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Avoiding Low-Earth Orbit Collisions – the Clock Is Ticking

There was a recent dispute between OneWeb and SpaceX regarding the possibility of a collision between two of their low-Earth orbit (LEO) satellites. OneWeb’s satellite (OneWeb-1078) was launched on March 25 and headed for its orbit at an altitude of 1,200 km when, in early April, it passed near a SpaceX satellite (Starlink-1546) in orbit at about 450 km.

There was no collision, but subsequently, OneWeb’s government affairs chief Chris McLaughlin said SpaceX had turned off their autonomous collision-avoidance system so OneWeb could maneuver around their satellite and SpaceX denied that they had switched the system off and said, “there was never a risk of collision.”

This sounds a little like a PR battle, but both sides may have been sincere because satellite tracking is imprecise. The satellites were being tracked by SpaceX, OneWeb, and two independent organizations, the Air Force 18th Space Control Squadron (18 SPCS) and LeoLabs which offers a commercial satellite tracking service. As we see in the plot shown below (source), their estimates of the probability of collision vary.

In addition to helping explain the dispute between SpaceX and OneWeb, the variance in these estimates illustrates the difficulty of accurately tracking and predicting satellite orbits. The incident also highlights the difficulty of communicating and cooperating in deciding on maneuvers to avoid collisions.

SpaceX and OneWeb began deploying their broadband Internet service constellations recently, but as of early 2020, LeoLabs was tracking about 14,000 objects in LEO that were 10 centimeters across and larger. About 1,700 were functional satellites working on other applications, and the rest were debris. We also had a debris-collision warning Last week when the astronauts en route to the International Space Station were instructed to put on their spacesuits due to the possibility of a collision with a piece of space junk.

Fast forward five years

The SpaceX-OneWeb and astronaut-debris events provide an early warning. There are around 3,000 satellites in LEO today, but how about five years from now? As shown below, the five would-be broadband constellation operators have the authorization to launch over 30,000 satellites and, if we add in pending requests for approval, the total increases to around 100,000. Furthermore, Russia and the European Union are working on broadband satellite plans, as are the US and Chinese militaries. And don’t forget the forthcoming large non-broadband constellations, like Geely’s Geespace constellation.


We’ve had a few scares recently, and the number of close calls requiring an automated or manual maneuver to avoid a collision will increase dramatically in the future. Runaway debris in LEO would cost us more than just having to give up the goal of global broadband service. It would disrupt critical applications we already depend upon in climate science, emergency response, agriculture, etc. I am confident that LEO broadband providers can find solutions to the technical problems they face, like low-cost antennas, inter-satellite laser links, and spectrum sharing. Still, collision avoidance is tougher because, in addition to technical innovation like improving the accuracy and resolution of terrestrial and space-based orbit tracking, it will take political action.

The map below shows that 72 nations own and/or operate satellites, but last week, English-speaking engineers at SpaceX and OneWeb were unable to agree on the orbit data and communicate and cooperate when it appeared that a collision might be forthcoming. If SpaceX and OneWeb cannot agree, what will happen when, for example, military satellites from China and the US are involved?

Space, like the oceans, is a global commons, and it is not in anyone’s interest to spoil it. We need global regulations, standards, procedures, and a means of enforcing compliance if we are to avoid collisions and mitigate debris. We are running out of time. We’ve been working on maritime law for centuries, and the UN International Maritime Council has 174 member states—have we begun talking about this issue with the Chinese?

It’s time to act

The European Space Agency (ESA) has produced a 12-minute video (with cool animations) that describes the debris problem and the current debris mitigation guidelines, which are neither universally followed nor adequate for the future. ESA projects for automating collision avoidance, refueling and repairing satellites in space, active debris removal, and technology to hasten the deorbiting of defunct satellites are mentioned in this call for action. Indeed the title of the video is “Time to Act.”

Update May 2, 2021:

Several readers pointed out that the Chinese ratified the UN Outer Space Treaty and Registration Convention in the 1980s. If one takes my question “have we begun talking about this issue with the Chinese?” literally, the answer is “yes.” But, clearly, the situation has changed since the 1980s so a more relevant question would have been “are SpaceX and Guowang engineers talking with each other?” I don’t know if we can wait for Outer Space Treaty-2.

Update June 1, 2021:

Ground segment market researcher Alexandre Corral predicts that “over 2,100 Earth observation satellites will be launched as part of about 70 constellations during the next decade, driven by the operators’ ambition to provide higher revisit with global coverage.” That is nothing like what SpaceX and the other broadband constellations anticipate, but it will add to congestion in LEO.

By Larry Press, Professor of Information Systems at California State University

He has been on the faculties of the University of Lund, Sweden and the University of Southern California, and worked for IBM and the System Development Corporation. Larry maintains a blog on Internet applications and implications at cis471.blogspot.com and follows Cuban Internet development at laredcubana.blogspot.com.

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Another aspect Karl Auerbach  –  May 4, 2021 11:18 PM

Among our friends are several prominent astronomers and astrophysicists.  Over dinner (and a conversation about the role of thorium and uranium in the creation of “Golilocks” planets likely to support life) I happened to mention Space X and their satellites.

A pall of horrified silence fell over the table.

Two of our friends have been active in the creation of the Vera C. Rubin observatory - Vera C. Rubin Observatory

That observatory will hold a unique telescope (and camera) that will be watching large parts of the sky.  For example it can pick up supernova events early enough that other telescopes can move to focus on the event as it happens.

However, satellites reflect sunlight.  And low earth satellites move quickly (a couple of years back one zipped through my own field of view when I was eyeballing through the 36” refractor [once the world’s largest telescope] on Mt. Hamilton.)  These satellites will create streaks across the photos being made by the Vera Rubin (and other) telescopes, damaging the research being performed.

Mt. Hamilton and other observatories often use strong lasers to help create sharper images despite atmospheric distortion.  Aircraft have to be warned to stay away from the laser beams.  Although satellites will be much higher up and the beams much attenuated I wonder what might happen when a low earth satellite’s orbit intersects with these lasers?  I hope not much, but then again I was quite surprised when I was blinded by some jerk with a green laser while on a landing approach.

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