In the fifties of the last century, there was an active search for new ideas and solutions in the field of strategic weapons. Some of the proposed ideas were of great interest, but proved to be overly difficult to implement and implement. So, since 1955, the United States has been developing a promising strategic cruise missile SLAM, capable of delivering several warheads at a distance of tens of thousands of miles. To obtain such characteristics, the most daring ideas were proposed, but all this ultimately led to the closure of the project.
First stages
By the mid-fifties, a specific situation had developed in the field of strategic weapons and delivery vehicles. Due to the development of air defense systems, bombers were losing their potential, and ballistic missiles still could not show a comparable range. It was necessary to further improve missiles and aircraft or develop other areas. In the United States at that time there was a simultaneous study of several different concepts at once.
The SLAM rocket as seen by the artist. Figure Globalsecurity.org
In 1955, there was a proposal to create a new strategic cruise missile with special capabilities. This product was supposed to break through enemy air defense due to supersonic speed and low flight altitude. It was required to ensure the possibility of autonomous navigation at all stages of the flight and the possibility of delivering a high-power thermonuclear warhead. Separately, the presence of a communication system was stipulated that would allow the recall of an attacking missile at any time of the flight.
Several American aircraft companies have started working on the new concept. Ling-Temco-Vought launched its project with the working name SLAM, North American called a similar development BOLO, and Convair came up with the Big Stick project. Over the next few years, the three projects were worked out in parallel, some state scientific organizations were involved in it.
Quite quickly, the designers of all firms participating in the program faced a serious problem. The creation of a high-speed low-altitude rocket made special demands on the propulsion system, and a long range - on the fuel supply. A rocket with the required characteristics turned out to be unacceptably large and heavy, which required radical solutions. By the beginning of 1957, the first proposals appeared to equip new missiles with nuclear ramjet engines.
At the very beginning of 1957, the Lawrence Radiation Laboratory (now Livermore National Laboratory) was connected to the program. She had to study the problems of nuclear engines and develop a full-fledged model of this kind. Work on the new power plant was carried out as part of a program codenamed Pluto. Dr. Ted Merkle was appointed to lead Pluto.
Product layout SLAM. Figure Merkle.com
In the future, there was a simultaneous work on a promising engine and three types of cruise missiles. In September 1959, the Pentagon determined the best version of the new weapon. The winner of the competition was Ling-Temco-Vought (LTV) with the SLAM (Supersonic Low-Altitude Missile) project. It was she who had to complete the design, and then build experimental missiles for testing and later establish mass production.
SLAM project
Special requirements were imposed on the new weapon, which led to the need to apply the most daring decisions. Specific proposals figured in the context of the airframe, engine, and even the payload and the way it was used. Nevertheless, all this made it possible to fulfill the customer's requirements.
LTV offered a canard cruise missile with a length of about 27 m and a take-off weight of about 27, 5 tons. It was envisaged to use a spindle-shaped fuselage of high aspect ratio, in the nose of which the front empennage was placed, and in the center and tail there was a delta wing of a small span. Under the fuselage, at an angle to the longitudinal axis, there was a protruding air intake bucket. On the outer surface of the rocket, starting solid-propellant engines should be installed.
According to calculations, the cruising flight speed should have reached M = 3, 5, and the main part of the trajectory had an altitude of only 300 m. In this case, an ascent to an altitude of 10, 7 km and acceleration to a speed of M = 4, 2 were envisaged. This led to serious thermal and mechanical loads and made special demands on the airframe. The latter was proposed to be assembled from heat-resistant alloys. Also, some sections of the cladding were planned to be made of radio-transparent materials of the required strength.
Rocket flight diagram. Figure Globalsecurity.org
The engineers ultimately managed to achieve outstanding structural strength and stability, exceeding the existing requirements. Because of this, the rocket received the unofficial nickname "flying crowbar". It is worth noting that this nickname, unlike the other, was not offensive and indicated the strengths of the project.
A special power plant made it possible to optimize the layout of the internal volumes by eliminating the need for fuel tanks. The nose of the fuselage was given under the autopilot, guidance equipment and other means. A payload compartment with special equipment was placed near the center of gravity. The tail section of the fuselage accommodated a nuclear ramjet engine.
The TERCOM type system was responsible for the SLAM missile guidance. On board the product, it was proposed to place a terrain survey radar station. Automation was supposed to compare the underlying surface with the reference surface and, on the basis of this, correct the flight trajectory. Commands were issued to the bow rudder cars. Similar tools have already been tested in previous projects and have shown themselves well.
Unlike other cruise missiles, the SLAM product had to carry not one warhead, but 16 separate warheads. Thermonuclear charges with a capacity of 1, 2 Mt were placed in the central compartment of the hull and had to be dropped one by one. Calculations have shown that dropping a charge from a height of 300 m seriously limits its effectiveness, and also threatens the launch vehicle. In this regard, an original system for firing warheads was proposed. It was proposed to shoot the block up and send it to the target along a ballistic trajectory, which made it possible to detonate at an optimal height, and also left enough time for the missile to leave.
Tests of the SLAM model in a wind tunnel, August 22, 1963. Photo by NASA
The rocket was supposed to take off from a stationary or mobile launcher using three solid-propellant starting engines. After gaining the required speed, the sustainer could turn on. As the latter, a promising product from the Lawrence Laboratory was considered. She had to create a ramjet nuclear engine with the required thrust parameters.
According to calculations, a SLAM rocket powered by the Pluto program could have an almost unlimited flight range. When flying at an altitude of 300 m, the calculated range exceeded 21 thousand km, and at maximum altitude it reached 182 thousand km. The maximum speed was reached at high altitude and exceeded M = 4.
The LTV SLAM project envisaged an original method of combat work. The rocket was supposed to take off with the help of starting engines and go to the target or go to a predetermined holding area. The high range of high-altitude flight made it possible to launch not only immediately before the attack, but also during the threatened period. In the latter case, the rocket had to stay in the given area and wait for the command, and after receiving it, it should be sent to the targets.
It was proposed to perform the maximum possible part of the flight at high altitude and high speed. Approaching the zone of responsibility of the enemy air defense, the rocket was supposed to descend to a height of 300 m and be directed to the first of the assigned targets. When passing next to it, it was proposed to drop the first warhead. Further, the rocket could hit 15 more enemy targets. After the ammunition was used up, a SLAM product equipped with a nuclear engine could fall on another target and also become an atomic bomb.
Experienced Tory II-A engine. Photo Wikimedia Commons
Also, two more options for inflicting damage on the enemy were seriously considered. During flight at a speed of M = 3, 5, the SLAM rocket created a powerful shock wave: during low-altitude flight, it posed a danger to ground objects. In addition, the proposed nuclear engine was distinguished by an extremely strong radiation "exhaust" capable of infecting the area. Thus, the missile could harm the enemy by simply flying over his territory. After dropping the 16 warhead, it could continue flying and only after running out of nuclear fuel could it hit the last target.
Pluto project
In accordance with the SLAM project, the Lawrence Laboratory was supposed to create a ramjet engine based on a nuclear reactor. This product had to have a diameter of less than 1.5 m with a length of about 1.63 m. To achieve the desired performance characteristics, the engine reactor had to show a thermal power of 600 MW.
The principle of operation of such an engine was simple. The incoming air through the air intake had to enter directly into the reactor core, be heated and ejected through the nozzle, creating thrust. However, the implementation of these principles in practice has proven to be extremely difficult. First of all, there was a problem with the materials. Even heat-resistant metals and alloys could not cope with the expected thermal loads. It was decided to replace some of the metal parts of the core with ceramics. Materials with the required parameters were ordered by Coors Porcelain.
According to the project, the core of a nuclear ramjet engine had a diameter of 1.2 m with a length of slightly less than 1.3 m. It was proposed to place 465 thousand fuel elements in it on a ceramic base, made in the form of ceramic tubes 100 mm long and 7.6 mm in diameter … The channels inside the elements and between them were intended for the passage of air. The total mass of uranium reached 59.9 kg. During engine operation, the temperature in the core should have reached 1277 ° C and maintained at this level due to the cooling air flow. A further rise in temperature by only 150 ° could lead to the destruction of the main structural elements.
Breadboard samples
The most difficult part of the SLAM project was the unusual engine, and it was he who needed to be checked and fine-tuned in the first place. Especially for testing new equipment, the Lawrence Laboratory has built a new testing complex with an area of 21 sq. km. One of the first was a stand for testing ramjet engines equipped with compressed air supply. The stand tanks contained 450 tons of compressed air. At a distance from the engine position, a command post was placed with a shelter designed for a two-week stay for the testers.
Tory II-A, top view. Photo Globalsecurity.org
The construction of the complex took a long time. In parallel, specialists headed by T. Merkle developed a project for an engine for a future rocket, and also created a prototype version for bench tests. In the early sixties, this work led to a product codenamed Tory II-A. The engine itself and a large number of auxiliary systems were placed on the railway platform. The dimensions of the engine did not meet the customer's requirements, but even in this form, the prototype could show its capabilities.
On May 14, 1961, the first and last test launch of the Tory II-A engine took place. The engine ran for only a few seconds and developed a thrust well below that required for a rocket. Nevertheless, he confirmed the fundamental possibility of creating a nuclear ramjet engine. In addition, there was reason for restrained optimism: measurements showed that the actual engine emissions are significantly lower than the calculated ones.
As a result of the Tory II-A testing, development began on an improved B engine. The new Tory II-B product was supposed to have advantages over its predecessor, but it was decided not to be built or tested. Using the experience of two projects, the following bench sample was developed - Tory II-C. From the previous prototype, this engine differed in reduced dimensions, corresponding to the limitations of the rocket airframe. At the same time, he could show characteristics close to those required by the SLAM developers.
In May 1964, the Tory II-C engine was prepared for its first test run. The check was to take place in the presence of representatives of the Air Force command. The engine was successfully started, and it worked for about 5 minutes, using all the air at the stand. The product developed a power of 513 MW and produced a thrust of a little less than 15.9 tons. This was still not enough for the SLAM rocket, but brought the project closer to the moment of creating a nuclear ramjet engine with the required characteristics.
The active zone of the experimental engine. Photo Globalsecurity.org
Experts noted successful tests in a nearby bar, and the next day they started working on the next project. The new engine, tentatively named Tory III, was supposed to fully meet the customer's requirements and give the SLAM rocket the desired characteristics. According to estimates of that time, an experimental rocket with such an engine could have made its first flight in 1967-68.
Problems and disadvantages
Tests of a full-fledged SLAM rocket were still a matter of the distant future, but the customer in the person of the Pentagon already had uncomfortable questions about this project. Both individual components of the rocket and its concept as a whole were criticized. All this negatively affected the prospects of the project, and an additional negative factor was the availability of a more successful alternative in the form of the first intercontinental ballistic missiles.
First, the new project turned out to be prohibitively expensive. The SLAM rocket did not include the cheapest materials, and the development of the engine for it became a separate problem for the Pentagon financiers. The second complaint was about product safety. Despite the encouraging results from the Pluto program, the Tory series engines contaminated the terrain and posed a danger to their owners.
Hence the question of an area for testing future prototype missiles followed. The customer demanded to exclude the possibility of a missile hitting the areas of settlements. The first was the proposal for tethered tests. It was proposed to equip the rocket with a tethered cable connected to an anchor on the ground, around which it could fly in a circle. However, such a proposal was rejected due to obvious shortcomings. Then came the idea of test flights over the Pacific Ocean in the area of about. Wake. After running out of fuel and completing the flight, the rocket had to sink at great depths. This option also did not fully suit the military.
Tory II-C engine. Photo Globalsecurity.org
The skeptical attitude towards the new cruise missile manifested itself in different ways. For example, from a certain time, the abbreviation SLAM began to decipher as Slow, Low And Messy - "Slow, low and dirty", hinting at the characteristic problems of the rocket engine.
On July 1, 1964, the Pentagon decided to close the SLAM and Pluto projects. They were too expensive and complex, and not safe enough to successfully proceed and obtain the desired results. By this time, about $ 260 million (more than $ 2 billion in current prices) had been spent on the program for the development of a strategic cruise missile and an engine for it.
Experienced engines were disposed of as unnecessary, and all the documentation was sent to the archive. However, the projects have yielded some real results. New metal alloys and ceramics developed for SLAM were later used in various fields. As for the very ideas of a strategic cruise missile and a nuclear ramjet engine, from time to time they were discussed at different levels, but were no longer accepted for implementation.
The SLAM project could lead to the emergence of unique weapons with outstanding characteristics that could seriously affect the strike potential of the US strategic nuclear forces. However, obtaining such results was associated with many problems of different nature, from materials to cost. As a result, the SLAM and Pluto projects were phased out in favor of less daring, but simple, affordable and cheap developments.
