Astronomers are concerned that Starlink satellites' reflection of sunlight may affect astronomical observations. What measures has SpaceX taken to mitigate this issue?

Okay, let's talk about Starlink satellite reflectivity and how SpaceX is trying to solve it.

This issue needs to be understood from the beginning. Astronomers typically need to expose a region of the sky for a long time with telescopes to capture very distant and faint galaxies. It's like trying to photograph fireflies on a dark night, requiring the camera shutter to be open for a long time.

The problem is that Starlink satellites, while not emitting light themselves, have surfaces, especially their antennas, that act like mirrors, reflecting sunlight. When these bright satellites pass through a telescope's field of view, they leave bright streaks on the images, "contaminating" the signals of the celestial bodies that are actually being observed. For astronomers, this is a disaster; precious data they've worked hard to collect could be ruined.

The astronomical community complained bitterly about this, and SpaceX did listen, taking a series of measures to "put sunglasses on the satellites."

SpaceX's Main Mitigation Measures

You can view these measures as SpaceX's "three-step strategy":

1. First Attempt: Black Paint (DarkSat)

• Idea: The most intuitive idea was, if it's reflective, why not just paint it black? Black absorbs light, reducing reflection.
• Action: SpaceX launched an experimental satellite called "DarkSat," painting the most reflective parts of the satellite with a special black coating.
• Result: It had an effect; the satellite did become dimmer. However, a new problem arose: black not only absorbs light but also heat. This caused the satellite's temperature to become too high, which could affect the normal operation and lifespan of internal precision electronic components. So, this solution was a temporary fix, not a long-term one.

2. Upgraded Solution: Adding a Sun Visor (VisorSat)

• Idea: Since painting it black caused "fever," let's try a different approach. Reflection is mainly because sunlight hits the bright surfaces of the satellite. Why not add a "sun hat" to block the sunlight?
• Action: SpaceX designed a device called a "Visor." This visor is made of a special material transparent to radio waves (so it wouldn't affect the satellite's communication functions). It deploys after the satellite is in orbit, like a brim, precisely blocking sunlight from hitting the satellite's brightest antenna array.
• Result: This was a very successful solution! "VisorSat" with the added visor reduced brightness by about 70% compared to the original satellites, proving significantly effective and without overheating issues. This became standard for most first-generation Starlink satellites launched afterward.

3. Fundamental Improvements for Next-Generation Satellites (Gen2)

• Idea: For the larger, more powerful second-generation (Gen2) Starlink satellites, SpaceX considered the light pollution problem from the very beginning of the design, aiming for a more thorough solution.
• Action:
  • Dielectric Mirror Film: They used a more advanced, cutting-edge film. This film acts like a directional mirror, reflecting most of the sunlight hitting it away from Earth into deep space, instead of absorbing it. This solves the reflection problem and also avoids satellite overheating.
  • Optimized Flight Attitude: SpaceX also uses software control to adjust the satellite's flight attitude during its ascent to its final orbit, making it "turn sideways" as much as possible towards observers on Earth to reduce the reflective area. It's like holding a mirror upright: it's dazzling when facing you directly, but much better when turned sideways, showing only an edge.

In Summary

Overall, SpaceX is indeed working hard to solve this problem, and their technical solutions are continuously iterating and upgrading. From simple "black paint" to clever "sun visors," and then to the cutting-edge film used on next-generation satellites, the effectiveness is getting better and better.

Of course, astronomers still have some concerns. Even if each satellite becomes very dim, there will be tens of thousands of Starlink satellites in the sky in the future. With such large numbers, the cumulative effect remains a challenge. So, this is still an issue that the astronomical community and SpaceX need to continuously communicate and collaborate on to solve. But at least, SpaceX's proactive attitude and engineering efforts are commendable.