Ion rocket is a kind of low power rocket, which has a long life and can continuously provide small thrust for more than 10 years.With the violent impact of atoms, the electrons in the outer layer of atoms fly out of the atomic nucleus and become charged ions.Accelerate these ions to a speed of 150000 kilometers per hour with a high-voltage electric field, and a high-speed ion stream is ejected from the nozzle to propel the rocket forward. First, use a high-power chemical rocket to send the aircraft into orbit around the earth, and then use this small thrust rocket to perform various special tasks.
The ion rocket mainly includes power supply, propellant storage tank, positive ion sourceElectrostatic accelerator(ion gun) electron source.Propellant is made of alkali metals that are easy to ionize. It is better to use cesium. First, it is heated into steam, and then the cesium steam passes through the high-temperature porous tungsten block. When the cesium atom is heated, it will lose the outer electrons, and make itself become a positively charged ion (sometimes it is not necessary to heat the tungsten block, but it can also be ionized by bombarding the cesium atom with electrons);The positive ions are then accelerated by a strong electric field with a large potential difference, and eject the rocket at a speed of 40-100 kilometers per second, so that the rocket can obtain thrust.At present, the electric field of the ion rocket has a potential drop of several thousand volts within a distance of several millimeters. In such a strong electric field, the positively charged ions are pushed out of the nozzle at a high speed due to the principle of electrostatic repulsion.In order not to make electrons in the ionrocket engineWhen the inner product is stored, an equal amount of electrons will be ejected from the electron source near the nozzle and added to the positive ion flow.
The power supply in the ion rocket continuously supplies electrical energy to hot cesium, tungsten and maintain a strong electric field.When electric energy is converted into kinetic energy of ejected ions, a part of energy is lost, so only 50% - 80% of its energy is used.However, this energy utilization rate is the highest compared with other electric rockets.[1]
working principle
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The ion propulsion system is characterized by high injection speed (>25000 m/s), high efficiency, long life and small size.When spacecraft is used for interstellar flight and deep space exploration, spacecraft needs a high speed increment, and the characteristics of ion thruster just meet this demand, which is suitable for undertaking spacecraft propulsion tasks.
Ion thruster is a device system that converts electric energy into kinetic energy of working medium, and then uses mechanical principles to generate reaction force.It is mainly composed of four subsystems: thruster subsystem, propellant supply subsystem, supply and distribution electronic system, and digital control and interface subsystem, as shown in Figure 1.
Figure 1
The basic components of thruster subsystem include discharge chamber, ion optical extraction system and neutralizer, as shown in Figure 2.In the discharge chamber, the electrons emitted by the hollow cathode collide with the propellant atoms to ionize them, enter the discharge chamber, and the ionized ions are accelerated and led out by the ion optical system to generate thrust.After these ions are accelerated to the required exhaust speed, the neutralizer will emit equal amounts of negative electrons into the ion beam to make the spacecraft surface quasi electrically neutral.The propellant supply subsystem is mainly used to store the required propellant and discharge the propellant from the storage tank at a certain flow rate.The function of the power supply and distribution electronic system is toPower converterThe power supply provided shall be converted into the power supply required by the thruster, and the corresponding overload, arc, fault and maloperation protection shall be adopted.The digital interface and control subsystem is used to control the power supply unit of the thruster and make the ion thruster start, ignite, discharge, apply high voltage, draw out beam current, operate stably, shut down, etc. according to certain procedures.
Figure 2
From the working principle of the thruster, the optimization of the thruster structure and the improvement of the working performance are mainly focused on the thruster performance research, plasma characteristics research, the space adaptability research of the thruster performance, the electromagnetic compatibility research of the thruster and spacecraft, the research of the interaction between the thruster plume and spacecraft, and the numerical model of the thruster.Ground tests mainly include: discharge chamber hollow cathode performance test;Thruster startup performance test;Ion optics system performance optimization test;Optimization design test of magnetic field;Flow rate control test;Plasma diagnostic test of thruster discharge chamber;Thruster plume test;Thrust measurement.
classification
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According to different ionization modes of ion thrusters, ion thrusters can be divided into five types: contact ion thrusters, DC discharge ion thrusters, electron bombardment ion thrusters (i.e. Kaufman type), radio frequency thrusters and field emission ion thrusters.Among them, the DC electron bombardment ion thruster has been greatly developed in the United States.The thrust of these thrusters is generated by high-speed jet ion beam.
Advantages and disadvantages
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Advantages of Ion Rocket
1）Ion engineIt is economical and can convert most of the input energy into thrust.
2) An ion engine can work for a long time, so it can make a small aircraft obtain a high speed, although the acceleration process is relatively slow.
3) Ion engines are inherently safe because they do not have to carry fuel that will burn or explode in outer space.
Deficiency of ion rocket
1) LinearParticle acceleratorIt takes a lot of energy to work.At present, the only way to provide such energy for a long time is nuclear fission, so there must be a shipboard reactor.
2) Getting and carrying enough fuel (hydrogen or helium) on long trips is indeed a problem.
3) Because the ion rocket accelerates slowly, it cannot be used as the launch device of spacecraft to send it into Earth orbit.It only applies to spacecraft that have entered space.[2]
Application
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The United States developed the ion rocket in July 1964, and the thrust of the first ion rocket was only 0.3 N.The former Soviet Union also began to conduct experiments in October 1966.This small thrust rocket will play an important role in future space navigation.
China's first test prototype of a new type of ion rocket engine using mercury as propellant passed the ministerial appraisal at the Lanzhou Institute of Physics, Ministry of Space Affairs.Ionsrocket engineIt is a kind of electric rocket and an emerging cutting-edge technology in the world. Its purpose is to use this rocket engine to accurately maintain the position and control the attitude of the satellite after the satellite is sent into space orbit by a high thrust rocket.The rocket engine with mercury as propellant is technically difficult and is still in the test stage internationally.It has small size.High control precision.The advantages of long service life adapt to the development trend of modern long-life satellites.Some famous Chinese rocket engine experts who participated in the appraisal believe that this LF8 ion rocket engine has reached the advanced level of international ion rocket engines of the same type.
