Propulsion for the MX-774B, Viking, and Vanguard
Meanwhile, several American engines drew upon knowledge of the V-2 but also built upon indigenous American experience from before and during World War II. The engines for the MX-774B test missile, the Viking sounding rocket, and the first stage of the Vanguard launch vehicle are examples. Although none of these engines by themselves contributed in demonstrable ways to later launch – vehicle engine technology, the experience gained in developing them almost certainly informed later developments.
Reaction Motors, Inc. (RMI) developed both the MX-774B power – 112 plant and the Viking engine. The MX-774B engine (designated XLR – Chapter 3 35-RM-1) evolved from the 6000C4 engine the firm had produced
during 1945 for the X-1 rocket plane. Both were comparatively small engines, the 6000C4 yielding 6,000 pounds of thrust and the XLR – 35-RM-1 having a thrust range of about 7,600 to 8,800 pounds. Like the V-2, both engines used alcohol as fuel and liquid oxygen as the oxidizer. The use of alcohol (95 percent ethanol for the MX-774B) suggested some borrowing from the V-2, but the XLR-35-RM-1 achieved a specific impulse of 227 lbf-sec/lbm, significantly higher than that of the V-2 engine. As in the V-2, the MX-774B engine fed the propellants using two pumps operated by the decomposition of hydrogen peroxide, but the U. S. powerplant employed four separate cylinders as combustion chambers rather than the single, spherical chamber for the V-2. Like the German engine, the XLR-35-RM-1 was regeneratively cooled.
As suggested in chapter 1, the major innovations of the MX-774B that influenced launch vehicles were swiveled (not gimballed) engines and light, pressurized propellant tanks that evolved into the “steel balloons" used on the Atlas missile. Both of these innovations were the work of Convair (especially Charlie Bossart), the airframe contractor for MX-774B, not RMI, but the four-cylindered engine was integral to the way swiveling worked, so the engine contractor deserves some of the credit. (Each of the four cylinders could swing back and forth on one axis to provide control in pitch, yaw, and roll; a gimbal, by contrast, could rotate in two axes, not simply a single one.) According to one source, the Germans had tried gimballing on the V-2 but had discarded the idea because of the complexities of rotating the 18-pot engine, and Goddard had patented the idea. But actual gimballing of an engine was apparently first perfected on the Viking. Meanwhile, the air force canceled the MX-774B prematurely, but it did have three test flights in July-December 1948. On the first flight, the engine performed well but an electrical-system failure caused premature cutoff of propellants. On the second flight, the missile broke apart from excessive pressure in the oxygen tank. The third flight was successful.21