Vehicle Description
The Delta III had the kerosene/oxygen first stage of a Delta II. However, the complex and less-efficient stack of upper stages was replaced with a more advanced hydrogen/oxygen stage. The boosters were noticeably larger. The new fairing fit larger payloads; the first stage was modified to accommodate the larger stack.
The upper stage burned high-performance cryogenic fuel in a proven Pratt & Whitney RL10 engine design. The liquid-hydrogen tank was 4 meters in diameter, covered in insulation derived from that of the Space Shuttle External Tank, and built by Mitsubishi Heavy Industries. The separate liquid-oxygen tank retained the 2.4 m diameter of previous Deltas. Both were structurally stable. The RL10 engine, from the Centaur upper stage, was in the new RL10B-2 configuration, with an extending nozzle. The nozzle fit in the vehicle stack for launch, then extended in space to increase expansion ratio and improve efficiency. The extending segments were uncooled carbon composites, made by SEP of France.
The solid rocket boosters were Alliant GEM-46s, sometimes referred to as GEM LDXL (Large Diameter Extended Length). These were 14.7 meters length and 1.17 m (46 inches) in diameter, versus 13 meters and 1.01 m (40 inches) for the GEMs on Delta II. Six were ignited on the launch pad, three were lit in flight. To maintain steering authority, three of the boosters had vectoring nozzles.
The payload fairing was a new design in composite materials, matching the upper stage hydrogen tank at 4 meters diameter.
To keep the vehicle at a reasonable length and avoid steering problems in high-altitude crosswinds, the first stage was shortened. The kerosene (RP-1) fuel tank, formerly 8 feet in diameter like the liquid oxygen tank, was a squat 4 meters, like the hydrogen tank. It too was made by Mitsubishi Heavy Industries. The new length also minimized changes to the launch tower.
In keeping with the 4-digit designation system from earlier Delta rockets, the Delta III is technically referred to as the Delta 8930.
Overall, payload to GTO (Geostationary-Transfer Orbit) was doubled versus the Delta II, with reasonable program costs and streamlined operations. However, the consecutive failures of the initial Delta IIIs, combined with the more-advanced Delta IV program and the successful Sea Launch venture, left the Delta III as an interim vehicle. However, technologies and components from the Delta III contributed to the development of the Delta IV.
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