SpaceX will reduce light pollution in the night sky from its Starlink satellites. The company has developed in-house technology solutions and methods that will have a hugely positive impact if adopted by all operators.
Space exploration is fundamental to SpaceX’s core mission. Therefore, the company has taken unprecedented steps to work with the astronomy community to better understand how it and all satellite operators can mitigate the effect that the reflection of the Sun from satellites can have on astronomical observations. The company has made the largest investment and has the strongest desire to provide Earth-based observers with skies free of light pollution from satellites. As a result of this collaboration, SpaceX has implemented innovative technology solutions and techniques. They will minimize the impact of Starlink satellites on the night sky.
Developed in-house, the dielectric mirrors on the surface of the satellites and extremely dark black paint for angled surfaces or those not conducive to mirror adhesion help absorb and redirect light away from the ground https://t.co/BXmfpIG495
— Starlink (@Starlink) September 16, 2023
More than 4,600 satellites belonging to different operators orbit the Earth. If you look at the clear night sky for a few minutes, you are almost guaranteed to see several flying over your area. This represents a worrying source of light for astronomers and is a well-known problem. SpaceX is trying to limit light pollution to protect the night sky and make it enjoyable for everyone. Using technological solutions and methods, the company reduces the brightness of Starlink satellites. Moreover, SpaceX not only independently developed this, but also invites other satellite operators to take advantage of the proposed measures.
Any satellite can be visible from Earth at night if it is illuminated by the Sun and scatters light to Earth observers. Satellites typically are visible when they are just over the dark side of the terminator (the day/night boundary on Earth), corresponding to the first several hours into the night and before dawn. Although it is already dark on Earth, the satellites are still illuminated by the Sun at their altitude and reflect light back to Earth. It is the scattered light that makes satellites visible longer. Spot reflections of sunlight on a reflective surface may reduce visibility. Therefore, the latest generation of Starlink satellites have special dielectric (non-conducting) mirrors installed.
In addition to the surface of the satellite body, a lot of light is reflected from the solar modules, and the back of the modules is illuminated as a kind of lampshade. Therefore, the back is painted black, which does not allow light to pass through. The front panel uses a dark red color (previously: white) between the solar cells. Parabolic antennas for communication with Earth’s surface are coated with special black paint.
In addition, the new satellites precisely detect the moment of crossing the “terminator” and fold the solar modules upward, so that the front part is no longer visible from Earth. This off-pointing maneuver results in a 25% reduction in available power for the satellite. Despite this cost, SpaceX has specifically designed the second-generation satellite to be able to accommodate this significant power reduction to minimize brightness as viewed from the ground. At certain stages of flight, especially during satellite deployment and approach to their respective target orbit, Starlink satellites will still be visible, but the company is working with astronomers further to make improvements here too.