The air regeneration system was closely integrated with the water recuperation system. Breath and perspiration would liberate more than one and one half liters of water daily per man, to be extracted by the system. This recuperated water, added to the utility water carried for cooking, dish washing and the laundry machines, would increase the utility at the expense of the slowly shrinking potable water. It would be necessary to sterilize such water by distillation, recondensation and germicidal additives, for it would be unthinkable to jeopardize hygienic standards on a lonely, year-long trip, where so many people would live in such restricted space and have access to such limited medical assistance. Measures to this end were considerably handicapped by the weight limitations which Peyton had found it necessary to impose upon the developing company.
But this was not all, for the constituency of the air was closely tied in with the type of glass to be used in the portholes. Experience on Lunetta had confirmed this. There was a high concentration of ultraviolet in the light impinging on these windows, being unaffected in its passage through empty space by any atmospheric filtering effects. This not only caused malignant conjunctivitis but also led to the formation of ozone in the living spaces. The Lunetta crews had frequently complained that she smelled of "artificial mountain sun," and that it eventually gave them headaches. For some time, development of special window glass had been under way. Such glass was to absorb a considerable proportion of the ultraviolet radiation and likewise to reduce somewhat the glare of the sunlight. It was a tough assignment, for most glasses slowly disintegrated under the strong ultraviolet light.
All this was completely novel to Dr. Woolf, who followed Peyton's remarks with rapt attention. But the longer he listened to the latter's dissertations on toilet problems and odors of ozone in space vessels, the more his mind concentrated upon a burning question which seemed to him vastly more important than all this detail, and to which he could find no answer with all the will in the world. Finally, he burst out when Peyton paused for a moment.
"Mr. Peyton," said he anxiously, "what about the temperature in these space ships?
Away back in school, I learned that the temperature in space is absolute zero, or minus 273 degrees Centigrade. With an outside temperature like that, how in the world are we going to keep warm?"
"Solar heating's the answer, Mr. Woolf," answered Peyton. "You're obviously under some misapprehension about maintaining temperatures in space ships. Space, you see, really has no temperature. What is temperature, anyway? It's only a way of expressing the rate of movement of molecules. The faster the molecules composing a body whirl about within it, the higher is its temperature. But space is composed of absolute vacuum and might as well have no molecules. So how can empty space have temperature?"
"Aren't you splitting hairs, Mr. Peyton?"
"Certainly not, although I must admit that right now we're interested in a somewhat different problem, namely, what temperature does a body suspended in empty space assume? The body, of course, consists of molecules, and these may have motion and therefore temperature.
"Let's consider the simplest case, namely a sphere floating somewhere in space, remote from the Earth and equidistant from the Sun. One half will be irradiated by the sun, the other will be shaded. Thus one side will absorb heat radiation and the sphere will become warm. From the shady side, heat will be lost by reradiation. The sphere will continue to grow warmer until the rate of radiation equals that of absorption. At the temperature where this occurs equilibrium is established. This temperature of equilibrium is primarily dependent upon the distance of the sphere from the Sun — the nearer it is to the latter, the more solar radiation is absorbed and the higher is the equilibrium temperature at which the sphere can reradiate the increased amount of heat absorbed."
"But does not the temperature attained by the sphere also depend upon the nature of its surface and above all on its color? A mirror finish reflects all radiation, while a black surface swallows it all."
"Quite right. But what applies to the irradiated surface also applies to the shaded side. A mirror finish does not reradiate, while a black one greatly furthers reradiation. If the sphere is completely shiny, it absorbs no heat on the sunny side and radiates none on the shady side. An entirely black sphere absorbs much and reradiates much. Either is the same with respect to the temperature of equilibrium.
"It's not quite so simple when intermediate colorations between mirror and black are concerned, for then the so-called spectral absorbtivity and emissivity play a considerable role. Solar radiation has a considerable portion of short wavelength energy, that is, visible and ultraviolet light, while the sphere, warmed but to moderate temperatures, radiates long wave, invisible infrared only. The absorptive capacity of some particular paint for short wave radiation may differ materially from its ability to reradiate long waves. Thus there are different temperatures of equilibrium for the sphere at identical distances from the Sun, and these vary according to the nature of the sphere's surface characteristics. But for a sphere whose surface is either completely reflective throughout the whole spectrum, or completely black in the absorptive sense, the temperature of equilibrium would be the same at the same distance from the Sun."
"You seem to be telling me," wondered Woolf, "that whether a space ship be painted with black or with reflecting paint, its temperature is wholly and solely dependent upon its distance from the Sun? Why then, the interior of the vessels ought to get colder and colder!
Because our distance from the Sun will increase constantly during our trip out to Mars."
"Now wait a minute," said Peyton, "that's another reason why we must take steps continuously to adjust our temperature of the sphere; we'll assume that it's black on one side and mirror-reflecting on the other. That will make its equilibrium temperature at any given distance from the Sun also dependent upon its attitude to the solar rays. If the black side is turned sunwards while the other is shaded, the sphere will heat up several hundred degrees, because it is absorbing much heat and can give off but little of it. But if we reverse its position and face the mirrored surface to the Sun, the mirrored hemisphere will permit no heat to be absorbed, while the black side will be radiating the accumulated heat into space. Under those conditions, and, make no mistake about it, under those conditions only, the sphere may finally reach absolute zero."
"What is done in practice?"
"Most of the exterior of the ship is polished to a mirror finish. Then the temperature simply remains exactly as it is, for there is neither heat absorption nor radiation to any extent. Being surrounded by vacuum, the vessels may be regarded as Brobdignagian thermos flasks, for in such flasks, that which was cold remains cold and that which was hot, hot.
"We regulate temperature accurately as follows: the reflecting surfaces of the ship are spotted by small, black areas, shielded by silvered Venetian blinds; the black surfaces under them are exposed and absorb heat when the blinds are open. When the blinds are closed, their reflecting surfaces prevent the absorption of radiation by the black areas. In practice, there's an automatic thermostatic control system which operates the blinds jointly with the air conditioning plant."
"Now I understand it. But tell me, how about the propellants stored aboard the vessels? Do we not also have to maintain them somewhere within a limited temperature range? Wouldn't they otherwise boil or congeal?"
"Quite right, they must be held quite accurately at one temperature. One factor is that the thin balloon fabric tanks could hardly withstand any such pressures as might be produced by extensive evaporation of the propellants. Another is the problem of maintaining accurately the predetermined mixture ratio between the two propellant components. This necessitates each of them being fed to the thrust unit at rather definite temperatures. The tanks will be painted aluminum. The propellant temperature will also be controlled by Venetian blinds, automatically operated by thermostats.