2021/1/15, Episode 2 of the Study Session2

(a series article about the discussion of the study session) this article translated by google translation.)

An inconvenient truth?　
Participants were surprised at the video played on the professor Kimura(speaker)'s PC through the online conferencing system. Innumerable points are plotted around the earth. "The red one is the satellite that is no longer in use and the yellow one is in use. It means that it is flying this much as of 1976." The video is displaying objects flying around the earth, advancing the time since 1957. You can see how the number is increasing through time. "You can see that the number is increasing, but you can see that it is even more crowded."
　When Apollo headed to the moon in 1967, It would have gone through an empty wilderness. Will the Artemis project reach the moon as if it were squeezing a PET bottle floating in the ocean? Currently, there are 9568 satellites orbiting the earth as of May 2020. The satellites in operation are known, but in addition to this, debris is orbiting. A satellite that has to be terminated should normally leave its orbit and re-enter the earth and burn out, but if it fails or breaks down, it will remain in orbit as garbage forever. And if they are on the same orbit, they will not hit each other, but if they are on slightly different orbits, they can collide 10 times faster than a bullet. This will result in a number of small pieces. In 2008, US and Russian satellites collided head-on, bringing the two pieces to 600 debris.
　The problem is that there is no way to collect these debris. PET bottles floating on the sea can be physically recovered, aside from the large number and cost issues. However, just as it is hopeless to catch microplastics that melt into the sea, no means have been established to catch debris that orbits.

Story of Orbital
　Prof. Kimura began by explaining what the orbit is. According to the laws of physics, if a satellite flies at a certain altitude at a certain speed, it rotates with the rotation of the earth. When looking up from the ground, it always looks the same place, that is, from the satellite, it is possible to always send radio waves to the same place and provide a service to relay communication. This orbit is called a "geostationary orbit". Below that, for example, the International Space Station (ISS) orbits the Earth in just 90 minutes ... that is, it can only be seen from the ground for a short time.
　It doesn't cost much to launch on a low orbit. Instead, the time spent over Japan is short, so we have to launch a lot. And it will be serviced by many satellites with the same function. A typical example is GPS. We need to just pick up one of the radio waves. However, meteorological satellites and the like must always face Japan, so it must be launched into geostationary orbit. The ISS is orbiting 500km overhead, but it must travel 36,000km overhead to reach geostationary orbit. This is as different as going from Tokyo to Osaka or going around the globe.
　If you try to reach a geostationary orbit, if you fail, the impact will be great, so satellites will cost more to create. But if it is a low orbit, the launch cost will be kept low, you will have to launch a lot. Then, each satellite would have to be made cheaply. So, in low earth orbit, some things will break down even if they do not collide.

Challenges so far
Next, Prof. Kimura introduced the challenges of debris removal so far using a video. A British company is trying to catch it using a net. The net released from the satellite launched for the experiment is once entwined with debris. But it is a very uneasy image whether the control is sufficiently performed, for the flexible material like a net in the environment of zero gravity. We felt very difficult to handle. https://www.youtube.com/watch?v=RvgctXXzIYA
Since the satellite has no place to grab, it is very difficult to catch. So, next, an experiment was conducted to poke it with a stick and drop it on the surface of the earth, but this also seems to have failed. In both cases, in order to catch debris, it is necessary to first get on the same orbit as the debris and set the relative velocity to zero. In order to do so, it is necessary to know the exact position of the debris and launch a new satellite toward it. The orbit of debris has been investigated to some extent by radar network observations from the ground, but it is not enough to actually approach it. For really removing debris, it is necessary for the removal satellite to approach the debris by itself.
Prof. Kimura is working on the development of a camera that autonomously discovers the position of space debris from images and approaches it. He also created a camera for the Hayabusa2, but he says it is a by-product of the debris removal camera. Currently, even if two debris are removed in a year, the increase in debris does not stop. It seems that about five debris should be removed every year. Who will pay for it? While I can't see any answer at all, the amount of garbage continues to increase.

The idea of reversal, End of Life Support
　Under such circumstances, Japanese space venture company Astroscale is trying to find one answer. They are currently experimenting toward their debris removal business.
It is difficult to catch when the satellite becomes terminated services or debris. This service makes the contract to remove the satellite when its service will be terminated, before it is launched. And the satellite installs item that can helps to catch it. This is exactly the same idea of home appliances and PC recycling services.
Currently, Astroscale is targeting only low earth orbit, and it may not be possible to remove debris that has become finer due to a collision. It may be possible to remove only satellites that have finished their services no trouble. But it can be said that reversing the way of thinking is a big step. If in the near future all launch satellites would be required to make this contract by regulation, the business could be fairly certain.
　Participants commented, "How about something like compulsory automobile liability insurance?" However, above all, the technology for collecting garbage has not been established, and there is also no way to know the situation when there was an actual accident. Insurance contracts may be difficult. Prof. Kimura is working every day to at least capture the situation with a camera. There is an urgent need to establish various technologies for capturing satellites. While Astroscale provides experimental and actual services, new technological innovations and cost reductions for removal satellites may be realized. And the technology and ideas might be useful for solving underwater microplastics in the future?

To be continue