Alarming boom in space junk

Space exploration is at an all-time high, resulting in a rapid increase in the number of rockets and satellite launches, augmenting research into the secrets of the universe but also contributing to an alarming boom in space junk. Over the past 15 years, the number of rockets launched per year has nearly tripled, and the number of satellites orbiting the planet has increased tenfold, according to Statista. The amount of space debris (old satellites and spent rocket stages) falling back to Earth has doubled over the past 10 years. A few hundred tonnes of old space junk now vaporises in the atmosphere every year.
The International Telecommunications Union claims that the applications for satellite spectrum have already crossed 1mn. While all of these launches may not be successful, experts are now saying that the number of spacecraft circling Earth may reach around 100,000. According to Space.com, the majority of these launches are attributed to mega constellation projects like SpaceX’s Starlink.
Most modern rockets use fossil fuels which release soot as a byproduct, which could potentially absorb all the heat and eventually lead to an increase in temperature in Earth’s upper atmosphere. This, combined with the increasing levels of aluminium oxides because of the atmospheric burning of satellites may upset the planet’s thermal balance. Both aluminium oxides and soot are known to damage ozone, the naturally occurring gas that keeps Earth safe from ultraviolet radiation.
About 40% of disused satellites burning up in Earth’s atmosphere these days belong to SpaceX’s Starlink megaconstellation, according to Andrew Bacon, the chief technology officer and co-founder of UK-based in-orbit manufacturing firm Space Forge. That amounts to “a minimum of 500kg of incinerated satellite trash a day”, added Bacon, who presented those numbers at the workshop on Protecting Earth and Outer Space from the Disposal of Spacecraft and Debris held at the University of Southampton in the UK last month.
These satellites are mostly made of aluminium, which turns into aluminium oxide when burned at high temperatures, such as those experienced by satellites hurtling through Earth’s atmosphere at orbital speeds. This aluminium ash accumulating at high altitudes worries scientists because of its potential to damage Earth’s protective ozone layer and alter its albedo — the ability to reflect sunlight — which could result in changes in the temperature of the upper atmosphere.
Jonathan McDowell, an astronomer at Harvard and Smithsonian and a leading space debris expert, agreed that Starlink satellites “are dominating” among the clutter incinerated in Earth’s atmosphere. “There is now a Starlink reentry almost every day,” McDowell told Space.com. “Sometimes multiple.”
According to a recent study published in the Geophysical Research Letters, concentrations of aluminium oxides in the mesosphere and stratosphere, the lowermost layers in the troposphere may increase by 650% in the coming decades, potentially causing ozone depletion. Another study, published last year by the US National Oceanic and Atmospheric Administration concluded that the increase in soot-producing rocket launches will have a similar effect on the ozone layer.
Researchers also hinted that the metallic ash, which is currently forming in the stratosphere because of satellite reentries might interfere with Earth’s magnetic field and weaken it over time, allowing more cosmic radiation to reach the planet’s surface.
Currently, the space industry contributes only about 0.1% to the overall damage to the ozone layer caused by humankind. That seems negligible, but researchers caution that, because satellites burn up at altitudes between 60 to 80km, the air pollution their incineration produces will remain in the air for decades, maybe centuries. The same goes for the soot and gases from rocket exhaust.
While research on atmospheric effects of rocket flights and satellite air pollution is still in its early stage, in a statement to Space.com, Munkwan Kim, an associate professor of astronautics at the University of Southampton said that “if we don’t take any action now or in the next five years, it might be too late.”