Dealing with Starlink Satellites

Starlink is a satellite internet constellation being constructed by SpaceX providing satellite Internet access. The constellation will consist of thousands of mass-produced small satellites in low Earth orbit, working in combination with ground transceivers. Wikipedia 

Well, that's good news for the needs of the public to gain access to the internet, but its bad news for the amateur astrophotography crowd. It turns out that these satellites can be quite bright and therefore a big problem for ground based observers. And because they are in low earth orbit and there will be lots of them (Starlink alone will consist of 12,000, and other companies are considering satellite constellations of their own) we may not be able to see any part of the sky that doesn't have a satellite passing through.

Astrophotographers take long exposure photographs (some exceeding 10 min in length) to capture the light needed to produce a good image. During that time, plenty of satellites could pass through the field of view and potentially ruin the image. 

In the past few weeks I have started to notice a considerable amount of Starlink satellites passing through my night sky and ending up in my photos. Here is a video of my last set of images of the Orion nebula taken on January 14. This video is a time-lapse of 20 images, each 5 minutes of exposure time (the typical time I use with my camera). You can see the Starlink satellites passing through on the far right, with another, unrelated satellite, passing through the center. This will only get worse as the number of satellites increase over the next few years.

However, all is not lost. Because of the post-processing done on astro images (see my post on image processing here) I take up to 100 subs to combine into a single image to increase the quality of the final photo, decreasing noise and increasing signal. This process can detect which pixels on the image appear on every sub (the signal) and which appear on only one sub (noise, or, in this case, a satellite trail). The processing then stacks the subs together but removes the unwanted pixels. 

Rejection-high

In the photo above, all the bright spots, streaks and lines are the pixels that were detected by my software as present on only a single sub (or were overexposed regions). These will be removed from the final image. You can see the lines of satellite trails on the right and the one that passed through the center. There are some spots throughout the image that will also be removed. These are overexposed areas of the image which are also removed as part of the processing.

The following photo is the processed image where the unwanted pixels were removed.

So, although the proliferation of these satellites will be a challenge for astro-photography, it can be managed. The software we rely on to stack and process our images does an amazing job in tackling the issue of these unwanted photo bombers!