Undersea Station: Portholes

(Update 15.07.2020: complete makeover of the article; replaced outdated information; added new aspects from different sources like NASA’s Human Integration Handbook, 2010)

Windows are essential and present the most important reason to operate an underwater habitat. They are necessary for operation, safety and marketing. In particular…

  • following external activities
  • through-the-hatch safety viewing
  • monitoring decompression/recompression
  • general photography

Further they are supportive for the crew psychology to

  • offset the claustrophobic effects of living in confined spaces and long-term isolation
  • provide motivational, recreational, educational, scientific and awe-inspiring experiences
  • provide natural illumination, ambience and day/night cycles

In terms of marketing, windows are probably the most important component of the system. They are fundamental reason for potential visitors to reserve a short or long stay, tool for observing the outside world and attraction to look from the outside into the inside (tourism marketing).

At the same time they are one of the weak points of the system and small irregularities of the material quality and seals could lead to the collapse of the structure. Therefore, the thickness and quality of the glass and fixtures should be designed according to highest possible load.

From these requirements is seems suitable to create two categories of windows:

  • safety windows (hatches, trunks and entrance)
  • mission windows (observations, psychology…)

General considerations

Traffic – Except for hatch windows, the windows should be located so that use of windows will not interfere with required traffic flow.

Tasks – The number, size, location, and orientation of windows must provide an optimum field of view to support expected tasks.

Lighting and Glare – The following are lighting and glare considerations for window location:

  • Glare – Bright interior illumination will reflect from a window surface and can interfere with the ability to see or take images through the window.
  • Light-sensitive activities – Exterior light entering through windows will interfere with light-sensitive activities such as sleeping, use of monitors or displays, or tasks requiring dark adaptation.
  • Natural light for illumination – A properly designed and located window can be used as a supplementary, alternative, or contingency source of internal spacecraft illumination.

Wındow Support

The usability of windows is made possible or enhanced by the use of support equipment located adjacent to windows, such as seats, mounts and brackets (for instruments, imagers, and cameras), and electronic connectivity (for communications, power, command, data, and imaging and video equipment and displays). This support equipment must be provided to the fullest extent possible. Other than for electronic connectivity, such support equipment should be temporary and unobtrusive wherever possible and practical. Temporary support equipment must be removable and replaceable by one crewmember in less than 15 seconds without the use of tools.

The architectural arrangement of equipment near windows should allow adequate volume for the performance of tasks by any crew member.

Connectivity for communications, power, command, data, and imaging and video equipment and displays must be provided within 1.5 m of all windows.

Condensation Prevention System (CPS)

Condensation formation on windows interferes with the safe execution of science, observation, photography, and other viewing tasks. For all windows a means to prevent condensation such as an electro-thermal or forced air condensation prevention system (CPS) must be provided to prevent condensation from forming on any window pane surface when the window is exposed to:

  • The normally expected range of environmental conditions.
  • Human breath condensation at a mouth-to-pane distance of 10 cm (metabolic rate = 30 (± 5) breaths/minute, single person).

Window Replacement

For a replacement of a window this proposal was made: “The window might be inserted from the inside into the slot and bolted to an outer ring. Should there be a problem with the seals or the window itself, a window cover would be placed from the outside. The water between window and cover would be pumped off (valve under the window-bay). The window can be taken off to the inside, repaired/replaced and installed back again. Then the interspace is flooded again and the backup dome removed.” In principle, this approach is likely to be able to operate. An important detail is, that the window size in general should not exceed the size of the entry hatch.


To be investigated

  • Is the Rayleigh Limit also relevant for windows in an underwater habitat?
  • How much does the quality of glass corrupt the sight during night time and the use of uv light?
  • What material has to be used to minimize degradation of windows and sealings under long-term exposition to salt and water?


Automatic window cover for emergencies

Another contribution suggested the idea of a safety dome in a 1-bar habitat: “A security dome could be permanently installed above the window on the outside. In case of a porthole burst, an alarm system could trigger the closing of the dome over the window slot. It would then be pressed onto the slot by the incoming water. The lower interior pressure would then block the inflow and seal the hole thus. This assumes of course that the respective seals at the edge of the dome are constantly cleaned. “

BOOT fair 2007

On the BOOT fair 2007, we also had the pleasure to talk to Arnd Schöttler, then director of the diving sports department of BOOT Dusseldorf. We were especially interested in the large windows of the diving tower, a pool, in which for example underwater rugby was demonstrated, while visitors of the fair watch from outside. He told us the glass panels were 8 cm thick and would each weigh 300kg. At first it might seem very heavy, on the other hand, these panels were not curved but flat, which increases the thickness and therefore the weight. The panels in the diving tower were apparently made by the company Röhm in Darmstadt several years ago.

BOOT 2007: Diving Tower

BOOT 2007: Diving Tower


This article contains adaptations from the Human Integration Handbook (HIDH), NASA/SP-2010-3407

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