Thor (rocket family)

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.

The first type of space launch mission Thor was asked to perform was testing of the warhead reentry vehicle for the Atlas missile. 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.

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 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. On April 13, 1960 a Thor-Ablestar launched Transit 1B, the first experimental satellite to demonstrate the feasibility of using satellites as navigation aids. 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. 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.

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