Problems of mega-constellations: junk orbiting the Earth

As I’ve explained in the last articles, mega-constellations will be a problem to the progress of astrophysics and the detection of possible impacts against meteorites. Moreover, they also present another problem, that could not only be prejudicial to the satellites, but it would also difficult to put more of them in orbit. This is the problem of space junk, which will be augmented by mega-constellations.

Nowadays more than 20 000 objects are orbiting the Earth, of which only 2 000 are active satellites. The rest are remains of rockets, metal pieces, broken pieces, disused satellites… This is space junk, fragments of objects that nobody wants and which represent an increasing problem. For decades, the quantity of space junk in our sky has increased exponentially, and the apparition of a colossal number of new satellites could aggravate even more this problem.

This is the last article in which I talk about the problems of mega-constellations. To have a clearer vision of the problem, I leave here the previous articles:

Problems of mega-constellations: the impact in astronomy

Problems of mega-constellations: asteroid impacts

The problems of space junk

The main problem of space junk is its velocity. For an object to orbit, it must have a very high speed. In the case of the Earth, it is about 27 000 kilometres per hour. In consequence, a collision, for small it might be, causes disastrous damages. For example, the satellite Sentinel 1A impacted against a fragment of 5 millimetres, and the crash provoked a hole of about 40 centimetres on the satellite. When an orbiting fragment impacts against a satellite or another object produces many other pieces of rubbish. This is an important problem: rubbish generates more rubbish.

Image of the impact of a fragment of 5 millimetres in diameter against the satellite Sentinel 1A, creating a hole of 40 cm on the satellite.

A collision generates lethal small fragments that collide, and create even more deadly fragments. These pieces take a long time to impact. In the case of the Low Earth Orbit (LEO), there is an object for each 50 000 000 square kilometres. But, with time, collisions succeed one after another, and with a higher concentration of fragments, more impacts take place, which creates even more fragments. This will provoke an exponential effect on the quantity of rubbish around the Earth.

During the last two decades, about 11 involuntary satellite collisions are produced every year. The ESA (European Space Agency) has said that the probability of impacts has been duplicated since the beginning of the 21st century. Moreover, the International Space Station (ISS) each time has to dodge more space junk to avoid important damages, and even lethal ones, to the station.

Space junk with SpaceX’s satellites

SpaceX’s mega-constellation (Starlink), has already put in orbit hundreds of satellites, and it hopes to increase the quantity of them to about 42 000. However, these satellites won’t be in orbit permanently. The Starlinks have a propulsion system that, when their fuel and technologies will be damaged, the only thing that will have to be done is to activate the small engines of the satellites to make them re-enter the atmosphere, and the friction with it will disintegrate them. If for any reason, the control of the satellite is lost, the little friction of the atmosphere will de-orbit it naturally in a period of one to five years. This number is much smaller than the recommended 25 years. However, OneWeb pretends to put its mega-constellation in such a high orbit, that in case of losing contact with any satellite, it would take the satellite centuries to re-enter the atmosphere. In this case, mega-constellations would increase much more the quantity of space junk.

Space junk with mega-constellations in orbit

The mentioned problems could be caused mainly by the active satellites. By increasing the number of orbiting satellites, not only does the possibility of a collision against a small object that is also orbiting increase, but it also increases the risk of a collision against another satellite. Mega-constellations will provoke an exponential increase of space junk orbiting the Earth.

In February 2009, two disused satellites, a military one Kosmos and another of telecommunications Iridium impacted, leaving more than 1 600 fragments in orbit. This collision surprised a lot. The orbits of the two satellites were registered and were maintained updated. The possibility of the impact that day between those two satellites was 3 out of 100 000, three times less than the possibility of impact against a lighting. It is discussed if this collision could have been foreseen or avoided, as maybe the systems that are used aren’t reliable enough and would have to be updated to a better version.

It is in this context in which it is intended to send to space tens of thousands of satellites, with orbits that cross with the ones of other satellites, and with many other orbiting objects. All this would increase the risk of collision between and against satellites. However, SpaceX’s satellites are equipped with an autonomous system to avoid collisions, that use the direct data from the United States Defence Department, but the problem is that precisely the data from the United States Defence Department didn’t foresee the Iridium’s collision.

The radar’s errors could be complemented with civil nets that followed the satellites using telescopes. But many governments have spy satellites around the Earth which they don’t want to be public.


As I’ve explained in previous articles, mega-constellations will suppose a problem for astrophysics’ progress, they will increase the risk of impact against an asteroid, and, as we’ve seen here, they will increase the quantity of space junk orbiting the Earth, which will also difficult putting more satellites in orbit.

However, I am not saying that mega-constellations wouldn’t have to exist. In the future, all these problems could be solved by placing telescopes on the Moon, making the satellites smaller or reducing their quantity without affecting the system… But we don’t leave in that future, and until that moment we will have to take measures based on today’s problems and risks.

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