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PGM-17 Thor

PGM-17 Thor

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Thor was the first operational ballistic missile
Ballistic missile
A ballistic missile is a missile that follows a sub-orbital ballistic flightpath with the objective of delivering one or more warheads to a predetermined target. The missile is only guided during the relatively brief initial powered phase of flight and its course is subsequently governed by the...

 of the U.S. Air Force (USAF). Named after the Norse god of thunder
Thor
In Norse mythology, Thor is a hammer-wielding god associated with thunder, lightning, storms, oak trees, strength, the protection of mankind, and also hallowing, healing, and fertility...

, it was deployed in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 between 1959 and September 1963 as an intermediate range ballistic missile (IRBM) with thermonuclear warheads. Thor was 65 feet (19.8 m) in height and 8 feet (2.4 m) in diameter. It was later augmented in the U.S. IRBM arsenal by the Jupiter.

A large family of space launch vehicle
Launch vehicle
In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....

s—the Delta rockets—were derived from the Thor design. A modified version is still in use as the first stage of the Delta II
Delta II
Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011...

.

Design and development



Fearful that the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 would deploy a long-range ballistic missile before the U.S., in January 1956 the USAF began developing the Thor, a 1500 miles (2,414 km) intermediate-range ballistic missile. The Thor program unfolded quickly, and within three years of the program’s inception the first of 20 Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 Thor squadrons became operational in the UK. The UK deployment carried the codename 'Project Emily
Project Emily
Project Emily was the deployment of American-built PGM-17 Thor Intermediate-range ballistic missiles in the United Kingdom between 1959 and 1963....

'. One of the advantages of the design was that, unlike the Jupiter IRBM, the Thor could be carried by the USAF's cargo aircraft of the time, which made its deployment more rapid; although the launch facilities were not transportable, and had to be built on site. The Thor was a stop-gap measure, however, and once the first generation of ICBM
Intercontinental ballistic missile
An intercontinental ballistic missile is a ballistic missile with a long range typically designed for nuclear weapons delivery...

s based in the U.S. became operational, Thor missiles were quickly retired. The last of the missiles was withdrawn from operational alert in 1963.

A small number of Thors, converted to "Thrust Augumented Delta" launchers, remained operational in the anti-satellite missile role as Program 437
Program 437
Program 437 was the second anti-satellite weapons program of the U.S. military. The US anti-satellite weapons program began development in the early 1960s and was officially discontinued on 1 April 1975. Program 437 was approved for development by U.S. Secretary of Defense Robert McNamara on...

 until April 1975. These missiles were based on Johnston Island
Johnston Atoll
Johnston Atoll is a atoll in the North Pacific Ocean about west of Hawaii. There are four islands located on the coral reef platform, two natural islands, Johnston Island and Sand Island, which have been expanded by coral dredging, as well as North Island and East Island , an additional two...

 in the Pacific Ocean and had the ability to destroy satellites in low Earth orbit. With prior warning of an impending launch, they could destroy a Soviet spy satellite soon after orbital insertion. These missiles remain in storage, and could be reactivated, though the W-49 Mod 6 warheads
W49
The W49 was an American thermonuclear warhead, used on the Thor, Atlas, Jupiter, and Titan I ballistic missile systems. W49 warheads were manufactured starting in 1958 and were in service until 1963, with a few warheads being retained until 1975....

 were all dismantled by June 1976.

Initial development as an IRBM


Development of the Thor was initiated by the USAF 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 mi (1,850.7 to 3,701.5 km) with a CEP of 2 miles (3.2 km). This range would allow Moscow
Moscow
Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...

 to be hit from a launch site in the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

.

The initial design studies were headed by Cmdr. Robert Truax
Robert Truax
Captain Robert C. Truax was a rocket engineer in the United States Navy, and companies such as Aerojet and Truax Engineering, which he founded...

 (US Navy) and Dr. Adolph K. Thiel (Ramo-Wooldridge Corporation, formerly of Redstone Arsenal
Redstone Arsenal
Redstone Arsenal is a United States Army base and a census-designated place adjacent to Huntsville in Madison County, Alabama, United States and is part of the Huntsville-Decatur Combined Statistical Area...

). They refined the specs to an IRBM with:
  • A 1750 miles (2,816.3 km) range diameter, 65 ft (19.8 m) long (so it could be carried by Douglas
    Douglas Aircraft Company
    The Douglas Aircraft Company was an American aerospace manufacturer, based in Long Beach, California. It was founded in 1921 by Donald Wills Douglas, Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas...

     C-124 Globemaster)
  • A gross takeoff weight of 110000 lb (49,895.2 kg)
  • Propulsion provided by half of the Navaho
    SM-64 Navaho
    The North American SM-64 Navaho was a supersonic intercontinental cruise missile project built by North American Aviation. The program ran from 1946 to 1958 when it was cancelled in favor of intercontinental ballistic missiles...

    -derived Atlas
    Atlas (missile)
    The SM-65 Atlas was the first intercontinental ballistic missile developed and deployed by the United States. It was built for the U.S. Air Force by Convair Division of General Dynamics at the Kearny Mesa assembly plant north of San Diego, California...

     booster engine (due, largely, to the lack of any alternatives at this early date) maximum speed during warhead reentry
  • Inertial guidance system with radio backup (for low susceptibility to enemy disruption)


On November 30, 1955 three companies were given one week to bid on the project: Douglas
Douglas Aircraft Company
The Douglas Aircraft Company was an American aerospace manufacturer, based in Long Beach, California. It was founded in 1921 by Donald Wills Douglas, Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas...

, Lockheed
Lockheed Corporation
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...

, and North American Aviation
North American Aviation
North American Aviation was a major US aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service...

.
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 was awarded the prime contract for the airframe and
integration. The Rocketdyne
Rocketdyne
Rocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...

 division of North American Aviation was awarded the engine contract, AC Spark Plug the primary inertial guidance system, Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...

 the backup radio guidance system, and General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

 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 were 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 shift axially within their housing, causing rapid wear and the bearings to seize.

First launches


Thor test launches were to be from LC-17
Cape Canaveral Air Force Station Launch Complex 17
Cape Canaveral Air Force Station Space Launch Complex 17 , previously designated Launch Complex 17 , was a launch site at Cape Canaveral Air Force Station, Florida used for Thor and Delta rocket launches between 1958 and 2011....

 at Cape Canaveral Missile Annex
Cape Canaveral Air Force Station
Cape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads...

. 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 LC-17B was just ready for the first test flight.

The first flight of the Thor IRBM was on January 25, 1957. The first airframe, number 101, was delivered in October of the previous year. The vehicle reached an apogee of 6 inches (152.4 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 destroyed the missile after seeing faulty data on a readout which indicated that the missile was 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 over-pressurization leading to tank rupture.

Thor vehicle 104 (August 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 (1,770.3 km) downrange. Estimated range without the extra load of the R and D instrumentation was 1500 miles (2,414 km).

1957 saw five more flights, the longest of which covered 2700 miles (4,345.2 km).

Deployment



Thor was deployed to the UK starting in August 1958, operated by 20 squadrons of RAF Bomber Command
RAF Bomber Command
RAF Bomber Command controlled the RAF's bomber forces from 1936 to 1968. During World War II the command destroyed a significant proportion of Nazi Germany's industries and many German cities, and in the 1960s stood at the peak of its postwar military power with the V bombers and a supplemental...

. The first active unit was No. 77 Squadron RAF
No. 77 Squadron RAF
No. 77 Squadron RAF was formed on 1 October 1916 at Edinburgh, and was equipped with B.E.2 and B.E.12 aircraft. The squadron disbanded at RAF Turnhouse on June 13, 1919....

 at RAF Feltwell
RAF Feltwell
RAF Feltwell is a Royal Air Force station in Norfolk, East Anglia that is currently used by the United States Air Forces Europe. The station is located about 10 miles west of Thetford, and is in the borough of King's Lynn at approximate Ordnance Survey grid reference .A former Second World War...

 in 1958, with the remaining units becoming active in 1959. All were deactivated by September 1963.

All 60 of the Thor missiles deployed in the UK 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 used an electric motor to roll back the missile shelter (essentially a long shed mounted on steel rails), then used a powerful hydraulic launcher-erector to lift the missile to an upright position for launch. Once it was standing on the launch mount, the missile was fueled and fired. The entire launch sequence took about 15 minutes. Main engine burn time was almost 2.5 minutes, boosting the missile to a speed of 14400 ft/s (4,389.1 m/s). Ten minutes into its flight the missile reached an altitude of 280 miles (450.6 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.

The Thor was initially deployed with a very blunt conical G.E. Mk 2 'heat sink' re-entry vehicle. They were later converted to the slender G.E. Mk 3 ablative RV. Both RVs contained a W-49 thermonuclear warhead
W49
The W49 was an American thermonuclear warhead, used on the Thor, Atlas, Jupiter, and Titan I ballistic missile systems. W49 warheads were manufactured starting in 1958 and were in service until 1963, with a few warheads being retained until 1975....

 with an explosive yield of 1.44 megaton
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

s.

Noteworthy Thor IRBM flights

  • 4 June 1962, failed Starfish
    Starfish Prime
    Starfish Prime was a high-altitude nuclear test conducted by the United States of America on July 9, 1962, a joint effort of the Atomic Energy Commission and the Defense Atomic Support Agency ....

     flight, Thor destroyed, nuclear device lost.
  • 20 June 1962, failed Bluegill Prime
    Operation Dominic I and II
    Operation Dominic was a series of 105 nuclear test explosions conducted in 1962 by the United States. Those conducted in the Pacific are sometimes called Dominic I. The blasts in Nevada are known as Dominic II. This test series was scheduled quickly, in order to respond in kind to the Soviet...

     flight, Thor destroyed, nuclear device lost.
  • 9 July 1962, Thor missile 195 launched a Mk4 reentry vehicle containing a W49 thermonuclear warhead to an altitude of 250 miles (402.3 km). The warhead detonated with a yield of 1.45 Mt of TNT (6.07 PJ). This was the Starfish Prime
    Starfish Prime
    Starfish Prime was a high-altitude nuclear test conducted by the United States of America on July 9, 1962, a joint effort of the Atomic Energy Commission and the Defense Atomic Support Agency ....

     event of nuclear test operation Dominic-Fishbowl
    Operation Dominic I and II
    Operation Dominic was a series of 105 nuclear test explosions conducted in 1962 by the United States. Those conducted in the Pacific are sometimes called Dominic I. The blasts in Nevada are known as Dominic II. This test series was scheduled quickly, in order to respond in kind to the Soviet...

    .

Launch vehicle



The Thor rocket was also used as a space launch vehicle
Launch vehicle
In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....

. It was the first in a large family of space launch vehicles—the Delta rockets. Thor's descendants fly to this day as the Delta II and Delta IV.

Operators


: United States Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

  • RAF South Ruislip
    RAF South Ruislip
    RAF South Ruislip was a non-flying Air Force station located in South Ruislip near London, England.The station opened in 1949 and was used by the United States Air Force as an administrative station to coordinate Third Air Force and 7th Air Division activities in Great Britain with the British...

705th Strategic Missile Wing
705th Strategic Missile Wing
The 705th Strategic Missile Wing is an inactive United States Air Force unit. It was last assigned to the Department of the Air Force, being stationed at South Ruislip Air Station, England...

 (1958-1960)


: Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

  • RAF Bomber Command

see Project Emily Stations and Squadrons

Specifications (PGM-17A)

  • Family: Thor IRBM, Thor DM-18 (single stage LV); Thor DM-19 (rocket 1st stage), Thor DM-21 (rocket 1st stage), Thor DSV-2D,E,F,G (suborbital LV), Thor DSV-2J (anti-ballistic missile), Thor DSV-2U (orbital launch vehicle).

  • Overall length: 19.82 m (65 ft)
  • Span: 2.74 m (9 ft)
  • Weight: 49800 kg (109,790.2 lb)
  • Empty weight: 3125 kg (6,889.4 lb)
  • Thrust (vac): 760 kN
  • Liftoff Thrust (sl): 670 kN (150,000 lbf)
  • Isp: 282 s (2.77 kN·s/kg)
  • Isp(sl): 248 s (2.43 kN·s/kg)
  • Burn time: 165 s
  • Core Diameter: 2.44 m
  • Maximum range: 2400 km (1,491.3 mi)
  • Ceiling: 480 km (298.3 mi)

Warhead
  • One W49. on Mk. 2. reentry vehicle
  • warhead mass: 1000 kg (2,204.6 lb)
  • Yield: equivalent to 1,440 kilotons of TNT (6.02 PJ)
  • CEP: 1 km (0.621372736649807 mi)

  • Boost Propulsion: Liquid fuelled rocket, LOX
    Liquid oxygen
    Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

     and Kerosene
    Kerosene
    Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

    .
  • Engines:
    • Rocketdyne LR79-NA-9 (Model S-3D); 666 kN (150000 lbf)
    • Vernier: 2x Rocketdyne LR101-NA; 4.5 kN (1000 lbf) each
    • Propellants: LOX/Kerosene (Thor kerosene propellant was referred to as 'RP1' by RAF users)
    • Thrust (vac): 760 kN
    • Isp: 282 s (2.77 kN·s/kg)
    • Isp (sea level): 248 s (2.43 kN·s/kg)
    • Burn time: 165 s
    • Mass Engine: 643 kg
    • Diameter: 2.44 m
    • Chambers: 1
    • Chamber Pressure: 4.1 MPa
    • Area Ratio: 8.00
    • Thrust to Weight Ratio: 120.32
    • Country: USA
    • First Flight: 1958
    • Last Flight: 1980
    • Flown: 145.
    • Comments: Designed for booster applications. Gas generator, pump-fed
  • Guidance: Inertial
  • Maximum speed: 17740 km/h (11,023.1 mph)
  • Development Cost US dollar
    Dollar
    The dollar is the name of the official currency of many countries, including Australia, Belize, Canada, Ecuador, El Salvador, Hong Kong, New Zealand, Singapore, Taiwan, and the United States.-Etymology:...

    s: $500 million
  • Recurring Price US dollars: $6.25 million
  • Total Number Built: 224
  • Total Development Built: 64
  • Total Production Built: 160
  • Flyaway Unit Cost: US$750,000 in 1958 dollars
  • Launches: 59
  • Failures: 14
  • Success Rate: 76.27%
  • First Launch Date: 25 January 1957
  • Last Launch Date: 5 November 1975

See also



  • Project Emily
    Project Emily
    Project Emily was the deployment of American-built PGM-17 Thor Intermediate-range ballistic missiles in the United Kingdom between 1959 and 1963....


External links