Over the years, man has sent thousands of satellites into Earth's orbit. However, many of these devices have given up over time and have been discarded. However, this gradually became a problem. Meanwhile several thousand non-functional satellites circle in the orbit of the earth. The problem with it is that they are dangerous, because they sometimes crash together with other still functioning satellites and thus damage these.
The estimates of artificial objects in orbit go up to 600,000 pieces. These objects have a minimum diameter of 1cm and the total weight of all objects is estimated up to 700.000 tons. That's just the rubble and every day there will be more. At Stuff in Space you can follow in real time all artificial objects in earth orbit and their exact positions. Of course all top secret military satellites are excluded. The site is operated by NASA's Orbital Debris Program.
These objects are mostly decommissioned satellites, satellites that have failed, had a malfunction and are no longer functioning. But not only satellites belong to the space junk - also used rocket stages, screws. bolts, solar modules, cables, circuit boards and much more. Everything that makes a satellite flies around up there. Some are smaller parts, but the danger of smaller parts is just as big as with the big ones, because they can develop very quickly into shots that can damage other satellites or even space vehicles without problems.
The International Space Station ISS has already experienced the dangerous nature of space debris several times. The station often had to fly evasive maneuver to avoid colliding with the scrap in orbit. In march 2012 the whole thing was so threatening for the space station that it had no time for an evasive maneuver and the crew had to look for protection in a docked space capsule at the last moment and could only pray that everything would go well.
In recent years there have been considerations on how this space debris could be removed in order to clean up the space up there, to alleviate the danger and to create space for new generations of satellites.
With Airbus (I had written about it here) other european participants and in cooperation with ESA and Space-X, the RemoveDEBRIS Mission startet under the direction of the University of Surrey and the mission was finally launched on 4 April 2018, brought to the ISS with the SpaceX mission CRS-14 and launched into orbit on 20 June 2018.
In September 2018, the mission tested catching system with a net. A subsatellite called DebrisSat-1 (DS-1) was launched and after a while successfully captured with the net.
The second test took place in october 2018, when another sub-satellite called DebrisSub-2 (DS-2) was launched and a 2D camera and 3D LIDAR technology ( i had written about the LIDAR technology here) were used to determine position and speed. This was used to test the visual identification of space debris.
In February 2019, the third test was finally carried out, in which a harpoon was fired at an obsolete solar module and captured. Despite the complexity of the experiment, according to reports from several news agencies it was a success.
In March, this month still, the last test will take place. The responsible persons want to introduce the controlled entry of the RemoveDEBRIS satellite into the earth's atmosphere with the help of a sail. If you would leave the satellite as it is, it would take another 2.5 years until it burns up by itself in the earth orbit. With controlled depreciation, it would take 8 weeks.
It will be hard to get rid of the junk in orbit and certainly we won't be able to get rid of everything, but the first step is now already done.