40 satellites lost due to solar activity

In February last year, about 40 satellites fell due to a magnetic storm of a very common scale. A research group such as a research institute identified it. Based on the observation data of the solar wind, which is the emission of particles, and atmospheric simulations, it was found that the atmospheric resistance that the satellite received at an altitude of 200 km was higher than expected. It turns out that even geomagnetic storms, which have never been seen as a problem, can have fatal effects on satellites.

 On February 3, last year, the US company SpaceX launched 49 small satellites by rocket, but due to an untimely magnetic storm, about 40 satellites failed to reach the target altitude and fell and were lost. The satellites separated from the rocket at an altitude of around 200 kilometers. The atmosphere is difficult to observe at this altitude, but it has been known to increase or decrease its density by up to 25% in the polar regions, and was thought not to affect satellites. This geomagnetic storm was seen as commonplace, but the loss of a large number of satellites drew attention. Based on the satellite’s flight data, the company said the satellite experienced 50% more atmospheric drag than usual.

The research group first examined in detail the observational data of solar activity from probes and other sources. As a result, it was found that two coronal mass ejections occurred about 12 hours apart, and particles reached the Earth, causing two magnetic storms.

 Furthermore, using the simulation model “Gaia” that can calculate the physical processes of the global atmosphere, it was shown that the atmosphere, which was heated by the magnetic storm at that time, expanded from the polar regions to low latitudes, and the density increased by 50% over a wide area. was done. This value was also consistent with SpaceX’s information that the air resistance was 50% higher.

 On the other hand, according to calculations based on an empirical model constructed from past satellite observation data, the density increase at this time was only about 25%. These results show that Gaia’s model is more reproducible than conventional models and can be predicted in real time.

 The intense heating of the atmosphere is said to be “Joule heat,” which occurs when the current in the atmosphere increases due to a magnetic storm and the atmosphere acts as a resistance.

Atmospheric density at an altitude of 200 km calculated by Gaia. The rate of change from before the occurrence of the geomagnetic storm is displayed at 9:00 pm UTC on February 4, 2018, when many satellites were lost. In fact, it changes every moment (provided by the National Institute of Polar Research)

 According to the research group, the density of the atmosphere is actually changing from minute to minute in each region, and it is not surprising that it temporarily reaches 50% to 100%. In this case, the unlucky satellite will fall under the resistance of the atmosphere.

 Tatsuho Kataoka, an associate professor of space physics at the National Institute of Polar Research, said, “Even though the universe is very close to us at an altitude of 200 kilometers, it’s the most mysterious space we don’t understand. It is being researched, but if we do not accurately understand even weak magnetic storms on a daily basis, there will be a large loss for space utilization.In order to judge things that change every moment in real time, observation and research are important.”

 The research group consisted of National Institute of Polar Research, National Institute of Information and Communications Technology (NICT), Seikei University, and Kyushu University. Gaia was developed by Kyushu University, Seikei University, and NICT. The results were published in the journal of space weather and space climate, an international magazine on space weather, on December 23, 2013.

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