Aerojet's First Series of Experiments, 1945-1946
[34] Hall's visit to Aerojet was fortunate in its timing. He believed that he brought a new idea to Young and Gordon because none of Aerojet's previous work or proposals on propellants mentioned liquid hydrogen as a fuel. To Gordon, however, here was his boss's boss-the Navy-voicing ideas similar to his own and he was eager to get started. After Hall returned to Washington, Aerojet was authorized to experiment with hydrogen and oxygen as part of their nitromethane contract. In less than a month, Young and Gordon operated the first recorded run of a hydrogen-oxygen rocket in the U.S. on 15 October 1945.* The run ended after 15 seconds when the uncooled thrust chamber burned out, but not before a thrust of 200 newtons (45 lb) and a chamber pressure of 25.5 atmospheres were recorded. From these, the experimenters estimated the exhaust velocity to be 2600 meters per second.6 They were undaunted by the burnout and began preparations to use a water-cooled thrust chamber. In the next test, they obtained a lower exhaust velocity, and in spite of water cooling, the chamber showed signs of overheating.**
From the first test in October until the end of the first phase of the work in June 1946, about 50 rocket runs were made at thrusts of 445 and 1780 newtons (100 and 400 lb) and chamber pressures of 20.4 and 34 atmospheres. The experimenters found it relatively easy to achieve high performance (3050 meters per second). Much of the work was concentrated on cooling and several methods were tried. One was a porous chamber through which water was forced as a form of transpiration or "sweat" cooling. Another was gaseous hydrogen flowing through the porous combustion chamber. The main method, however, remained water cooling.
As had other experimenters since the eighteenth century, the Aerojet research team found that hydrogen and oxygen ignite very readily and burn over a wide range of mixture ratios. Rapid burning meant that the combustion chamber could be small, and this led Young to his idea of the ultimate small thrust chamber-the "flared tube." [35] Essentially it was a straight wall tube for the combustion chamber with a flare for the expansion portion of the nozzle, as shown at the top of figure 8. Young experimented to find the minimum size tube chamber and soon became confident that he could use from 1/10 to 1/20 the volume normally used for rocket thrust chambers. This was a great step forward, for a tiny combustion chamber meant less mass for the vehicle and less surface area to cool-both big advantages. He became a missionary for the idea, and set forth to sell the Navy an expanded program.