  The operation of an intelligent reflecting surface (IRS) under predictable
receiver mobility is investigated. We develop a continuous time system model
for multipath channels and discuss the optimal IRS configuration with respect
to received power, Doppler spread, and delay spread. It is shown that the
received power can be maximized without adding Doppler spread to the system. In
a numerical case study, we show that an IRS having the size of just two large
billboards can improve the link budget of ground to Low Earth Orbit (LEO)
satellite links by up to 6 dB. It also adds a second, almost equivalently
strong, communication path that improves the link reliability.
