HD55-NAVAHO

The Navaho Cruise Missile--A Burst of Technology

Dale D. Myers, North American Aviation, Later Deputy Administrator, NASA, Ret.

Fig 1 XSM-64 (G-26)

The Navaho Program

The Navaho missile Program, because of its very difficult requirements, spawned a new generation of aerospace applications that revolutionized the aerospace industry in the US. Starting with WW II new aerospace technologies from Germany, the program set new baselines for aerodynamically efficient supersonic configurations, advanced rocket engines, practical, accurate inertial navigation, and new materials and processes. Although the program was canceled in 1957 because breakthroughs in warhead size reduction and reentry technologies made intercontinental ballistic missiles feasible, the navigation system, the rockets, and the improved materials and processes from Navaho contributed heavily to that feasibility, and set the stage for our spectacular space program.

The first half or the 20th century had been a bonanza of progress in aviation. Speeds had increased from 40 to 400 mph in about four decades. Slight nudging of supersonic speed had occurred experimentally. Payloads were up, altitudes were up, and for the U.S., production had peaked in 1945 and then crashed.

In 1945, the U.S. began to get microfilm covering the aeronautics and space activities of Germany for the period through World War II. We were all amazed. The U.S. had concentrated on production of aircraft to give us the advantage in air power. The Germans, recognizing resource limitations, tried to beat us with technology.

Their technology was outstanding, covering swept wings, axial flow turbojets, alcohol/oxygen 56,000 lb rocket engines, the V-2, the V-1 buzz bomb, vertical takeoff rocket powered interceptors, flying wings, rocket antiaircraft missiles, and the beginning of inertial navigation.

In 1945, after V-J Day, the aerospace industry was decimated. North American Aviation, for example, dropped from about 100,000 to 6500 employees in about two months. North American built the Navion private airplane, and a small group started looking at the German technology for applications. At the same time, the Army Air Corps, seeing the jump in technology that Germany had, and being impressed with the guided missile technology particularly, started a series of guided missile programs with the industry, partially to retain some capability.

Programs were initiated such as Rascal, a rocket powered, air launched missile, and Bomark, a ground to air ramjet powered interceptor. A series of subsonic, turbojet powered missiles included Matador, a ground-to-ground missile; Regulas, a Navy sea-to-shore missile; and Snark, a long range missile. Navaho, with a long range supersonic goal, started with a boost-glide missile, based on the German A4b. The MX-770 program started in December, 1945. Note that all the ground to ground missiles were cruise or glide missiles. That was because it was generally agreed at that time that warheads were so large that intercontinental ballistic missiles would be huge, that reentry was not feasible, and that navigation to 1 mi accuracy was not possible. (I'll speak later to this point.)

In May 1946, North American Aviation formed the Aerophysics Laboratory. Dr. William Bollay was it's Director.

The specified performance at that time was 500 mi, supersonic boost-glide, 1 mi accuracy, and a 3000 lb warhead. By 1946, we had a 3 1/2-in supersonic wind tunnel, were blowing up small liquid rockets in our empty east parking lot, were trying out solid fueled ramjets, and were dreaming about inertial navigation accuracy, new high performance rockets, and the other new technologies that would be required.

In 1948, the range requirement was increased to 1,000 mi. We abandoned the boost-glide (A4b) approach, and added ramjets for cruise. We looked at ramjets mounted on the wing tips but expected flutter. We looked at mounting them on the vertical upper and lower tail. We looked at ramjets ducted through the body. (For the ducted body configuration, we considered a Mach 3.5 rocket powered aircraft as the first stage to take the missile, riding piggyback, to its cruise speed.) The evolution of the program is shown on Fig. 2.

By mid-1947, North American Aviation had started the development of a major new rocket engine test facility, and a Supersonic wind tunnel. By 1950 they had brought in Curtis Wright for ramjet development, and Thompson Products for the auxiliary power unit. We even studied nuclear rockets, since, at that time, media opinion had not turned against this form of energy. For guidance, we had developed an outstanding capability to invent new navigational sensors and instruments.

After the Armed Services Unification Act in 1947, the Army and the Air Force reached painful agreement on what performance domain each was to pursue, and that created a need to extend the range. By 1950, the requirements were extended again, this time to 5,500 n.m., one quarter mile accuracy, Mach 2.75, and up to 15,000 lb payload.

Today, that major change in specification probably would call for a new competition. Then, it caused us to go back to ground zero, review all the potential technologies that we could reach, and totally reconfigure the program. In a period of 3 months, we developed a canard configuration using side inlets leading to buried ramjets. The missile would be boosted beyond cruise speed with a parallel expendable booster. It would be guided by pure inertial navigation. (We had considered radio guidance for the boost phase, and had developed the first daylight star tracker, but, because of the progress of double integrating accelerometers and reversing (NAVAN) gyroscopes, neither was needed.) The Mach number would be 3.25, and the altitude 80,000 ft., zooming to 90,000 ft just prior to dive-in.

In order to fly at that Mach number, we would need stainless steel and titanium sheet, and we would need many other weight-saving ideas. By 1950 we were doing the first flight testing of inertial navigators, but they used vacuum tubes for computers. No large ramjets had been built, and no air supply existed to test them. With some difficulty, 75,000 lb alcohol/oxygen rocket engines were just getting into test.

It became clear that we had so many technical breakthroughs to make that we could not totally define the system, so we proposed, and the Air Force accepted, a three-phase program with a schedule as shown on Fig. 2 & 3.

I. Build a full scale model of an intermediate range ramjet, and power it with turbojets (X-10), as shown on Fig. 4.

II. Build a ramjet with 2,500 mi range. Fly it at Mach 2.75, so it could use essentially the same airframe (aluminum wings, stainless fuselage) as the turbojet version (XSM-64), as shown on Fig. 1 & 8.

III. Advance the state of the art, and then build the ultimate 5,500 n.m., Mach 3.25, 15000 lb. payload version, with 1/4 mile CEP accuracy (XSH-64A), as shown in Fig. 5.

The X-10 and the XSM-64 were designed to be recoverable by conventional landing gear, using a fully automatic landing system, with a radar altimeter controlling flare. The XSM-64A was optimized for range on the premise that most flight test considerations would be developed on the two previous models before the final one flew. Therefore, the XSM-64A had no landing gear, and had a small, all movable vertical surface.

The X-10 first flight was in October 1953; 15 flights were flown at Edwards AFB, and 12 more from the skid strip at Cape Canaveral, which was shared with Snark. Eight flights were flown with one missile. In 1956, the X-10 flew Mach 2.05, using the Westinghouse J-40-8 with afterburner. The flight was totally under the control of the N-6 inertial navigator, including a supersonic reentry (Mach 1.3 at sea level).

The X-10 had these characteristics that were ahead of their time;

1. Delta wing with fully powered delta canard.

2. Twin verticals for directional stability at high angles of attack; Landing speed was still 150 mph, which drove tire technology.

3. Fully inertial guidance control, using the first transistorized navigation computer.

4. Fully automatic landing system, except for lateral control on the runway, where ground clutter destroyed the accuracy of the SCR-584 radar.

5. "Hero Pilot" for lateral control on the runway. (He tracked the bird through a transmitting transit from the end of the runway that the vehicle was approaching in its rollout).

That the vehicle was never converted to be manned was a great regret of mine. General Boyd, then at Wright Field, wanted to add a cockpit, but could not get enough support. The X-10 flew beautifully on radio command and on inertial navigation, and I believe it could have made a very interesting X airplane.

The XSM-64, with the same appearance and general configuration as the X-10, flew first on November 6, 1956. It was vertically launched, using two 120,000 lb kerosene/oxygen rocket engines from the (now named) Rocketdyne Division of North American Aviation, Inc. A parallel booster was used. In place of the turbojets, Curtis Wright 48-inch diameter ramjets were mounted. The inlets were half-round spike inlets with boundary layer bleed. Cooling was with ammonia, and electrical power was supplied by a separate Thompson Products gas generator powered APU. Wings and surfaces were aluminum, and flight speed was Mach 2.75. By this time in the program, automatic circuit continuity and automatic checkout were being used extensively.

Navaho had a formal reliability program, with FMEA's and a rigorous test and qualification program to deal with the new 600 degree Fahrenheit temperatures and the high vibration levels. Testing was carried to the extent that every booster was live fired as a total system prior to flight. In spite of this care, the XSM-64 flight test. program could not be labeled a resounding success. In looking back, I believe we (and the whole missile industry) were putting too many new technologies together without the incisive systems analysis that is more prevalent today.

By 1955, the design of the final vehicle had begun. Stretching to meet (the now) 6,500 n.m. at Mach 3.25 with a (now) 1 mi accuracy, here are some (but not all) of the "firsts" applied to the program.

The Airframe

Canard Configuration

Early supersonic wind tunnel tests of the A4b supersonic glider showed a very strong center of pressure movement as the Mach number increased. Tests in the Aberdeen 13-in. wind tunnel and in a 3 1/2-in. tunnel at North American showed that a fully controlled delta canard, with a delta main wing gave almost constant center of pressure, and yielded positive lift with trim. This advantage has been applied to many aircraft since, such as the Swedish Gripen, the French Raphael, and the US B-70.

Parallel Booster

When the 5,500-n.m. requirement was imposed, ramjets were selected and optimized at Mach 3.25. A booster was necessary. Studies of the loads imposed on the missile-booster interface with a series booster, led to a choice of parallel booster. Booster separation was aerodynamic, after explosive bolts broke the physical connections. The concept was later used by the Shuttle, the Buran, and seems to be favored for the now National Launch System.

Structure

Navaho developed the first use of titanium skin for aircraft application, and it developed forming and welding processes. The material was later used by several aircraft, notably the SR-71.

Pressure stabilized stainless steel tanks were originally designed for the Navaho missile, but the rough environment that the missile took in equipment installation and ground handling caused us to stiffen it with longerons. The concept was used very successfully on the Atlas missile.

Chem-milling (etching out unwanted material) was developed for aluminum, titanium, and steel. Aluminum chem-milling is now used on almost every aircraft and liquid powered space booster in the world.

Automatic inert gas shielded fusion welding was developed for high strength aluminum alloys and for stainless steel.

Fuel cooling, cooled low pressure hydraulic fluid to cool the high pressure actuators, metallic seals, and ammonia-water cooling of electronics all led to applications in advanced missiles and aircraft.

Guidance and Control

The first all inertial navigation system was conceived by Peenamunde scientists working on the boost-glide A4b. When the U.S understood its implications, MIT (as overall monitor), North American Aviation (Navaho) and Northrop (Snark) were designated as development centers. German scientists at Huntsville and Wright Field worked closely with these centers.

North American invented double integrating accelerometers, and the NAVAN reversing gyro concept. At the same time, radio guidance during boost was considered and a single "Cycloptic" daylight star tracker for platform correction was developed and flight tested. Navaho, with its relatively short flight time (3 hr), was able to meet its requirements without radio guidance or a star tracker.

The N-6 navigator flow in 1956 at Mach 2.05 in the X-10 and at Mach 3.0 in the XSM-64 in 1957. For these flights, a completely transistorized computer with etched circuit boards was used; this was another first.

Although different means of improving accuracy developed later, the mechanization, computational techniques, and detailed management of these systems comes from the Navaho inventions and extrapolation of the early German work.

Inertial navigation systems for commercial transports, ballistic missiles, submarines, and fighter aircraft all have a heritage to Navaho. An N-6 Navaho navigator, with only minor modifications, guided the Nautilus submarine under the ice to the North Pole, another first.

Rocket Propulsion

As in the case of the airframe, the technology was not in hand for the Navaho motors, and a phased program was undertaken, including the assembly of the German V-2 engine (which was not fired), and the development of a new 75,000-lb engine for an early version of Navaho. By 1950, the requirement change on NAVAHO caused the 75,000-lb engine to be dropped (but picked up by the Army where a modified version was used in Redstone).

A new revolutionary 120,000-lb engine was then developed. This engine became the basis of a whole new generation of rocket engines because of its new features:

1. Kerosene as fuel, rather than alcohol

2. Flat injector faces

3. Tubular fuel cooled nozzle

4. High speed turbopump with a single gas generator running multiple chambers

5. Boot strap starts, using the prime fuels for the gas generator

The thrust-to-weight ratio of this engine was almost five times the German V-2 engine. The comparison of the engines is shown on Fig. 6.

By the late fifties, versions of this engine were being developed for Navaho, Atlas, Redstone, Jupiter, Thor, and the Apollo S1b. Many of its features are still used in modern engines such as the shuttle SSME and the now NLS.

Ramjet Propulsion

Using the work of Tony Ferri of NACA and Oswatisch of Germany, North American started high Mach number inlet studies in 1947 and was able, with the help of NACA, to develop a high efficiency spike inlet for the Curtis Wright 48-in. Ramjet. Segmented ramjets were seriously considered as per Hermes II, but we concluded that as large air supplies became available, better overall efficiency, range and reliability could come from two large circular engines.

The missile was over-boosted, in order to start the inlet and to retain 100 percent capture of the air. Fuel control kept the internal inlet normal shock near the throat to maximize engine efficiency. Vortex generators were used internally in the subsonic inlet flow. Although internal instrumentation was primitive, the overall performance of the missile was as predicted, indicating that the engine performance was good.

Facilities

Major rocket engine test facilities were built at Rockotdyne, Edwards AFB and Tullahoma.

Major Air Supplies for Ramjets (and later-turbojets) were built at NASA Lewis Laboratories and Tullahoma.

New supersonic wind tunnels were built at Wright Patterson AFB, NACA, and North American Aviation.

New integrated circuit development facilities were installed at North American Aviation's Autonetics Division.

Operations

The operations concept called for:

1. Air Transport fully assembled in environmentally controlled boxes

2. Minimum field assembly

3. Mobile launcher

4. Automatic sequencing checkout

Cancellation

In July, 1957, the program was canceled. The only reference that I can find says "the program cost too much." But remember, Navaho had proven the feasibility of:

1. High impulse light weight rocket engines

2. Highly accurate fully inertial guidance

3. Light weight stainless pressurized tanks

At the same time, re-entry technology was being solved and warheads were getting smaller. The combination showed that intercontinental ballistic missiles were feasible, and the National will shifted away from cruise missiles.

Summary

The legacy of Navaho was encapsulated beautifully by Robert Hotz, long time editor of Aviation Week, who, in an Editorial entitled “How Research Investments Pay Tremendous Dividends" wrote this: "The case history of the Navaho research and development program should be carefully studied by every congressman concerned with military appropriations, by the comptrollers at all levels of the executive branch of the government, and by the taxpayers whose $700 million were invested and who stand to collect the real benefit from these dividends in a stronger defense capability and new additions to the dynamic technology that is required to keep the civilian economy rolling. It is a prime example of how a wise investment in military research and development can pay handsome dividends for the future."

Bob Hotz's 1957 words are just as applicable today. Programs like SDI, the NASP, and the NLS are hard programs to do, and, because they are hard, engineers are stretching hard to meet their requirements. That's good for those programs, but it's also good for the overall status of technology to be applied to other military and commercial applications in the future.

As we often said in those days after the Navaho cancellation, "The operation was a success, but the patient died.” Navaho technology fed commercial and military aircraft, but its major contribution was to our space program, where light weight, high performance rocket engines, advanced electronics, and light weight structures allowed us to quickly regain the lead. Redstone missiles sent our first satellite into orbit, and launched our first astronauts, both with the Redstone rocket, slightly modified from the interim Navaho rockets. Our first orbiting Astronaut, John Glenn, rode an Atlas missile with a first cousin of Navaho for rockets.

That head start on the technologies needed for space opened the heavens to mankind.

Bibliography

1. Development of a Strategic Missile and Associated Projects. Aerophysics Lab. Report 1347, October, 1951

2. Navaho Mission. North American Aviation, Unpublished report, 1956

3. Development of the Jupiter Propulsion System. Julian Braun. Sixth Army R and D Unit Scientific Symposium. Corvallis, Oregon, August 12, 1958

4. Papers and Charts from the work of Ralph Oakley. Rockwell International, December, 1961

Recollections and notes of:

Martin Boe -- structure

Tom P. Dixon -- rockets

Alan J. Grant -- guidance

Dale D. Myers -- overall

Oran W. Nicks -- ramjet

Norman F. Parker -- guidance

William C. Perkins -- Titanium

I particularly want to thank the six Navaho program ex-co-workers listed above for their extra effort in supplying data for this report, and to Dr. Shirley Thomas for her continuing support in obtaining data. Ms. Elyse Nicholson of Rockwell International supplied photographic help.

Table 1. Requirement Revisions, 1950

Overall Objective -- 5,500 n.m., up to 15,000 lb payload

Later changed to 6,500 n.m.

Accuracy-1,500 ft CEP (later changed to 1 n.m.)

Speed -- Greater than Mach 2.75

Altitude -- Greater than 70,000 ft

Intermediate Objective -- 2.500 n.m. (later changed to 3,600 n.m.)

Table 2 Resulting Performance, 1957

Name	Mach No	Range nm	Max. Alt ft	Warhead lb	CEP nm	Length ft	Gross Wt lb	Flt. Date
X-10 Demonstrated	2.05	625	45000	Instruments	N/A	68	35000	Oct 1953
XSM-64 Demonstrated	2.99	1075	65000	Instruments	< One	68	65000	Nov 1956
XSM-64A Estimated	3.25	4400	75000	15000	One	89	120000	N/A
		5500	80000	5000