In the foreseeable future, NASA experts expected not only to send a man into space, but also to solve several other problems. In particular, they considered the possibility of working in outer space, outside the ship. For a complete solution of tasks in such conditions, a certain apparatus was required with which the astronaut could freely move in the right direction, maneuver, etc. At the very beginning of the sixties, NASA requested assistance from the Air Force, which by this time managed to conduct several similar programs. In addition, she hired several enterprises. aviation industry, which was proposed to develop their own versions of a personal aircraft for the space program. Among others, such an offer was received by Chance-Vought.
According to the available data, even at the stage of preliminary studies, NASA experts came to conclusions regarding the optimal form factor of promising technology. It turned out that the most convenient individual means of transportation would be a knapsack with a set of low-power jet engines. It is these devices ordered contracting companies. It should be noted that other variants of the device were also considered, however, it was precisely the knapsack that was put on the astronaut's back that was recognized as optimal.
General view of the spacesuit from Chance-Vought and the SMU apparatus. Photo of Popular Science
Over the next few years, Chance-Vout conducted a series of studies and shaped the vehicle for space. The project received the designation SMU (Self-Maneuvering Unit - “Self-Maneuvering Device”). In the later stages of the development of the project and during the tests, a new designation was applied. The device was renamed AMU (Astronaut Maneuvering Unit - "Device for maneuvering an astronaut").
Probably, the authors of the SMU project knew about the developments of the Wendell Moore team from Bell Aerosystems, and also knew about other developments in this area. The fact is that the jetpacks of the Bell company and the spacecraft that appeared a little later had to have the same engines, although they had different characteristics. The SMU product was proposed to be equipped with jet engines operating on hydrogen peroxide and using its catalytic decomposition.
The process of catalytic decomposition of hydrogen peroxide by this time was actively used in various techniques, including in some early jetpacks. The essence of this idea is to supply "fuel" to a special catalyst that causes the decomposition of a substance into water and oxygen. The resulting gas-vapor mixture has a sufficiently high temperature, and also expands at high speed, which allows it to be used as an energy source, including in jet engines.
It should be noted that the decomposition of hydrogen peroxide is not the most economical source of energy in the context of reactive backpacks. For the formation of thrust, sufficient to lift a person into the air, requires too much "fuel". Thus, in Bell's projects, the 20-liter tank allowed the pilot to hold no more than 25-30 in the air. However, this was only valid for flying on Earth. In the case of open space or the surface of the moon, due to the lower (or absent) weight of the astronaut, it was possible to provide the required characteristics of the device without an unacceptably high consumption of hydrogen peroxide.
In the course of the project, the SMU had to resolve several major issues, the main of which, of course, was the type of jet engine. In addition, it was necessary to determine the optimal layout of the entire device, the composition of the necessary equipment and a number of other features of the project. According to reports, the study of these issues eventually led to the design of the original space suit, which was proposed to be used with the SMU / AMU product.
Major design work was completed in the first half of 1962, shortly thereafter, Chance-Vought manufactured a prototype space jetpack. In the autumn of the same year, the apparatus was first shown to the press. In the November issue of Popular Science, images of the proposed system were first published. In addition, the article in this journal outlined the layout and some basic characteristics.
In one of the photos published by Popular Science, an astronaut was depicted in a new spacesuit, on whose back was an SMU machine. The proposed spacesuit had a spherical helmet with a lowered face shield and a well-developed lower part, with which he was supposed to rest on the astronaut's shoulders. There were also several connectors for connecting the spacesuit with jetpack systems. The suit from Chance-Vought was markedly different from modern products for this purpose. It was carried out as light as possible and, apparently, was not equipped with a set of protective equipment that is necessary to meet current requirements.
The knapsack itself was a rectangular block with a concave front wall and a set of tools for mounting on the astronaut's back. So, on top of the front wall there were two characteristic "hooks" with which the satchel rested on the astronaut's shoulders. In the middle part there was a lap belt, on which was located a cylindrical control panel with several levers. Several cables and flexible pipelines were also provided for connecting the knapsack to the spacesuit.
The need to ensure long-term work outside the spacecraft, as well as the imperfection of the technologies of the time, affected the layout of the device. At the top of the SMU product was a large block of a closed-cycle oxygen system. This device was designed to supply a breathing mixture to an astronaut's helmet, followed by pumping exhaled gases and removing carbon dioxide. Unlike hoses for supplying the respiratory mixture from a ship or compressed gas cylinders, the system with carbon dioxide absorbers did not impair the astronaut's maneuverability and allowed to remain in open space for a long time.
SMU without back panel. Photo of Popular Science
According to reports, during the demonstration to journalists, the SMU was not equipped with a working life support system. This equipment was not yet ready to work and needed additional checks, which is why it was replaced with a simulator of similar weight and dimensions on a prototype. It was in this configuration that the device took part in the first tests. Moreover, work in this direction was seriously delayed, because of which even a later prototype, built at the end of 1962, was tested without an oxygen system and was equipped only with its simulator.
The lower left part of the body (relative to the pilot) was given for the placement of the hydrogen peroxide tank. To the right of it was a set of other equipment for various purposes. At the top of the lower right compartment was a radio station providing two-way voice communication, batteries and power supply for the equipment were installed under it, as well as a cylinder for compressed nitrogen in the fuel supply system and a gas regulator.
On the side faces of the upper surface of the jetpack, four miniature engines with their own nozzles were provided (two on each side). The same engines were on the bottom surface of the case. In addition, two engines of similar layout were located in the center of the bottom surface. In total, 10 engines were available to emit reactive gases. The nozzles of all engines were turned and inclined to different sides and had to be responsible for creating thrust directed in the right direction.
Each engine, according to available information, was a small block with a plate catalyst that provokes the decomposition of fuel. Before the catalyst there was a valve controlled by a solenoid. All ten engines were proposed to be connected with the fuel tank, which, in turn, was connected to a cylinder for compressed gas.
The principle of operation of the engines was simple. Under the pressure of compressed nitrogen, hydrogen peroxide was supposed to enter the pipelines and reach the engines. At the command of the control system, the engine solenoids should have opened the valves and ensured access of the “fuel” to the catalysts. Next was the decomposition reaction with the release of the gas-vapor mixture through the nozzle and the formation of thrust.
The nozzles were arranged in such a way that by synchronous or asymmetric switching of the engines it was possible to move in the right direction, make turns or adjust their position. For example, the simultaneous switching on of all engines directed backward allowed to move forward, and the turn was carried out due to the asymmetric switching on of engines of different sides.
The first version of the device SMU received a relatively simple control panel, made in a cylindrical case and located on the waist belt. On the side, under the right hand, there was a lever for controlling the forward movement forwards or backwards. On the front wall placed the lever to control the pitch and yaw. Above there was another lever that was responsible for roll control. In addition, toggle switches were provided to turn on the engine, radio station and autopilot. With the help of such controls, the pilot could deliver hydrogen peroxide to the right engines and thereby control his movements.
In addition to manual control, the SMU had automatic devices designed to facilitate the work of an astronaut. If necessary, he could turn on the autopilot, which with the help of a gyroscope and relatively simple electronics had to monitor the position of the jet pack in space, correcting it if necessary. It was assumed that such a regime would be applied during long work at one place, for example, when servicing instruments on the outer surface of a spacecraft. In this case, the astronaut got the opportunity to perform various jobs, and the automatics had to keep an eye on maintaining the desired position.
Presented to journalists version of the SMU jet pack weighed about 160 pounds (about 72 kg). When used on the moon, the weight of the apparatus was reduced to 25 pounds (11,5 kg), and when operating in Earth orbit, the weight should have been completely absent.
Model of SMU jetpack during testing. Photo from the report
According to the publication of Popular Science, the presented sample of the SMU apparatus, according to calculations, allowed the astronaut to fly up to 1000 feet (304 m) with hydrogen peroxide at one refueling station. Traction engines, according to the developers, enough to move a fairly large cargo. For example, the possibility of moving an object, such as a spacecraft, weighing up to 50 t, was claimed. At the same time, the astronaut had to develop a speed on the order of one foot per second.
A few months before the SMU apparatus was shown to journalists, in the middle of 1962, the prototype was taken to Wright-Patterson Air Force, Ohio, where it was to be tested. To carry out all the necessary tests, specialists of the Ministry of Defense were involved in the project, as well as special equipment. For example, a special aircraft KC-135 Zero G, used for research under conditions of short-term weightlessness, was chosen as the platform for testing.
The first flight with “zero gravity” passed 25 on June 62, and over the following months several dozen tests of the performance of the jetpack under weightless conditions were carried out. During this time, it was possible to establish the fundamental possibility of using such systems in practice. In addition, some characteristics and basic flight data were confirmed. So, engine thrust was enough to fly in the air atmosphere and perform some simple maneuvers.
Successful tests of the SMU did not stop the design work. By the end of 1962, the development of an updated version of the astronaut jet pack was launched. In the modernized version of the project, it was proposed to change the layout of the device, as well as to make some other adjustments to the design. Due to all this, it was supposed to improve the performance, first of all, the stock of "fuel" and the basic flight data. After the start of work on the updated project, a new name, AMU, appeared, which soon began to be applied in relation to the previous SMU product, due to which some confusion was possible.
According to reports, the upgraded AMU outwardly almost did not differ from the base SMU. The exterior of the hull has not undergone major changes, the system of fastening the device on the astronaut's back has remained the same. At the same time, the layout of the internal aggregates changed drastically. The flight range at the 300 m level did not suit NASA, which was why it was proposed to use a new fuel tank. AMU jetpack received a large tank for hydrogen peroxide of great length, which occupied the entire central part of the hull. The volume of the new tank was 660 cube. inches (10,81 L). On the sides of this tank located other equipment.
Among other units, the tank for compressed nitrogen of the hydrogen peroxide pressurization system has been preserved. According to the project, the nitrogen should have been supplied to the fuel tank under pressure at the level of 3500 psi (238 atmosphere). However, less pressure was used during the tests: on the order of 200 psi (13,6 atm). The prototype of the AMU was equipped with engines of different power. So, the nozzles responsible for moving back and forth developed thrust at the level of 20 pounds, used for moving up and down - on 10 pounds.
In the future, the AMU could have received a life support system, but even by the time the tests began, such equipment was not yet ready. Because of this, an experienced AMU, like its predecessor, received only the layout of the desired system with similar dimensions and weight. After completing all the necessary design work and testing, the oxygen system could be installed on a space jetpack.
Soon after the end of the assembly, at the very end of 1962 or at the beginning of 1963, the AMU was sent to Wright-Patterson base for testing. A specially equipped KC-135 Zero G aircraft again became the “testing ground” for its inspections. Various checks continued until at least the end of the 1963 spring.
In mid-May 1963, the authors of the project prepared a test report. By this time, as stated in the document, over a hundred flights along a parabolic trajectory were carried out, during which the operation of jetpacks under conditions of weightlessness was checked. During the tests, despite the short duration of flights with zero gravity, it was possible to master the control of both devices, as well as to verify their ability to transport the pilot or cargo.
An AMU satchel during testing. Photo from the report
In the final part of the report it was stated that the jetpack of the AMU in its current form has satisfactory characteristics and can be used to solve the tasks assigned to it. It was also noted that thrust engines up to 20 pounds is sufficient for a controlled flight in the right direction and perform various maneuvers. The selected location of the nozzles of the engines provided, as written in the report, excellent control over the apparatus by placing the pilot-haversack system at an equal distance from the center of gravity.
The autopilot as a whole showed itself well, but needed improvements and additional tests. In some situations, this device could not properly respond to the change in the position of the knapsack. In addition, it was proposed to “teach” the control automation to ignore small (up to 10 °) deviations of the apparatus from the specified position. This mode allowed to significantly reduce the consumption of hydrogen peroxide.
The astronauts, who in the future had to use the AMU product, had to undergo a special training course, during which they could not only master control, but also learn to “feel” the device. The need for this has been proven by several test flights under control of a pilot with an insufficient level of training. In such cases, the pilot acted slowly and did not differ in accuracy of control.
In general, the authors of the report highly appreciated both the AMU device itself and the results of its tests. It was recommended to continue work on the project, continue to improve the entire structure and its individual components, and also pay attention to some flight modes. All these measures made it possible to count on the appearance of a workable jetpack for astronauts, fully suitable for solving all the tasks assigned.
NASA and Chance-Vought, as well as a number of related organizations, took into account the tester report and continued work on promising projects. By the middle of the decade, based on the SMU / AMU design, a new device was developed, which was even planned to be tested in open space.
Further work in the field of space jetpacks was crowned with success. In the early eighties, the first MMU spacecraft used in the equipment of the Space Shuttle spacecraft were sent to space. This equipment was actively used in various missions in solving various tasks. Thus, the idea of a jetpack, despite a lot of failures, reached practical application. True, they began to use it not on the Earth, but in space.
Jet pack turns astronaut into human spacecraft. Popular Science. 1962, No.11
Letho S. The Great American Jet Pack: The Quest for the Ultimate Individual Lift Device. Chicago Review Press, 2013
SMU / AMU Test Report: