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Aviation History
1976
1976 - 0061.PDF
FLIGHT International, w/e JO lanuary 1976 8! cost is $29-3 million at the rate of two a year, but with the Centaur replaced by a Transtage the configuration becomes the Titan IIIC and the coat of a launch goes down to $23-2 million at the rate of three missions a year. (Cost figures aire based on 1974 prices; here and throughout this article). Titan IIIC is used by America's Defence Depart ment to fly its reconmaissance and other military pay loads, and was selected by Nasa to launch the ATS-6 satellite in May 1974. Medium-weight payloads launched by Nasa use the Atlas SLV-3D/Centaur D, a combination: of the old Atlas ICBM and the high-energy Centaur upper stage. The project, started in 1958, was developed at the Lewis Centre and became operational in May 1966, when it sent; Surveyor I to the surface of the Moon. By itself Atlas could deliver to low orbit some 3,0001b, and about 6,0001b with an Agena upper stage. With the Centaur Lox/LH2 stage, however, the configuration can lift 11,0001b to low orbit or 4,0001b to synchronous height. Since the first test-flight; in May 1962, 36 Atlas/Centaurs have launched missions to Mars, Venus, Mercury and Jupiter. Planetary flights have now largely passed to the more powerful Titan IIIE/Centaur, but two> Atlas/Centaurs will boost Pioneer probes to Venus in 1978; these are the only planetary flights scheduled to use the older rocket. Present and future responsibilities centre on the Intelsat communications satellites periodically sent into synchro nous orbit over the Atlantic, Pacific and Indian Oceans. Nasa has spent nearly $700 million on the Centaur pro gramme (as applied to Atlas and Titan vehicles) and with a unit launch cost of less than $19 million Atlas/Centaur is a readily available and comparatively economic rocket, suitable for many intermediate payloads. It has demon strated a success rate of 83 per cent on all test and operational flights, and 89 per cent on purely operational flights. Nasa's workhorse, the Delta launch vehicle, started life almost 20 years agoi when the Defence Department: began development of the Thor IRBM, and by 1958 the USAF had conceived a second stage in the hope that the vehicle would be able to send small probes to the Moon. Thor-Able, as it was designated, never achieved much success. Only five flights were attempted, of which two were failures. In 1959 work commenced on a modified three-stage version of Thor, called Thor-Delta, and the first launch was success fully conducted in May 1960. Two years later studies began on an augmented Thor. By strapping three solid-propellant rockets to the first stage the lifting capability was in creased and several versions emerged with Agena or Delta upper stages. The final configuration to be developed was the Improved Delta, with extended first and second stages which in creased propellant capacities by 80 and 120 per cent respectively. The version known as Delta 2914 employs nine strap-on boost rockets, and its first-stage engine is the H-I originally developed for Nasa's Saturn I and Saturn IB vehicles. The second stage now carries a single TRW AJ10 motor, which was; formerly used to land the Apollo Lunar Module; on the Moon's surface. A derivative of the Delta 2914, designated the 3914, cam lift a heavier payload through the extra thrust provided by an advanced version of the Castor solid-piropellanjt rocket. These new boosters each have a thrust of 85,0001b compared with the; 63,500lb push of the earlier units. This enables the 3914 to lift 2,0001b to synchronous orbit, better ing the 2914 by 25 per cent. The 3914 was developed by McDonnell Douglas under private contract to RCA to place the latter's 20,0001b, 24-channe;l Satcom communication satellite in synchronous orbit. Though Nasa gave advice and monitored the technical aspects of the vehicle, no US Government money was allocated: the space agency was reluctant to finance a venture which would be of benefit only to the industrial sector. The Delta is available in two-stage or three-stage ver sions, with three, six or nine strap-on boosters; a 93 per cant success rate ensures its continued use for medium- weight Earth-orbit payloads.
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