It concludes that large constellations of bright satellites in low Earth orbit will fundamentally change ground-based optical and infrared astronomy and could impact the appearance of the night sky for stargazers worldwide.
The report – Impact of satellite constellations on optical astronomy and recommendations toward mitigation – is the outcome of a recent SATCON1 virtual workshop involving 250 scientists, engineers, satellite operators, and other stakeholders. NOIRLab stands for the National Optical-Infrared Astronomy Research Laboratory, a US national centre for night-time optical and infrared astronomy.
The report concludes that the effects of large satellite constellations on astronomical research and on the human experience of the night sky range from “negligible” to “extreme”.
Specifically, the report offers two main findings. First, that LEOsats disproportionately affect science programs that require twilight observations, such as searches for Earth-threatening asteroids and comets.
“During twilight the Sun is below the horizon for observers on the ground, but not for satellites hundreds of kilometers overhead, which are still illuminated. As long as satellites remain below 600 kilometers (not quite 400 miles), their interference with astronomical observations is somewhat limited during the night’s darkest hours. But satellites at higher altitudes, such as the constellation planned by OneWeb that will orbit at 1,200 kilometers (750 miles), may be visible all night long during summer and for much of the night in other seasons. These constellations could have serious negative consequences for many research programs at the world’s premier optical observatories. Depending on their altitude and brightness, constellation satellites could also spoil starry nights for amateur astronomers, astrophotographers, and other nature enthusiasts.”
The report’s second finding is that there are at least six ways to mitigate harm to astronomy from large satellite constellations:
- Launch fewer or no LEOsats. This is the only option identified that can achieve zero astronomical impact.
- Deploy satellites at orbital altitudes no higher than ~600 km.
- Darken satellites or use sunshades to shadow their reflective surfaces.
- Control each satellite’s orientation in space to reflect less sunlight to Earth.
- Minimize or eventually be able to eliminate the effect of satellite trails during the processing of astronomical images.
- Make more accurate orbital information available for satellites so that observers can avoid pointing telescopes at them.
You can download the report from the noirlab.edu website.
In June, SpaceX launched another 60 of its Starlink satellites and they featured, for the first time, a deployable visor to block sunlight from hitting the brightest spots of the spacecraft. This was in response to concerns about light pollution previously raised.
See also: Viewpoint: Why collaboration on the ground is vital for LEO satellite constellations in the sky