Only 10 years ago, only about a thousand operational satellites could orbit around our planet. The problem is that in a decade, there will be dozens or even hundreds of thousands. Experts have been sounding the alarm for years: Earth‘s orbit is too crowded. There are too many satellites in orbit above our heads. But how many satellites can we actually launch into space before it becomes a problem?
Space analysis above our heads
Jonathan McDowell is an astrophysicist and astronomer at the Harvard-Smithsonian Center for Astrophysics. His usual research area is the super-energetic phenomena of the universe such as black holes in galactic centers. In recent years, however, the researcher has gained visibility for work in a completely different field of space research. In his monthly digital circular called Jonathan’s Space Report (ref.), McDowell keeps track of the increasing number of satellite launches and the increasing number of objects in Earth’s orbit.
The project began with the ambition to “provide pedantic historical documentation of the space era” but it soon became a chronicle of the environmental destruction of space near Earth. In his frequent appearances in the media, McDowell has expressed his opinions on the matter. “It will be like an interstate highway during rush hour in a snowstorm with everyone driving too fast” he said. The situation in orbit according to his opinion will become even more extreme when the satellite mega-constellations of SpaceX, OneWeb, and Amazon Kuiper become a reality.
The first signs that things are getting a bit too tense are already present. McDowell’s British colleague, Hugh Lewis, is another voice that often sounds repeated alarms. On his Twitter page, he describes in detail the increase in so-called conjunction events, situations in which two objects in space approach each other. In a post on January 13th (ref.), Lewis stated that “The total number of conjunctions expected for 2022 was 134% higher than the number for 2020 and 58% higher than 2021, exceeding 4 million”.
Mega-satellite constellations
If we take SpaceX’s Starlink as an example, according to information from the company owned by Elon Musk presented to the Federal Communication Commition (FCC) last December, the autonomous collision prevention system had to execute 26,037 maneuvers to avoid dangerous impacts. This means that each Starlink satellite of the almost 4,000 launched to date has performed an average of 12 avoidance maneuvers during that period.
But the size of the current SpaceX constellation is less than 10% of what the company intends to implement. Within the next 10 years, the number of Starlink satellites in orbit could rise to 42,000. If we add the 4,000 OneWeb satellites, the 3,200 Amazon satellites, and the 13,000 Guowang Chinese system satellites, the situation will soon become very hot.
“Number of evasive maneuvers is increasing nonlinearly. By 2028, the Starlink constellation could have performed a total of one million maneuvers to avoid collisions. We are potentially talking about hundreds, if not thousands, of maneuvers per day” Lewis said. In short, in less than five years, Starlink satellites could run out of fuel due to the enormous number of avoidance maneuvers they will have to perform.
Not just satellites.
Operational satellites, however, are only a part of the problem. According to estimates by the ESA, the space near Earth is filled with around 36,500 pieces of space debris larger than 10 centimeters, approximately one million objects ranging from 1 to 10 cm, and a surprising 130 million fragments smaller than 1 cm. The amount of smaller debris in particular continues to increase as larger objects collide with each other at enormous orbital velocities, producing clouds of fragments.
“Number of minor collisions is already increasing significantly. We are seeing debris from objects that should not actually create any. They were probably hit by something small, even though they continue to function after” said McDowell. While larger fragments over 10 cm are regularly monitored, the trajectories of smaller pieces are mostly unknown, and collisions occur without warning.
However, debris experts are more concerned about encounters between large debris such as dead satellites or used rocket stages. Such a scenario took place on January 27 of this year between the upper stage of a decades-old Russian rocket and a long-defunct Russian satellite. Neither object was able to maneuver to avoid each other, and the impact did not occur by just 6 meters. The incident would have generated thousands of dangerous fragments that would remain in orbit for centuries.
How many satellites are safe in orbit?
So how many satellites can safely be in Earth’s orbit? The answer to this question is not simple. Lewis states that some orbital altitudes are more vulnerable than others. For example, Starlink satellites orbit at 550 kilometers above our heads. Objects at this altitude usually do not clutter space after they cease operations, burning up upon impact with the atmosphere. But this natural ability to purify Earth’s orbit decreases with altitude.
Above 1,000 kilometers, the atmosphere cannot clean up this space. The OneWeb constellation will inhabit this treacherous altitude band, as will Chinese Globalstar. Most mega-constellation operators ensure that their satellites have enough fuel at the end of the mission to deorbit into the Earth’s atmosphere. But the likelihood of technical malfunctions worries experts. In 2012, the ESA was unable to remove a 9-tonne Earth observation satellite from its 772 km orbit around Earth. The spacecraft will continue to orbit the planet for centuries and is now one of the most dangerous debris in orbit.
“In five to ten years, we will have between 20,000 and 100,000 satellites. I am very skeptical that at the maximum number of 100,000 things can be managed safely” McDowell said. “I think we will see regulations to limit the number of satellites at each orbital altitude, as is done for geostationary orbits” he added. The latter are assigned by the International Telecommunication Union. In lower orbits, licenses are instead issued by national entities that have no obligation to coordinate with each other. So whatever happens, it is unlikely that companies will maintain the status quo for long.