Managing the impacts
Immediately after the first Starlink satellites launched in 2019, the astronomical community reached out to several satellite operators — including SpaceX, Amazon Kuiper, and OneWeb — to try to work together to reduce the impact on astronomy. So far, most of the design and engineering work to achieve this goal has been with SpaceX, as they are the first with a large satellite fleet in operation.
SpaceX has experimented with numerous strategies to reduce the amount of light Starlink reflects back to Earth, such as painting various components of satellites black. The company also tried added visor shades to block sunlight from reaching reflective surfaces, and reoriented satellites so that less of the reflective surface is pointed toward Earth. However, SpaceX found that the visors interfered with the satellites’ communications and also added a significant amount of drag, requiring satellites to burn more fuel to stay aloft. In place of the visors, SpaceX has added a special coating designed to reflect light strongly in one direction, away from Earth.
These early experiments demonstrated that Starlink satellites in their operational orbits could be darkened from visual magnitude 5.0 to about 6.0 or 6.5, close to the limit of the unaided eye. However, they appear brighter in redder wavelengths, which could still impact infrared astronomy.
These efforts reveal the complex nature of the sudden transformation in humanity’s use of LEO. On the one hand, we must be clear: Even the most heroic efforts by satellite operators cannot eliminate a substantial impact on astronomy. The SATCON1 workshop concluded that a visual magnitude of 7.0 for satellites at altitudes of 370 miles (600 kilometers) or lower was needed to mitigate the most severe impacts on images from facilities like the Rubin Observatory. This includes the removal of crosstalk trails — secondary image artifacts caused when a bright object affects the readout of other pixels. But this still leaves the main bright streak to be dealt with — a complex problem to correct.
The use of lower altitudes — which can reduce how long satellites are visible overnight — is also a compromise, as it is less effective for telescopes at higher latitudes. And the lower the constellation, the more satellites are needed to achieve global coverage. In the end, there is no way to make LEO satellites invisible even to the smallest amateur telescopes, let alone 8-meter behemoths.
On the other hand, we acknowledge the substantial time, effort, and money SpaceX has invested in redesigning its satellites. The interaction between astronomers and satellite operators has been both constructive and cordial.
The good news is that, in principle, it appears most Starlink satellites can be made invisible to the human eye once they are in their operational orbits. And although the internet and communication services offered by companies like SpaceX are not humanitarian missions, they have support from many geographically isolated constituencies and the potential to benefit those afflicted by natural disasters and other crises.
Charting the future of space
The transformation of human access to space is not a black-and-white issue. Astronomy is just one of many communities that can lay claim to a legitimate use of space. Comprehensive solutions to managing space in this new era will need the creativity and cooperation of many more parties, such as regulatory bodies and environmental groups. And it will require elevating the voices of those who are traditionally ignored and marginalized each time a new frontier is repurposed.
This is a challenge, but it can also be an opportunity. The world is sorely in need of such collaborative efforts, and perhaps the frontier of space can serve as a canvas on which humanity can seek visionary solutions.
If you’d like to help, the authors welcome you to apply to join the new International Astronomical Union Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (https://cps.iau.org).
We also encourage you to seek out a dark site to marvel at the night sky, because it may soon not look the same.
How to dim a satellite
There are numerous strategies that can potentially reduce the impact of satellite trails on astronomy. However, many of them come with trade-offs.
Orbiting at a higher altitude will reduce a satellite’s apparent brightness to ground observers. But it will also be lit by the Sun for more of its orbit, making it visible across more of the sky and during more of the night.
Satellites can be oriented so reflective surfaces like solar panels reflect light away from Earth, but this can reduce the amount of sunlight they gather and the power they generate. SpaceX says it will design its next generation of Starlink satellites to cope with less power.
To limit the amount of light reflecting off the bottom of the satellite body, SpaceX tried installing sun visors. However, the company said that these interfered with the laser communication links the satellites need to expand their coverage to remote regions. The visors also increased drag, removing the satellites from orbit more quickly. As an alternative, the company is developing mirror films that can scatter and direct light away from Earth. Using darker materials and black paint can also limit reflectivity by absorbing light. However, it can also raise temperatures and reduce the performance of components like solar arrays.