Since last May, Elon Musk’s SpaceX has been launching satellite constellations called Starlink in batches of 60 per launch, and since last May astronomers have been voicing their concerns about how these bright and numerous objects will affect astronomical observations. A new study out confirms their worries.
As reported in Astronomy & Astrophysics, Olivier Hainaut and Andrew P. Williams from the European Southern Observatory (ESO) produced a conservative estimate for how the complete mega-constellations, as they're being called, from SpaceX, Amazon, OneWeb, and others will affect astronomy. When all the launches are complete, somewhere between 30,000 and 40,000 new satellites are expected to be located in low-Earth orbit.
For the ESO facility, which houses the current Very Large Telescope and upcoming Extremely Large Telescope, one-in-30 long exposures will be affected by the satellite trails during twilight hours, and one-in-200 will be affected for shorter exposures.
More concerning is the situation for Wide-Field surveys. These can scan large areas of the sky at once and are crucial for the next breakthrough in astronomy. Looking at the Vera C. Rubin Observatory in the US, the team writes in the paper that up to “up to 30% of the exposures would be lost during the first and last hours of the night, and almost 50% of the twilight exposures would be contaminated.”
These are conservative estimates.
The team suggests some mitigation solutions. Observing towards the opposite direction of the Sun (so that the satellites are in the shadow of Earth) will help, as will avoiding areas of the sky where the satellites will pass through. These will require detailed knowledge of the orbits of these mega-constellations though, and some of them can automatically move. These approaches are also both laborious and costly, and given that the observatories are publicly funded, the question that many are asking is why is it up to them to fix a problem created by private companies.
Musk has said that they are working on lowering the albedo of future Starlink satellites, so they will have lower reflectivity, and that they will "tweak satellite orientation to minimize solar reflection during critical astronomical experiments" when needed, but is it enough?
There is also a discussion over the increase in space junk due to these new satellites. Currently, about 34 000 objects greater than 10 centimeters (4 inches) in size are orbiting Earth. Most of them are fragments of rockets and other satellites. Only 5,500 are satellites and of those, only 2,300 work. The satellite constellations will add a huge number of new objects and it is paramount that safely deorbiting into the atmosphere is part of their operational life.
This study focused specifically on optical and infrared telescopes but there are also concerns regarding radio, millimeter, and submillimeter observatories, too. The impact of this new era of private satellites on those will be revealed in further studies.