Problems of mega-constellations: the impact in astronomy

During the last years, astronomers have had each time more problems finding a place without light pollution, due to the cities. It is for this reason that the astronomical observatories are situated in true sanctuaries of darkness, in deserts or places without inhabitants. But, now, mega-constellations will have an impact on astronomy.

But, recently, with the increasing quantity of satellite mega-constellations orbiting the Earth, light pollution could come from the sky. The observatories need long exposures to be able to photograph very distant objects, as very little light from them arrives at us. In consequence, if a satellite crossed in front of the telescope at that moment, it would leave one or several light trails through the image that would let it useless.

This could be fixed with some image processing, but this would require making more photos of the object, which supposes to waste the time that has the telescope to operate, and, therefore, it would produce delays.

Orbits of the satellites

To start with, we have to look over the orbits that will follow the satellites. The satellites of SpaceX’s mega-constellation (the Starlinks), and presumably those of other companies, (OneWeb, Amazon, Facebook, Telesat,…) will be located in the low Earth orbit, between 200 and 2000 kilometres. Starlink’s satellites orbit, specifically, in the inferior section of the low Earth orbit.

The fact that they are situated in the low Earth orbit makes the issues not to be so considerable. When it will be night and the observatories work, the Earth’s shadow will block most of the Sun’s light, preventing it to bounce against the satellites, so they will only be visible mainly near the horizon.

If they were situated higher above, the problems would be bigger, as more sunlight would reach them, which would be reflected and it would compromise the images made by the observatories.

Brightness of the satellites

In the first launches it was discovered that, during the deployment phase, the Starlinks were very bright. So brilliant, that they were visible from a city. This worried astronomers a lot, as if they were bright enough to be seen at first sight, mega-constellations would have an adverse impact on astronomy.

For this reason, SpaceX worked in making them less bright. They put on the satellites a darker coating to reduce reflectivity. These are the named DarkSats. But these also presented a problem, as their electronics heated up too much.

To solve it, SpaceX developed the named VisorSats. These have a parasol that spreads out and shades the satellites. Although these efforts, no matter how dark the satellites are, telescopes will always end up detecting them. The Vera Rubin, for example, is about 20 000 000 times more sensible than the human eyes. If a satellite goes through, reflecting the Sun’s light, it will leave a light trail that will have to be treated.

Other frequencies

The problem doesn’t end here. The satellites could also be disruptive in the frequency of infrared, and, most likely, in radio frequencies. The problem here is that the electromagnetic waves that mega-constellations pretend to use are the ones that the radio-astronomers use. This would cause a background sound that would damage many measures. SpaceX says that it will solve it, but we don’t know if other companies will be equally considered. Mega-constellations impact on astronomy covers many areas.

Foretell the trajectory of the satellites

The satellites’ trajectories can be predicted and make measures before or after the satellites passed. However, this presents some issues:

  • In the first place, the orbits of the satellites could be dynamic. To know when the satellite will pass, the orbits would have to be updated in real-time. SpaceX has said that he will make them public, but it remains to be seen whether other companies, of other countries and different objectives, will also accept it.
  • In the second place, this would damage the efficiency of many observatories, which have many demands to observe different regions of the sky. If besides they have to wait for a satellite to cross, many projects won’t be able to be carried out or they will receive their data much after than expected.
  • Apart, many events in the sky are unique, where there isn’t time to wait for a satellite to go through, like supernovas, occultations, gravitational lenses… Mega-constellations will suppose a delay in the progress of astrophysics.

Telescopes in space

A possible solution to all these problems would be to send the telescopes to space, where satellites wouldn’t be a problem, and, what’s more, we would get rid of the atmosphere, which clouds the images. This is an option that Elon Musk (owner of SpaceX and Tesla) has sometimes said.

Nevertheless, we also find some problems to this solution:

  • One of them is that, once in space, we cannot touch any more the telescope. It is economically prohibitive to go there and change sensors, mirrors, tools… The Hubble is one of the few telescopes in which this effort was made. This condemns the spatial telescopes to be a lot less updated than those which are on the Earth’s surface. This leads us to the second point.
  • The spatial telescopes are developed thanks to the tests done in terrestrial telescopes. Without telescopes on Earth, we would have to be sending a lot of tests to space before finding the optimal design. All this would be translated into a money loss. That to say, the spatial telescopes need, in a big part, the terrestrial observatories. If their operations are hindered, it also harms those in space.


In summary, mega-constellations won’t suppose the end of astronomy on Earth, but they will suppose a true obstacle in many observations, as the ones that are made in the twilight (where the satellites are seen the most), those of long exposure (where there are more possibilities for a satellite make useless an image), and in determined moments of the year, where there are more satellites than in other ones. Mega-constellations will have a bad impact on astronomy.

Moreover, the obstacle that these mega-constellations suppose in the astronomic observation can hinder the fact to predict possible asteroid impacts, which could suppose a big danger for the human specie. I will talk about this in the next article.

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