Illustration: Test of the mechanism of rotation (scanner) of the PHEBUS instrument’s telescope during functional ground tests at the ESA/ESTEC test centre in Noordwijk, Holland, in October 2017, after integration of the instrument into The Bepi Satellite (formerly known as MPO : Mercury Planetary Orbiter).
As a reminder, the light collecting system of the instrument includes a stray light baffle and an off-axis parabolic mirror, the assembly acting as a telescope (visible part of the instrument outside the satellite). The telescope is mounted on a one degree-of-freedom scanning system (“scanner”) provided by the Russian Space Agency (IKI). This scanner allows us to turn the telescope with a precision less than a degree in order to adjust the line of sight of the instrument. More details here.
In order to preserve the integrity of the pointing mechanism during the launch phase, trying in terms of vibration, a locking system was installed, blocking the rotation of the scanner. This one was unlocked on October 22, 2018 (see the News Phebus is behaving well!)
During non-operational periods the telescope is in its “parking” position, facing into a support (“parking bracket”) attached to the spacecraft, and protecting the telescope’s entrance as illustrated in the video.
During the operational phases, the line of sight of the telescope is adjusted by rotating the pointing mechanism, by sending specific telecommands.