According to Hesselgren: "The unit of highest dignity which can be found in architecture is the experience of architectonic room and the interplay between external and internal room, and exterior" . Architectonic room is both sculptural and spatial. It can be viewed as a tectonic object, entered, and occupied. Exterior room is the outdoor space bounded by the exterior of a building and its surrounding landscape (both natural and man-made). The element that most distinguishes exterior from interior room is the ceiling - its height, form, color, texture, and whether it is natural or artificial. (Forest canopy and open sky are also ceilings.)
Visually, architecture manifests complex figure-ground relationships that change as the viewer moves around and through it. From the outside, it is a figure against the ground of the landscape. From the inside, it is the ground against which other interior figures are viewed. Windows are perceived as figures against the ground of the wall: one can imagine sliding a window over a wall (this happens in cartoons and CAD programs), though structurally it is of course impossible. Norberg-Schulz stresses the importance of the figure-ground relationship in the identification of place: "In general any enclosure becomes manifest as a 'figure' in relation to the extended ground of the landscape. A settlement loses its identity if this relationship is corrupted" . Hesselgren goes on to hypothesize: "The perception of outdoor restricted space is an essential factor for a happy life" .
All this poses several problems for space station design. Due to technical difficulties and hazards, it is almost inconceivable for a crew member to take a leisurely stroll outside, just for a change of scenery. Even if he could, he would find the restricted outdoor space to be limited to the nooks and crannies defined by modules, trusses, antennas, solar collectors, and free-flying pallets in constellation. Beyond the immediate vicinity of the station, the outdoor space is the most unrestricted imaginable - an infinite void that provides no sense of place.
Forays into unrestricted space with the free-flying manned maneuvering unit (MMU) seem to support the statements of Norberg-Schulz and Hesselgren. Shuttle astronaut Robert Stewart (mission 41-B, 1984) took the MMU on one of its first test flights, and turned his back on the Earth and the orbiter to face the blackness of space. "That was very spooky ... I was not prepared for my mental reaction to it. But when I couldn't see the Earth or the orbiter, I spent 10 or 15 seconds like that. And then I got to feeling, 'Boy, it's really lonely out here. Let's turn around and see if the Earth and the orbiter are still there.' ... When I couldn't see anything else, just blackness and me, I got to wanting to feel some contact with something. When I turned around, things were normal again, and I could go about my business" .
Also, as Hesselgren points out, a filled distance appears greater than an empty distance. Several important factors for depth perception - such as superposition, atmospheric haze, parallax of movement, and reference horizon - do not occur in empty space. The ironic result is that infinite empty space has a shallow quality. It's difficult to distinguish a small close object from a large distant one, and according to Stewart, depth perception is limited to about 70 or 80 feet .
Be that as it may, extravehicular activity is still carefully managed and authorized only when necessary to perform certain critical tasks - not for recreation. Until such time as space suits become safer and easier to use, the perception of outdoor restricted space will have to happen from within the confines of the station, or not at all.
This leads naturally to the discussion of windows. It has been said that the history of architecture is the history of windows: the character of a building is largely determined by their size, shape, and distribution. The psychological importance of the views they provide - particularly to shut-ins - should not be underestimated. Ulrich found that surgery patients with a view to a small stand of deciduous trees recovered quicker, took fewer potent analgesics, and registered fewer negative comments in the nurses' notes, than matched patients with a view to a "comparatively monotonous ... largely featureless" brick wall . Oberg and Oberg document the popularity of windows among both American and Soviet space crews. The Skylab window, "whose very existence was the subject of ferocious and drawn-out debate", was "constantly smudged with nose- and fingerprints" that testified to its psychological as well as scientific value .
Because of the technical problems they pose, some engineers have suggested forgoing windows in spacecraft, in favor of closed-circuit television cameras and monitors. There are several strong arguments against such a move. No monitor in existence can match the resolution of the human eye or its sensitivity to variations in color and brightness. In fact, even photographic film has failed to record all of the details observed by astronauts through their windows. With video technology, there are always questions: Is the equipment working properly? Are the colors true or "enhanced"? Is the image real, computed, or prerecorded? The old saying - "Seeing is believing" - does not apply to video. Perhaps most importantly, replacing windows with video monitors would rob the astronauts of their few remaining cues to depth perception: parallax of movement (Earth and star field relative to immediate surroundings), binocular convergence, and focus. Video technology literally brings the outside in, and in so doing, destroys the distinction between out and in. Video certainly has an important role to play, but it is a complement to direct visual observation, not a replacement .
Norberg-Schulz points out that "the sky is as large as the space from which it is seen" . Thus, constraints on the number and size of windows and the infrequent opportunities for extravehicular activity create another irony of spaceflight: for the casual observer, the view of space is better from Earth than it is from space.