The Soyuz is one of the spacecrafts that refurnish the International Space Station, and today the only one to transport personnel. To allow the passing of the load it has to couple to the ISS with a complex manoeuvre. Pilots use a viewer to measure with precision the position and the approach speed. Thanks to small boosters managed through a direction regulator they align the spacecraft to the ISS to couple it. The astronauts can use this viewer also to watch the surrounding space.