18 minutes.
Thor was noted as forming a good basis for a space launch vehicle early in its development.
The first space launch type of mission Thor was asked to perform was the testing of the Atlas reentry vehicle. For these three tests a Thor core stage was topped by a second stage named Able using the Aerojet AJ-10-40 engine from the Vanguard second stage. The first such launch, 116, was lost due to turbopump failure of the main engine. The results of two succeeding attempts are unknown to this author.
Thor vehicle 127 was a three stage Thor-Able-Star. The Able stage from the Atlas reentry vehicle tests was upgraded (to become the Able I) and topped with a third stage consisting of an unguided Altair X-248 solid rocket motor. The mission was to place the 84 lb (38 kg) Pioneer spacecraft into lunar orbit where it would take pictures of the lunar surface with a TV camera. The mission ended prematurely at 77 seconds after launch due to yet another turbopump failure.
Thor formed the core of the Thor-Agena vehicle used to launch the United State's first spy satellites as part of the Corona program.
In January of 1959 the newly formed National Aeronautics and Space Administration released a report entitled "The National Space Vehicle Program". This report addressed the nation's space launch needs.
"Our approach up to this time has been much too diverse in that we fire a few vehicles of a given configuration, most of which have failed to achieve their missions, and then call on another vehicle to take the stage. In this situation no one type of vehicle is tested with sufficient thoroughness and used in enough firing to achieve a high degree of reliability"
The report proposed four vehicles to form the core of the U.S. spacefleet:
Eleven of the twelve initial Delta flights were successful. The total project development and launch cost came to $43 million, $3 million over budget. An order for 14 more vehicles was let before 1962.
| 1 | 13may60 9:16 pm GMT. | Payload: echo 1. pad 17a. Good first stage. second stage attitude control system failure. vehicle destroyed. |
| 2 | 12aug60. | good flight. echo 1A placed into 1035 mile (1666 km), 47 degree inclination orbit. |
| 3 | 23nov60. | Tiros 2. good flight. |
| 4 | explorer 10. placed into elliptical 138,000 mile (222,000 km) orbit. 78 lb (35 kg) | |
| 5 | 12july61. | tiros 3. |
| 6 | 16aug61. | explorer 12 Energetic Particle Explorers. EPE-1. highly elliptical orbit. |
| 7 | 8feb62. | tiros 4. |
| 8 | 7mar62. | OSO-1 (orbiting solar observatory). 345 mile (555 km), 33 degree orbit. |
| 9 | 26apr62. | Ariel 1. Ariel 1 was seriously damaged by Starfish Prime |
| 10 | 19jun62. | tiros 5 |
| 11 | 10jul62. | Telstar 1. Also damaged by Starfish Prime. |
| 12 | 18sep62. | tiros 6 |
Block II MB-3 engine, 170,000 lbf (756 kN) vs. 152,000 lbf (676 kN)
13. EPE2
14. EPE3
15. 13dec62. Relay 1, second nasa communications sat. nasa's first active one.
16. 13feb63. pad 17b. Syncom 1. Thiokol Star 13B solid rocket as apogee kick motor.
20. july63? Syncom 2. Geosynchronous orbit, but inclined 33degrees due to the limited performance of the Delta.
The Thrust Augmented Thor, or TAT, was developed to handle the growing recon sats of the Corona program. It added three Castor solid rocket strapon boosters--each providing 53,000 lbf (236 kN) thrust--to the standard Thor core stage. The boosters were lit on the ground and jettisoned after burnout.
25. 19aug64. Syncom 3. First true Geosynchronous sat.
26. Intelsat 1
First Delta E. 6nov65. launches GEOS 1.
1. 14dec66. biosatellite 1.
2. 7sep67. biosatellite 2
4jul68. Explorer 38.
See also: List of missiles
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