The Low Earth orbit (LEO for friends) is the region of space between sea level and an altitude of about 2000 km. If you happen to be passing by, you will come across many communication satellites, such as those of the Iridium satellite constellation which provide global coverage for satellite phones, including the next generation of Android smartphones, the International Space Station (ISS for chums), observation satellites, spy satellites, the Hubble telescope, the list goes on. Click on this thumbnail for a scaled and detailed infographic of the regions of space surrounding our beloved planet.
The LEO zone is the blue segment closest to Earth. This region is slowly starting to become cluttered with debris, because, just like we do with our junk on solid ground, when a satellite has breathed its last, we leave it floating around.
In this 2010 United Nations document, two major sources of debris are identified: accidental or intentional break-ups of orbital objects and those deliberately released during rocket launches. That can include dead spacecrafts, defunct satellites, lost equipment from various manned space missions, rocket boosters, specks of paint, weapons and satellites destroyed by those weapons. These debris can collide and produce smaller pieces. (Have you seen the movie Gravity with Sandra Bullock and George Clooney? Bad, don’t watch.) To date, we can count more than 25,000 objects larger than 10 cm, 500,000 between 1 and 10 cm and 100 million particles larger than 1 mm for 9,000 metric tonnes (9 × 106 kg) of detritus — you’ll find all the details on this fantastic NASA FAQ sheet.
The Kessler syndrome
So what’s the big deal? Space is vast, isn’t it? It turns out that some people have given serious thought to this question. According to NASA debris scientist Donald J. Kessler, above a certain density threshold, collisions between debris could cause a domino effect, or chain reaction, where an entire region of space would quickly become inaccessible due to the excessively high risk of colliding with a particle. To illustrate, a 1 kg object travelling at 10 km/s could break up a 1000 kg spacecraft.
It seems that problems have already started to surface. Starlink by SpaceX is an ambitious project aimed at providing high-speed internet almost anywhere on Earth (more on that megalomania in the 2nd part), including the deployment of 12,000 small satellites in LEO, with a possible extension to a staggering 42,000 satellites, 5,000 of which are already in use. According to this space.com article, Starlink has performed 25,000 collision-avoidance manoeuvres in the 6-month period from December 2022 to May 2023, a total of 50,000 such manoeuvres since the first launch in 2019 and possibly 1 million manoeuvres by 2028. The number of manoeuvres is said to be growing exponentially, doubling every six months. Sounds like a chain reaction to me.
Of course, mitigation measures and technological fixes are proposed such as robotic garbage collection or propelling dead satellites into special junk orbits, but they are all expensive, and the situation could spiral out of control. I have to admit, I don’t always clean up my mess and I’m a 60-year-old grown-up. But humankind? She behaves like a sloppy dirty toddler.