SpaceX started launching their second-generation satellites with technological and operational changes that carry through with their agreement with the National Science Foundation (NSF), the American Astronomical Society, and the International Astronomical Union in 2019 to protect the dark Skies. In that agreement, SpaceX committed to implement a new design for their Starlink satellites to reduce their brightness to 7th magnitude and to maintain its satellites in orbital elevations that reduce the number of avoidance areas in the sky [1].
[Starlink-second-gen.jpg] Credit: SpaceX
In 2022, SpaceX shared technological solutions and techniques planned for their second-generation satellites in order to make them invisible to the naked eye, even at their standard operational altitude [2]. In a statement released at “X” on September 2023, when their improved second-generation satellites were launched, Starlink reiterated its commitment to support astronomy — “We firmly believe in the importance of protecting the night sky for all to enjoy, which is why the Starlink team has been working with leading astronomers around the world to reduce satellite brightness.”
If you like to look at the stars, you might have noticed bright objects moving fast across the night sky. These are also seen by ground-based observatories and cover a considerable area of recorded images, hence raising the concerns of the astronomical community on the possible impacts to scientific discoveries. The satellites are most visible from Earth during the first hours going into the night and before sundown. These are visible because they reflect the sunlight, and the time they are visible depends on their altitude; satellites at higher altitudes are illuminated by the Sun longer. The brightness also depends on the material used for its surface and how much light it reflects. Another contributing factor is the solar arrays, which have solar cells that can scatter sunlight into the ground.
To further reduce the brightness of the Starlink constellation, the second-generation satellites will employ three advanced brightness mitigation techniques, which include an improved Dielectric Mirror Film, an opaque pigment for the solar panels' backsheet, and a low reflective black paint to cover many of its components. Another change would be to its flight operations. SpaceX will refine its satellite's attitude and solar array pointing techniques during orbit, raising, and deorbiting.
SpaceX started using a dielectric mirror film in their first-generation satellites. This film is a radio frequency transparent mirror film that scatters the majority of the reflected sunlight away from Earth and replaced the bottom chassis “sun visors” in the first-generation satellite, which created drag and blocked the laser links that SpaceX needed to expand coverage to the most remote regions of the world.
[ image BrightnessMitigationDieletricMirror.jpg Credit: SpaceX]. For its second-generation satellites, SpaceX is using an improved version of the dielectric mirror film to cover the bottom chassis. This film is 10x better at reducing observed brightness than the first-generation film.
[dielectric
mirror image]
Even with its first-generation satellites, SpaceX started implementing brightness mitigation changes to its solar arrays, like using a darker material between the solar cells. This was also one of the first design concessions SpaceX made for astronomy, as darkening this material increases solar array temperature and consequently reduces performance.
[image BrightnessMitigationSolarArray.jpg Credit: SpaceX] For the second generation, SpaceX went beyond by developing an opaque pigment to cover the backsheet of the solar arrays, which otherwise can be lit up by the Sun like a lamp shade. SpaceX also changed flight operations for this generation of satellites by pointing the solar arrays away from the Sun when crossing the day-night line (or terminator). This off-pointing maneuver results in a 25% reduction in available power for the satellite, so SpaceX had to implement a more costly design.
Finally, SpaceX is using its new “Low Reflectivity Black” paint, which, compared to the darkest available space stable paint, has a five-times lower specular peak. This paint is used to cover all possible components that have complex geometries, minimizing the brightness and glints that occur when the Sunlight is reflected from their surfaces and intersects the Earth.
SpaceX plans to continue working closely with the astronomical community to mitigate the effect of all satellite operations on their observations; however, SpaceX cannot reduce this effect alone, so all satellite operators must work together. With this in mind, SpaceX is going further in its support for astronomy by offering its dielectric mirror film at cost to other satellite constellations.
[1] Reference my blog. https://www.onerocketmom.com/post/spacex-to-improve-starlink-gen-2-satellites-to-help-astronomers
[2] SpaceX 2022 Brightness Mitigation Best Practices for Satellite Operators, https://api.starlink.com/public-files/BrightnessMitigationBestPracticesSatelliteOperators.pdf