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| - The Navaho program began as part of a series of guided missile research efforts started in 1946. Designated MX-770, the original intent of the program was the development of a winged V-1 missile that could deliver a nuclear (fission) warhead over a distance of . This was more than double the range of the V-1 as well as having a larger payload. Design studies showed the promise of still greater ranges and by 1950 the vehicle had evolved from a ground-launched winged V-1, to a range ramjet powered winged V-1, to a air-launched, ramjet-powered, winged V-1 (actually designated XSSM-A-2), to finally a plus rocket boosted ramjet powered cruise missile. The design evolution finally ended in July 1950 with the issuing by the Air Force of Weapon System 104-A. Under this new requirement the purpose
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| abstract
| - The Navaho program began as part of a series of guided missile research efforts started in 1946. Designated MX-770, the original intent of the program was the development of a winged V-1 missile that could deliver a nuclear (fission) warhead over a distance of . This was more than double the range of the V-1 as well as having a larger payload. Design studies showed the promise of still greater ranges and by 1950 the vehicle had evolved from a ground-launched winged V-1, to a range ramjet powered winged V-1, to a air-launched, ramjet-powered, winged V-1 (actually designated XSSM-A-2), to finally a plus rocket boosted ramjet powered cruise missile. The design evolution finally ended in July 1950 with the issuing by the Air Force of Weapon System 104-A. Under this new requirement the purpose of the program was the development of a range nuclear missile. Under the new requirements of WS-104A, the Navaho program was broken up into three guided missile efforts. The first of these missiles was the North American X-10, a flying subrange vehicle to prove the general aerodynamics, guidance, and control technologies for vehicles two and three. The X-10 was essentially an unmanned high performance jet, powered by two afterburning J-40 turbojets and equipped with retractable landing gear for take off and landing. It was capable of speeds up to Mach 2 and could fly almost . Its success at Edwards AFB and then at Cape Canaveral set the stage for the development of the second vehicle: XSSM-A-4, Navaho II, or G-26. Step two, the G-26, was a nearly full-size Navaho nuclear vehicle. Launched vertically by a liquid-fuel rocket booster, the G-26 would rocket upward until it had reached a speed of approximately Mach 3 and an altitude of . At this point the booster would be expended and the vehicle's ramjets ignited to power the vehicle to its target. The G-26 made a total of 10 launches from Launch Complex 9 (LC-9) at Cape Canaveral Air Force Station (CCAFS) between 1956 and 1957. Launch Complex 10 (LC-10) was also assigned to the Navaho program, but no G-26's were ever launched from it (it was only used for ground tests of the planned portable launcher). The final operational version, the G-38 or XSM-64A, was the same basic design as the G-26 only larger. It incorporated numerous new technologies: Titanium, gimballed rocket engines, Kerosene/Lox fuel combination, full solid-state, etc. None were ever flown, the program being cancelled before the first example was completed. The advanced rocket booster technology went on to be used in other missiles including the Atlas intercontinental ballistic missile and the inertial guidance system was later used as the guidance system on the first U.S. nuclear-powered submarines. Development of the first stage rocket engine for the Navaho began with two refurbished V-2 engines in 1947. That same year, the phase II engine was designed, the XLR-41-NA-1, a simplified version of the V-2 engine made from American parts. The phase III engine, XLR-43-NA-1 (also called 75K), adopted a cylindrical combustion chamber with the experimental German impinging-stream injector plate. Engineers at North American were able to solve the combustion stability problem, which had prevented it being used in the V-2, and the engine was successfully tested at full power in 1951. The Phase IV engine, XLR-43-NA-3 (120K), replaced the poorly cooled heavy German engine wall with a brazed tubular ("spaghetti") construction, which was becoming the new standard method for regenerative cooling in American engines. A dual-engine version of this, XLR-71-NA-1 (240K), was used in the G-26 Navaho. With improved cooling, a more powerful kerosene-burning version was developed for the triple-engine XLR-83-NA-1 (405K), used in the G-38 Navaho. With all the elements of a modern engine (except a bell-shaped nozzle), this led to designs for the Atlas, Thor and Titan engines.
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