housed the propellant and served as the combustion chamber, a pyrogen unit for engine ignition, a nozzle, and a thrust termination device. Unlike the main engine, all components formed one unit. In operation, the vernier engine ignited two seconds after separation from the main thrust unit. The vernier unit then propelled the missile body until the desired velocity was attained, and when this requirement was satisfied, cutoff occurred. Squibs were used for the thrust termination device, and the engine nozzle was blown away 75 . Although the two foregoing units were the major portion of the propulsion system, other devices, already discussed in part, were equally important in solving the  target range problem. These included a missile roll control system, and a spatial attitude control system. NAA delivered its first nonflyable main engine to ABMA in July 1956, and the Agency began a static test program in September. At first, the tests progressed smoothly with a number of static firings lasting for several seconds; but, by November, four thrust chambers had burned out, causing delay while ABMA and NAA were investigating the problem. Strengthening modifications to the thrust chamber eliminated the difficulty, and in January 1957 the static testing program was progressing satisfactorily 76 . ABMA received its first flyable engine in September 1956; and, during inspection, a number of design deficiencies were noted. Within a short time—November—the second engine was delivered. Both of the _____________________________

(75) ABMA Rpt DSD-TR-4-60, Vernier Engine Operation, 21 Jan 60, Hist Off files. (76) JUP Dev Plan, FY 58, 29 Sep 56; JUP Prog Rpt for Nov 56, 8 Dec 56; JUP Prog Rpt for Jan 57, 8 Feb 57, Hist Off files.