  The effect of satellite constellations on observations in the visible and IR
domains is estimated, considering 18 constellations in development by SpaceX,
Amazon, OneWeb, and others, with over 26,000 satellites, constituting a
representative distribution. This study uses a series of simplifications and
assumptions to obtain conservative, order-of-magnitude estimates of the
effects.
  The number of illuminated satellites from the constellations above the
horizon ranges from ~1600 right after sunset, decreasing to 1100 at the end of
astronomical twilight, most of them (~85%) close to the horizon (< 30deg). The
large majority of these satellites will be too faint to be seen with the naked
eye: at astronomical twilight, 110 brighter than mag 5. Most of them (~95%)
will be close to the horizon. The number of naked-eye satellites plummets as
the Sun reaches 30-40 deg below the horizon, depending on the latitude and
season.
  The light trails caused by satellites would ruin a small fraction (below the
1% level) of exposures using narrow to normal field imaging or spectroscopic
techniques in the visible and near IR during the first and last hours of the
night. Similarly, the thermal emission of the satellite would affect only a
negligible fraction of thermal IR observations. However, wide-field exposures,
as well as long medium-field exposures,would be affected at the 3% level during
the first and last hours of the night. Furthermore, ultra-wide imaging
exposures on a very large telescope (eg NSF's Rubin Observatory, LSST), would
be significantly affected, with 30 to 40% of such exposures being compromised
during the first and last hours of the night.
  Coordination between the astronomical community, satellites companies, and
government agencies is therefore critical to minimise and mitigate the effect
on astronomical observations, in particular on survey telescopes.
