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update: From Nature.com News article: SpaceX launch highlights threat to astronomy from ‘megaconstellations’:

But an upcoming, cutting-edge telescope could be in bigger trouble. The US Large Synoptic Survey Telescope (LSST) will use an enormous camera to study dark matter and dark energy, asteroids and other astronomical phenomena. It will survey the entire visible sky at least once every three nights, starting in 2022. Because the telescope has such a wide field of view, satellites trailing across the sky could affect it substantially, says Tony Tyson, an astronomer at the University of California, Davis, and the LSST’s chief scientist.

He and his colleagues have been studying how up to 50,000 new satellites — an estimate from companies’ filings with the US government — could affect LSST observations. Full results are expected in a few weeks, but early findings suggest that the telescope could lose significant amounts of observing time to satellite trails near dusk and dawn.


This interesting answer to What is the LSST's plan to address frequent satellite trails in data? quotes:

From the LSST webpage:

The first group of Starlink satellites are sufficiently bright during dawn and dusk (when LSST would be surveying) that the trail would exceed sensor saturation, generating uncorrectable artifacts in the data. If instead these satellites were painted flat black making them a factor of 25 fainter, satellite trails should be less of a challenge for LSST due to its specific design.In that case LSST's frequent imaging of the same region of sky will provide enough data to correct for unsaturated satellite trails or other anomalies.

If something is black at visible wavelengths it will absorb sunlight much more readily, but if it is black at thermal infrared wavelengths it will also reradiate heat absorbed much more readily as well.

Question: Is it feasible to paint SpaceX Starlink satellites black so as not to frequently saturate the CCDs of the Large Synoptic Survey Telescope (main site)? Or would that be to hot without adding a separate thermal radiator of some kind?

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    $\begingroup$ I guess this is about cutting peaks. Satellite reflections are far from diffuse, which causes occasional flashes. Thermal radiation would still have the same amount of energy, but be almost perfectly diffuse. $\endgroup$ – Hohmannfan Oct 2 at 14:28
  • $\begingroup$ @Hohmannfan that's a really good point! Satellites (especially smallsats) are rarely brighter than the brightest stars and planets unless they flare. Hmm... I've just asked How do large telescopes, especially plans for the LSST, avoid saturation artifacts from the brightest stars and planets? $\endgroup$ – uhoh Oct 3 at 3:06
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    $\begingroup$ The question needs to be asked: does the solar panel or the body of the Starlink satellites reflect light more often? $\endgroup$ – CourageousPotato Oct 9 at 8:45
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In general satellites are not "painted". They are covered in a variety of Multi-Layer Insulation (MLI) blankets with varying optical qualities. I have seen MLI in silver, black, and gold - sometimes on the same spacecraft. In addition, spacecraft often have radiators (most usually silver) and sometimes even louvers that cover radiators.

A spacecraft is not a monolithic thermal node. It will have areas that are naturally much warmer than others due to component power dissipation. It will also have areas that need to be kept colder than others - such as batteries or thermal instruments.

One additional consideration is that one of the largest components of optical glare/reflections are the cover glasses on the solar cells of the arrays. Clearly you would not want to paint these black.

So the answer to the question - yes the optical surfaces of a Starlink satellite can (and should, in my opinion) be changed to reduce reflections. However, it is far from a simple "paint the spacecraft black"

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    $\begingroup$ Spot on. Worth adding that its something that would, in the normal run of things, have to be addressed in the initial design phase rather than as a modification, because of the (likely) strong knock-on effects. That doesn't mean of course its not possible; nor does it say anything about whether it would be expensive or not. $\endgroup$ – Puffin Nov 20 at 18:10

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