SpaceX just released a new paper detailing how the company is reducing the brightness of its Starlink Gen 2 satellites. As a part of their effort to protect the night sky, they will also be offering the reflective film they developed to other satellite manufacturers at cost.
SpaceX’s paper, SpaceX makes renewed effort to protect the night sky, the company talked in general about the ways in which different satellites can impact the night sky and explained how the company is doing its best to reduce the brightness of their Starlink constellation. With the thousands of Starlink satellites in orbit, it will remain important for them to continue to reduce the brightness of the satellites as it moves to the new, larger Gen 2 satellites.
As the paper explains, “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 night and before dawn.” Many satellites are visible shortly after sunset, and the higher an orbit a satellite is the later after sunset and earlier before sunrise it may be visible. Part of the reason that the brightness of Starlink satellites has been so controversial is the pure number of them needed in orbit. There are already thousands operational, and SpaceX plans to continue expanding the constellation with second generation Starlink Satellites launch on the company’s Starship rocket. Shortly after each Starlink launch, there is a train of more than 50 satellites that will light up in the sky. While many SpaceX fans have enjoyed seeing them overhead, as they spread out and raise their orbits, its concerning for those who want to capture a clear picture of the night sky.
In order to reduce the brightness, SpaceX had used darker satellites and sunshades to minimize the reflection of light from the Sun back onto Earth by absorbing the light. But the satellites cannot entirely absorb light, so they are implementing a few new ways to control reflection from second generation Starlink Satellites. The document outlines the three ways SpaceX will reduce the brightness of the larger Gen 2 satellites to even less than the smaller Gen 1 satellites.
- Dielectric Mirror Film
- Solar Array Mitigations
- Black Paint
The mirror film is used to reflect light internally and control the angle of reflection of that light while allowing radio waves to pass directly through. With a mirror-like surface, you can angles the sunlight away from the surface of the Earth, rather than towards it, to minimize the visibility of the satellites around dawn and dusk. In addition to implementing the film on its own satellites, the company plans to offer it for sale at-cost to other satellite constellation operators.
In a similar way, the solar cells of the second generation satellites will adjust their angle to reflect light away from the Earth when passing the terminator.
Finally, and the most straightforward mitigation technique, is the use of a new black paint. The company developed a space-stable paint to use on every other component – such as antenna and brackets.
These techniques will keep the satellites hidden while operational, but the paper notes that while performing specific maneuvers – such as orbit raising, station keeping burns, and deorbiting – the satellites will be visible.
I highly recommend reading SpaceX’s full paper for a more detailed understanding of how they are implementing each of these methods, and the specific techniques used to make them work. While there is no perfect solution to make the satellites totally invisible, these are all important steps to keep the night sky as clear as possible. This, alongside SpaceX’s other efforts toward sustainability of space, is a great move to see.