Recently, the official website of the US Space Exploration Technology Corporation (SpaceX) released a message saying that due to the geomagnetic storm, as many as 40 of the 49 starlink satellites launched by the company on February 3 have fallen into the atmosphere the next day and are about to be damaged. The company stressed that the risk of these deorbited satellites colliding with other satellites is "zero."
Data map: The "Falcon 9" rocket is launched. Xinhua News Agency (Courtesy of the US Space Exploration Technology Corporation)
Luo Bingxian, a researcher at the National Space Science Center of the Chinese Academy of Sciences, told science and technology daily reporters that as of February 12, public information showed that 5 starlink satellites launched in this batch had been confirmed to crash, more than 10 were still in orbit, and the rest of the satellites were still unclear.
"The chances of these deorbited satellites colliding with other satellites are relatively low, but it is a bit absolute to say that the risk is 'zero'." Lei Jiuhou, a professor at the School of Earth and Space Sciences of the University of Science and Technology of China, told science and technology daily reporters that if satellites are launched in the near future, it is still necessary to avoid the airspace passing through the runaway satellites.
At an orbital altitude of about 210 kilometers, the Starlink satellite suffered the lowest level of geomagnetic storms
What is a geomagnetic storm? Luo Bingxian explained that the solar wind arrived at the earth, bringing about a disturbance in the earth's magnetic field, and if the disturbance was violent, it was a geomagnetic storm. In years of solar activity, geomagnetic storms occur more frequently and at higher levels.
"The geomagnetic storms encountered during the destruction of the Starlink satellites are the lowest level of geomagnetic storms." Luo Bingxian told the Science and Technology Daily reporter that the geomagnetic Kp index is usually used to characterize the strength of geomagnetic disturbances, the Kp index is divided into 0 to 9 levels, and Kp=5 indicates that a low-level geomagnetic storm has occurred. Space weather monitoring shows that on February 4, local time, the starlink satellites suffered a geomagnetic storm of Kp=5 at about 210 kilometers.
"Geomagnetic storms of this magnitude, from 1957 to the present, occur on average more than 50 days a year. In high solar years, more than 120 days a year occur. Luo Bingxian said that low-level geomagnetic storms have little impact on ordinary satellites in orbit and are basically controllable.
Kp=9 is a strong geomagnetic storm, the earth's radiation environment, atmospheric environment will undergo drastic changes, the relevant institutions will make corresponding early warning, protection and evasion measures for strong geomagnetic storms.
Talking about the principle and process of this geomagnetic storm, Lei Jiuhou said that with the explosion of the sun's surface, the general earth will be attacked by three rounds: electromagnetic radiation enhancement (flare, about 8 minutes to reach the earth), high-energy particle flow (about 1 hour to reach the earth), and high-speed plasma clouds ejected from the solar corona.
Image source: Visual China
"This Starlink satellite event was caused by the Sun's M-magnitude flare on January 29, accompanied by a moderate-intensity coronal ejection event on January 30." Lei Jiuhou went on to say that after the plasma mass carried by the solar wind arrived near the Earth on February 3, it interacted with the Earth's magnetic field, causing violent disturbances in the magnetosphere and ring current systems in the Earth's space by compressing the top of the Earth's magnetosphere and causing magnetic field reconnection, resulting in geomagnetic storms.
Experts: Geomagnetic storms are only triggers, damage or disasters to "satellite propulsion strategies"
Although Elon Musk and his companies have many innovations and breakthroughs in the field of space exploration, their "Starlink" plan proposed in 2014 has been widely criticized. The project was originally planned to launch 12,000 satellites into space, but the company has been approved to build about 30,000 more, potentially increasing the total number of satellites to 42,000. As of the end of December 2021, the company has reportedly launched nearly 1,900 satellites.
"'Natural disasters' are combined with 'man-made disasters.'" According to Lei Jiuhou's analysis, this starlink satellite event was caused by a geomagnetic storm that caused the earth's atmosphere to be heated, causing the satellite's resistance to increase and unable to ascend to orbit. However, Lei Jiuhou pointed out that the damage to these satellites may be mainly caused by satellite propulsion strategies and satellite design, and the increase in atmospheric resistance is only an inducement.
It is understood that the Starlink satellite operates near an orbit of 500 kilometers, with an inclination angle of about 55 degrees. Why did it fall at an altitude of 210 km this time?
Luo Bingxian pointed out that the propulsion strategy of the Starlink satellites launched in this batch is to first use rockets to send satellites into a predetermined orbit of 210 kilometers, and then use electric thrusters to send satellites to higher places. However, the satellite encountered a geomagnetic storm when it was stuck at 210 kilometers.
"The satellite is in an orbit of 210 kilometers, and at this time, the electric propulsion method is adopted, and the atmospheric resistance and propulsion may be roughly equivalent. However, this geomagnetic storm led to an increase in atmospheric resistance and the failure of the propulsion effect. In addition, in the design of the satellite, it cannot return to the ascending state when it enters safe mode. Lei Jiuhou said.
According to Space Exploration Technologies, a magnetic storm that occurred on Feb. 4 had a serious impact on the satellites, warming the atmosphere in the area where the satellites were located, increasing in density, and exposing the satellites to atmospheric resistance by up to 50 percent more than they had been at previous launches.
Luo Bingxian analyzed the rationality of this data. "After calculations and observations, it was confirmed that this geomagnetic storm caused an increase in atmospheric density. In addition, in the process of the satellite's altitude decline due to atmospheric resistance, it will encounter an increasingly dense atmosphere. Taken together, it is reasonable for the atmospheric resistance of satellites to rise by 50% in a short period of time. He said.
In Lei Jiuhou's view, if the satellite is sent to a higher orbit at 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 destroyed quickly. He added that satellites are generally pushed into higher orbits and will not dock at an altitude of 210 kilometers. Because the atmospheric density decays with the altitude index, the orbit rises by 100 km, the atmospheric resistance is 1-2 orders of magnitude lower, and the atmospheric resistance at the orbital altitude of 400-500 km is relatively small.
"These star-chain deorbited satellites crashed down from about 210 kilometers, and when they re-entered the atmosphere, they would burn up, no space debris would be generated, and no satellite parts would hit the Earth's surface." Luo Bingxian said.
For the risk of deorbiting star-chain satellites, Lei Jiuhou said that these satellites are at a low-orbit altitude of about 210 kilometers, the resistance is relatively large, the life that can be maintained is relatively short, and in the case of no control, it is estimated that ten days or more will basically burn out during the fall. In addition, there are few other satellites in this orbit, so the probability of collision is relatively low.
How much does geomagnetic storm affect artificial satellites?
Lei Jiuhou said that during geomagnetic storms, high-energy particles from the sun settle and (current) Joule heating, when it is easy to see the increase in aurora activity in the polar region, and at the same time cause the temperature of the global upper atmosphere to increase. The atmosphere expands, and the density of the atmosphere near the satellite's orbit increases, making the satellite's resistance increase.
In addition, there are many other effects, such as changes in atmospheric composition, changes in atmospheric circulation, plasmas in the corresponding regions ionized by the atmosphere, and the ionosphere commonly referred to as the ionosphere also undergoes drastic changes, affecting satellite and ground communications.
It is worth emphasizing that during geomagnetic storms, the magnetic field structure that protects the earth will change, and many satellites in higher orbits, such as synchronous satellites, will be exposed to different magnetic fields and plasma environments, thus being directly attacked by high-energy particles, and even causing some satellite devices to fail.
Luo Bingxian told reporters that a powerful solar eruption event could lead to strong geomagnetic storms and affect satellites in orbit or infrastructure on the ground, as in the 20th century, as there were two famous examples.
In 1979, the United States's "Skylab" (Skylab) was in orbit during the high solar activity year, due to the cumulative effect of multiple geomagnetic storms, the expansion of the Earth's atmosphere made the "Skylab" suffer from a sharp increase in atmospheric resistance, the orbit attenuation accelerated, and the "Skylab" fell into the atmosphere faster than expected and burned.
In 1989, a geomagnetic storm overloaded the power grid in quebec, Canada, causing a widespread power outage in the region that lasted 9-12 hours. It is also reported that during almost the same period, thousands of targets in the US space target tracking system needed to be relocated, and the tracking and identification of newly launched flying objects was difficult.
Source: Science and Technology Daily