ДОПОЛНИТЕЛЬНЫЕ ТЕКСТЫ ДЛЯ ПЕРЕВОДА

1. APPLICATION OF ELECTRIC-PROPULSION SYSTEM

(Для перевода без словаря)

Ап electrically powered spacecraft will probably be used for a round trip to some distant planet. A comparison between an electric and a conventional system for a proposed trip to Mars will show definite advantages of an electric system. For an eight-man crew to go on a 500-day trip to Mars, the weight of the electric and conventional system would be 450,000 and 8,000,000 pounds respectively. Both systems would have to be assembled in an Earth orbit. It would, however, take only two boosters to lift the material for the electric system while forty boosters would be needed for the conventional one. Electric power propulsion and all other needs would be generated by a nuclear-fission turbo-electric system.

There is, however, one problem that has not yet been discussed-the radiator equipment. Vapour exhausted from the turbine must be cooled and condensed before it returns to heat exchanger and the cycle is repeated. The cooling is accomplished with a radiator. This creates a weight problem, since a great deal of surface area is required for efficient heat exchange. Besides, to make the electric system practical, a large number of engines would be required because present designs are for engines generating only a small amount of thrust.

Much research has been conducted on electric propulsion systems as they can produce such low thrusts and can run for long periods. This means a high degree of reliability will have to be attained for such systems. Even with the large amount of research already accomplished, the electric system is still in a stage of development. Lighter and more powerful units must be developed if we want such systems to fulfil the promise they offer for interplanetary travel.

respectively - соответственно

* assemble - собирать

exhaust - выбрасывать, выпускать

2. ION PROPULSION

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In the various devices for ion propulsion now under development each molecule of the propellant (usually assumed to be an alkali metal, notably cesium) is caused to have an electric charge; that is, the propellant is ionized. This might be accomplished by passing the propellant over heated metal grids. It is then possible to accelerate the charged molecules, or ions, to very high veioci-

ties througli a nozzle by means of an electric field. (Electrons are accelerated in a television tube in this fashion). The performance of such an ion engine is very good, with values of specific impulse reaching as high as 20,000 seconds. However, the amount of electric power required is very large, so weight ofthe power-generating equipment becomes a major obstacle to an e ficient vehicle. It is supposed that some type of nuclear fission (or fusion, farther in the future) could be used to supply the energy for the electric power plant, although this step would still not eliminate the need for heavy electric generators, unless direct conversion of fission to electrical energy in large quantities becomes practical.

For example, an ion rocket offering 20,000 seconds of specific impulse, using cesium for the propellant would require about 2,100 kilowatts of electric power to produce 1 pound of thrust, assuming good efficiency. Optimistic estimates of electric power supply weight indicate that the power unit in question would weigh about 8,500 pounds. The weight of the ion accelerator itself is small in comparison. Therefore, an ion rocket can accelerate itself only very slowly (about 1/10,000 of 1 g in this example).

The primary consideration in obtaining useful thrust from ion or plasma rockets is the construction of lightweight electric power supplies. A gross reduction in electrical generation equipment, as compared with the most advanced modern equipment, is required to make the electric rocket really interesting for flight in the solar . system.

3. OUR GALAXY

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Our Galaxy proved to be a spiral system.

The question whether the spiral nebulae were island universes outside our own Universe continued to be debated for quite a long time. It has been only within recent years that the question has been finally settled. The key to the whole question was to find the distances of these nebulae, because if their distances were known we would at once know whether they were inside or outside our btellar system; we would also know their size and would be able to decide whether they were at all comparable in size with our own system. The problem was solved when it was found that within some of these nebulae there were stars which showed all the characteristics of the pulsating stars. The nebulae in which these stars were found were those of largest apparent size and therefore presumably the nearest to us. Their periods of pulsation were determmed and their distances were mferred. They were found to be of the order of a million light-years. This was conclusive evidence that the spiral nebulae were outside our stellar Universe and that the were, in fact, island universes.

The size of these other universes proves to be of the same general order as that of our own Universe, It is found also that they are, like our Universe, in slow rotation; they may be thought of as gigantic celestial Catherine wheels spinning round, with their vast spiral arms. They seem also to contain about the same amount of matter as our own system.

The general similarity between our Galaxy and the external universes suggested, by analogy, that our Galaxy is probably a spiral system.

If the Sun had been at some considerable distance from the central plane of the system, marked out by the Milky Way, the spiral arms could readily have been observed. But situated, as it is, practically in the central plane, it is not favourably placed for the spiral arms to be detected. The obscuring dust clouds in the plane of the Milky Way dim the distant stars and make it impossible to trace out the spiral arms, if they exist, with any certainty by optical or photographic observations. The development of radio-astronomy has removed this difficulty, for the dust clouds do not obscure radiations in the radio wavelength. Clouds of hydrogen gas emit radiations with a wavelength of 21 cms, and it has proved possible by radio methods to determine the direction and distance of these clouds, which are found to trace out well-defined spiral arms analogous to those observed in the spiral galaxies. Our Galaxy has in this way proved to be, as was suspected, a spiral system.

4. THE SPEED OF COMPUTERS

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Speed of operation is the one basic achievement on which all the great developments of the last two decades in automatic computing have rested. We can now multiply two long numbers, of as many as twelve digits each, in the time taken by a rifle bullet to travel about a tenth of an inch. This speed in itself may not be very exciting, but whenever you get such an immense change in a capability you must look for the possibility of some qualitative effects. Take travel for instance. Over a century and a naif we have progressed from horseback to railways, cars and aeroplanes, a speed increase of perhaps fifty times. This, as you know, has had a certain qualitative effect on peoples lives. But in computing we are dealing with a factor, not of fifty, but of a million.

Let us look at two other fields where similar increases have occured: printing and communication. An early printing press was capable of printing about 10,000 words per hour. Its modern equivalent is capable of printing something of the order of 10" words per hour, and is therefore about a million times faster than its predecessor.