  The number of satellites launched into Earth's orbit has almost tripled in
the last three years due to the increasing commercialisation of space. Multiple
satellite constellations, consisting of over 400,000 individual satellites,
have either been partially launched or are proposed for launch in the near
future. Many of these satellites are highly reflective, resulting in a high
optical brightness that affects ground-based astronomical observations. Despite
this caveat, the potential effect of these satellites on gamma-ray-observing
Imaging Atmospheric Cherenkov Telescopes (IACTs) has largely been assumed to be
negligible due to their nanosecond-scale integration times. However, this
assumption has not been verified to date. As IACTs are sensitive to optical
wavelength light, we aim to identify satellite trails in data taken by the High
Energy Stereoscopic System (H.E.S.S.) IACT array. In particular, this study is
aimed at quantifying the potential effects on data quality and extensive air
shower event classification and reconstruction. Using night sky background
measurements from H.E.S.S., we determined which observation times and pointing
directions are affected most by these satellite trails. We then evaluated their
impact on the standard Hillas parameter variables used for event analysis. Due
to the brightest trails, false trigger events can occur, however, for most
modern analyses, the effect on astronomical results will be minimal. We observe
a mild increase in the rate of trail detections over time, which is partially
correlated with the number of satellite launches. Overall, the fraction of
H.E.S.S. data affected is currently minimal. We note that these trails could
still have a non-negligible effect on future Cherenkov Telescope Array
observations if advanced analysis techniques designed to lower the energy
threshold of the instrument are applied.
