Techrecipe

How to dispose of used satellites in outer space

There are more than 500,000 satellites and rocket fragments called space fragments around the earth, and they are moving at a speed of 28,000 km/h. Such space debris can cause a great hindrance to future space development, so it is a big task in space development to dispose of the finished satellite without debris. How do we actually destroy satellites?

The number of rocket launches over 60 years from 1960 to 2020 was approximately 5,250. In addition, 42,000 artifacts launched by rockets such as satellites were identified, and more than half of them, or more than 23,000, were launched from the United States.

Most of the cosmic debris flying around the earth are small things like screws and debris between only 5cm and 10cm. However, colliding with such small fragments not only causes the satellite to fail, but also leads to a large amount of new space fragments being generated. There are reports of the first accident in the history of space development in which the US and Russian communication satellites collided with each other in 2009, and it is known that hundreds of space debris occurred in the collision.

Despite such an accident, measures to prevent satellite collisions or abnormal access still do not exist in the form of international laws that countries active in space development such as China, Russia, and the United States and private space companies such as Boeing, SpaceX, and Blue Origin must comply. Does not.

However, in 2007, the UN guidelines for reducing space debris were established. Three methods are described for the satellite processing that has played a role in this guideline: reentry into the atmosphere, orbit the grave, and remove it directly from space. When the satellite re-enters the atmosphere, 80% of its body is burned by high heat. However, the remaining 20% of the burnt falls on Earth. In January 1997, in Oklahoma, USA, a fragment of Delta II, a US launch rocket, re-entered the atmosphere and burned down against the shoulder of a woman who was walking. Fortunately, the woman was safe.

However, such a disaster is very rare. It is thought that it is very dangerous for satellite debris to fall from the sky, but most of the satellites that reenter the atmosphere fall into the sea, which accounts for more than 70% of the planet.

Of course, the point at which the satellites fall is also almost determined, and because it is estimated that the damage from the fall will be the lowest, it is said that there are many cases where the fall point is set in the middle of New Zealand and South America. Therefore, this area is sometimes referred to as a spaceship graveyard or space modum.

The spaceship cemetery is about 10,000 km 2 . There are no routes or routes established in this area. If the satellite can be controlled from the ground, dropping it into the spacecraft graveyard is a low-budget method.

However, there is a high cost of development for the satellite. If parts such as engines and antennas can be recovered, they can be repaired and reused, and there is a possibility that development costs can be reduced. In recent years, a satellite development project that can minimize and reuse satellite consumption caused by re-entry to the atmosphere is underway.

Tomb orbit guidance is to convert the satellite into an orbit dedicated to the satellite that has completed its role. For example, when destroying a geostationary satellite that appears to be stationary when viewed from the earth, it is more common to transition to a grave orbit, 200 to 300 km higher than the original orbit, rather than re-entry the satellite into the atmosphere. However, since this method needs to change the speed and orbit of the satellite, the drawback is that it will cost development or fuel.

So, the process of direct removal from space is being studied recently. The European Space Agency, for example, has announced that ClearSpace One, a mission to launch satellites to remove space debris, will be carried out in 2025. This mission was invented by Swiss startup Clearspace. Dedicated satellites that have launched large space fragments, such as old satellites, are physically captured by robotic arms and re-enter the atmosphere as they are, and each satellite is burned to remove space fragments. In addition, various methods of recovering space debris have been devised, such as a device to recover with a harpoon and a spacecraft to recover by wrapping it with a huge membrane.

However, it is not difficult to imagine that SpaceX has already launched the Starlink program, which launches more than 4,000 satellites, and the number of satellites floating in space will increase in the future. However, space development is required that not only launch satellites, but also consider how to dispose of them.