When it comes to space engines, the first thing that may come to mind is a high-thrust chemical rocket engine, such as the SRB solid booster developed by Orbital ATK in the United States, which has an average thrust of 1200 tons per unit. Such a large thrust can send 24 adult African elephants into space at the same time.
A chemical rocket engine is a power device that uses the chemical energy of the propellant to carry out chemical reactions in the combustion chamber to produce high-temperature and high-pressure gas, and the high-speed air flow is sprayed backwards to produce a counter-effecting thrust. Due to the large thrust and mature technology, chemical rocket engines are widely used in modern space fields such as satellites and manned spacecraft launches.
However, as space exploration missions diversify, the shortcomings of chemical rocket engines are becoming more and more obvious. Due to the relatively heavy chemical fuel and the violent combustion reaction, the working time of the chemical rocket engine is very short, which cannot provide a long-term power supply for the spacecraft, and the economic cost is also very high. In addition, chemical rocket engines have always had safety problems.
In order to solve the power problem of long-term orbital operation of spacecraft and the long-term power supply problem of deep space probes, as early as the 1960s and 1970s, scientists began to develop electric rocket engines that were completely different from chemical rocket engines.
The same is the electric rocket engine, the technical route chosen by the United States is the ion thruster directly accelerated by the electric field, and the electrostatic ion thruster has been developed; The technical route chosen by the Soviet Union was the use of the Hall effect to generate thrust ion thrusters, and the Hall thruster was developed.
Compared with the electrostatic ion thruster, the Hall thruster has a higher thrust density and better comprehensive performance, so after the collapse of the Soviet Union, the United States got a full set of data and soon created the Hall thruster, while the electrostatic ion thruster developed by itself was abandoned.
Hall thrusters work by capturing electrons emitted from the cathode by a cross-electromagnetic field, which rotates around magnetic field lines and drifts in an angular direction within the discharge zone. Angular drift electrons collide with propellant molecules entering the ring discharge chamber through the anode and ionize, forming a plasma in which the ions accelerate axially under the action of the electromagnetic field and spew out at high speed, thereby generating thrust. The electric field generated by the magnetic field accelerates the charged ions, forming a plasma jet that propels the spacecraft forward.
Hall thrusters generally use elements that are easy to ionize and have a relatively large ionic mass as fuel, and mercury was used in the early days, and later abandoned because of toxicity, and then later used xenon, krypton, bismuth, iodine, argon and even metals such as magnesium and zinc. Different elements have different emission spectra at high temperatures, so the colors emitted by Hall thrusters using different fuels are also different.
The thrust generated by the early Hall thrusters was milliniu-level, and the thrust of a single thruster was about twenty or thirty millianns, and such thrust could not even be lifted by a piece of A4 paper (1 milliniu thrust is equal to 0.10204 grams, and the weight of an A4 paper is 4.3659 grams).
However, for spacecraft operating in a space environment, such thrust is enough. For example, the LT-100 Hall thruster used by the Continental Tiangong space station provides only 80 millinius of thrust per engine, which is enough to help the space station maintain its orbital altitude.
Although the thrust of the Hall thruster is not worth mentioning compared to traditional chemical rocket engines, the real strength of it lies in the high specific impulse, high efficiency, and high speed.
Specific impulse is the impulse produced per unit of propellant, which is an important physical parameter used to measure engine efficiency. The higher the engine specific impulse, the greater the speed increase that the propellant can produce under the same conditions, and the higher the engine efficiency.
Because the specific impulse of the Hall thruster can kill the chemical rocket engine in a second, its combustion efficiency is also extremely dusty, and its fuel consumption is less than one-tenth of that of the existing chemical rocket engine. At the same time, because the Hall thruster can work for a long time, it can provide a continuous acceleration to the spacecraft flying in deep space, making it faster and faster, thus reaching a very impressive final speed.
At present, the world's largest thrust Hall thruster is the American X3 Hall thruster, with xenon as the working medium, the maximum thrust reaches 5.4 Niu. The continent's most advanced Hall thruster is the HET-450, which uses Kr as the working medium and has a maximum thrust of 4.6 Nm. Although the thrust of the U.S. X3 is 0.8 ng higher than that of the continental HET-450, it should be noted that the X3 is a three-channel Hall thruster, while the HET-450 is a single-channel Hall thruster. In addition, the HET-450 has a maximum specific punch of up to 5100 seconds when krypton is used as a working medium, while the X3 has a maximum specific punch of only 2650 seconds when using krypton as a working mass.
Taken together, Continental's HET-450 Hall thruster has greater potential and greater efficiency.
From the current point of view, the research and development technology of Hall thrusters is only in the hands of a few space powers, of which China and the United States are the strongest. This black technology, which is indispensable for exploring the universe and the stars and seas, has been highly sought after by countries around the world since its inception.
At present, the only technical bottleneck of hall thrusters may be that its power consumption is too high. The maximum power of the X3 Hall thruster in the United States is 102 kilowatts, while the average power of all eight giant solar panels of the International Space Station totaling 2500 square meters is only 84 to 120 kilowatts. In other words, an X3 Hall thruster can eat almost all of the power generated by the International Space Station, which is a veritable electric tiger.
The mainland's HET-450 Hall thruster has a maximum power of 105 kilowatts, and the solar panel power generation system of the Chinese space station, which provides power, is also facing a situation where the power supply is stretched. Fortunately, the HET-450 Hall thruster installed on the Chinese space station does not need to be in operation all the time.
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