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The image Photo ID: ISS049-E-003166 can be found in Flikr and Wikimedia Commons as well as in Spaceflight Now.

There is a long (perhaps 1 meter?) green structure that is sticking out from the side of a Soyuz spacecraft. It has windows on the end that look like they might be for the mirrors of a periscope used for docking.

What is it for? What kind of optics are in there? Presumably during launch it is not deployed like this; is it mechanically extended like a submarine periscope, or does it fold out after a fairing deploys after launch?

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  • $\begingroup$ see also space.stackexchange.com/questions/3232/… $\endgroup$ – JCRM Jan 24 '18 at 15:46
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    $\begingroup$ Did you google soyuz periscope before asking? $\endgroup$ – Russell Borogove Jan 24 '18 at 16:28
  • $\begingroup$ @RussellBorogove I could guess that it's most likely a periscope just by looking at it. But a search did not help with "What kind of optics are in there?" or how it is configured (tucked away) during launch. I still can't really understand from the drawing in this answer if it's truly folded, or how it would be extended laser. $\endgroup$ – uhoh Jan 24 '18 at 16:46
  • $\begingroup$ @RussellBorogove there are also eight little windows at the base, and they seemed to be mentioned in this link, in the paragraph containing the term "Vzor periscope device". nasa.gov/mission_pages/station/structure/elements/soyuz/… So I believe the optics are a bit complex. $\endgroup$ – uhoh Jan 24 '18 at 16:53
  • $\begingroup$ Nice image of where it's located relative to the crew; i.stack.imgur.com/jKiq7.jpg $\endgroup$ – uhoh Jan 24 '18 at 16:56
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The Russian designation for the device (at least the transliterated designation) is BCK-4. Here's the writeup on it from the Soyuz Crew Operations Manual (reference at bottom of answer).

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BCK-4 COSMONAUT VISUAL SYSTEM

BCK-4 Purpose

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 (Fig. 1). enter image description here

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.

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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”).

ВНУК-К NIGHT TIME CONTROL VISOR

ВНУК-К Purpose

The ВНУК-К Night Visor is used for visual monitoring the spacecraft heading attitude through the BCK-4 at the shadow part of the orbit and for observing faintly illuminated object through the window.

ВНУК-К Composition

The ВНУК-К сonsists of (Fig. 2): collective, objective, electronic/optical converter ЭОП(brightness converter) and biocular.

The Infrared rays are passing through the collective (adapter of BCK-4 and ВНУК-К optical systems), then through the objective and are focused at the ЭОП converter input plane. The ЭОП converts the IR signal into video image which is viewed by the cosmonaut via the biocular. The biocular and objective are fixed to the ЭОП by screwed joints and the collective is connected to it by means of special pin locks. For the spacecraft heading attitude monitoring a rotatable grid is used. The ВНУК-К Visor principal controls are located at the ЭОП converter:

  • “Сеть” toggle switch - for power supply switching ON;
  • “Яркость” knob - for brightness adjustment;
  • Grid control knob. The Visor field of view can be closed by means of a shutter located in the collective, the shutter control knob having only two positions: “Откр” (Open) “Закр” (Closed).

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Crew Operation with ВНУК-К

ВНУК-К is used at the shadowed part of the spacecraft orbit for monitoring orbital attitude system (ОСК) and for the target acquisition and its attitude monitoring during approach and docking in the shadow. When operated jointly with the ВСК-4 it is necessary to: take the covers off, open the shutter, switch ON the “Сeть” toggle switch at the ВНУК-К and using the “Яркость” knob adjust the image brightness to optimal level. To monitor the spacecraft heading attitude using the “Сетка” knob match the grid vertical strokes with the terrain run direction and read the angle on the knob scale. When the ВНУК-К is operated in autonomous mode it is necessary to dismount he collective. Other operations are similar to those of the joint mode with the ВСК-4. After every 5 hours of the ВНУК-К continuous operation an interval of 30 minutes is necessary.

Reference "Soyuz Crew Operations Manual (SoyCOM) (ROP-19) (Final) , Yu. A. Gagarin Cosmonaut's Training Center, NAS15-10110, 0004AE7a (ROP-19), April 1998" which is in English, although translated, it's an OK job.

You can find a copy at this page.

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  • $\begingroup$ The translation is indeed OK, but the style is optimized for people already accustomed to reading similar material. I'm getting that this is generally used to look at points on the Earth for "heading attitude" but I don't know if that's different than just attitude. It has an ND filter used when view is bright. View direction "0 degrees (“Ориент”) (Attitude Monitor) and 84 degrees (“Причал”) (Berthing)." controlled by motor-driven mirror (assumed to be inside the dual-windowed green box at the end). Here's what I don't understand yet: 1) is this like an SLR in that it focuses an image onto a.. $\endgroup$ – uhoh Mar 29 '18 at 1:21
  • $\begingroup$ ..ground glass screen, and one just looks at the screen? 2) It says that the ВНУК-К includes an IR imaging sensor and a display, which is viewed through a "binocular". There is mention of an objective, but I don't know if that's part of the ВНУК-К or it refers to a component that is part of the BCK-4. 3) Does one take the ВНУК-К and put it on top of the BCK-4 and use it when necessary, then remove and stow it when viewing directly using visible light? (I don't have FLASH, rats!) $\endgroup$ – uhoh Mar 29 '18 at 1:27
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    $\begingroup$ I can't confirm it's a "binocular". The text consistently says "biocular" so I don't know if that's something different or not. I couldn't get the document at first either, I thought the page didn't work, but @Innovine successfully got it which made me look into it and find the Flash requirement. $\endgroup$ – Organic Marble Mar 29 '18 at 15:11
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    $\begingroup$ I don't have FLASH but I visited the site and found that there is a download button that works, yay! $\endgroup$ – uhoh Apr 1 '18 at 17:53
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It is used for star alignments, which is a backup system in case of serious navigation errors. It can also be used for manual docking operations, if required.

As is mentioned in this question, it is discarded prior to reentry. During launch, it is under the shroud, as seen below.

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    $\begingroup$ Is it not also used during docking approach? My 17 seconds of googling suggested so. $\endgroup$ – Russell Borogove Jan 24 '18 at 16:28
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    $\begingroup$ Soyuz normally docks automatically, but yes, it can be used for manual docking. Added that in. $\endgroup$ – PearsonArtPhoto♦ Jan 24 '18 at 16:32
  • $\begingroup$ @RussellBorogove there is a flip mirror (like an SLR) so that it can view forward, or straight out the end, thus the two windows $\endgroup$ – uhoh Jan 24 '18 at 16:47
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    $\begingroup$ @PearsonArtPhoto from the drawing I can't really make out where the periscope is. Is it folded somehow? $\endgroup$ – uhoh Jan 24 '18 at 16:49
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    $\begingroup$ The source linked in the other question suggests it uses the earth for attitude information, not stars. $\endgroup$ – JCRM Jan 24 '18 at 17:50
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@OrganicMarble's thorough and well-sourced answer does an excellent job. I happened to have spotted the screen in this (currently) six year old NASA Johnson video Inside the Russian Soyuz Spacecraft. Here's a screen shot and a brief transcription of some of the information explained by NASA astronaut "Mike Fincke, a veteran of the Soyuz and Shuttle..."

You can see the actual location of the periscope's screen from the viewpoint of the astronauts, and how it might be used to view situations, for example if moving manually if the Kurz system has an issue.

You can see there’s a screen right here, it’s a periscope that looks out either in front of the vehicle, or below us, as well as some control sticks here so we can actually manually fly from the center seat.

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below: Earthy visiting the Soyuz capsule and checking out the periscope's screen. Source David Saint-Jacques/CSA

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