Thor (rocket family)

Thor Able with Pioneer 1 at Cape Canaveral in Florida

Thor was an American space launch vehicle derived from the PGM-17 Thor intermediate-range ballistic missile. The Thor rocket was the first in a large family of space launch vehicles that came to be known as Delta. A derivative of the Thor was still in service as of 2014, as the first stage of the Delta II.

Origins and early history

Thor Able on display at LC-26B of the Air Force Space & Missile Museum

The first type of space launch mission Thor was asked to perform was testing of the warhead reentry vehicle for the Atlas missile.^[1] 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 April 23, 1958 due to a turbopump failure in the main engine. The recovery of the reentry vehicles on the succeeding two attempts were not successful. Three mice, one on each vehicle, died in these tests.^[2]

The Able stage from the Atlas reentry vehicle tests was upgraded (to become the Able I) with a third stage consisting of an unguided Altair X-248 solid rocket motor. A Thor Able I was used in an attempt to place the 84 lb (38 kg) Pioneer 0 spacecraft into lunar orbit where it would take pictures of the lunar surface with a TV camera. The mission ended prematurely at 73.6 seconds after launch on August 17, 1958, due to a turbopump failure.

On August 7, 1959 a Thor-Able was used to successfully launch Explorer 6, the first satellite to transmit pictures of Earth taken from orbit.

Ablestar

Ablestar was a liquid rocket stage burning hypergolic propellants fed from gas-pressurized propellant tanks. It was used as the upper stage, and provided improved performance.^[3] On April 13, 1960 a Thor-Ablestar launched Transit 1B, the first experimental satellite to demonstrate the feasibility of using satellites as navigation aids.^[4] On June 22, 1960, a Thor-Ablestar launched the first Galactic Radiation and Background (GRAB) electronic intelligence (ELINT) satellite for the United States Navy. These now-declassified satellites, operated under a cover story of providing solar radiation data, included an electronics package to detect Soviet air defense radar signals.^[5] GRAB-1 was thus the world's first successful reconnaissance satellite, preceding the first Corona mission to return film (Discoverer 14 on August 18) by almost two months. On 1961-06-29 the Ablestar stage used to launch Transit 4A became the first object to unintentionally explode in space, creating at least 294 trackable pieces of space debris.^[6]

Thorad-Agena D with SERT-2 satellite at Space Launch Complex 2 East (SLC-2E), Vandenberg AFB, California.

Thor and the Corona program

Thor formed the core of the Thor-Agena vehicle used to launch the early Corona (also known as "Keyhole" and "Discoverer") satellites from Vandenberg AFB.^[7] These were the first photographic spy satellites, used for photographic surveillance of the Soviet Union, China and other areas. Thor-Agenas were used as launch vehicles for Corona satellites from June 1959 through May 1963.

Thor spawns Delta

A fourth modification to Thor for space launch purposes, the Thor-Delta, has proven to be the longest-lasting of all Thor-derived rockets. Members of the Delta rocket family derived from the Thor-Delta continue to launch satellites and space probes.

By 1969 the Thor core was being used regularly both in Delta vehicles and in the USAF Standard Space Launch Vehicle (SLV-2), with thrust augmentation and a variety of upper stages.

Use with Agena upper stage

The Thrust-Augmented Thor (TAT) was used with the Agena upper stage, as was the Thrust-Augmented Long Tank Thor/Agena, capable of sending payloads ranging from 1400 to about 2800 pounds into 100-nautical-mile (190 km) polar circular orbits.^[8]

Thrust Augmented Thor

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.

Thorad

The Thorad-Agena (pictured) was developed from Thor. It used a Thor, modified for use as a Delta rocket, to launch an Agena upper stage.

Long Tank Thor

• Tapered fuel tank changed to cylindrical.
• Both tanks lengthened.
• Core stage 14 feet (4.3 m) longer.
• 49,000 lb (22,000 kg) more propellant.

See also

• Comparison of orbital launchers families
• Comparison of orbital launch systems
• List of Thor-Able launches
• List of Thor-Ablestar launches

Notes

1. Deny Rocket Lag. Atlas Firing Keynotes U.S. Missile Build-Up, 1959/01/29 (1959). Universal Newsreel. 1959. Retrieved February 22, 2012.
2. "Thor Able". Encyclopedia Astronautica.
3. "Able-Star". Encyclopedia Astronautica.
4. "Transit 1B - NSSDC ID: 1960-003B". NASA NSSDC.
5. "GRAB: 1st Recon Satellite". U.S. Navy.
6. "Orbital Debris: A Chronology" (PDF). NASA JSC. 1999. p. 18.
7. "Corona". NASA.
8. Bleymaier, Joseph S. "Future Space Booster Requirements". USAF.