Payload – Optics

Because the science instrument has to fit in a Cubesat mission, the optical configuration selected for the telescope is a very compact, yet very simple, one. The telescope is based on a 5 cm off-axis parabola, which reflects the light coming from the stars on a folding mirror. After this second reflection, the light is injected into the single-mode fiber, placed in the focal plane of the main parabola. The total system has a focal length of 13.5 cm, and yet it fits almost perfectly in a 10 x 10 x 10 cm^3 single Cubesat unit!

Overview of the mechanical structure of the science instrument on-board PicSat.

This system is extremely compact, but it has one major drawback: because it uses an off-axis parabola, its overall optical quality rapidly degrades if the system is not perfectly aligned and/or if the target is not centered. To make sure that the telescope can be tunned on the ground, and that the alignment will resist to the vibrations during the launch, an adjustment system has been designed of the mount of the secondary mirror. The M2 support, which holds the secondary mirror (M2) is mounted on the head block with 3 screws. A set of peelable washers are placed between the head block and the M2 support on each screw, allowing for a very fine and robust tunning of the tip, tilt, and focus of the instrument.

Mount of the secondary mirror.