Twice in the last two months of 2021, the International Space Station (ISS) had to be steered out of the way of harm. In the first instance, on November 10, the ISS was threatened by a speeding breakup fragment of an anti-satellite test conducted by China in 2007 (Fengyun-1C). And, on December 3, the ISS had to scurry out of the way of another debris—a catalogued and tracked piece of the upper stage of a Pegasus rocket.
According to NASA’s Orbital Debris newsletter, the ISS has so far had to conduct 30 collision avoidance manoeuvres since 1999 .
Today, at a time when there is an explosive growth in the number of satellites proposed to be sent up, the risk of collision with space debris is also increasing exponentially. In the last six-odd decades, mankind has made some 6,200 launches (excluding failures) and put up about 13,100 satellites, of which 8,410 remain in orbit today 2022 and 5,800 of them are still functional .
If you think that it is like too many up there, wait, there is more to come. Going by the stated plans of companies like Google, SpaceX and OneWeb, humans are going to put up more satellites for circling the earth in the next 7-8 years than in the last sixty years.
Even that shouldn’t be a problem. If you take it that the doughnut-shaped region called ‘Low Earth Orbit’ (LEO), where most utility satellites orbit, is a region about 800 kilometres thick, it is a hell of a lot of space. A few tens of thousands of satellites will form a very thin traffic. To compare, if you have 10,000 cars running in the same direction in the region between the Tropic of Cancer and the Tropic of Capricorn, it’s no big deal, right? The chances of collision are practically nil.
However, it is not as simple as that. The scene up there is different. Estimates vary depending on the size of the debris. Categorised majorly into three sizes, the LEO has 36,500 debris pieces greater than 10 cm, 1,000,000 in the range of 1 cm to 10 cm and 130 million measuring between 1 mm to 1 cm.
This number is estimated to rise to — hold your breath—100 billion by 2029.
Just as the Kuiper Belt, a monstrous river of rocks and ice that is orbiting the sun a little beyond Neptune, there is a huge swarm of debris in the LEO, each piece of which is traveling at mind-boggling speeds that vary with where it is. At an altitude of 400 km where the International Space Station roams around—the speed of an object would be about 28,000 km an hour, or 7.6 km a second (if it slows, it will fall into earth’s atmosphere and burn.) At such speeds, even a tiny shard is lethal.
How did we end up with this? Orbiting objects—mostly satellites but also the upper stages of rockets (that have done their job of launching the satellites and are now wandering around the earth without a purpose) -- explode and break into thousands of fragments. This could happen due to a number of reasons.
One common reason is—us. Anti-satellite tests have resulted in a huge number of fragments, each traveling ten times faster than a bullet. On November 15, 2021, Russia intentionally destroyed a defunct, Soviet era satellite, called Cosmos 1408, in order to test an anti-satellite system. Cosmos 1408 broke into over 1,500 pieces. Anti-satellite tests, so far conducted by the US, Russia, China and (once by) India, is a big problem, because they create thousands of pieces of debris. Though the debris created by India's Anti satellite test seems to have all the debris decayed or disintegrated. In April this year, the US announced it would not do any anti-satellite tests anymore, but other countries could continue to do them .
Another reason for the debris is the natural explosion of defunct satellites and upper stages of rockets. Again, this happens because most of these objects still have some residual fuel in their tanks. In the harsh and hostile space environment, the mechanical integrity of their skins ‘fatigues’, leading to fuel leaks and self-ignition. Furthermore, surface coatings also peel off and become part of the debris.
Info-graphic source: ESA
Space debris poses a clear and present danger to satellites – both in orbit today and those set to be launched – and indeed to all space missions in general, as rockets on the launch pad have to wait for the times when no piece of debris would cross their path. According to one estimate, the assets up there are today worth $ 35 billion, again a number which will soar manifold in the next decade. These are, literally, sleeping with the enemy .
Globally, efforts are on at a frenetic pace to find solutions. There are two broadly recognized ways of dealing with space debris. One is through ‘de-orbiting’ satellites or larger objects—bringing them down, so that they plough through the earth’s atmosphere causing enough friction-heat to burn them to dust. The second is to equip satellites with systems that enable them to dodge a piece of debris. However, innovation has no end as industry players are coming up with revolutionary ways of dealing with the issue of space debris.
National Space agencies as well as private players have been investing their time and money to foster innovation in active debris removal. In one such collaborative effort the European Space Agency along with a start-up is set to launch a robotic net into space to catch a specific piece of space debris. Furthermore, in another project the ESA has installed laser stations in some parts of Europe from where they’re planning to target large pieces of space debris to break them to the size of a centimetre. Astroscale, a private sector start-up along with JAXA successfully tested its magnetic debris capture system in orbit .
Dealing with the debris is an emerging branch of space science and business. It is a very happening area. A combination of mitigation and remediation measures is needed to overcome the negative trends which will, with time, evolve into a catastrophic state if no effective action is undertaken. Space debris remediation poses complex technical and legal issues which explains the slow pace of remediation.
 https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv26i1.pdf https://sdup.esoc.esa.int/discosweb/statistics/  https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv26i1.pdf  https://spacenews.com/op-ed-herding-rockets-improved-space-traffic-management-will-accelerate-industry-growth https://astroscale.com/astroscales-elsa-d-successfully-demonstrates-repeated-magnetic-capture/