Delta III

Boeing Company

The commercial development of the Delta III was driven by growth in GTO payloads, most of which are now too heavy for the Delta II. Performance enhancement is accomplished with larger strap-on motors (Alliant Technosystems GEM-46)  and a new cryogenic second stage. Delta III also includes a larger fairing.
Delta III uses large diameter extended length (LDXL) GEMs, also called GEM-46. Three of the ground-lit motors have hydraulically gimbaled nozzles. The primary change for Delta III first-stage is a shorter, larger-diameter fuel tank. The Delta III second stage is an new cryogenic stage, powered by an Pratt & Whitney RL-10B-2 engine. The engine is similar to the RL-10A-4 flown on the Atlas IIA, with the addition of a large carbon-carbon extendible nozzle cone for added performance. The propellant  tanks are separate, self-supporting structures for simplified production and operations. Second-stage avionics are mounted on an equipment shelf below the LOX tank. The nozzle  exit cone supplied by SEP of France and the propellant tanks produced by Mitsubishi of Japan.
The Delta III 13.1-ft. fairing was designed using the same techniques and materials as the  10-ft. design of Delta II, but has much more volume to accommodate larger payloads (length 35.5 ft.).
The first two launches in 1998 and 1999 failed.