This is part 2 of my blog on Space-junk. Please read part 1 before you read this part, to have a better understanding and flow of thought.
Welcome back! In this part, we will explore a few more aspects of this problem and then try to understand some of the major solutions proposed to tackle this issue. Gear up folks... here we go.
3) Variation of the threat in different earth orbits (EOs):-
The greatest threat for space debris collisions is for satellites and other functional orbiters in the Low Earth Orbit (LEO), which is located at less than 2000km above the Earth’s surface. In this orbit, the density of man-made objects is the highest, thus being the most hazardous region. A very interesting concept was proposed by NASA scientist, Donald J. Kessler in 1978 regarding the critical density limit for debris in the LEO. He argued that if the density of objects in the LEO went beyond this critical tipping point, it could cause a very long cascading effect, or a chain reaction in which a collision creates more debris parts which in turn create more collisions and so on, eventually rendering the whole orbit unusable. This collisional cascading was named the “Kessler Syndrome” in his honour.
The Geosynchronous Earth Orbit (GEO) offers an intermediary level of threat, as it harbours fewer satellites, and in terms of hazard measurement, less Kinetic Energy than the LEO, but more than the High Earth Orbit (HEO).
The least amount of space debris is found in the High Earth Orbit (HEO), which is situated above the Geosynchronous Earth Orbit (GEO), at a height of 35,786+ km from sea level. Here, the atmospheric thickness and gravitational attraction of the Earth is substantially low, thus delaying orbital decay. Hence, if debris is caught in an orbit at this height, it will take millennia for it to naturally de-orbit!
4) Excess cost incurred by space agencies for deciding trajectories which avoid space debris:
According to a study conducted by the Organisation for Economic Co-operation and Development (OECD) using data provided by the European Space Agency (ESA), for orbit missions in the Geostationary Earth Orbit (GEO), 5-10% of the total mission cost is used only for the fuel and planning of the special trajectories to stay clear of the debris (This itself can amount to millions of dollars!). For the missions in the LEO, this figure may be as high as 15%!
This cost includes modifying the design of the satellite, surveillance and tracking of potential space debris colliders, the excess fuel needed for debris avoidance manoeuvres etc. These are totally unnecessary costs, and create only an additional financial burden on the space agency launching the satellite, and subsequently on world governments! This is aptly summarised in OECD’s report, which states, “Space debris protection and mitigation measures are already costly to satellite operators, but the main risks and costs lie in the future, if the generation of debris spins out of control and renders certain orbits unusable for human activities.”
5) Different approaches to mitigate this problem:-
- The most important problem in conquering the space-junk problem, as stated earlier, is not a technical or engineering problem. It is more of a “lack of incentive” issue. This is because, only clearing the debris on a temporary basis via nets, harpoons etc. will not help, as it will only motivate the space agencies to launch even more satellites. This is aptly stated by Mr. Akhil Rao, assistant professor of economics at Middlebury College and the lead author of a relevant paper, “This is an incentive problem more than an engineering problem. What’s key is getting the incentives right.” So clearing debris manually via nets, harpoons or huge robot arms is ineffectual.
2. A plausible-at-first-sight solution seems to be detonating and breaking the debris into smaller pieces, to minimize risk of collisions with large objects. However, this will result in increased difficulty for tracking the hazards, and further aggravate the problem, as mentioned in the Kessler Syndrome above. So, even this approach is deemed to fail miserably.
3. Another approach to tackle this problem is the use of “graveyard orbits” and “keep out zones” for active satellites. The graveyard orbits have already been partially implemented, and space agencies across the globe have clear guidelines on how to decommission, de-orbit a satellite as it nears its end of life, and re-orbit it in the “graveyard orbit”. This can be understood as a sort of permanent parking place for satellites that have finished their job. The caveat is, operators of the satellite need to exactly identify when a satellite is almost nearing its end, and start the de-orbiting process just before the fuel finishes or control over the satellite is compromised. If this is optimised and regulated well enough, it could be a decent solution.
4. The final approach, which even gets the incentives right, and thus is the most promising choice currently, is introducing the concept of “orbital use fees” – a tax on orbiting satellites. According to a PNAS research article published in June 2020, authored by Mr. Akhil Rao and his colleagues, these can be straight up standardized costs that need to be paid upon launch, or they could be orbit-specific too; as different orbits harbour differing levels of collision risk, as explained above. The fees per satellite would have to increase over time, to reflect the financial as well as ecological value of “cleaner orbits”. This would force the satellite operators on rethinking the absolute necessity of their launch, as well as force them to “weigh the expected lifetime value of their satellites against the cost to industry of putting another satellite into orbit and creating additional risk” as suggested in the article.
- For this approach to work efficiently, however, the researchers found, all countries launching satellites would need to participate—that's about a dozen having full-fledged independent launch capabilities (NASA, ISRO, ESA etc.), and more than 30 that only own satellites. In addition, each country would need to charge the same fee per unit of collision risk for each satellite that goes into orbit, although each country could collect revenue separately.
- This approach also brings in more benefits, such as quadrupling the overall value of the satellite industry by 2040. This extra revenue could help create more employment in this sector, and provide an additional financial resource to the space agencies, thus encouraging them to plan and execute more and more interplanetary missions!
Whichever approach is adopted by the space agencies and governments around the world, one thing is for certain! Humanity’s quest to expand its reach into the cosmos and become an interplanetary species is everlasting. Right from the ancient past, we have always found solutions to problems, and come out on top as a species. From discovering how controlled fire can keep wild animals in check, to inventing the wheel and revolutionising long distance transport; all these happened as a result of the human creativity, grit and intelligence! All we have to do now is to acknowledge space debris as a global threat and actively start working on it! If we get the incentives right, we can be sure that we will find many new and better approaches, work upon them and eventually start another paradigm shift, which can turn out to be the most important one in the distant future, of finally breaking our shackles of being limited to just one planet, and become a space-faring civilisation !