The power of "electric push" is small and lasting, helping mankind to sail the sea of stars

In February 2022, something big happened in the international space community: 40 of the 49 "Starlink" satellites launched by SpaceX have now fallen into the atmosphere and burned. The picture shows that on May 6, 2021, local time, in Kansas, USA, the SpaceX satellite crossed the sky. (People's Vision/Photo)

In February 2022, something happened in the international space community: 40 of the 49 "Starlink" satellites launched by SpaceX have now fallen into the atmosphere and burned down, with a direct loss of about $20 million. The cause of the disaster was that the solar storm that erupted on January 30 affected the Earth, and the geomagnetic storm that followed sharply increased the atmospheric density of the 200 km low Earth orbit, exceeding the lifting capacity of the "Hall Electric Push".

And just before that, in January 2022, the Aerospace Science and Technology Group Fifth Academy 510 announced: high-power "Hall electric propulsion technology" has made a major breakthrough, in the ground test, the single-channel HET-450 with Xe as the working medium maximum power of 105 kilowatts, the maximum thrust of 4.6 Ox, to Kr as the working medium of the highest specific impulse of more than 5100 seconds, marking China in the field of high-power electric propulsion technology, 100 kilowatts of "Hall electric push" performance reached the international advanced level, single-channel technology comparable to the United States multi-channel X3 type " Hall electric thrust "maximum power 102 kW, maximum thrust 5.4 Nm level.

What is the "Hall electric push" involved in these two space incidents?

It is a type of "electric propulsion system" (also known as: electric rocket engine). According to the working mass acceleration method, "electric push" can be divided into three types: electric heat, electromagnetic type and electrostatic type. At present, the more popular ones are "Hall electric push" and "ion electric push" two modes.

The "Hall electric push" in the electromagnetic thruster uses electrical energy to form a plasma in the working medium, and under the action of the external electromagnetic field Lorentz force, it accelerates into a high-temperature high-speed plasma jet to generate thrust. The thrust is small, but the work time is long (the technical term "specific punch"). The technology is simpler, but the specific impulse is lower, and it is mainly used for satellites to raise their orbit and adjust their attitude.

Electrostatic thrusters, also known as "ion thrusts", are higher than "Hall thrusts" and have more advanced performance, and can be used for long-term acceleration of interstellar voyages, but the technology is also more complex.

So, how is "electric thrust" different from the traditional rocket engines often seen in the news?

Chemical energy rocket engine, fuel consumption is extremely large, the work time is very short, when the fuel is used up, the spacecraft can only carry out inertial movement, for interstellar flight, this engine is obviously inadequate.

Take the lunar rocket "Saturn 5" as an example: the first stage is equipped with 2075 tons of liquid oxygen / kerosene propellant, all burned in 2 minutes and 34 seconds, generating 3500 tons of thrust, most of which is used to push the rocket to carry more than 2000 tons of fuel, and its specific impulse is only more than 300 seconds, which is only enough to send 47 tons of payload to the moon. To send very small masses into space, huge and expensive rockets must be used.

The "electric push" is to give the spacecraft a small, continuous force through long-term work, resulting in a small acceleration. According to the common sense of physics, this continuous, slow acceleration, as long as the accumulation time is long enough, can also make the object reach a very high speed.

More ideal aerospace flight, will take the traditional chemical energy rocket, first accelerate the spacecraft to the first, second or third cosmic speed, and then start the "electric push", through months or even years of continuous slow acceleration, so that the spacecraft speed of 30-300 km / s. NASA experts hope that in this way, the time to fly to Mars will be shortened from the current 6-7 months to 39 days, so as to save a lot of fuel, food, water, air, and reduce the damage caused by cosmic ray radiation by astronauts. And in the longer term: reaching a speed of 1‰ of light will allow humans to fly to the outer planets of the solar system and even explore the "Kuiper Belt" farther away.

So far, a number of deep space exploration missions have used "electric thrust", such as: NASA's "Dawn" probe for asteroids; Japan's "Hayabusa" probe for comets; and ESA's "SMART-1" probe for the moon, one of its purposes is to verify the use of "electric push" to send future probes into orbit around Mercury.

The advantage of "electric push" is that it can work for a long time, and its weakness is that the thrust is too small, which in itself constitutes a risk factor. In order to save launch costs, the SpaceX "Starlink" project only sent the satellite into a low-Earth orbit about 200 kilometers above the ground, and then in a few months, it was slowly pushed up to a normal operating orbit of 540 kilometers with "electric thrust". However, in the sudden geomagnetic storm, the rise of atmospheric particles in low-Earth orbit increased the running resistance of the satellite by 50%, and the thrust of "electric thrust" was too small to overcome the thin atmospheric resistance in low orbit, and eventually fell into the atmosphere under the action of gravity and burned. This is the ordeal encountered by "electric push" in the process of developing applications, but how can development be costless? How can you see a rainbow without experiencing wind and rain. Technology is perfected through continuous trial and error, continuous iteration. It is impossible not to make mistakes, of course, it is best to find problems in the experimental stage, low-cost trial and error is king, but sometimes, some problems must be found in the real environment, and it is also a helpless thing, welcome to the real world.

The road to deep space has been opened, the older generation has invented rockets and landed on the moon; our generation will create and witness more miracles, in the next 30-40 years that we can see, human beings will re-land on the moon and colonize Mars; and our children and grandchildren will sail as far as Jupiter, Saturn, and even farther. The little "electric push" has begun to sail the galaxy, which will surely push mankind to the sea of stars.

(The author is a historian and military scholar)

(This article is only the author's personal opinion and does not represent the position of this newspaper)

Mei Yijun