Rudi Beichel of Huntsville had previously worked closely with Aerojet, and then came to work for Aerojet directly in 1956. His initial assignments included managing several small rocket programs, then the proposal for conversion of the Titan I first stage to burn LO2/LH2.
In mid-1960, after Aerojet lost the Saturn main engine competition, they formed a task force under Beichel to study large advanced technology rockets. This resulted in an unsolicited proposal to NASA for a "Design Study of a Large Unconventional Liquid Propellant Rocket Engine and Vehicle," and a contract was granted in early 1961. Designs were prepared for a variety of concepts. These included:
Other studies resulting in design of a single chamber LOX/LH2 engine with 11 million kgf thrust. But NASA interest in such advanced concepts dwindled, and finally settled on the relatively conservative 680,000 kgf M-1.
Meanwhile Beichel discovered that Bill Schnare at Edwards AFB had a similar interest in large, high performance rockets. The Air Force also believed that a very high performance ARES (Advanced Rocket Engine System) would allow the development of a single-stage ICBM with the range and payload performance of the Titan II.
Aerojet's ARES contract had a total value of about $20 million, supplemented by considerable corporate IR&D funds, and ran from 1962 to 1968
Initial development work focused on high chamber pressure operation, and used a regeneratively cooled tube bundle engine. The very high heat flux resulted in nozzle throat burnout, despite extensive film cooling. Even the use of auxiliary tubes (smaller in diameter than the main tubes, and laid in the "valley" between the main tubes) to carry additional film cooling propellant flow to the throat area did not solve the problem. Transpiration (sweat) cooling was suggested, but previous programs had shown that serious problems might be expected with pore clogging/non-uniformity , structural considerations, and severe manufacturing difficulties.
At this point, Robert Kuntz came forward with the idea of making the chamber of a stack of thin metal plates that had coolant channels photo-etched in their surfaces. Mueggenberg, LaBotz, and Schoenman did the design and heat transfer work, and Aerojet's platelet technology, the basis for many future Aerojet products, was created. Photo-etched platelets were also adopted for the main propellant injection, making it possible to achieve very intimate mixing of the injected propellants, as well as intricate and low volume flow passages.
Another innovation was the use of a complex, vane type, ramjet injector, fabricated by use of the platelet technology. The combination of this chamber and injector allowed achieving the objective of testing at 45,000 kgf thrust and a primary chamber pressure of 320 atm using N2O4 and Aerozine-50 propellants. For development testing, the high propellant feed pressures were achieved by using a piston driven intensifier in series with Titan engine turbopumps. The ARES design featured a single shaft turbopump, and an integrated single pressure vessel in a staged combustion cycle configuration. Subsequent work included Single Stage to Orbit (SSTO) studies, tri-propellants (dual-fuel engine), dual expander concepts, and air augmentation.
In the end the development problems and a USAF policy decision that all future ICBMs would use solid rocket propulsion killed ARES.
Note: Indicated specific impulse estimated based on use in a Titan 2-sized rocket with a Titan 2 payload but single stage to orbit performance.