«Windows» in orbit, or All about portholes

When looking at a spacecraft, the eyes usually run up. Unlike an airplane or a submarine with extremely "licked" contours, outside there is a mass of all kinds of blocks, structural elements, pipelines, cables ... But there are also details on board that are clear at first glance to anyone. Here are the portholes, for example. Just like airplane or sea! In fact, this is far from the case ...

From the very beginning of space flights there was a question: "What is overboard - it would be nice to see!" That is, of course, there were certain considerations on this score - astronomers and pioneers of cosmonautics did their best, not to mention science fiction writers. In Jules Verne's novel From Earth to the Moon, the heroes go on a lunar expedition in a shell equipped with glass windows with shutters. Through large windows, the heroes of Tsiolkovsky and Wells look into the Universe.

When it came to practice, the simple word "window" seemed unacceptable to space technology developers. Therefore, what the cosmonauts can look through from the ship to the outside is called, no less than special glass, and less "ceremoniously" - portholes. Moreover, the porthole for people proper is a visual porthole, and for some equipment it is an optical porthole.

The windows are both a structural element of the spacecraft shell and an optical device. On the one hand, they serve to protect the instruments and crew inside the compartment from the external environment, on the other hand, they must ensure the operation of various optical equipment and visual observation. Not only, however, observation - when on both sides of the ocean they drew equipment for "Star Wars", through the windows of warships they were going to take aim.

Americans and English-speaking missilemen in general are baffled by the term "porthole". They ask again: "Are these windows, or what?" In English, everything is simple - there is a window in the house or in the Shuttle, and there are no problems. But English sailors say porthole. So Russian space builders are probably closer in spirit to overseas shipbuilders.

Two types of windows can be found on observation space vehicles.

The first type completely separates the imaging equipment located in the pressurized compartment (lens, cassette unit, image receivers and other functional elements) from the “hostile” external environment. Zenit spacecraft are built according to this scheme.

The second type of windows separates the cassette part, image receivers and other elements from the external environment, while the lens is located in an unpressurized compartment, that is, in a vacuum. This scheme is used on spacecraft of the "Yantar" type. With such a scheme, the requirements for the optical properties of the illuminator become especially stringent, since the illuminator is now an integral part of the optical system of the imaging equipment, and not a simple "window into space".

It was believed that the astronaut would be able to control the spacecraft based on what he could see. To a certain extent, this was accomplished. It is especially important to "look ahead" during docking and when landing on the moon - there American astronauts have repeatedly used manual control during landing.

For most astronauts, the psychological concept of top and bottom is formed depending on the environment, and portholes can also help with this. Finally, portholes, like windows on Earth, serve to illuminate the compartments when flying over the illuminated side of the Earth, the Moon or distant planets.

Like any optical device, a ship's window has a focal length (from half a kilometer to fifty) and many other specific optical parameters.

When creating the first spacecraft in our country, the development of windows was entrusted to the Scientific Research Institute of Aviation Glass of the Minaviaprom (now it is the Scientific Research Institute of Technical Glass). The State Optical Institute named after V.I. S.I. Vavilov, Research Institute of the rubber industry, Krasnogorsk Mechanical Plant and a number of other enterprises and organizations. The Lytkarinsky Optical Glass Plant near Moscow made a great contribution to the melting of glasses of various brands, the manufacture of illuminators and unique long-focus lenses with a large aperture.

The task turned out to be extremely difficult. Still, the production of aircraft lanterns was mastered at one time for a long and difficult time - the glass quickly lost its transparency, covered with cracks. In addition to ensuring transparency, the Patriotic War forced the development of bulletproof glass, after the war, the increase in the speeds of jet aircraft led not only to an increase in strength requirements, but also to the need to preserve the properties of the glazing during aerodynamic heating. For space projects, glass, which was used for lanterns and aircraft windows, was not suitable - not the same temperatures and loads.

The first space windows were developed in our country on the basis of the Decree of the Central Committee of the CPSU and the Council of Ministers of the USSR No. 569-264 of May 22, 1959, which provided for the beginning of preparation for manned flights. Both in the USSR and in the USA, the first windows were round - it was easier to design and manufacture them. In addition, domestic ships, as a rule, could be controlled without human intervention, and, accordingly, there was no need for a too good survey "on the plane". Gagarin's "Vostok" had two windows. One was located on the entrance hatch of the descent vehicle, just above the astronaut's head, the other at his feet in the body of the descent vehicle.

It is not out of place to recall by the names of the main developers of the first windows in the Scientific Research Institute of Aviation Glass - this is S.M. Brekhovskikh, V.I. Alexandrov, H.E. Serebryannikova, Yu.I. Nechaev, L.A. Kalashnikov, F.T. Vorobiev, E.F. Postolskaya, L.V. King, B.P. Kolgankov, E.I. Tsvetkov, S.V. Volchanov, V.I. Krasin, E.G. Loginova and others.

For many reasons, when creating their first spacecraft, our American colleagues experienced a serious "mass deficit". Therefore, they simply could not afford the level of automation of control of the spacecraft, similar to the Soviet one, even taking into account the lighter electronics, and many functions for controlling the spacecraft were confined to experienced test pilots selected to the first cosmonaut corps. At the same time, in the original version of the first American spacecraft "Mercury" (the one about which it was said that the astronaut does not enter it, but puts it on himself), the pilot's window was not provided at all - there was no place to take even the required 10 kg of additional mass.

The porthole appeared only at the urgent request of the astronauts themselves after Shepard's first flight. A real, full-fledged "pilot's" porthole appeared only on the Gemini - on the crew's landing hatch. But it was made not round, but of a complex trapezoidal shape, since for full manual control when docking, the pilot needed a forward view; on the Soyuz, by the way, for this purpose a periscope was installed on the porthole of the descent vehicle. Corning was responsible for the development of the windows for the Americans, and the JDSU division was responsible for glass coatings.

On the command module of the lunar Apollo, one of the five portholes was also placed on the hatch. Two others, providing rendezvous when docked with the lunar module, looked ahead, and two more "side" ones allowed a glance perpendicular to the longitudinal axis of the ship. The Soyuz usually had three windows on the descent vehicle and up to five on the utility compartment. Most portholes are at orbital stations - up to several dozen, of various shapes and sizes.

An important stage in the "window building" was the creation of glazing for space aircraft - Space Shuttle and Buran. "Shuttles" are planted like an airplane, which means that the pilot needs to provide a good view from the cockpit. Therefore, both American and domestic developers have provided for six large windows of complex shape. Plus a pair in the roof of the cab - this is already to ensure docking. Plus rear windows for payload operations. And finally, through the porthole on the entrance hatch.

In the dynamic sections of the flight, completely different loads act on the front windows of the Shuttle or Buran, different from those to which the windows of conventional descent vehicles are subject. Therefore, the strength calculation is different here. And when the shuttle is already in orbit, there are “too many” windows - the cockpit overheats, the crew gets extra “ultraviolet”. Therefore, during orbital flight, some of the windows in the Shuttle cockpit are closed with Kevlar shutters. But the "Buran" inside the windows had a photochromic layer, which darkened under the action of ultraviolet radiation and did not let the "excess" into the cockpit.

The main part of the porthole is, of course, glass. “For space,” not ordinary glass is used, but quartz. At the time of Vostok, the choice was not very great - only SK and KV brands were available (the latter is nothing more than fused quartz). Later, many other types of glass were created and tested (KV10S, K-108). They even tried to use SO-120 plexiglass in space. The Americans, on the other hand, know the Vycor brand of thermal and shock-resistant glass.

For windows, glasses of different sizes are used - from 80 mm to almost half a meter (490 mm), and recently an eight-hundred-millimeter "glass" appeared in orbit. The external protection of "space windows" is discussed later, but to protect the crew members from the harmful effects of near ultraviolet radiation, special beam-splitting coatings are applied to the windows of the windows operating with non-stationary installed devices.

The porthole is not only glass. To obtain a solid and functional design, several glasses are inserted into a holder made of aluminum or titanium alloy. Even lithium was used for the Shuttle's windows.

To ensure the required level of reliability, several glasses were initially made in the window. In which case, one glass will break, and the rest will remain, keeping the ship sealed. Domestic windows on the Soyuz and Vostoks had three glasses each (on the Soyuz there is one two-glass window, but it is covered with a periscope for most of the flight).

On "Apollo" and "Space Shuttle" "windows" are mainly three-glass, but "Mercury" - their "first swallow" - the Americans have already equipped with a four-glass porthole.

Unlike the Soviet ones, the American porthole on the Apollo command module was not a single assembly. One glass worked as part of the shell of the bearing heat-shielding surface, and the other two (in fact, a two-glass window) were already part of the pressurized circuit. As a result, these windows were more visual than optical. Actually, taking into account the key role of the pilots in the management of the Apollo, such a decision looked quite logical.

On the Apollo's lunar cockpit, all three windows themselves were single-glass, but from the outside they were covered by an external glass that did not fit into the pressurized circuit, and from the inside - by an internal safety plexiglass. Single-glass windows were also installed later on orbital stations, where the loads are still less than those of the descent vehicles of spacecraft. And on some spacecraft, for example, on the Soviet interplanetary stations "Mars" in the early 70s, in one clip were actually combined several windows (two-glass compositions).

When a spacecraft is in orbit, the temperature difference on its surface can be a couple of hundred degrees. The expansion coefficients of glass and metal are naturally different. So, seals are placed between the glass and the metal of the clips. In our country, they were dealt with by the Research Institute of the rubber industry. The construction uses vacuum-resistant rubber. The development of such seals is a difficult task: rubber is a polymer, and cosmic radiation over time "chops" polymer molecules into pieces, and as a result, "ordinary" rubber simply crumbles.

Upon closer examination, it turns out that the design of domestic and American "windows" differ significantly from each other. Almost all glass in domestic designs is in the form of a cylinder (of course, with the exception of glazing for winged vehicles of the Burana or Spiral type). Accordingly, the cylinder has a side surface that needs to be specially treated to minimize glare. For this, the reflective surfaces inside the window are covered with special enamel, and the side walls of the chambers are sometimes even pasted over with semi-velvet. The glass is sealed with three rubber rings (as they were first called - sealing rubber bands).

The windows of the American Apollo ships had a rounded side surface, and a rubber seal was stretched over them, like a tire on a car rim.

It will no longer be possible to wipe the glass inside the window with a cloth during the flight, and therefore absolutely no debris should get into the chamber (inter-glass space). In addition, the glass should neither fog up nor freeze. Therefore, before the launch, not only the tanks, but also the windows are refueled at the spacecraft - the chamber is filled with especially pure dry nitrogen or dry air. To "unload" the glass itself, the pressure in the chamber is provided for half that in the sealed compartment. Finally, it is desirable that the inside surface of the compartment walls is not too hot or too cold. For this, an internal plexiglass screen is sometimes installed.

Glass is not metal; it breaks down in a different way. There will be no dents here - a crack will appear. The strength of the glass depends mainly on the condition of its surface. Therefore, it is hardened by eliminating surface defects - microcracks, notches, scratches. For this, the glass is etched, tempered. However, glasses used in optical devices are not usually handled this way. Their surface is hardened by the so-called deep grinding. By the beginning of the 70s, the outer glasses of optical windows had learned to be strengthened by ion exchange, which made it possible to increase their abrasion resistance.

To improve light transmission, the glass is coated with a multilayer antireflection coating. They may include tin oxide or indium oxide. Such coatings increase light transmission by 10–12%, and they are applied by reactive cathode sputtering. In addition, indium oxide absorbs neutrons well, which is useful, for example, during a manned interplanetary flight. Indium in general is the "philosopher's stone" in the glass industry, and not only in the glass industry. Indium-coated mirrors reflect most of the spectrum equally. In rubbing knots, indium significantly improves abrasion resistance.

In flight, the windows can also get dirty from the outside. Already after the start of flights under the Gemini program, the astronauts noticed that fumes from the heat-shielding coating were settling on the glass. Spacecraft in flight generally acquire a so-called accompanying atmosphere. Something leaks from the hermotsecs, small particles of screen-vacuum thermal insulation "hang" next to the ship, products of combustion of fuel components during operation of orientation engines are right there ... In general, there is more than enough debris and dirt to not only "spoil view ", but also, for example, disrupt the operation of on-board photographic equipment.

Developers of interplanetary space stations from NPO im. C.A. Lavochkin, they say that during a spacecraft flight to one of the comets, two "heads" - nuclei were found in its composition. This was recognized as an important scientific discovery. Then it turned out that the second "head" appeared due to fogging of the window, which led to the effect of an optical prism.

Window glasses should not change light transmission when exposed to ionizing radiation from background cosmic radiation and cosmic radiation, including as a result of solar flares.

The interaction of electromagnetic radiation from the Sun and cosmic rays with glass is generally a complex phenomenon. Absorption of radiation by glass can lead to the formation of so-called "color centers", that is, to a decrease in the original light transmission, and also cause luminescence, since part of the absorbed energy can immediately be released in the form of light quanta.

The luminescence of the glass creates an additional background, which lowers the contrast of the image, increases the noise-to-signal ratio and can make normal operation of the equipment impossible. Therefore, glasses used in optical illuminators must have, along with high radiation-optical stability, a low level of luminescence. The magnitude of the luminescence intensity is no less important for optical glasses operating under the influence of radiation than the resistance to coloration.

Among the factors of space flight, one of the most dangerous for windows is the micrometeor effect. It leads to a rapid drop in the strength of the glass. Its optical characteristics also deteriorate.

Already after the first year of flight, craters and scratches reaching one and a half millimeters are found on the outer surfaces of long-term orbital stations. If most of the surface can be screened from meteoric and man-made particles, then the windows cannot be protected like that.

To a certain extent, they are saved by the hoods, which are sometimes installed on windows through which, for example, on-board cameras work. At the first American space station, Skylab, it was assumed that the windows would be partially shielded by structural elements. But, of course, the most radical and reliable solution is to cover the windows of the "orbital" outside with controllable covers. This solution was applied, in particular, on the Soviet orbital station of the second generation "Salyut-7".

There is more and more "garbage" in orbit. In one of the Shuttle's flights, something clearly man-made had left a rather noticeable pothole-crater on one of the windows. The glass withstood, but who knows what might come next? .. This, by the way, is one of the reasons for the serious concern of the "space community" with space debris. In our country, professor of the Samara State Aerospace University L.G. Lukashev.

The portholes of the descent vehicles operate in even more difficult conditions. When descending into the atmosphere, they find themselves in a cloud of high-temperature plasma. In addition to pressure from inside the compartment, external pressure acts on the porthole during descent. And then the landing follows - often on the snow, sometimes in the water. In this case, the glass is rapidly cooled. Therefore, special attention is paid here to the issues of strength.

“The simplicity of a porthole is an apparent phenomenon. Some opticians say that creating a flat window is a more difficult task than making a spherical lens, since it is much more difficult to construct a mechanism of "exact infinity" than a mechanism with a finite radius, that is, a spherical surface. And, nevertheless, there have never been any problems with the windows ", - this is probably the best estimate for the spacecraft assembly, especially if it sounded from the lips of Georgy Fomin, in the recent past - the first deputy general designer of the State Research and Development Space Center" TsSKB - Progress " .

Not so long ago - on February 8, 2010, after the flight of the Shuttle STS-130 - an observation dome appeared on the International Space Station, consisting of several large quadrangular windows and a round eight-hundred-millimeter window.

The Cupola module is designed for Earth observation and manipulator operation. It was developed by the European concern Thales Alenia Space, and built by Italian machine builders in Turin.

Thus, today the Europeans hold the record - such large windows have never been put into orbit either in the United States or in Russia. The developers of various "space hotels" of the future are also talking about huge windows, insisting on their special significance for future space tourists. So “window building” has a great future, and windows continue to be one of the key elements of manned and unmanned spacecraft.

The Kupol is a really cool thing! When you look at the Earth from the window, it is the same as through the embrasure. And in the "dome" there is a 360-degree view, you can see everything! The earth from here looks like a map, yes, most of all it resembles a geographic map. You can see how the sun goes away, how it rises, how the night is approaching ... You look at all this beauty with some fading inside. "

From the diary of cosmonaut Maxim Suraev.

Based on materials from the Izvestia Nauki website

Source: https://tybet.ru/