Over the coming years the number of space debris, sometimes referred to “space junk” is set to grow rapidly (Wang, X. & Liu, J. 2019). When satellites reach the end of their life cycle, the large majority of these satellites end up floating around stuck in their space orbits for a long period. These redundant satellites increase the hazard of other satellites colliding with them or a future scenario of a satellite falling back to earth onto populated area. In a space debris incident in 2007, the Chinese weather satellite Fungyun FY-1C was destroyed by a missile test creating space debris, which caused much international criticism (BBC News 2020a). Over time satellites in the low Earth orbit eventually fall back to Earth and burn up, but this is very dependent on factors such as the mass of the satellite and aerodynamics properties (Stack Exchange 2016). Some satellites can take many hundreds of years to fall back to Earth and burn up in the lower atmosphere, which is much richer in oxygen concentrations.
In this article I will only talk about the four main earth space orbits as descriptions can get quite complex, especially if I begin to include orbits known as the Lagrange points which are subdivided into many different parts. The closest orbit to Earth is the low Earth orbit (LEO) that reaches an altitude of 2000km and contains most of the manmade scientific satellites and weather satellites (figure 1). The second is the Medium Earth orbit (MEO) that starts from an altitude of 2000km and goes below the next orbit knows as the geosynchronous orbit (GSO). The GSO matches the Earth’s rotation and is at a height of 35,786km (NASA 2009), so is ideal for satellites that require a fixed obit to match the Earth’s rotation. The last orbit is known as the supersynchronous orbit or the “graveyard orbit” that sits above the GSO and contains redundant man made satellites that will likely sit in their orbit for millions of years (Wikipedia 2020).
Most of the space junk tends to be located in LEO because the majority of satellites tend to use this orbit. The reason for LEO being the first choice for most satellites is the cost factor, as less rocket fuel needs to be used in launches. In addition, over time, the majority of man-made satellites in LEO will eventually fall back to Earth due to the Earth’s gravitational pull and atmospheric drag (Earth Observatory 2020) and crash into the Pacific Ocean location known as the Point Nemo. Most human space travel tends to use LEO such as the International Space Station (ISS), but because of the risk of space junk such as left over rocket part stages and paint chips that have fallen off old rocket parts, the ISS has to adjust its orbit from time to time.
In the higher orbits such as MEO satellites designed for navigation and communication such as the Global Positioning system GPS tend to use this orbit. The GSO is the most highest and tends to be reserved for geostationary satellites that monitor a single location for use in communications or satellites monitoring solar activity (Earth Observatory 2020). In the higher orbits such as MEO and especially GSO, the Earth’s gravitational pull is much less.
The US Space Agency Surveillance network tracks 23,000 objects and 17,000 objects bigger than 17cm according to a Whitehouse report in 2017 (Thune et al. 2017). As redundant satellites increase in number, a space junk cloud is building up fast. The space junk effect is made worse by debris colliding with each other that continue to multiply over the decades and centuries. Even the International Space Station that uses LEO needs to have a boost once a year to lift its orbit and occasional orbit adjustments due to potential space debris. The situation is becoming so serious that even just a few months ago LeoLabs, a California ground based radar company, announced a 1-100 chance of two satellites colliding on 29th Jan 2020 (Spacenews.com 2020a) – luckily this never happened!
Over the next decade, the number of satellites is set to increase hugely in number especially in LEO. One example is with the StarLink project owed by SpaceX, which aims with its megaconstellation of 12,000 satellites to provide low-cost internet to remote locations (StarLink 2020). The U.S. Federal Communications Commission (FCC) authorized StarLink to fly the 12,000 satellites in 2019 (Spacenews.com 2020b). However, Starlink on their main website states their satellites will activate their deorbiting system, if they become inoperable or when they reach the end their life of 1-5 years and burn up in the Earth’s atmosphere (StarLink 2020). Another company called OneWeb also have similar plans to launch a large number of satellites, up to 648, to provide internet services (OneWeb 2020).
In one experiment by the Japanese Space Agency (JAXA) in 2017, to test a possible solution in retrieving space junk in LEO, was included its ISS resupply vessel called Kounotori 6 (JAXA 2020). In this experiment, an Integrated Tether (EDT) used an electrified line 2,300 feet long to knock debris out of their orbit towards the Earth’s atmosphere to burn up. Unfortunately, the Tether encountered release technical errors on its rollout, so had to be released from the Kounotori 6 resupply ship to burn up in atmosphere (Space.com 2017).
In early February 2020, I was lucky enough to interview world-renowned Finnish space scientist Pekka Janhunen (Pekka Janhunen 2012), who is most famous for his Electric Solar Wind Sail invention. In the interview, Pekka touched upon the increasing number of space debris. In 2013, an experimental 1kg satellite called ESTCube-1, using Pekka’s electric solar wind sail concept, was launched to catch solar wind for providing small amounts push trust on a satellite. Unfortunately, the experiment with ESTCube-1 had a technical error in its space orbit, so the concept could not be proven in a real space environment. However, the concept of using an electric solar wind sail to manoeuvre a satellite could be modified for moving defunct satellites into higher space orbits such as the graveyard orbit where they can be monitored safely away from Earth’s gravitational forces.
In a recent exciting development on 25th February, two American satellites docked at a height of 36,000km, in which a satellite (Mission Extension Vehicle-1) grabbed hold of a defunct satellite called Intelsat-901 (BBC News 2020b). The concept was to test how old satellites could be retrieved back or even given a new life by refuelling the old satellite (Northrop Grumman 2020). This experiment was successful and Northrop Grumman plans further experiments for the future.
In a research journal by Annette Toivonen published in 2017, she proposed a Sustainable Future Planning Framework (figure 2) for companies operating in space to focus on creating environmentally oriented sustainable ways. In the space tourism industry, it is forecast to grow by the year 2030 to revenue of $100 billion (Fawkes, S. 2009), so as Annette states in her research it would be prudent to include some kind of sustainable planning for space companies. For companies such as StarLink and OneWeb sustainable planning for their satellites is going to become increasingly important because without it the LEO becomes increasingly congested, which increases the chances of a collision between satellites, space debris or even space craft carrying astronauts.
Therefore, with all these increasing numbers of space satellites orbiting our planet, how do we regulate LSO and GSO orbits? First of all we have the Outer Space Treaty agreed in 1966 by the United Nations Committee on the Peaceful Uses of Outer Space (UN COPUOS), which promotes the peaceful use of outer space, so we don’t have near space objects near the Earth carrying nuclear weapons or weapons of mass destruction, so that’s a great start (UNOOSA 2020). There is also the Inter-Agency Space Debris Committee (IADC) formed in 1993 whose purpose is provide a forum for international governments to agree a consensus with issues of man-made and natural debris in space (IADC 2020). As of 2020, there are 13 Space Agency members at IADC. In 2019, European Space Agency commissioned a consortium, led by Swiss start-up ClearSpace, to lead a mission to remove debris from space (ESA 2020). These agreements are a good basis to lead to an international law one day that would force private space companies and national space agencies to deal with their space junk in a sustainable manner, but we will continue to have a lawless situation in LEO, MEO and geosynchronous orbits. Until an international law is agreed, we unfortunately have a slim chance that a satellite or space debris will one day fall out of the sky and hit a populated area.
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