Tag Archives: Douglas SM-75 Thor

17 August 1958

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Thor-Able 127 being prepared for launch at the Cape Canaveral Air Force Station. (U.S. Air Force)

17 August 1958: In what was the first attempt to launch a spacecraft beyond Earth orbit, Thor-Able 1 (Missile Number 127) was to place a small instrumented satellite in orbit around the Moon. Called Pioneer,¹ the satellite carried a television camera, a micrometeorite detector and a magnetometer.

The mission was carried out by the U.S. Air Force Ballistic Missile Division and the Advanced Research Projects Agency (ARPA).

The Thor-Able lifted off from Launch Complex 17A at the Cape Canaveral Air Force Station, Florida, at 12:28:00 UTC, 4 minutes behind schedule.

73.6 seconds into the flight, at an altitude of 9.9 miles (16 kilometers), the first stage of the rocket exploded. Telemetry from the upper stages continued and was tracked until impact in the Atlantic Ocean.

An investigation found the cause of the explosion to be a turbopump failure. It was determined that a bearing in the pump’s gearbox seized, halting the flow of liquid oxygen.

The Thor Able was a two-stage orbital launch vehicle which was developed from the Douglas Aircraft Company’s SM-75 Thor intermediate-range ballistic missile.

Designated Thor DM-19, the first stage was 60.43 feet (18.42 meters) long and 8 feet (2.44 meters) in diameter. Fully fueled, the first stage had a gross weight of 108,770 pounds (49,337 kilograms). It was powered by a Rocketdyne LR-79-7 engine which burned liquid oxygen and RP-1 (a highly-refined kerosene rocket fuel) and produced 170,565 pounds of thrust (758.711 kilonewtons). This stage had a burn time of 2 minutes, 45 seconds.

The second stage was an Aerojet General Corporation-built Able, a second stage for the U.S. Navy’s Vanguard rocket. It was 21 feet, 6.6 inches (6.57 meters) long with a maximum diameter of 2 feet, 9 inches (0.84 meters), and had a gross weight of 5,000 pounds (2,268 kilograms). It used an Aerojet AJ10-101 rocket engine which burned a hypergolic mixture of nitric acid and UDMH. The second stage produced 7,711 pounds of thrust (34.300 kilonewtons) and burned for 1 minutes, 55 seconds.

Thor-Able second stage being prepared to mount to the Thor 127 first stage. (Drew ex Machina)

The Altair X248 third stage was developed by the Alleghany Ballistics Laboratory for the U.S. Navy’s Vanguard rocket. It was 4 feet, 11 inches (1.499 meters) long, 2 feet, 7 inches (0.787 meters) in diameter, and weighed 505 pounds (229 kilograms). It was powered by a solid fuel rocket engine producing 2,300 pounds (10.231 kilonewtons) of thrust. Its burn time was 38 seconds.

Thor-Able 127 lifts off from Launch Complex 17A, 17 August 1958. (NASA)

The first Pioneer space probe is today designated Pioneer 0. It was built by the Ramo-Wooldridge Corporation’s Space Technologies Laboratory (STL) in Redondo Beach, California.

The lunar probe was the fourth stage  of the Thor-Able launch vehicle. It was 74 centimeters (2 feet, 5.13 inches) in diameter, 76 centimeters (2 feet, 5.9 inches) long, and weighed 38.1 kilograms (83.996 pounds). The probe’s external shell was constructed of metal and fiberglass. It carried 11.3 kilograms (24.9 pounds) of instruments designed to measure magnetic fields, radiation and micrometeorites. It also carried an infrared camera system intended to obtain close-up images of The Moon’s surface. Pioneer 0 was spin-stabilized, turning 108 r.p.m.

The probe was equipped with a Thiokol TX-8-6 solid rocket engine to decelerate it for entry into lunar orbit. The rocket engine was the main structural component of the probe. There were 8 vernier rockets to correct its trajectory.

Space Technologies Laboratory Pioneer lunar orbiter. (STL/Drew ex Machina)

The Thiokol TX-8 was produced at the U.S. Army’s Longhorn Army Ammunition Plant near Karnack, Texas. It was designed to power the GAR-1 Falcon radar-homing air-to-air guided missile (later designated AIM-4 Falcon). The rocket motor weighed 11 kilograms (24.3 pounds).

Arrangement of equipment within the Pioneer lunar orbiter. (Drew ex Machina)

¹ Pioneer 0 was also known as Able 1.

© 2024, Bryan R. Swopes

9 July 1962, 09:00:09 UTC, T + 13:41

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Fireball of Operation Dominic-Fishbowl Starfish Prime, 248 miles (399.1 kilometers) above the Pacific Ocean, 9 July 1962. (U.S. Department of Defense)

9 July 1962: At 09:00:09 UTC, the United States detonated a thermonuclear warhead over the Pacific Ocean. This was part of the Operation Dominic-Fishbowl test series at Johnston Island, and was designated Starfish Prime.

A Thor missile is launched from Johnston Island. Note the instrumentation pods at the base of the rocket. (Johnston Memories)

At 08:46:28 UTC, a Douglas Thor DSV2E orbital launch vehicle, serial number 195,  was launched from missile complex LE-1 on Johnston Island, carrying a W-49 warhead in an AVCO Corporation Mk-2 reentry vehicle. The rocket also carried three instrumentation pods which were jettisoned at pre-selected altitudes. The W-49 reached a peak altitude of 600 miles (965 kilometers) along a ballistic trajectory, and then began to descend.

Starfish Prime fireball was visible from Honolulu, Oahu, Hawaii, 898 miles (1,445.2 kilometers) from Ground Zero. “Widespread red air glow (6300 å) amid dark clouds, caused mostly by x-ray-excited atomic oxygen (i.e., oxygen by photoelectrons liberated by Starfish X-rays)” (Commission to Assess Threat to the United States from Electromagnetic Pulse (EMP) Attack, 2004, at Page 5)
Starfish Prime (atomicarchive.com)

The W-49 detonated 36 kilometers (22 miles) southwest of Johnston Island at an altitude of 400 kilometers (246 miles) with an explosive yield of 1.45 megatons. The point of detonation deviated from the planned Air Zero by 1,890 feet (576 meters) to the north, 2,190 feet (668 meters) east, and +617 feet (188 meters) in altitude. The fireball was clearly visible in the Hawaiian Islands, more than 800 miles (1,288 kilometers) away.

The electromagnetic pulse (EMP) damaged electrical systems in The Islands, cutting power, damaging equipment and interrupting telephone systems. Brilliant auroras were visible, lasting about 7 minutes.

Telstar, an American communications satellite that was placed in Earth orbit the following day, was also damaged by residual radiation from the detonation.

The Starfish Prime experiment was for the purpose of “Evaluation of missile kill mechanisms produced by a high altitude nuclear detonation.” The electromagnetic effects on communications were also studied.

A Douglas SM-75/PGM-17A Thor IRBM. (U.S. Air Force)
A Douglas SM-75 Thor IRBM (DM-18A) is launched at Launch Complex 17B, Cape Canaveral Air Force Station, Florida, 12 May 1959. (U.S. Air Force)

The Thor DSV2E was an orbital launch variant of the Douglas Aircraft Company SM-75 Thor IRBM. This was a single-stage nuclear-armed intermediate-range ballistic missile, 61 feet, 3.91 (19.692 meters) long and 8 feet, 0.00 inches (2.438 meters) in diameter. With the Mk-2 reentry vehicle, the overall length of the missile was 63 feet, 7.38 inches (19.390 meters). It weighed 109,800 pounds (49,805 kilograms) at liftoff and 6,889 pounds (3,124 kilograms) at burnout.

The SM-75 was powered by one Rocketdyne LR79-NA-9 rocket engine which produced 150,000 pounds of thrust (667.23 kilonewtons). Two Rocketdyne LR101-NA-9 vernier engines of 1,000 pounds thrust (4.45 kN), each, provided directional control and thrust adjustments. The Thor was fueled with kerosene and liquid oxygen sufficient for 156 seconds of main engine burn time.

The Thor could reach a maximum speed of 11,020 miles per hour (17,735 kilometers per hour) and had a maximum range of 1,500 miles (2,414 kilometers).

The W-49 thermonuclear warhead was designed by the Los Alamos Scientific Laboratory (LASL) and is believed to be a development of the earlier B-28 two-stage radiation-implosion bomb. It incorporated a 10-kiloton W-34 warhead as a gas-boosted fission primary, and had a one-point-safe safety system. The warhead had a diameter of 1 foot, 8 inches (0.508 meters) and length of  4 feet, 6.3 inches (1.379 meters). It weighed 1,665 pounds (755 kilograms).

The flash from the Starfish-Prime detonation, photographed from Maui in the Hawaiian Islands 15 seconds after detonation. (Los Alamos National Laboratory)
The flash from the Starfish-Prime detonation, photographed from Maui in the Hawaiian Islands, 15 seconds after detonation. (Los Alamos National Laboratory)

© 2020, Bryan R. Swopes