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ground-based launching facilities combined to make possible the creation of a powerful carrier-rocket and its extensive utilization for space exploration. An advanced carrier-rocket was used to orbit the Voskhod and Soyuz spacecraft. More complicated four-,stage modifications of the Vostok carrier-rocket injected into orbit — the Luna automatic probes (from Luna-4 to Luna-14), hte Mars-1 probe and the Venera series (from 1to 8).

9. Protection of Astronauts from Radiation

Various means and measures are employed. In the first place

Finally, protective materials are employed in the construction of spaceships.

Soviet spaceships are protected against cosmic radiation. The intensity of such radiation is monitored by modern onboard instrumentation and the information is constantly transmitted to Earth. This makes it possible to keep constant watch on the radiation hazard. Astronauts are also provided with several types of personal dosimeters for research purposes and for monitoring the radiation level. Besides this, biological objects, such as bacteria, living cells, seeds and the like, provided with their own dosimeters may be placed in the ship’s cabin. This makes it possible to check radiation intensity and also the biological effects of radiation.

of cosmic radiation before and during flights and forecasts radiation intensity during different periods of time. Soviet scientists have developed a system for predicting solar flares and for choosing the safest time for a flight in this respect.

10. Propulsion Systems

In order to be an effective military weapon, a guided missile must move at a high speed. It must do so in order to better its chances of intercepting enemy missiles or aircraft when used defensively, and to decrease its chances of being intercepted when used offensively. Missiles are moved in a desired direction and at a desired speed in response to applied forces. These forces

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are known to be produced by the propulsion system (power plant).

One method of obtaining motion in a guided missile is to raise it above the earth’s surface and allow it to fall freely toward the earth. In this case, the motive power is supplied by the gravitational pull of the earth. (A freely falling body accelerates at the rate of approximately 32 feet per second). When dropped within the earth’s atmosphere, it accelerates until such time as its aerodynamic drag balances the gravitational force pulling it

bomb. The control of such a missile is obtained by the movement of aerodynamic surfaces (ailerons and rudders) in response to control signals. These controlled gravity bombs have many limitations; and other sources of motive power are used more extensively in guided missiles.

In order to meet the requirement that some guided missiles move with high speeds, it is necessary to propel them in some other manner. This requirement has been met by the use of jet-propulsion systems. These systems are essentially high-speed power plants and, therefore, they are very suitable for guided missile use. The following section is a discussion of the general principles of jet propulsion, and the types of thermal-iet motors used in guided missiles.1

11. Principles of Jet Propulsion

Jet-propulsion systems are referred to as reaction motors because they operate on the reaction principle. This principle was stated first in Sir Isaac Newton’s third law of motion, which says that for every action there is an equal and opposite reaction. This means that if a man pushing a car exerts a force of 150 pounds on the-car, the car exerts an equal and opposite force of 150 pounds on the man. This principle, which reveals that all changes in motion are the result of applied forces and their reactions, is applicable to all types of motors as well as to jets.

In the propeller-driven aircraft, a certain weight of air passes through the propeller blades in a given amount of time. The action of the propeller increases the velocity of this weight of air in a direction opposite to that of the motion of the aircraft. Some force must act on the air in order to accelerate it rearward because all motion is the result of applied forces. The propeller, driven by the reciprocating engine, supplies the motive force necessary to increase the momentum of the air, and the equal and opposite force, or reaction, is the thrust which moves the aircraft through the air. The air passes around the aircraft, however, and

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is not ejected from within the motor. In jet propulsion, matter is increased in momentum and ejected from within the motor. This fact makes jetpropulsion different from other forms of propulsion.

.rifle;, a nozzle corresponds to the muzzle of the rifle; and the molecules of gases of combustion correspond to the bullets of the rifle. When the rifle is fired, powder is burned and gases are generated at high temperature and pressure. These gases will try to expand in all directions with the same force. But, because the cartridge case prevents expansion in all directions except toward the muzzle, the gases can only escape by pushing the bullet out of the barrel. In the rocket, fuel is burned in the combustion chamber and a large volume of gases is generated at high temperature and pressure. Since there is no bullet -to push out of the way, as in the case of the rifle, these gases escape through the nozzle at an extremely high velocity — about 5,000 feet per second. The reaction (recoil) of the rifle is very short in duration because only a small amount of powder is burned in a very short time. In. the rocket, however, fuel is burned for a much longer time, and the ejection of billions of molecules of gases causes a sustained reaction which is the thrust of the rocket.

This discussion shows that the reaction which propels a jet engine occurs within the engine, and does not occur as the result of the exhaust gases pushing against the air.

12. Classification of Thermal-Jet Motors

Jet motors used in guided missiles depend on heat energy for the force necessary to accelerate the ejected matter, and are called thermal jets (“thermal” meaning “heat”). The heat energy is supplied by alchemical reaction, usually an oxidation (burning) process. In order for this oxidation process to occur, two substances are required — a fuel and an oxidizer, a substance having a large oxygen content.

Thermal jets are classified by the manner in which the oxygen is acquired. The two main classes are: rockets, which carry their own oxidizer as well as fuel; and atmospheric jets, which utilize the oxygen in the atmosphere. The rocket operates independently of its surroundings, while the atmospheric jet is an air-breathing motor, and is limited to operation within the earth’s atmosphere.

We know rockets to consist of three major parts — propellant, combustion chamber, and nozzle. The propellant is the combination of fuel and oxidizer necessary for the chemical reaction which generates the gases that are accelerated to high velocity and pass through the exhaust nozzle. Rockets are

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in most short-range missiles. The liquid-propellant rocket is much more complicated than the solid-propellant. Because it can be cooled effectively and since the flow of propellant can be controlled by valves, the liquid-propellant rocket can operate for longer periods of time, and is applicable to .long-range missiles.

There are two main types of solid-propellant rockets — restricted-burning and unrestricted-burning. In the restrictedburning rocket the propellant is allowed toburn on only one

~surface'at a time. An example of restricted-burning is'the manner in which a cigarette burns. In the unrestricted-burning rocket the

a smokeless or black powder charge, which, in turn, ignites the propellant.

In liquid-propellant rockets, the propellant is fed into the combustion chamber at a controlled rate. The main components of a liquid-propellant rocket are: (1) propellant tanks for storage of both fuel and oxidizer, (2) a propellant feed system for introducing the fuel and oxidizer into the combustion chamber at the desired rate, (3) a combustion chamber, and (4) a nozzle.

Either type may be constructed so that cooling of the combustion chamber is accomplished by circulating the fuel around it.

Atmospheric jets.— Atmospheric jets, take air from the atmosphere, increase its pressure, and feed it into the combustion chamber where it is combined with the fuel. There are two basic methods of increasing the pressure of the incoming air — by using a mechanical compressor, or by utilizing the action of

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a diffuser (a duct of varying cross section designed to convert high-speed airflow into low-speed flow at increased pressure). The three types of atmospheric jets are: turbojets, pulse jets, and ram jets.

Turbojets are considered to be the only type of atmospheric jet which use mechanical compressors. They are particularly suited for use in long-range missiles because of their low specific fuel consumption. In addition, the turbojet is the only atmospheric jet capable of delivering sufficient static thrust (thrust developed with the vehicle not in motion) to enable a missile to take off under its own power. Turbojets are classified according to the type of compressor employed. The two types used are the centrifugal or radial flow, and the axial flow.

The pulse jet, which is sometimes referred to as an intermittent jet, or resojet, is another type of atmospheric thermal jet. It is characterized by its pulsing operation which iscontrolled by a bank of air valves located at the rear of the diffuser. These air valves are spring loaded and are normally open so that air can pass through them to the combustion chamber. When the air enters the combustion chamber it is mixed with fuel and ignited.

combustion chamber overcomes the spring tension and closes the air valves, thus causing the gases to expand out of the tailpipe. The escape of the gases causes the pressure in the combustion chamber to be reduced, and the springs to open the air valves. This allows air jo enter the combustion chamber again, and combustion reoccurs. This cycle is repeated about 50 times per second.

Pulse jets develop approximately 500 pounds of thrust per square foot of area under static conditions, and 780 pounds of thrust at a speed of about 350 miles, per hour. This increase in thrust is due to the increased compression of the air by the diffuser. The maximum speed of pulse jets is about 450 miles per hour; and their specific fuel consumption is roughly one-sixth that of a rocket, but is still higher than the turbojet. Pulse jets are economical, light, simple to construct, noisy, and limited to low speeds. They have a very limited application at present for power plants for test missiles.

The ram jet is a compressorless type of thermal jet, as is the. pulse jet. It is unlike the pulse jet, however, in that it has no valve bank to restrict the flow of gases to one direction. Also, the combustion process in the ram jet is continuous, while that of the pulse jet is intermittent. The ram jet utilizes the action of. the diffuser to create a “pressure barrier” which prevents the gases from escaping in the forward direction. In order for this diffuser action to occur, the ram jet must be boosted to a suitable speed, and consequently it cannot produce static thrust,

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Ram jets are classified according to operating speed — subsonic and supersonic. The basic difference is in the diffuser design. The ram jet has a higher specific fuel consumption than the turbojet, but at supersonic speeds the ratio of engine weight to developed horsepower is far superior to that of any other atmospheric jet. Ram jets are limited in range only by the amount of fuel that they can carry, and can operate up to a theoretical altitude of about 90,000 feet.

Guided missiles must travel at supersonic speeds to reduce effective countermeasures to a minimum, and thermal-jet engines are the only known propulsion devices capable of operating at these speeds. Each of the basic, thermal-jet engines discussed in this section has different operating characteristics. For example, the turbojet has a low specific fuel consumption, the pulse jet is simple and economical to construct, the rocket is not limited to operation within the earth’s atmosphere, and the ram jet jnust be boosted to sufficient speed for operation. Each type of jet engine has definite missile applications because of the widely different requirements of the guiding system, launching system, missile size, speed, and tactical use. No one type is the ideal guided missile propulsion system.

13. Electric Propulsion System

Definite mission studies are being made for all types of electrical' propulsion methods. For the near term and for low thrust missions of durations of theorder of one year, resistojets appear to be most promising. For station-keeping" and attitude control for longer than one year, low powered contact ion sources as well as resistojets have considerable merit. For deep space probes and satellites, ion engines appear to have a clear advantage. However, deep space probes and satellites bring to

specific power blow 50 lb/kw. Actually some positive progress in solar electric power has been made. In the long range program,

extreme distances to Pluto. No single propulsion system is suitable for all missions in our solar system. The three major classes of propulsion systems, chemical, nuclear, and electric, can be shown to be complementary to one another. In general, it can be said that the more distant destination, the greater a velocity increment that must be imparted to the vehicle. Further, since the destination is more distant, the payload .for a given number of

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tasks to be performed will be larger. Finally, the mission study shows that the optimum exhaust velocity for a mission increases with the duration of the mission. These considerations enable us to lay out the mission regimes in which the various propulsion systems are most applicable. The chemical rockets are mainly restricted to short duration relatively low payload missions. The maximum capability of a- pure chemical propulsion system will probably extend to small manned mission to Mars and instrumented capsule landings on Mars and Venus. The intermediate regime of the nuclear rocket will probably enable it to perform larger payload missions to Mars and probe missions to Jupiter and Mercury. The most advanced missions which are also the ultimate missions lie in the regime of the ion rocket. These missions extend all the way out to Pluto for both manned and unmanned flights. As an example of the superiority of the electric propulsion system for the most distant missions to Pluto, a flight to Pluto with a chemical rocket would take approximately 30 years, whereas a flight to Pluto with an electric propulsion rocket would take three years and deliver a larger payload. Thus, all these propulsion devices are needed for the complete exploration of our solar system with electric propulsion carrying

in space exploration, the electric propulsion must be brought along as a complete system so that it will be available when needed.

14. Guidance Systems

The guidance and control component of any guided missile determines the proper flight path to hit the target, and controls the missile so that it follows this determined path. It -accomplishes this “path control” by the processes of (1 ) tracking, in which the positions of the target and the missile are continuously determined; (2) computing, in which the tracking information is used to determine the directions necessary for control; (3) directing, in which the directions are sent to the control units; and (4) steering, which is the process of using the directing signals to move the missile control surfaces by power units. The first three processes of path control are performed by the guidance system, and steering is done by the control system.

In order for these processes to be accomplished, the missile must be in stable flight. That is, the missilemust be capable of developing forces which restore it to straight and level flight when it is disturbed by some outside influence, such as a gust of wind. The control of missile stability is called attitude control,

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and is usually accomplished by an autopilot, which is a part of the control system.

Missile guidance may be divided iqto three phases — launching, midcourse, and terminal. In the launching phase the missile is brought to the proper speed and position so that the midcourse or terminal guidance processes can assume control. The midcourse phase is the major part of the guidance cycle in that here most of the corrections are made for changes in course. The terminal phase, which occurs as the missile approaches the target, requires very high accuracy since the missile may have to make sharp turns and undergo high accelerations, especially against moving targets.

In some missiles a single guidance and control system may be used for all three phases; in others a different guidance system may be used for each phase in conjunction with a single control system. Also, a separate guidance and control system may be required for each phase. A single missile may utilize one of many combinations of basic guidance systems. These basic types of systems are divided into four groups— (1 ) self-contained, (2) beam-rider and-command, (3) baseline, and (4) homing.

15. Steering and Guiding Rockets

Methods for steering large rockets during powered flight all

its thrust must be so aligned as to point to the rocket’s center of gravity. If the thrust force F is out of alignment and passes the center of gravity at a distance L, a turning moment will result that is equal to F X L. A large rocket is steered by shifting this

The force of a rocket’s thrust is always parallel to that of the flow of exhaust gas, but acts in the opposite direction. In a liquidpropellant rocket, the combustion chamber with the exhaust nozzle is usually swiveled to and fro like the outboard motor of a small

Older types of liquid:fuel rockets were often controlled by jet vanes. Jet vanes do not deflect theentire jet but only part of it. The effect of a jet vane can be compared with that of a rudder located in the propeller downwash of a larger inboard motorboat.

Unlike liquid-fuel rockets, solid rockets do not have separate thrust chambers. In a solid rocket the basic airframe serves simultaneously as propellant-storage- container and thrust chamber, and sw.iveling the thrust chamber would not be possible.

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makes it relatively easy to run an automatic checkout, over a radio link, even after launch and while a rocket is in flight.

One particular automatic safety feature deserves special mentioning in connection with automatic checkout. Large, multiengine rockets must be prevented from taking off with inadequate thrust. To accomplish this, the rocket is fixed to the launch platform by a multiple clamp-down mechanism, which is released only after there is clear evidence of adequate rocketengine performance.

The technique of holding rockets down during, thrust build­ up was tried, off and on, during the early years of guided-missile development. It became standard procedure with the advent of

all engines involved in the takeoff. The decision to release the clamp-down mechanism (commonly called the “tail grab”) is made by the launch director on evidence that all engines are “in the green” In modern launch facilities the procedure is often automated; that is, the tail-grab signal is activated automatically when all the engine read-outs are within pre-specified limits. All engines are shut off if this condition is not met within a few seconds.

17. Subsonic Flight

At subsonic speeds, sustained flight by missiles and other heavier-than-air craft is dependent on forces 'produced by .the motion of aerodynamic surfaces through the air. If the surfaces, or airfoils, are. well designed, the streams of air flowing over, under, and around them are smooth, conforming Jo the shapes of the foils. If, in addition, the airfoils are set at the proper angle and if the motion is fast enough, the airflow will support the weight of the aircraft.

Flight forces.— The principal forces acting on a missile in level flight are known to be thrust, drag, weight, and lift. Like any other force, each of these is a vector quantity and not only has a magnitude, or amount, but is associated with a particular direction in space.

Thrust, which is supplied by the propulsion system, is directed along the longitudinal axis of the missile and is the force which

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