Chapter 19 PROBLEM OF TRAFFIC Long-distance interplanetary expeditions and the problem of traction It is well known that today the basis of human space expansion is still liquid fuel rockets. However, available and promising liquid fuel rockets, to

Rod design

Rod design The rod between the front and rear legs is made of a rod with a 3 mm thread (see Fig. 11.10). The original design has a rod length of 132mm center to center. The rod is inserted into holes on the front and back legs of the robot and can be secured using

At the end of 2012, Yang Juan, a professor at the Chinese Academy of Sciences, presented a translation of her article describing a prototype of a unique electromagnetic rocket engine. On paper, it looks much more interesting than the ion engines available today, if only because it does not require the consumption of a working fluid, but this is the main reason for doubts. Just recently, one could only dream of this type of electric rocket engine.

Unlike all other types of rocket engines, here acceleration must be achieved due to directed microwave radiation. The fact that electromagnetic waves create pressure has been known since the time of Maxwell, but the description of the operating principles of EmDrive raises many questions.

Figuratively speaking, such an engine is similar to a microwave oven, to which a resonating cavity in the form of a closed truncated cone has been added. In theory, the emitted microwaves exert pressure on the internal cavity, which is not compensated in only one direction. This is how (according to Ms. Juan) EmDrive develops jet thrust.

Unfortunately, this operating principle of EmDrive raises many doubts and is reminiscent of the sad experience of installing an experimental “propulsion device without jet mass ejection” on the Yubileiny satellite in 2008.

The good news is that EmDrive at least does not belong to the notorious inertioids - a type of device whose operation without interaction with the external environment is impossible. Doubts also apply to most of the stated characteristics. In addition to the fact that, in comparison with the best ion engines, EmDrive promises to provide a longer service life, it is declared to be approximately ten times less mass with the same power and greater (720 mN) thrust. For more information about the history of EmDrive development, see the article by Evgeny Zolotov.

During deep space exploration, energy for EmDrive will most likely be generated by conventional RTG modules. In the inner region of the Solar System (conventionally, up to the main asteroid belt), we can limit ourselves to solar batteries. The battery life of a spacecraft with an electromagnetic engine and solar batteries will be practically limited only by wear and tear, since it has no consumable components on board.

=====Ion and plasma engines =====

Unlike chemical jet engines, ion engines do not produce the sudden and very spectacular release of hot gases, which, in fact, propel traditional rockets. Their thrust is usually measured not in tons, but in grams. If such an engine on Earth is placed on a table, it will not have enough strength to move. But whatever these engines lack in thrust, they more than make up for in runtime; in the vacuum of outer space they can work for years.

A typical ion engine resembles the inside of a television tube - a kinescope. An electric current heats up the filament, which in turn creates a stream of ionized atoms, such as xenon, which are then ejected through the nozzle. Instead of a jet of hot, explosive gas, the ion engine emits a weak but constant stream of ions.

Recently, as part of the HyperV project, funds were raised through Kickstarter to improve the pulsed plasma engine. Almost any gases will work as a working fluid. The engine itself promises to be much cheaper to manufacture and operate than existing analogues.

The main advantage is versatility. By adjusting the ratio of thrust to specific impulse, one engine can be used for different tasks.

Plasma engine is a more powerful version of ionic. An example of such an engine is VASIMR (variable specific impulse magnetoplasma rocket - magnetoplasma rocket with variable specific impulse); It uses a powerful plasma stream to accelerate in space. This engine was developed by astronaut and engineer Franklin Chang-Diaz. The hydrogen in it is heated to temperatures of several million degrees using radio waves and magnetic fields. The very hot plasma is then ejected through the rocket nozzle, generating significant thrust. On Earth, prototypes of such engines have already been created and tested, but none of them have yet flown into space. Some developments propose using solar energy to heat the plasma in the engine. Others propose using the energy of nuclear decay (this, of course, raises additional safety problems - after all, a large amount of nuclear materials will have to be sent into space, and spacecraft are subject to all sorts of accidents).

But neither the ion nor the plasma engine is strong enough to take us to the stars. This will require jet engines based on completely different principles. One of the major problems in developing a starship is the enormous amount of fuel required to travel even to the nearest star, and the long period of time that this journey will require.

Theoretically gigantic solar sail can reach speeds up to half the speed of light. A ship with such a sail would only take about eight years to reach the nearest stars. The mover based on this principle is also good because all its principles are already known. To create it, it is not necessary to discover new physical laws. But other problems arise in full force - both economic and technical. The construction of a sail several hundred kilometers across, as well as the construction of thousands of powerful lasers on the Moon, represent a very serious engineering problem - and the technologies necessary to implement the project may not appear any time soon. (The main problem of an interstellar solar sail is returning. To bring the ship back to Earth, you will have to build a second battery of lasers on the moon near the target star. Or perform a rapid gravitational maneuver near this star, which will help gain speed for the return journey. Then lasers on the Moon sails can be used to slow down so that the ship can safely land on Earth.)

=====Direct-flow fusion engine =====

There is more than enough hydrogen in the universe, so a ship with such an engine could collect hydrogen. e. fuel - along the way, during movement in outer space. Essentially, such an engine would have an inexhaustible and always available source of fuel. The collected hydrogen would then be heated to several million degrees—enough for nuclear fusion—and release energy.

The principle of a ramjet nuclear engine was proposed in 1960 by physicist Robert Bussard; Later, Carl Sagan also popularized it. Bussard calculated that a ramjet fusion engine weighing about 1000 tons could theoretically maintain a constant acceleration of 1 g, i.e. comparable to the effect of earth's gravity. Let's imagine that this acceleration is maintained throughout the year. During this time, the ship will accelerate to 77% of the speed of light; this is already quite enough to seriously consider the prospects of interstellar travel.

The results of these studies turned out to be highly controversial. The missiles turned out to be extremely complex, and tests often ended in failure. Very strong vibrations arose in the nuclear engine, the shells of the fuel assemblies burst, and the rocket fell apart. Another ongoing problem was corrosion due to the burning of hydrogen at high temperatures. Ultimately, in 1972, the Nuclear Missile Program was closed.

=====Pulse nuclear engine =====

Another theoretical possibility is to use a series of nuclear mini-bombs as propulsion. For example, the Orion project involved sequentially releasing small thermonuclear bombs behind the ship so that it could “ride” the shock wave from their explosions. Theoretically, such a system could accelerate a spacecraft to speeds close to the speed of light.

In the late 1950s and 1960s. Careful calculations were carried out for an interstellar ship based on this principle. According to estimates, he could fly to Pluto and back in a year, reaching a speed of 10% of the speed of light. But even at this speed, it would take 44 years to fly to the nearest star. Scientists considered options when a space ark with such a propulsion device would fly in space for several centuries; generations would change in the crew, and many would have to live their entire lives in this moving little world so that their descendants could reach nearby stars.

In 1959, General Atomics released a report in which it assessed the size of the Orion-class spacecraft. The largest version, called “super-Orion” in the report, was supposed to weigh 8 million tons, have a diameter of 400 m and ride on the shock wave of more than a thousand hydrogen bombs.

The main problem associated with this project is the possibility of contamination of the launch area with nuclear fallout. Dyson estimates that nuclear fallout from each launch could cause fatal cancer in up to ten people. In addition, the electromagnetic pulse from the explosion is so large that it would certainly cause a lot of short circuits in nearby electrical systems.

The rocket ship of the Daedalus project turned out to be so huge that it would have to be built in outer space. It was supposed to weigh 54,000 tons (almost all the weight was rocket fuel) and could accelerate to 7.1% of the speed of light, carrying a payload weighing 450 tons. Unlike the Orion project, designed to use tiny atomic bombs, The Daedalus project involved the use of miniature hydrogen bombs with a mixture of deuterium and helium-3 and an ignition system using electron beams. But huge technical problems and concerns about nuclear propulsion meant that the Daedalus project was also shelved indefinitely.

The Longshot project looked more realistic and was based on the use of a laser-fusion engine. The star chosen was Alpha Centauri B. The flight time increased to a century, and the mission did not involve return. Unlike the Daedalus project, Longshot relied primarily on existing rather than emerging technologies. At the last stage, it became obvious that the ship would need about 264 tons of a mixture of helium-3 and deuterium, which could not be obtained in such quantities at a reasonable cost.

Space elevator

The problem is that the cable for a space elevator would have to withstand a tension of about 60-100 GPa. Steel breaks at about 2 GPa of tension, which defeats the purpose of the idea. According to scientists, carbon nanotube fiber should withstand pressure of 120 GPa, which is noticeably higher than the required minimum. After this discovery, attempts to create a space elevator resumed with renewed vigor.

=====From a gun to the skies =====

Another clever way to launch a ship into space and accelerate it to fantastic speeds is to shoot it from a rail-mounted electromagnetic “gun”, which was described in the works of Arthur Clarke and other science fiction authors. The project is currently being seriously considered as a possible part of the Star Wars missile defense shield.

The method is to use electromagnetism energy to accelerate the rocket to high speeds instead of rocket fuel or gunpowder.

In its simplest form, a rail gun consists of two parallel wires or rails; the missile, or missile, "sits" on both rails, forming a U-shaped configuration. Michael Faraday also knew that a force acts on a frame with an electric current in a magnetic field. (Generally speaking, all electric motors operate on this principle.) If you pass an electric current of millions of amperes through the rails and the projectile, an extremely powerful magnetic field will arise around the entire system, which, in turn, will drive the projectile along the rails, accelerating it to enormous speed and will be thrown out into space from the end of the rail system.

During testing, electromagnetic rail guns successfully fired metal objects at enormous speeds, accelerating them over a very short distance. What's great is that, in theory, a regular rail gun is capable of firing a metal projectile at a speed of 8 km/s; this is enough to put it into low-Earth orbit. In principle, NASA's entire rocket fleet could be replaced with rail guns that would fire payloads directly from the surface of the Earth into orbit.

The rail gun has significant advantages over chemical guns and missiles. When you fire a gun, the maximum speed at which the expanding gases can push the bullet out of the barrel is limited by the speed of the shock wave. Jules Berne, in the classic novel From the Earth to the Moon, fired a projectile carrying astronauts to the Moon using gunpowder, but in fact it is not difficult to calculate that the maximum speed that a gunpowder charge can impart to a projectile is many times less than the speed required to fly to the Moon . A rail gun does not use the explosive expansion of gases and therefore does not depend in any way on the speed of propagation of the shock wave.

But the rail gun has its own problems. Objects on it accelerate so quickly that they tend to be flattened due to collision... with air. The payload is severely deformed when it is fired from the muzzle of the rail gun, because when the projectile hits the air, it is as if it had hit a brick wall. In addition, during acceleration the projectile experiences enormous acceleration, which in itself can greatly deform the load. The rails must be replaced regularly, since the projectile also deforms them when moving. Moreover, overloads in a rail gun are fatal to people; human bones simply cannot withstand such acceleration and will collapse.

One solution is to install a rail gun on the moon. There, outside the Earth's atmosphere, the projectile will be able to accelerate unhindered in the vacuum of outer space. But even on the Moon, the projectile will experience enormous overloads during acceleration, which can damage and deform the payload. In a sense, a rail gun is the opposite of a laser sail, which gains speed gradually over time. The limitations of a rail gun are determined precisely by the fact that it transfers enormous energy to the body over a short distance and in a short time.

A rail gun capable of firing a vehicle towards the nearest stars would be a very expensive construction. Thus, one of the projects involves the construction in outer space of a rail gun with a length of two-thirds of the distance from the Earth to the Sun. This gun would store solar energy and then expend it all at once, accelerating a ten-ton payload to a speed equal to a third of the speed of light. In this case, the “projectile” will experience an overload of 5000 g. Of course, only the most resilient robot ships will be able to “survive” such a launch.

=====Specific impulse and engine efficiency =====

When it comes to comparing the efficiency of different types of engines, engineers usually talk about specific impulse. Specific impulse is defined as the change in impulse per unit mass of fuel consumed. Thus, the more efficient the engine, the less fuel is required to launch the rocket into space. Impulse, in turn, is the result of the action of a force over a certain time. Chemical rockets, although they have very high thrust, operate for only a few minutes and therefore have a very low specific impulse. Ion engines, capable of operating for years, can have high specific impulse with very low thrust.

A rocket capable of reaching the speed of light would have the highest possible specific impulse. Its specific impulse would be about 30 million. Below is a table of specific impulses characteristic of various types of jet engines.

Motor type(Specific impulse)

Solid fuel(250)

Liquid(450)

Ionic(3000)

Plasma VASIMR (1000-30,000)

Atomic(800-1000)

Thermonuclear direct-flow (2500-200,000)

Nuclear pulse(10,000-1,000,000)

On antimatter (1,000,000-10,000,000)

One of the main indicators of the efficiency of a rocket engine is specific thrust, or specific impulse. These synonymous terms mean the same thing, but in different formulations.

Specific thrust is the engine thrust divided by the second weight consumption of the working fluid

where the second flow rate is taken, naturally, under conditions given to the Earth's surface.

The specific impulse is understood as the impulse created by the engine per kilogram of the weight of the discarded working fluid. The difference between specific thrust and specific impulse is only that the first is measured in , and the second - in . Both in size and in dimension, nothing changes. Specific thrust and specific impulse are measured in seconds, and terminological adherence is determined only by established traditions. In some groups, out of habit, they use one term, in others, another. In conversational communication, the unit “second” is usually ignored and replaced with the word “unit”. For example, you can hear: “The engine provides 315 units of specific thrust...” or - “This allows you to increase the specific impulse by three units...”. According to expression (1.5)

Specific thrust, as we see, is determined primarily by the exhaust velocity W a, which depends not only on the properties of the fuel, but also on the design features of the engine. Depending on the design of the engine, the conditions of fuel combustion and the flow of combustion products change. In all types of rocket engines, there is a mass consumption for the internal needs of the engine, as they say, for service purposes. For example, the consumption of hydrogen peroxide decomposition products for turbine operation and the consumption of compressed gas when venting from containers. Naturally, when calculating the specific thrust, this necessary but unproductive mass consumption must be summed up with the main one, which somewhat reduces the value of the specific thrust.

The higher the specific thrust, the more advanced the engine is, and each additional unit of specific thrust is highly valued, especially for the main propulsion systems of space rockets.

Specific thrust depends on flight altitude. Therefore, when they want to characterize the efficiency of an engine, they usually call it empty specific thrust

Where W e- effective exhaust velocity in m/sec.

The value of the void specific thrust of modern rocket engines for all existing types of chemical rocket fuels lies in the range from 250 to 460 units.

The State Standard (GOST 17655-72, Liquid rocket engines. Terms and definitions) has now introduced another parameter for liquid rocket engines that characterizes efficiency, namely, specific thrust impulse of liquid propellant rocket engine- Jy. It differs from specific impulse in that thrust refers not to weight, but to mass flow per second

and is not measured in sec, and in n s/kg, i.e. in m/s. The specific thrust impulse of a liquid propellant rocket engine is the already familiar effective exhaust velocity, the use of which now extends to the atmospheric portion of the flight. The specific thrust impulse of a rocket engine is related to the specific thrust by an obvious relationship:

and in numerical terms:

The verbosity of the term provokes its abbreviation, and the specific thrust impulse of a rocket engine is often called specific impulse, which entails a semantic distortion. However, the tenfold numerical difference helps. If in the technical documentation for a chemical fuel engine the specific impulse is indicated in hundreds of units, then we are really talking about a specific impulse measured in sec; if it is in thousands, there is no doubt that this is the specific thrust impulse of the rocket engine, expressed in m/s.