Satellite swarms may impact exploration of the night sky
The introduction of 26,000 new megaconstellation satellites could have a significant effect on ground-based astronomy, according to a new study commissioned by the European Southern Observatory. Twice as many satellites could be visible to the naked eye in the coming years, as companies like SpaceX, OneWeb and Amazon pursue their ambitious orbital agendas.
Human technological progress seems to inevitably come hand in hand with ever-increasing pollution to the natural environment. On Earth, industrialization has altered the global climate with potentially far-reaching and dramatic consequences, and the advent of modern-day consumerism has seen the oceans contaminated with plastic waste.
As we gain greater mastery of the orbital domain, the space environment is also beginning to fall victim to humanity's polluting nature. Currently proposed mega-satellite constellations could see well over 26,000 satellites launched into near-Earth orbit in the coming years, compared to the 5,500 functional and derelict probes that are now crisscrossing the night sky.
Megaconstellations are vast collections of satellites that fly in formation in low-Earth orbit. SpaceX is already establishing its Starlink project, which Elon Musk hopes will one day provide global access to low-cost internet. The company is busily launching sats 60 a time tucked neatly in the fairings of its Falcon 9 rockets. SpaceX is not the only company looking to use satellite swarms to provide internet services. OneWeb is also looking to create an orbital network of probes hundreds strong, as is the global giant Amazon.
This proliferation of satellite technology, and the advent of megaconstellations, creates more than just physical pollution in the form of defunct probes, and in a worst-case scenario debris from an orbital collision. It also has the potential to seriously interfere with astronomy observations. These swarming probes – sometimes with sunlight glinting off their shiny bodies – will heedlessly travel through the sight lines of powerful telescopes that are capturing delicate observations of cosmic objects, lowering the quality of the data set.
The scientists behind the recent study modelled the impact that megaconstellation satellites may have on ESO telescopes that make visible light and infrared observations, such as the Very Large Telescope, located in the Atacama Desert, Chile. The paper considered a range of factors, and the different methods by which the telescopes observe the heavens.
The results of the study suggest that observations that depended on short-term exposures would only be affected by satellite photobombs 0.5 percent of the time, mostly during twilight hours. At this time soon after dusk, or just before dawn, astronomers are actively observing the night sky, yet there is enough sunlight peeking around the curve of the Earth to illuminate the swarms of metallic probes passing overhead.
Telescopes that require longer exposures of around 1,000 seconds would be affected roughly 3 percent of the time around the twilight period.
Wide-field, long-exposure observations that are used to stare unblinkingly at the night sky searching for fleeting events such as supernovae would be the worst affected by the constellations. As an example, the US National Science Foundation’s Vera C. Rubon Observatory would have 30 to 50 percent of its exposures compromised by satellite invasions, depending on the time of year.
The study also mentions two key ways that astronomers could attempt to mitigate the damage wreaked by the satellite swarms on their observations. The first would be to schedule their telescopes to capture the sky when no satellite is present in a given region.
Satellite paths are predictable, and so this is a viable technique. However, it would not work for every type of observation. For example, it may not be possible to avoid satellite contamination when long-duration, wide-field exposures are needed. It could also make it more complicated to allocate telescope time to astronomers with conflicting priorities.
The second method involves interrupting a telescope’s vigil by figuring out exactly when a bright satellite will pass through the field of view, and closing the shutter prior to the moment of contact. This would be a challenging technique to implement, and simply wouldn’t work for wide-field observations, as the satellite incursions would be too intrusive.
On the industry side, manufacturers can work to darken the skins of their satellites, thus making them less reflective. SpaceX has already attempted this approach with one of its Starlink satellites, though the practice would have to be widespread in order to be effective.
The study also touches on the effect that the megaconstellations may have on the public’s view of the night sky. According to the researchers, 1,600 probes will appear above the horizon at mid-latitude locations. Most will be relatively low in the sky.
However, it is estimated that around 250 megaconstellation satellites will occupy the sky above 30 degrees of the horizon. This could result in twice the number of visible satellites streaking across the night sky relative to the present day.
The study is intended to be a simple evaluation of the effects of satellite swarms on scientific observations, rather than a comprehensive look at potential disruptions. The researchers had to draw a number of educated guesses regarding important elements – such as the distribution and brightness of a satellites – in order to create conservative estimates.
The authors note that their results are "likely to err on the pessimistic side," and that further research using more sophisticated models will help reveal the nature of the future disruption, and to explore its effects on radio, millimeter and submillimeter wavelength observations.
The paper has been published in the journal Astronomy and Astrophysics.