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Original title: There is a reason for the deorbit of the Starlink satellite in the lowest-level geomagnetic storm
Source: Science and Technology Daily
Recently, the official website of SpaceX announced that due to a geomagnetic storm, as many as 40 of the 49 Starlink satellites launched by the company on February 3 had or will fall into the atmosphere the next day. damaged. The company emphasized that the risk of these deorbiting satellites colliding with other satellites is “zero.”
What is a geomagnetic storm? Luo Bingxian, a researcher at the National Space Science Center of the Chinese Academy of Sciences, explained to a reporter from Science and Technology Daily on the 13th that the solar wind reaches the earth and brings disturbance to the earth’s magnetic field. If the disturbance is severe, it is a geomagnetic storm. In years of high solar activity, geomagnetic storms occur more frequently and at higher levels. The geomagnetic Kp index (grade 0-9) is usually used to characterize the strength of geomagnetic disturbance.
Space weather monitoring shows that on February 4, local time, the batch of Starlink satellites encountered a Kp=5 geomagnetic storm at about 210 kilometers away. “This is the lowest-level geomagnetic storm and has little impact on ordinary satellites in orbit.” Luo Bingxian said.
It is understood that Starlink satellites are deployed in a low-Earth orbit of about 550 kilometers. Why did they fail to “hold” the “shock” of the lowest-level geomagnetic storm this time around the 210-kilometer orbit?
“‘Natural disaster’ and ‘man-made disaster’ are combined.” Lei Jiuhou, a professor at the School of Earth and Space Sciences, University of Science and Technology of China, pointed out that this Starlink satellite event was caused by a geomagnetic storm that caused the earth’s atmosphere to be heated, which increased the resistance of the satellite. rather than being able to raise the track. “The geomagnetic storm may just be the trigger, and the satellite damage may be mainly caused by the satellite’s propulsion strategy and design.” He emphasized.
Luo Bingxian said that the propulsion strategy of the Starlink satellites launched in this batch is to first use a rocket to send the satellite into a predetermined orbit of 210 kilometers, and then use an electric thruster to send the satellite to a higher place. In this regard, Lei Jiuhou said, “The satellite uses electric propulsion on an orbit of 210 kilometers, and the atmospheric resistance and propulsion may be roughly the same. However, the geomagnetic storm causes the atmospheric resistance to increase and the propulsion function to fail. In terms of design, this batch of satellites is designed. Link satellites enter the safe mode and cannot return to the ascending orbit.”
“If the Starlink satellite is sent to a higher orbit from the beginning, even if it encounters a stronger geomagnetic storm, or even a disturbance that is many times stronger, it will not cause the satellite to be quickly damaged.” Lei Jiuhou explained that the atmospheric density increases with the height index. Attenuation, the orbit is lifted by 100 kilometers, and the atmospheric resistance is 1-2 orders of magnitude lower. Therefore, the atmospheric resistance at the orbit altitude of 400-500 kilometers is relatively small. “Generally, the satellite will be pushed to a higher orbit and will not be docked at an altitude of 210 kilometers,” he said.
Luo Bingxian said that after calculations and observations, it was confirmed that the geomagnetic storm caused an increase in atmospheric density (about 10%). In addition, as the satellite descends due to atmospheric drag, it encounters a denser and denser atmosphere. Taken together, it is possible for the atmospheric drag on satellites to increase by 50% in a short period of time.
Regarding the risk of deorbiting Starlink satellites, Luo Bingxian said: “These satellites crash down from about 210 kilometers, and they will burn up after re-entering the atmosphere. There will be no space debris, and no satellite parts will hit the earth’s surface.”
Lei Jiuhou added that the process is estimated to take a few days or more. “The probability of collision with other satellites is relatively low, but it is a bit absolute to say that the risk is ‘zero’. If a satellite is launched in the near future, it is still necessary to avoid the airspace passing through the out-of-control satellite.”
According to reports, the “Starlink” plan was proposed by Elon Musk in 2014, and a total of about 42,000 satellites are planned to be launched into space. As of January 2022, the program has launched 2,000 satellites.
The impact of geomagnetic storms on artificial satellites cannot be underestimated. Lei Jiuhou said that a powerful solar eruption event may lead to a strong geomagnetic storm, which will increase the resistance of satellites, affect satellite and ground communications, and even cause some satellite devices to fail.
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Responsible editor: Li Tong