In the mid-forties, the American military department initiated a program to develop several new missile systems. Through the efforts of a number of organizations, it was planned to create several long-range cruise missiles. These weapons were supposed to be used to deliver nuclear warheads to targets on enemy territory. Over the next few years, the military has repeatedly adjusted the requirements for projects, which led to corresponding changes in promising technology. In addition, the uniquely high requirements meant that only one new missile was able to reach military service. Others remained on paper, or did not leave the testing stage. One of these "losers" was the SM-64 Navaho project.
Recall that in the summer of 1945, shortly after the end of the war in Europe, the American command ordered to study the captured samples of German equipment and documentation on them in order to obtain important developments. Soon thereafter, a proposal appeared to develop a promising surface-to-surface cruise missile with high range characteristics. Several leading defense industry organizations were involved in the creation of such weapons. Among others, Rocketdyne, a division of North American Aviation (NAA), has applied for the program. Having studied the available technologies and their prospects, the NAA specialists proposed an approximate project schedule, in accordance with which it was supposed to create a new rocket.
Early work
It was proposed to develop a project for a new weapon in three stages. During the first, it was necessary to take as a basis the German V-2 ballistic missile in the A-4b version and equip it with aerodynamic planes, thus making a projectile aircraft. The second phase of the proposed project involved the removal of a liquid-propellant jet engine with the installation of a ramjet engine. Finally, the third stage of the program was intended to create a new launch vehicle, which was supposed to significantly increase the flight range of the combat missile created in the first two stages.
Rocket XSM-64 / G-26 at the launch site. Photo Wikimedia Commons
Having received the necessary documents and units, the Rocketdine specialists began research and design work. Of particular interest are their experiments with available engines of various types. Without the required test base, the designers tested them right in the parking lot next to their office. To protect other equipment from reactive gases, a gas baffle was used, in the role of which an ordinary bulldozer acted. Despite the strange appearance, such tests allowed us to collect a lot of necessary information.
In the spring of 1946, NAA was awarded a military contract to continue developing a new cruise missile. The project received the official designation MX-770. In addition, until a certain time, an alternative index was used - SSM-A-2. In accordance with the first contract, it was required to build a missile capable of flying at a range of 175 to 500 miles (280-800 km) and carrying a nuclear warhead weighing about 2 thousand pounds (910 kg). At the end of July, an updated technical task was issued, requiring an increase in the payload to 3 thousand pounds (1.4 tons).
In the early stages of the MX-770 project, there were no special requirements for the range of a promising missile. Naturally, a range of the order of 500 miles was already a rather difficult task, given the available technologies, but higher performance was not required until a certain time.
The situation changed in mid-1947. The military came to the conclusion that the required range was insufficient to solve the existing combat missions. Because of this, major changes were made to the requirements for the MX-770 project. Now the rocket had to be equipped only with a ramjet engine, and the range had to be increased to 1,500 miles (about 2, 4 thousand km). Due to some difficulties of a technological and design nature, the requirements were soon softened to a certain extent. At the beginning of the spring of the 48th, the missile range was changed again, and the requirements were adjusted taking into account the further development of the project. So, the early experimental missiles were supposed to fly at a distance of about 1000 miles, and the later ones required a three times longer range. Finally, mass-produced missiles for the army had to fly 5,000 miles (over 8,000 km).
Takeoff of XSM-64 rocket. Photo Spacelaunchreport.com
New requirements from July 47 forced North American Aviation engineers to abandon their previous plans. Calculations have shown that it is not possible to fulfill the technical task using ready-made German developments. The rocket and its units had to be developed from scratch, using the existing experience and technology. In addition, the experts finally decided to build a cruise missile with a full-fledged power plant and an additional upper stage, and not a two-stage system with an upper stage and a glider equipped with a warhead and not having its own engine.
The appearance of the updated requirements also allowed the specialists of the developer company to formulate the main provisions of the project, in accordance with which further work should be carried out. So, it was decided to create a new inertial navigation system for use as guidance equipment, and research in a wind tunnel made it possible to determine the optimal shape of the rocket airframe. It was found that the most efficient aerodynamic configuration for the MX-770 would be the delta wing. The next stage of work on the new project implied the study of the main issues and the creation of units in accordance with the updated requirements and plans.
Further calculations proved the effectiveness of the use of a ramjet engine. The existing and promising designs of such a power plant promised a noticeable increase in performance. According to calculations of that time, a ramjet rocket had a third longer range than a similar product with a liquid engine. At the same time, the required flight speed was ensured. The consequence of these calculations was the intensification of work on the creation of new ramjet engines with improved characteristics. Already in the summer of 1947, the NAA engine division received an order to modernize the existing experimental XLR-41 Mark III engine with an increase in thrust to 300 kN.
Flying laboratory X-10. Photo Designation-systems.net
In parallel with the engine upgrade, North American specialists worked on the N-1 inertial navigation system project. At the preliminary stages of the project, calculations showed that monitoring the movement of the rocket in three planes would provide a sufficiently high accuracy in determining the coordinates. The calculated deviation from the real coordinates was 1 mile per hour of flight. Thus, when flying to the maximum range, the circular probable deflection of the rocket should not have exceeded 2, 5 thousand feet (about 760 m). Nevertheless, the design characteristics of the N-1 system were considered insufficient from the point of view of the further development of rocket technology. With an increase in the range of the missile, the KVO could increase to unacceptable values. In this regard, in the fall of the 47th, the development of the N-2 system began, in which, in addition to inertial navigation equipment, a device for orientation by stars was included.
Based on the results of the first studies of the updated project, related to the change in customer requirements, the plan for the development of the project and testing of finished missiles was adjusted. Now, during the first stage, it was planned to test the MX-770 rocket in various configurations, including when launched from a carrier aircraft. The purpose of the second stage was to increase the flight range to 2-3 thousand miles (3200-4800 km). The third stage was intended to bring the range up to 5 thousand miles. At the same time, it was necessary to increase the payload of the rocket to 10 thousand pounds (4.5 tons).
The bulk of the design work on the MX-770 rocket was completed in 1951. However, the development of this weapon was associated with many difficulties. As a result, even after the 51st, the designers of Rocketdyne and NAA had to constantly refine the project, correct the identified shortcomings, and also use various auxiliary equipment for additional research.
Experimental Support Project
In order to facilitate the work and study the available proposals in 1950, the development of an additional project RTV-A-5 was agreed. The goal of this project was to create a radio-controlled aircraft with an aerodynamic appearance similar to a new type of combat missile. In 1951, the project was renamed X-10. This designation remained until the very closure of the project in the mid-fifties.
X-10 in flight. Photo Designation-systems.net
The RTV-A-5 / X-10 product was a radio-controlled aircraft with an elongated streamlined fuselage, elevators in the nose, a delta wing in the tail and two keels. At the rear of the fuselage sides there were two nacelles with Westinghouse J40-WE-1 turbojet engines with a thrust of 48 kN each. The device had a length of 20, 17 m, a wing span of 8, 6 m and a total height (with a tricycle landing gear extended) of 4.5 m. an altitude of 13.6 km and fly at a range of up to 13800 km.
The design of the X-10 airframe was developed on the basis of the MX-770 rocket design. With the help of tests of the radio-controlled aircraft, it was planned to test the prospects of the proposed airframe when flying in different modes. In addition, at a certain stage of the program, there was a similarity in terms of onboard equipment. Initially, the X-10 received only radio control equipment and an autopilot. At the later stages of testing, the prototype aircraft was equipped with the N-6 inertial navigation system, which was proposed for use on a full-fledged rocket.
The first flight of the X-10 product took place in October 1953. The aircraft successfully took off from one of the airfields and completed the flight program, upon completion of which it made a successful landing. Test flights of the flying laboratory continued until 1956. During this work, NAA specialists checked various features of the existing design, and also collected data for further improvements to the MX-770 project.
X-10 during landing. Photo Boeing.com
Thirteen X-10 aircraft were built for use in the tests. Some of this technique was lost during the main tests. In addition, in the fall and winter of 1958-59. North American conducted a series of additional tests in which three more drones were lost due to accidents. Only one X-10 survived until the end of the program.
Product G-26
After checking the proposed aerodynamic appearance with the help of a radio-controlled aircraft, it became possible to build experimental missiles. In accordance with existing plans, first the NAA company began construction of simplified prototypes of a promising cruise missile. These vehicles received the factory designation G-26. The military gave this technique the name XSM-64. In addition, it was at this time that the program received the additional designation Navaho.
From a design point of view, the XSM-64 was a slightly enlarged and modified version of the unmanned X-10. At the same time, significant changes were made to individual structural elements, as well as the introduction of new units into the complex. In order to achieve the required flight range, the experimental rocket was built according to a two-stage scheme. The liquid first stage was responsible for lifting into the air and initial acceleration. And the cruise missile was a cruise missile with a payload.
Diagram of the G-26 rocket. Figure Astronautix.com
The launch stage was a unit with a conical head fairing and a cylindrical tail section, on which two keels were attached. The length of the first stage was 23.24 m, the maximum diameter was 1.78 m. When ready for launch, the stage weighed 34 tons. It was equipped with one North American XLR71-NA-1 liquid engine with thrust of 1070 kN, running on kerosene and liquefied oxygen. …
The cruise stage of the XSM-64 rocket retained the main features of the X-10 product, but was equipped with a different type of engine, and also had a number of other features. At the same time, the landing gear was retained after the test flight. With a launch weight of 27, 2 tons, the main stage had a length of 20, 65 m and a wing span of 8, 71 m. 36 kN each. To control the missile, guidance equipment of the N-6 type was used. In addition, for some tests, the missile was equipped with radio command control.
The launch of the XSM-64 rocket was proposed to be carried out from a vertical launcher. The first stage with a liquid engine was supposed to lift the rocket into the air and deliver it to an altitude of at least 12 km, developing a speed of up to M = 3. After that, it was planned to launch the ramjet engine of the sustainer stage and reset the starting stage. With the help of its own engines, the cruise missile was supposed to rise to an altitude of about 24 km and move towards the target at a speed of M = 2.75. The flight range, according to calculations, could reach 3500 miles (5600 km).
The XSM-64 project had several critical technical and technological features. So, in the design of the sustainer and launch stage, parts from titanium and some other newest alloys were widely used. In addition, all electronic components of the rocket were built exclusively on transistors. Thus, the Navajo rocket became one of the first weapons in history without lamp equipment. The use of the "kerosene + liquefied oxygen" fuel pair can be considered no less a technical breakthrough.
Test launch on June 26, 1957, LC9 launch complex. Photo Wikimedia Commons
In 1956, a launch complex for XSM-64 / G-26 missiles was built at the US Air Force base at Cape Canaveral, which made it possible to begin testing promising weapons. The first test launch of the rocket took place on November 6 of the same year and ended in failure. The rocket was in the air for only 26 seconds, after which it exploded. Soon, the assembly of the second prototype was completed, which also went for testing. Until mid-March 1957, NAA and Air Force specialists conducted ten test launches, which ended with the destruction of experimental missiles within a few seconds after launch or directly at the launch site.
The first relatively successful launch took place only on March 22, 57th. This time the rocket stayed in the air for 4 minutes 39 seconds. At the same time, the next flight, on April 25, ended with an explosion literally over the launch pad. On June 26 of the same year, the Navaho rocket again managed to fly a fairly large distance: these tests lasted 4 minutes 29 seconds. Thus, all missiles launched during the tests were destroyed at launch or in flight, which is why they could not return to base after the flight was completed. Ironically, the saved chassis assemblies turned out to be useless cargo.
End of the project
Tests of the G-26 or XSM-64 missiles showed that the product developed by the NAA did not meet the customer's requirements. Perhaps, in the future, such cruise missiles could demonstrate the required speed and range, but as of the summer of 1957, they were not very reliable. As a result, the implementation of the rest of the plans was in question. After a relatively successful (in comparison with the mass of others) launch on June 26, 1957, the customer, represented by the Pentagon, decided to revise its plans for the current project.
The development program for the MX-770 / XSM-64 long-range cruise missile has faced enormous challenges. Despite all efforts, the authors of the project failed to bring the missile's reliability to the required level and ensure an acceptable flight duration. Further refinement of the project took time and also raised serious doubts. In addition, by the end of the fifties, notable advances were made in the field of ballistic missiles. Thus, further development of the Navajo project was impractical.
Experienced rocket in flight. January 1, 1957 Photo Wikimedia Commons
In early July, the air force command ordered the curtailment of all work on the unsuccessful project. The concept of a long-range or intercontinental-range cruise missile armed with a nuclear warhead was deemed dubious. At the same time, work continued on another project of similar weapons: the strategic cruise missile Northrop MX-775A Snark. Soon it was even brought into service, and in 1961 these missiles were on alert for several months. However, the development of this weapon was associated with a lot of difficulties and costs, which is why it was removed from service shortly after the start of full-fledged operation.
After the order signed in July 1957, no one considered the XSM-64 product as a full-fledged military weapon. Nevertheless, it was decided to continue some work in order to collect information necessary for the implementation of future projects. On August 12, the NAA and the Air Force conducted the first launch of the series, codenamed Fly Five. Until February 25 of the 58th, four more flights were performed. Despite all the efforts of the developer, the rocket was not very reliable. Nevertheless, in one of the XSM-64 flights, Navaho was able to reach a speed of the order of M = 3 and stay in the air for 42 minutes 24 seconds.
In the fall of 1958, the existing Navajo rockets were used as platforms for scientific equipment. Within the framework of the RISE program (literally "rise", there was also a transcript of Research in Supersonic Environment - "Research in supersonic conditions"), two research flights were carried out, which, however, ended in failure. During the flight on September 11, the XSM-64 main stage could not start its engines, and then fell. On November 18, the second rocket rose to an altitude of 77 thousand feet (23.5 km), where it exploded. This was the last missile launch of the Navaho project.
Project G-38
It should be recalled that the G-26 or XSM-64 rocket was the result of the second phase of the MX-770 project. The third was to be a larger cruise missile that fully meets the customer's requirements. The development of this project started even before the start of tests of the G-26. The new version of the rocket received the official designation XSM-64A and the factory G-38. It was planned that the successful completion of the XSM-64 tests would open the way for newer development, but constant setbacks and lack of progress led to the closure of the entire project. By the time this decision was made, the development of the XSM-64A project was completed, but it remained on paper.
Diagram of the G-38 / XSM-64A missile. Figure Spacelaunchreport.com
The G-38 / XSM-64A project in the final version, presented in February 1957, was a modified version of the previous G-26. This missile was distinguished by its increased size and a different composition of onboard equipment. At the same time, the principles of launch and other features of the project remained almost unchanged. The new rocket was supposed to have a two-stage design with an upper stage and a cruise missile-like sustainer stage.
In the new project, it was proposed to use a larger and heavier first stage with engines of increased power. The new launch stage had a length of 28.1 m and a diameter of 2.4 m, and its weight reached 81.5 tons. It was to be equipped with a North American XLR83-NA-1 liquid engine with a thrust of 1800 kN. The tasks of the launch stage remained the same: the rise of the entire rocket to a height of several kilometers and the initial acceleration of the sustainer stage, which is necessary to launch its ramjet engines.
The marching stage was still built according to the "duck" pattern, but now it had a diamond-shaped wing. The length of the rocket increased to 26.7 m, the wingspan was up to 13 m. The estimated starting weight of the sustainer stage reached 54.6 tons. Two Wright XRJ47-W-7 ramjet engines with a thrust of 50 kN each were proposed as a power plant. Such a power plant was to be used to reach an altitude of about 24 km and fly at a speed of M = 3.25. The estimated flight range was at the level of 6300 miles (10 thousand km).
It was proposed to equip the XSM-64A Navaho rocket with the N-6A inertial navigation system with additional astronomical equipment that increases the accuracy of the course calculation. As a payload, the rocket was supposed to carry a W39 thermonuclear warhead with a capacity of 4 megatons in TNT equivalent. Prototypes of the G-38 sustainer stage were planned to be equipped with a bicycle-type landing gear for returning to the airfield after a successful test flight.
Outcomes
After several unsuccessful and relatively successful (especially against the background of others) test launches of the XSM-64 / G-26 rocket, the customer, represented by the Air Force, decided to abandon the further development of the Navaho project. The resulting cruise missile had extremely low reliability, which is why it could not be considered as a promising strategic weapon. The fine-tuning of the structure was considered too complicated, costly, time-consuming and unprofitable. The result of this was the abandonment of further development of the rocket as a promising means of delivering nuclear weapons. However, in the future, seven missiles were used in new research projects.
One of the reasons for the closure of the SM-64 project was its excessive cost. According to available data, by the time this decision was made, the project cost taxpayers about $ 300 million (in prices of the fifties). At the same time, such investments of money did not lead to real results: the longest flight of the G-26 rocket lasted a little more than 40 minutes, which was clearly not enough for a full-fledged use with a rocket flight at full range. In order to avoid further spending with dubious efficiency, the project was closed.
Museum sample of the Navajo rocket at Cape Canaveral. Photo Wikimedia Commons
Despite the closure of the project, the development of a promising strategic cruise missile has yielded some results. The Navajo project, as well as other similar developments, became the reason for carrying out a lot of research work in the field of materials science, electronics, engine building, etc. In the course of these studies, American scientists have created a lot of new technologies, components and assemblies. Subsequently, new developments created as part of an unsuccessful cruise missile project were most actively used in the development of new systems for various purposes.
The most striking example of the use of developments on the MX-770 / SM-64 project is the AGM-28 Hound Dog air-launched cruise missile project, created by North American in 1959. The use of ready-made developments affected the mass of features of this product, primarily on the design and characteristic appearance. Such missiles were used by US strategic bombers over the next several decades.
Several samples of equipment created as part of the MX-770 project have survived to our time. The only surviving example of the X-10 flying laboratory is now in the museum at Wright-Patterson Air Force Base. It is also known that the launch stage of the XSM-64 rocket is on display at the Veterans of Foreign Wars (Fort McCoy, Florida). The best known surviving specimen is a fully assembled G-26 rocket stored in an open area at Cape Canaveral Air Base. This product in red and white paint consists of a launch and sustainer stage and clearly demonstrates the design of the complete rocket.
Like many other developments of its time, the SM-64 Navaho cruise missile turned out to be too complex and unreliable for practical use, and also had an unacceptably high cost. However, all the costs of creating it have not been wasted. This project made it possible to master new technologies, and also showed the inconsistency of the original concept of an intercontinental cruise missile, which until a certain time was considered promising and promising. The failure of the Navajo project and other similar developments to a certain extent spurred the development of ballistic missiles, which still remain the main means of delivering nuclear warheads.
