Delta Upper Stages

One example of this influence was a second stage used on the Delta launch vehicle featuring an Aerojet engine designated AJ10-118F. This was the F model in a series of engines originally derived from the Vanguard second stage. This particular engine was similar to the Transtage propulsion unit (AJ10-138), but the two were not identical. Both used a fiberglass combustion chamber impregnated with resin and an ablative lining for cooling. Like the Titan II en­gines, both used a mixture of 50 percent hydrazine and 50 percent UDMH as the fuel, igniting hypergolically with a nitrogen-tetroxide oxidizer. This replaced the IRFNA used on earlier versions of the AJ10-118 and increased the specific impulse from more than 265 to upward of 290 lbf-sec/lbm. The F version of the engine had a thrust of between 9,235 and 9,606 pounds, well above the roughly 7,575 pounds of the earlier versions, and it was capable of up to 10 starts in orbit. The new engine completed its preliminary design in 1970 but did not fly until July 23, 1972.59

Another Delta upper stage that used storable propellants was TRW’s TR-201 second-stage engine. Design of this engine began in October 1972, its combustion chamber made of quartz phenolic, with cooling by ablation as had been true of the AJ10-118F, but the TR-201 weighed only 298 pounds in contrast to the Aerojet engine’s reported dry weight of 1,204 pounds. Both engines burned nitrogen tetroxide with a 50/50 mixture of hydrazine and UDMH, igniting hypergolically, but the TRW propulsion unit yielded 9,900 pounds of thrust, whereas the Aerojet unit yielded a maximum of 9,606 pounds. The newer system did provide only 5 instead of 10 restarts.60