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Delta 2914 |
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In 1959, NASA's Goddard Space
Flight Center commissioned Douglas to create a civilian launch vehicle based on
Thor-Able and to produce and integrate 12 launch vehicles. As this
would be the fourth modification of the Thor vehicle (after Able, Able-Star, and Agena),
it would be called Delta (radio code word for the fourth letter of the alphabet).
The original Thor-Delta used a Thor booster powered by a Rocketdyne
MB-3 engine burning liquid oxygen and kerosene; and upper stages derived from Vanguard:
the Aerojet AJ-10-118 (nitric acid/hydrazine) second stage previously used in Thor-Able,
and the Allegheny Ballistics Laboratory X-248 solid motor as a third stage. This
continuing use of available parts allowed Delta to be ready just 18 months after receiving
the go-ahead. It could place a 100 pound payload in geostationary transfer orbit,
though it was used for lower orbits only, and was initially regarded as an interim vehicle
until more powerful rockets could be developed.
In response perhaps to the successes of the first batch, in 1962
Douglas Aircraft began a series of upgrades and modifications which would increase Delta's
capacity tenfold. The Thor name was dropped from subsequent models, and eventually
34 different versions were developed.
As it was never used in the manned space flight program, Delta never
received the name recognition enjoyed by the Atlas, Titan and Jupiter; it has been the
unsung workhorse of the US space program. It success rate has been exceptional and
includes the following launch "firsts": Echo I in 1960, the first communication
satellite in Earth orbit to relay voice and TV signals from one ground station to another;
Syncom I in 1963, the first geostationary satellite; and Early Bird in 1965, the first
Intelsat (International Telecommunications Satellite Organization) satellite. Delta also
launched may Explorer satellites, Pioneer interplanetary probes and most of the satellites
in the TIROS and Landstat series.
The Delta A used an improved MB-3 engine (Block II), and the B model
was an A with a lengthened second stage using higher energy oxidizer. The C model added a
bulbous fairing for greater payload space and used as its third stage the X-258 motor
developed for the Scout rocket. The Delta D, also known as the Thrust Augmented Delta,
took the C and added three Castor I strap-on solid boosters from the Thrust Augmented
Thor-Agena D. These boosters gave the Delta the extra thrust necessary to propel the
Syncom satellites into geosynchronous transfer orbits. |
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