Flown Soyuz Descent Module Navigational Internal  Cabin Periscope VSK-4 (VZOR).

The BCK-4 Cosmonaut Visual System is designed for the spacecraft attitude monitoring in orbital flight phase, docking procedure monitoring and space object visual observation.

BCK-4 Composition

The BCK-4 has external and internal (cabin) parts which are installed on the window located in the CA o Module at the spacecraft “-Y” axis. The instrument visor axis is 6 inclined relative “-Y” axis. The external part consists of the central viewing tube and the peripheral tubing unit . The instrument line of sight can only be in two fixed positions: 0 degrees (“Ориент”) (Attitude Monitor) and 84 degrees (“Причал”) (Berthing). The position is changed by turning the mirror unit in the central tube head using an electric motor. The cabin part includes the instrument body with elements of the two optical systems and the control knob panel.

The “Центр. Светофильтр” (Central Light Filter) knob is used to insert a neutral light filter into the central optical system field of view.The “Экран” (Screen) knob is used for focus adjustment by moving the screen along the visor axis. Rotating the “Светофильтр периф ep” (Peripheral Light Filter) knob a dark light filter can be introduced into any of the eight peripheral tubes. The “Шторка” (Shutter) knob purpose is to shut off the field of view of all the eight peripheral tubes simultaneously.

Crew operations with the BCK-4

Throughout all the orbital flight the crew uses the BCK-4 as the principal instrument for monitoring the spacecraft attitude and attitude maneuvers for which the visor axis is set into the “Ориент” position by КСП-Л В-18 command.

The basic attitude - orbital Earth coordinate system (OCK) with preset heading angle is considered established when the reference object (Earth) apparent run direction in the central system field of view is parallel to the heading indicator stroke rotated at the preset angle. And the Earth horizon in the screen peripheral zone must be parallel to the corresponding strokes or coincide with them.

For approach/docking the visor line is set in the “Причал” position by the КСП-Л В-17 command. At the range of 2 km the crew selects the screen according to the illumination conditions. In the shadow the lens screen is used and in the sunlight the matte screen is preferable. At this range it is possible to estimate the range using the screen grid. Charts and tables for range determination by the target angular size are included into the FDF ((“Nominal Modes”).

Extremely Rare Artefact. Periscope put on special stand for display. Good condition.