"Existential threat" to optical astronomy: warning about satellite plans | heise online
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Current plans to place more than 1.7 million satellites into Earth orbit pose an “existential threat” to optical astronomy; in large cities, their artificial light points could soon be the only visible objects in the night sky. This is warned by the European Southern Observatory (ESO) based on a new study, the results of which are to be incorporated into a statement to the US Communications Commission FCC. The research institution refers in particular to the gigantic plans by SpaceX for a million new satellites alone and Reflect Orbital for significantly fewer but considerably brighter satellites.
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Satellites brighter than the full moon
In the summary, ESO recalls that the number of active satellites in Earth orbit has increased to over 14,000 since 2019, more than two-thirds of which are from SpaceX's Starlink satellite internet. In addition, there are almost 20,000 inactive satellites and space debris. The consequences for astronomy can already be illustrated; several time-lapses show the countless light trails over ESO's observatories in Chile. However, these are not even remotely comparable to what we would see when looking up at night if the current plans for further megaconstellations were approved and realized.
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Time-lapse recording of satellites over ESO's Extremely Large Telescope
(Source: F. Kamphues, ESO/M. Kornmesser)
While the brightness in the night sky for SpaceX & Co.'s satellites is, in a way, just a by-product, it is the core point of Reflect Orbital's plans. The startup wants to launch giant mirrors into space, which reflect sunlight onto the Earth's surface at night so that solar systems can generate electricity for longer. Although there are already justified doubts about how realistic the company's promises are, a prototype is to be launched this year. If one were directly in such a light cone – which is only intended to be directed at solar farms – such a satellite would appear four times brighter than the full moon, writes ESO. This is likely to fuel criticism that such a satellite does not provide enough light for the solar systems.
Even if one is not in such a light cone, each of these satellites would be brighter in the night sky than the “morning star” Venus. At the same time, Reflect Orbital intends to expand its fleet to 50,000 such satellites by 2035. From downtown Munich, one would only see hundreds of these satellites after their realization, no real stars anymore. For pure stargazing, the other planned satellites would not be quite so problematic, but the consequences for astronomy would be devastating. At ESO's Very Large Telescope (VLT), for example, the calculated loss for two hours after dark would correspond to a reduction in the usable field of view by 28 percent.
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Time-lapse recording of satellites over ESO's Very Large Telescope
(Source: F. Kamphues/ESO)
Maximum 100,000 satellites
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ESO names further consequences of a possible realization and speaks of “drastic consequences.” These could only be averted if the total number of existing and future satellites is limited to 100,000, says lead author Olivier Hainaut. However, this is not a rigid limit; at this number, the expected losses would be at the level of other failures: “clearly I'd prefer 50 000.” The number also only applies if the apparent brightness of all satellites remains below magnitude 7. Otherwise, the total number would have to be significantly reduced. The research paper has been accepted for publication in Astronomy & Astrophysics. It is primarily aimed at the FCC, which must approve the majority of the satellites.
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