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 very powerful, 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.

Specific impulse is measured in seconds. An average rocket with a chemical engine can have a specific impulse of up to 400-500 s. Thus, the specific impulse of the shuttle engine is 453 s. (The highest specific impulse achieved so far for a chemical jet engine was 542 s; this engine used an exotic mixture of hydrogen, lithium and fluorine as fuel.) The SMART-1 ion engine had a specific impulse of 1640 s. For nuclear rocket engines this parameter reaches 850 s.

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)

Fusion direct-flow (2500-200,000)

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

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

(In principle, the laser sail and ramjet engine carry no fuel reserve at all, and therefore specific impulse is not an essential characteristic for them; nevertheless, these designs have their own problems.)

Space elevator

One of the serious obstacles to the implementation of many stellar projects is that, due to their enormous size and weight, the ships cannot be built on Earth. Some scientists propose collecting them in outer space, where, thanks to weightlessness, astronauts can easily lift and move incredibly heavy objects. But today critics rightly point to the prohibitive cost of space assembly. For example, the complete assembly of the International Space Station will require about 50 shuttle launches, and its cost, including these flights, is approaching $100 billion. This is the most expensive scientific project in history, but the construction of an interstellar space sailboat or ship with a ram funnel in outer space cost would be many times more expensive.

But, as science fiction writer Robert Heinlein liked to say, if you can rise 160 km above the Earth, you are already halfway to any point in the solar system. This is because with any launch, the first 160 km, when the rocket strives to escape the bonds of gravity, “eat up” the lion’s share of the cost. After this, the ship, one might say, is already able to reach either Pluto or further.

One way to dramatically reduce the cost of flights in the future is to build a space elevator. The idea of ​​climbing to the sky on a rope is not new - take, for example, the fairy tale “Jack and the Beanstalk”; a fairy tale is a fairy tale, but if you take the end of the rope into space, the idea could well come true. In this case, the centrifugal force of the Earth's rotation would be enough to neutralize the force of gravity, and the rope would never fall to the ground. She would magically rise vertically upward and disappear into the clouds.

(Imagine a ball that you spin on a string. The ball does not seem to be affected by gravity; the fact is that the centrifugal force is pushing it away from the center of rotation. In the same way, a very long rope can hang in the air due to the rotation of the Earth.) There is no need to hold the rope; the rotation of the Earth will be enough. Theoretically, a person could climb such a rope and rise straight into space. Sometimes we ask physics students to calculate the tension in such a rope. It is easy to show that even a steel cable cannot withstand such tension; This is why for a long time it was believed that a space elevator could not be realized.

The first scientist to become seriously interested in the problem of the space elevator was the Russian scientist-visionary Konstantin Tsiolkovsky. In 1895, inspired by the Eiffel Tower, he imagined a tower that would rise straight into outer space and connect the Earth with a “star castle” floating in space. It was supposed to be built from the bottom up, starting from the Earth, from where engineers would slowly build a space elevator to the heavens.

In 1957, Russian scientist Yuri Artsutanov proposed a new solution: build a space elevator in reverse order, from top to bottom, starting from space. The author imagined a satellite in geostationary orbit at a distance of 36,000 km from the Earth - from the Earth it would appear motionless; from this satellite it was proposed to lower a cable to Earth and then secure it at the lowest point. 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.

A wider audience was introduced to the space elevator idea later; in 1979, Arthur C. Clarke's novel "The Fountains of Paradise" was published, and in 1982, Robert Heinlein's novel "Friday" was published. But as progress in this direction stalled, it was forgotten.

The situation changed dramatically when chemists invented carbon nanotubes. Interest in them increased sharply after the publication in 1991 of the work of Sumio Iijima from Nippon Electric. (It must be said that the existence of carbon nanotubes has been known since the 1950s, but they were not paid attention to for a long time.) Nanotubes are much stronger, but at the same time much lighter than steel cables. Strictly speaking, their strength even exceeds the level required for a space elevator. 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.

In 1999, a major NASA study was published; it envisioned a space elevator in the form of a ribbon approximately one meter wide and about 47,000 km long, capable of delivering a payload weighing about 15 tons into orbit around the Earth. The implementation of such a project would instantly and completely change the economics of space travel. The cost of delivering cargo into orbit would immediately decrease by 10,000 times; Such a change cannot be called anything other than revolutionary.

Currently, delivering one pound of cargo into low-Earth orbit costs at least $10,000. Thus, each shuttle flight costs approximately $700 million. A space elevator would bring delivery costs down to $1 per pound. Such a radical reduction in the cost of the space program could completely change the way we think about space travel. With a simple push of a button, you could launch an elevator and ascend into outer space for the same price as, say, a plane ticket.

But before we build a space elevator that can easily take us to the skies, we have to overcome very serious obstacles. Currently, the longest carbon nanotube fiber produced in the laboratory does not exceed 15 mm in length. A space elevator would require nanotube cables thousands of kilometers long. Of course, from a scientific point of view this is a purely technical problem, but it needs to be solved, and it can be stubborn and difficult. Nevertheless, many scientists are convinced that it will take us several decades to master the technology for producing long cables from carbon nanotubes.

The second problem is that, due to microscopic disturbances in the structure of carbon nanotubes, obtaining long cables may be problematic at all. Nicola Pugno of the Politecnico di Turin estimates that if just one atom in a carbon nanotube is out of place, the strength of the tube can immediately decrease by 30%. Overall, defects at the atomic level can rob a nanotube cable of 70% of its strength; in this case, the permissible load will be lower than the minimum gigapascals, without which it is impossible to build a space elevator.

In an effort to spur private interest in developing a space elevator, NASA has announced two separate competitions. (The Ansari X-Prize competition with a prize of $10 million was taken as an example. The competition successfully fueled the interest of enterprising investors in creating commercial rockets capable of lifting passengers to the very edge of outer space; the announced prize was received in 2004 by the SpaceShipOne ship.) NASA competitions are called Beam Power Challenge and Tether Challenge.

To win the first one, a team of researchers must create a mechanical device capable of lifting a load weighing at least 25 kg (including its own weight) up a cable (suspended from, say, a crane boom) at a speed of 1 m/s to a height of 50 m. The task may seem simple, but the problem is that this device does not need to use fuel, batteries or an electrical cable. Instead, the robotic lift must be powered by solar panels, solar reflectors, lasers or microwave radiation, i.e., from those energy sources that are convenient to use in space.

To win the Tether Challenge, a team must submit two-meter pieces of tether weighing no more than two grams each; Moreover, such a cable must withstand a load 50% greater than the best example of the previous year. The goal of this competition is to stimulate research into developing ultra-lightweight materials strong enough to be stretched 100,000 km into space. The winners will receive prizes of $150,000, $40,000, and $10,000. (To highlight the challenge, no one was awarded the prize in 2005, the first year of the competition.)

Of course, a working space elevator can dramatically change the space program, but it also has its drawbacks. Thus, the trajectory of satellites in low-Earth orbit is constantly shifting relative to the Earth (because the Earth rotates beneath them). This means that over time, any of the satellites could collide with a space elevator at a speed of 8 km/s; this will be more than enough to break the cable. To prevent a similar catastrophe in the future, it will be necessary either to provide small rockets on each satellite that would allow it to bypass the elevator, or to equip the tether itself with small rockets so that it can move out of the path of the satellites.

In addition, collisions with micrometeorites can become a problem - after all, the space elevator will rise far beyond the Earth's atmosphere, which in most cases protects us from meteors. Since such collisions cannot be predicted, the space elevator will have to be equipped with additional protection and perhaps even fail-safe backup systems. Atmospheric phenomena such as hurricanes, tidal waves and storms can also pose a problem.

Gravity maneuver

There is another way to accelerate an object to a speed close to the speed of light - using the “sling effect”. When sending space probes to other planets, NASA sometimes forces them to maneuver around a neighboring planet in order to take advantage of the “sling effect” to further accelerate the device. This is how NASA saves valuable rocket fuel. This is how Voyager 2 managed to fly to Neptune, whose orbit lies at the very edge of the solar system.

Freeman Dyson, a physicist from Princeton, has put forward an interesting proposal. If someday in the distant future humanity manages to discover two neutron stars in space, revolving around a common center at high speed, then an earthly ship, flying very close to one of these stars, can, due to a gravitational maneuver, gain a speed equal to almost a third speed of light. As a result, the ship would accelerate to near-light speeds due to gravity. Theoretically, this could happen.

Other scientists suggest using our own luminary for this purpose. This method was used, for example, by the crew of the starship Enterprise in the film Star Trek IV: The Voyage Home. Having hijacked a Klingon ship, the crew of the Enterprise sent it along a trajectory close to the Sun to break through the light barrier and return back in time. In the movie When Worlds Collide, the Earth is threatened by an asteroid collision. To escape from the doomed planet, scientists build a giant structure like a roller coaster. Moving down the hill, the rocket ship picks up enormous speed, then turns at the bottom at a small radius - and forward into space.

But in reality, none of these ways to accelerate using gravity will work. (The law of conservation of energy says that a cart on a roller coaster, accelerating on the descent and slowing down on the ascent, ends up at the top at exactly the same speed as at the very beginning - no increase in energy occurs. In the same way, turning around the stationary Sun , we will end up at exactly the same speed with which we started the maneuver.) Dyson's method with two neutron stars could, in principle, work, but only because neutron stars move quickly. A spacecraft using a gravitational maneuver receives an increase in energy due to the movement of a planet or star. If they are motionless, such a maneuver will do nothing.

And Dyson's proposal, although it may work, will do nothing to help today's Earth scientists - after all, in order to visit rapidly rotating neutron stars, you will first need to build a starship.

From the gun to the sky

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 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.

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.

Specific impulse

Specific impulse or specific thrust(English) specific impulse) is an indicator of the efficiency of a rocket engine. Sometimes both terms are used interchangeably, meaning that they are, in fact, the same characteristic. Specific thrust usually used in internal ballistics, while specific impulse- in external ballistics. The dimension of specific impulse is the dimension of speed, in the SI system of units it is meter per second.

Definitions

Specific impulse- characteristic of a jet engine, equal to the ratio of the impulse (amount of motion) it creates to the flow rate (usually mass, but can also be related, for example, to the weight or volume) of fuel. The greater the specific impulse, the less fuel must be spent to obtain a certain amount of movement. Theoretically, the specific impulse is equal to exhaust speed combustion products may actually differ from it. Therefore, specific impulse is also called effective (or equivalent) exhaust velocity.

Specific thrust- characteristic of a jet engine, equal to the ratio of the thrust it creates to the mass fuel consumption. It is measured in meters per second (m/s = N s/kg = kgf s/i.e.) and means, in this dimension, how many seconds a given engine can create a thrust of 1 N, while expending 1 kg fuel (or thrust of 1 kgf, having consumed 1 t.e.m. of fuel). With another interpretation, the specific thrust is equal to the ratio of thrust to weight fuel consumption; in this case it is measured in seconds (s = N s/N = kgf s/kgf). To convert weight specific thrust into mass thrust, it must be multiplied by the acceleration of gravity (approximately equal to 9.81 m/s²).

Approximate calculation formula specific impulse(exhaust velocity) for chemical fuel jet engines looks like:

where T k is the gas temperature in the combustion (decomposition) chamber; p k and p a are the gas pressure in the combustion chamber and at the nozzle exit, respectively; y is the molecular weight of the gas in the combustion chamber; u is a coefficient characterizing the thermophysical properties of the gas in the chamber (usually u ≈ 15). As can be seen from the formula to a first approximation, the higher the temperature of the gas, the lower its molecular weight and the higher the ratio of pressures in the RD chamber to the surrounding space, the higher specific impulse .

Comparison of efficiency of different types of engines

Specific impulse is an important engine parameter characterizing its efficiency. This value is not directly related to the energy efficiency of the fuel and the thrust of the engine; for example, ion engines have very little thrust, but due to their high specific impulse are used as shunting engines in space technology.

• One can note a humorous moment associated with this formula: since it does not have its own name, experts usually call it the “Y-formula” - in the film comedy “Operation “Y” and other adventures of Shurik” students writing the conclusion of the formula on the floor of the corridor deduce exactly this formula

see also

Notes

Wikimedia Foundation.

• 2010.
• Perpendicularity

Ermolino

Specific impulse See what “Specific impulse” is in other dictionaries: - rocket engine, an indicator of the efficiency of a rocket engine; identical to specific thrust (See Specific thrust) ...

Great Soviet Encyclopedia specific thrust impulse of liquid propellant rocket engine (liquid rocket engine chambers)

- specific impulse of the engine (chamber) The ratio of the thrust of the rocket engine (chamber of the rocket engine) to the mass consumption of fuel of the rocket engine (chamber of the rocket engine). Notes 1. The specific thrust impulse of the rocket engine (LPRE chamber) is measured in vacuum and on the ground. 2. The specific thrust impulse of the rocket engine (LPRE chamber) is equal to ...- rocket engine, specific impulse of a rocket engine, the ratio of the thrust of a rocket engine to the second mass flow rate of the working fluid (derivative of the thrust impulse by the consumed mass in a given time interval). Expressed in N(·)s/kg ​​= m/s... Encyclopedia of technology- volumetric specific impulse of the engine (chamber) The ratio of the thrust of the rocket engine (chamber of the rocket engine) to the volumetric fuel consumption of the rocket engine (chamber of the rocket engine). Note The volumetric specific impulse of the liquid propellant engine (LPRE chamber) is also equal to the derivative of the thrust impulse of the liquid propellant engine (LPRE chamber) with respect to... ... Technical Translator's Guide

Impulse (values)- Impulse (lat. impulsus blow, push, impulse): Wiktionary has an article “impulse” ... Wikipedia

Explosion impulse- (a. explosion impulse, blast surge; n. Explosionsimpuls; f. impulsion explosive; i. impulso de la explosion) a quantity characterizing the dynamic. the impact of an explosion, numerically equal to the product of the excess pressure of the explosion products by... ... Geological encyclopedia

ROCKET ENGINE IMPULSE- basic characteristics of a rocket engine. Total (full) I. r. d. product cf. thrust values ​​for the operating time in Ns. Udelny I. r. d. ratio of thrust to second mass flow rate of the working fluid in N*s/kg = m/s; at the design operating mode of the engine... ... Big Encyclopedic Polytechnic Dictionary

Specific impulse- an indicator of the efficiency of a jet engine. Sometimes the synonym “specific thrust” is used for jet engines (the term has other meanings), while specific thrust usually used in internal ballistics, while specific impulse- in external ballistics. The dimension of specific impulse is the dimension of speed, in SI units it is meters per second.

Definitions

Specific impulse- characteristic of a jet engine, equal to the ratio of the impulse (amount of motion) it creates to the flow rate (usually mass, but can also be related, for example, to the weight or volume) of fuel. The greater the specific impulse, the less fuel must be spent to obtain a certain amount of movement. Theoretically, the specific impulse is equal to exhaust speed combustion products may actually differ from it. Therefore, specific impulse is also called effective (or equivalent) exhaust velocity.

Specific thrust- characteristic of a jet engine, equal to the ratio of the thrust it creates to the mass fuel consumption. It is measured in meters per second (m/s = N s/kg = kgf s/i.e. m) and means, in this dimension, how many seconds can this engine create a thrust of 1 N, having spent 1 kg fuel (or thrust of 1 kgf, having spent 1 i.e. m of fuel). With another interpretation, the specific thrust is equal to the ratio of thrust to weight fuel consumption; in this case it is measured in seconds (s = N s/N = kgf s/kgf) - this value can be considered as the time during which the engine can develop a thrust of 1 kgf using a mass of fuel of 1 kg (i.e. e. weighing 1 kgf). To convert weight specific thrust into mass thrust, it must be multiplied by the acceleration of gravity (assumed equal to 9.80665 m/s²).

The approximate formula for calculating the specific impulse (exhaust velocity) for jet engines using chemical fuel looks like [ clarify]

Where T k is the gas temperature in the combustion (decomposition) chamber; p k and p a is the gas pressure in the combustion chamber and at the nozzle exit, respectively; M- molecular weight of the gas in the combustion chamber; u- coefficient characterizing the thermophysical properties of the gas in the chamber (usually u≈ 15 ). As can be seen from the formula to a first approximation, the higher the temperature of the gas, the lower its molecular weight and the higher the ratio of pressures in the RD chamber to the surrounding space, the higher the specific impulse.

Comparison of efficiency of different types of engines

Specific impulse is an important engine parameter that characterizes its efficiency. This value is not directly related to the energy efficiency of the fuel and the thrust of the engine; for example, ion engines have very little thrust, but due to their high specific impulse they are used as maneuvering engines in space technology.

• One can note a humorous moment associated with this formula: since it does not have its own name, experts usually call it the “Y-formula” - in the film comedy “Operation “Y” and other adventures of Shurik”, students writing the conclusion of the formula on the floor of the corridor derive exactly this formula.

see also

Write a review about the article "Specific impulse"

Notes

Used literature and sources

Links

• Tom Benson, / The Beginner's Guide to Aeronautics // Glenn Research Center, NASA (English)
• Z. S. Spakovszky, / 16.Unified: Thermodynamics and Propulsion // MIT, 2006 (English)

An excerpt characterizing Specific Impulse

Rocket engines are one of the pinnacles of technological progress. Materials working at the limit, hundreds of atmospheres, thousands of degrees and hundreds of tons of thrust - this cannot but amaze. But there are many different engines, which ones are the best? Whose engineers will rise to the podium condescendingly explaining to the losers that they lost because of the savagery of the people, the terrible history and the terrible political regime of their country? The time has finally come to answer this question frankly.

Unfortunately, you can't tell just how great the engine is by looking at it. We have to dig into the boring numbers of the characteristics of each engine. But there are many of them, which one should you choose?

More powerful

Despite all their power, solid fuel boosters can hardly be called a symbol of technical progress, because structurally they are just a steel (or composite, but that doesn’t matter) cylinder with fuel. Secondly, these boosters died out along with the shuttle in 2011, undermining the impression of their success. Yes, those who follow the news about the new American super-heavy rocket SLS will tell me that new solid fuel boosters are being developed for it, the thrust of which will already be 1600 tons, but, firstly, this rocket will not fly soon, not earlier than the end of 2018 . And secondly, the concept “let’s take more segments with fuel so that the thrust is even greater” is an extensive development path; if desired, you can put even more segments and get even greater thrust, the limit has not yet been reached, and it is imperceptible that this path led to technical excellence.

The second place in terms of thrust is held by the domestic liquid engine RD-171M - 793 tons.

Four combustion chambers are one engine. And man for scale

It would seem that here he is, our hero. But if this is the best engine, where is its success? Okay, the Energia rocket died under the rubble of the collapsed Soviet Union, and Zenit was finished off by the politics of relations between Russia and Ukraine. But why does the United States buy from us not this wonderful engine, but the half-size RD-180? Why does the RD-180, which began as a “half” of the RD-170, now produce more than half the thrust of the RD-170 - as much as 416 tons? Strange. Unclear.

The third and fourth places in terms of thrust are occupied by engines from rockets that no longer fly. For some reason, the solid propellant UA1207 (714 tons), which stood on Titan IV, and the star of the lunar program, the F-1 engine (679 tons), were not helped to survive to this day by outstanding power indicators. Maybe some other parameter is more important?

More efficient

Specific impulse shows how many seconds the engine can develop 1 Newton of thrust on one kilogram of fuel

Thrust record holders are, at best, in the middle of the list if you sort it by specific impulse, and F-1s with solid rocket boosters end up deep in the tail. It would seem that this is the most important characteristic. But let's look at the leaders of the list. With an indicator of 9620 seconds, the little-known electric propulsion engine HiPEP is in first place.

This is not a microwave fire, but a real rocket engine. True, the microwave is still a very distant relative...

The HiPEP engine was developed for a closed probe project to explore the moons of Jupiter, and work on it was stopped in 2005. During testing, the prototype engine, according to the official NASA report, developed a specific impulse of 9620 seconds, consuming 40 kW of energy.

The second and third places are occupied by the not yet flown electric jet engines VASIMR (5000 seconds) and NEXT (4100 seconds), which showed their characteristics on test benches. And engines that have flown into space (for example, a series of domestic SPD engines from the Fakel Design Bureau) have performance ratings of up to 3000 seconds.

SPD series engines. Who said "cool backlit speakers"?

Why haven't these engines supplanted all others yet? The answer is simple if we look at their other parameters. The thrust of electric jet engines is measured, alas, in grams, and they cannot work at all in the atmosphere. Therefore, it will not be possible to assemble a super-efficient launch vehicle using such engines. And in space they require kilowatts of energy, which not all satellites can afford. Therefore, electric propulsion engines are used mainly only on interplanetary stations and geostationary communication satellites.

Well, okay, the reader will say, let’s discard electric jet engines. Who will hold the record for specific impulse among chemical engines?

With an indicator of 462 seconds, the leaders among chemical engines will be the domestic KVD1 and the American RL-10. And while the KVD1 has flown only six times as part of the Indian GSLV rocket, the RL-10 is a successful and respected upper stage and upper stage engine that has been performing well for many years. In theory, it is possible to assemble a launch vehicle entirely from such engines, but the thrust of one engine of 11 tons means that dozens of them will have to be installed on the first and second stages, and there is no one willing to do this.

Is it possible to combine high thrust and high specific impulse? Chemical engines have run into the laws of our world (well, hydrogen and oxygen do not burn with a specific impulse greater than ~460, physics prohibits it). There were projects for nuclear engines (,), but this has not yet gone further than projects. But, in general, if humanity can combine high thrust with high specific impulse, this will make space more accessible. Are there other indicators by which you can evaluate an engine?

More intense

Combustion chamber RD-180 in the museum. Pay attention to the number of studs holding the combustion chamber cover and the distance between them. You can clearly see how difficult it is to hold back those trying to tear the lid off 258 atmospheres of pressure

Fourth place goes to the Soviet RD-0120 (216 atm), which holds the lead among hydrogen-oxygen engines and flew twice on the Energia launch vehicle. Fifth place is also taken by our engine - RD-264 on the fuel pair asymmetrical dimethylhydrazine/nitrogen tetroxide on the Dnepr launch vehicle, operating at a pressure of 207 atm. And only in sixth place will be the American Space Shuttle RS-25 engine with two hundred and three atmospheres.

More reliable

Large photo on the link

The opposite is also true - an engine that does not have outstanding thrust or specific impulse values, but is reliable, will be popular. The longer the history of using the engine, the greater the statistics, and the more bugs in it they managed to catch from accidents that had already happened. The RD-107/108 engines on the Soyuz trace their origins back to the very engines that launched the first satellite and Gagarin, and, despite modernization, have rather low parameters today. But the highest reliability largely makes up for it.

More accessible

Merlin-1D engine. The exhaust from the gas generator is like on the Atlases sixty years ago, but it’s accessible

TWR

Price

Conclusion

The best rocket engine is one that which you can produce/buy, while he will have thrust in the range you require(not too big or small) and will be effective as much( specific impulse, combustion chamber pressure) what's his price will not become too heavy for you.

And, in conclusion, a small hit parade of engines that I personally consider the best:

RD-170/180/190 family. If you are from Russia or can buy Russian engines and you need powerful engines for the first stage, then the RD-170/180/190 family would be an excellent option. Efficient, with high performance and excellent reliability statistics, these engines are at the forefront of technological progress.

Be-3 and RocketMotorTwo. The engines of private companies involved in suborbital tourism will only be in space for a few minutes, but this does not prevent one from admiring the beauty of the technical solutions used. The BE-3 hydrogen engine, restartable and throttleable over a wide range, with a thrust of up to 50 tons and an original open phase change design, developed by a relatively small team is cool. As for RocketMotorTwo, with all my skepticism towards Branson and SpaceShipTwo, I cannot help but admire the beauty and simplicity of the hybrid engine design with solid fuel and gaseous oxidizer.

F-1 and J-2 In the 1960s these were the most powerful engines in their classes. And one cannot help but love the engines that gave us such beauty:

RD-107/108. Paradoxical? Low parameters? Only 90 tons of thrust? 60 atmospheres in the chamber? Turbopump drive from hydrogen peroxide, which is 70 years out of date? All this does not matter if the engine has the highest reliability, and the cost is close to