2.11.2022

A new study has predicted that there is a chance of 6 to 10% that uncontrolled rocket re-entry would cause casualties in the coming decade.

Rockets are extensively used in space explorations to launch various objects like satellites into space. Parts of the rockets are often left in orbit, which can be a potential problem in the future. This is because the leftovers of the rockets, especially when in low enough orbit, can re-enter Earth’s atmosphere in an uncontrolled manner. Low Earth orbit is considered to be an Earth-centred orbit with an altitude of 2,000 kilometres or less.

The uncontrolled re-entry of rockets holds the possibility of colliding with objects on Earth, including humans, aeroplanes or buildings. In fact, there have been past instances of leftover parts of rockets hitting objects on Earth and, in some cases, causing damage. Even though there have been no substantial casualties caused by such collisions, such events can potentially happen in the future.

A study published in Nature Astronomy a few months back assessed the likelihood of casualties posing a risk to human lives by such uncontrolled reentry of rockets. In their research, the team from the University of British Columbia, Canada, predicted that there is a chance of 6 to 10% that such events would cause casualties in the coming decade.

The research also highlighted that the major brunt of such events is expected to be disproportionately borne by the Global South, which indicates that prominent launching states bring risk to the rest of the world. Essentially, the people at greater risk of being affected by rocket debris belong to the countries that are not so active in space exploration.

However, researchers propose that the casualty expectation can be avoided as controlled re-entry of the rocket leftovers is very much possible with technological advancements. Nonetheless, this involves a greater cost for each launching event, which can be a strong reason why it is not usually preferred by governments and companies involved in launching. The researchers argue that governments must come to a collective decision to bring back the rockets' leftovers safely to Earth in a controlled manner. The controlled re-entry implies that a rocket's remnants are programmed to hit either in oceans or areas without human habitats.

“Is it permissible to regard the loss of human life as just a cost of doing business, or is it something that we should seek to protect when we can? And that's the crucial point here: we can protect against this risk," argues lead author of the study, Dr. Michael Byers, professor at the University of British Columbia.

The researchers analysed more than 30 years’ data from a public satellite catalogue and assessed the potential threat to human lives for the next decade while considering the rates of uncontrolled rocket re-entries, their orbits along with human population data. With the help of two different methods, the research revealed that with the current trend of space launches, the chance of casualties in a decade increased to 6 to 10%.

In this context, we can refer to the brouhaha about the Chinese launch and the potential risk of uncontrolled re-entry associated with it. A plethora of reports has appeared in several international media that the long march 5B rocket from the Wenchang Spacecraft Launch site is yet another Chinese project that would create huge space debris and uncontrolled re-entry.

Notably, the reference for such apprehension about Chinese endeavour is what happened in May of 2020, when a portion (18 t core stage) of a Long March 5B rocket re-entered the atmosphere from the orbit in an uncontrolled manner. The rocket was used for launching an unmanned crew capsule used for experimental purposes. Debris from the rocket struck two villages in Ivory Coast with damages to some buildings. One year, in a similar incident, another portion of a Long March 5B rocket re-entered the Earth and, this time, made its way to the Indian Ocean. This was used for launching a part of the Tiangong Space Station into low earth orbit.

China has received heavy criticism for these incidents and is now at centre stage.

However, the new Nature Astronomy research reveals that it is not only China that all the blames are to be placed upon. Other spacefaring states, including the USA, also make similar choices of uncontrolled re-entry. For instance, back in 2016, the second stage of the SpaceX rocket was kept abandoned in its orbit, and just one month later, it made a re-entry via Indonesia, where two fuel tanks the size of a refrigerator hit the ground.

Importantly, the researchers estimated that the USA owns the highest share of global casualty expectation (41% according to their estimate) while China and Europe have a share of 17% expectancy of a global casualty, with Russia having 14% and the rest of the world 11%. This shows that the gross number of space activities with the possibility of uncontrolled rocket re-entry is a greater threat where the USA outnumbers other countries.

The researchers said that the Orbital Debris Mitigation Standard Practices or the ODMSPs are applied to all launches in the USA, which makes it mandatory that all launches are required to have the risk of casualty as a result of uncontrolled re-entry remains below 1 in 10,000. However, according to the researchers, the US Air Force waived the requirements made by ODMSP in 37 out of the 66 launches between 2011 and 2018. Similarly, NASA also waived the requirements seven times between 2008 and 2018.

Commenting on the cumulative risk of such events, Aaron Boley, a co-author of the study, said in a statement, “ Risks have been evaluated on a per-launch basis so far, giving people the sense that the risk is so small that it can safely be ignored. But the cumulative risk is not that small. There have been no reported casualties yet, and no mass casualty event, but do we wait for that moment and then react, particularly when it involves human life, or do we try and get in front of it?”

However, the risks can be avoided with the current technology, where engines can reignite to guide a rocket to remote areas of an ocean. However, this involves extra cost, and there are no multilateral agreements that can mandate companies to make these changes, according to Michael Byers. The researchers argue for a collective decision by governments to stipulate that rockets are guided back to the Earth safely after they are used for launches into the space.

Quelle: NEWS CLICK