Talking about my country’s first electrically-propelled satellite “Asia-Pacific-6E”: They are all satellites, so what’s new this time?

Since January 23 this year, when my country's first all-electric propulsion satellite "Asia-Pacific 6E" officially started its journey of electric propulsion orbit change, the satellite has played an important communication role in orbit. "Asia-Pacific 6E" uses the Dongfanghong-3E satellite platform, has a design life of 15 years, is equipped with 25 Ku-band transponders and 3 Ka-band transponders, and has a communication capacity of more than 30Gbps. Its successful launch and operation have attracted widespread attention from the media and a large number of space enthusiasts, and the reason is that the satellite adopts an all-electric propulsion design. So, what are the advantages of electric propulsion satellites?

Schematic diagram of the Asia-Pacific 6E satellite (Photo provided by the Fifth Academy of China Aerospace Science and Technology Corporation)

Electric propulsion technology brings high specific impulse

The electric propulsion system uses electrical energy instead of chemical energy as the main power of the satellite. It is currently the most advanced space propulsion technology and has received increasing attention and favor from major space powers. Countries and organizations such as Russia, Europe, the United States, and Japan have long invested electric propulsion systems in the aerospace field, and the use of electric propulsion technology on commercial satellites in Europe and the United States has been popular for many years.

The reason why electric propulsion technology is popular is that it has many advantages. Traditional spacecraft such as satellites mainly use chemical energy rocket engines, relying on fuel and oxidant combustion jets to provide thrust. Since chemical fuels are restricted by factors such as energy density, the engine specific impulse is not high, while the specific impulse of a rocket engine is equivalent to the fuel consumption rate of a car engine, which is a key indicator that restricts the performance of engines and spacecraft. Even large engines that use the highest energy liquid hydrogen fuel and implement optimized designs, such as the US RL10B-2 engine, can only achieve a specific impulse of 465 seconds.

Satellites need to carry a lot of fuel to change orbits, adjust attitudes and maintain orbital altitude. Most of the weight of communication satellites using traditional chemical energy engines is taken up by fuel. The biggest advantage of electric propulsion technology is the high specific impulse brought by the different working principles. Even Hall electric propulsion engines with lower specific impulse can generally achieve a specific impulse of more than 1500 seconds.

High specific impulse means reducing the amount of fuel carried and increasing the ability to carry payloads, which is of great economic significance for spacecraft with extremely high launch costs and also brings huge advantages to satellite design.

Electric push can be divided into two categories

At present, the widely used electric propulsion technology is mainly divided into two categories: ion electric propulsion and Hall electric propulsion. Ion electric propulsion belongs to electrostatic electric propulsion, that is, the working fluid is dissociated into ions and electrons in an electrostatic field, and high-speed ions are ejected to generate thrust. Hall electric propulsion belongs to electromagnetic electric propulsion, which uses the Hall effect to ionize the working fluid and accelerate the ion ejection to generate thrust.

Compared with ion propulsion, Hall propulsion has the advantages of simple technology and structure, but the specific impulse is lower at the same technical level. The United States and the Soviet Union have developed and used electrothermal propulsion, which uses electrical energy to heat the working fluid into steam jet to generate thrust, and the specific impulse is between chemical energy engines and Hall propulsion. Although electrothermal technology is the simplest and the lightest, its specific impulse advantage is not obvious and it is rarely used now.

The main advantage of electric propulsion technology is that the engine has a high specific impulse. Even for electrothermal propulsion, such as the US MR-510 arc propulsion, its specific impulse is about 600 seconds, which is much higher than the specific impulse of chemical energy engines. The old Hall propulsion developed by the Soviet Union/Russia, such as the widely used pps1350g engine, has a specific impulse of 1660 seconds. For example, the old ion propulsion NSTAR used by the US Deep Space 1 probe has a specific impulse of 3100 seconds.

Nowadays, some countries have developed a new generation of electric propulsion engines. Hall electric propulsion can achieve a duration of more than 3,000 seconds, and there are many examples of ion electric propulsion that can reach more than 4,000 seconds. The more advanced concept of magnetoplasma thrusters and variable specific impulse magnetoplasma rockets can even achieve a specific impulse of 6,000 seconds and 12,000 seconds.

According to the Tsiolkovsky formula, the improvement of engine specific impulse can exponentially improve the payload mass ratio. For example, a geostationary communication satellite weighing 4.8 tons and designed for a 15-year lifespan carries 3 tons of chemical fuel and tanks. If ion electric propulsion is used, 810 kilograms of fuel can be saved. If an all-electric propulsion solution is used, the weight of the satellite can be reduced to less than 2 tons.

As my country's first all-electric propulsion satellite, "Asia-Pacific 6E" has a body mass of only about 2 tons. The mass of the same-level communication satellites using traditional chemical energy engines is generally around 5 tons, so the performance advantage brought by electric propulsion is quite obvious.

Asia-Pacific 6E satellite (Photo provided by the Fifth Academy of China Aerospace Science and Technology Corporation)

Broad application prospects

At present, the United States and Russia have the most profound accumulation of electric propulsion technology and the most outstanding engineering practices and commercial applications. Especially on U.S. commercial communications satellites, electric propulsion has become a standard configuration.

European spacecraft manufacturers have also introduced and independently developed various electric propulsion engines and developed their own electric propulsion satellites. In addition to developing traditional large commercial communication satellites, Airbus Space and Defense has also developed OneWeb satellites that use electric propulsion. Japan's electric propulsion technology is also remarkable. Due to Japan's poor competitiveness in the field of commercial communication satellites, its fame is mainly reflected in deep space probes such as Hayabusa.

In 2012, my country launched Shijian-9, the first satellite to achieve electric propulsion in a Chinese satellite, filling the gap in the application of electric propulsion technology in orbit. This satellite enabled my country to break through and master ion electric propulsion and Hall electric propulsion technologies, and is now actively researching and applying the next generation of electric propulsion and various new concept electric propulsion technologies.

With the successive commissioning of communication satellites of platforms such as "Dongfanghong-4E" and "Dongfanghong-3E", as well as the emergence of the Dongfanghong-5 satellite platform, my country's electric propulsion satellites have gradually become mainstream.

As the most advanced and powerful spacecraft propulsion method, electric propulsion technology is an important development direction of space propulsion technology and has gradually become a standard configuration for new-generation satellites. At the same time, electric propulsion technology is not only increasingly used in various commercial communication satellites, but also in deep space exploration, which requires high speed increments, and is also a field where electric propulsion technology can be used.

The United States, represented by the Deep Space 1 probe and the Dawn probe, has seen more and more probes begin to use electric propulsion technology. Even in the field of manned spaceflight, which is extremely demanding in terms of technical reliability and relatively conservative in the application of new technologies, electric propulsion technology has been applied. my country's Tianhe core module is already equipped with an electric propulsion engine, and the power energy module of the lunar gateway space station that the United States plans to build will use a new generation of high-power electric propulsion engines with more advanced performance.

In addition, the United States also plans to use electric propulsion engines as the main engines for future manned Mars exploration complexes.

Of course, electric propulsion technology is not a panacea that can perfectly solve all problems. Although electric propulsion engines have high specific impulse, they are limited by power supply and engine design, and their thrust is far less than that of chemical engines. In situations that require high thrust, rapid response, and rapid orbit change, chemical engines are still very useful. (Author: Zhang Xuesong)