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duration of tfie voyage will be different, as measured by the two men, the exact amount of the difference depending upon how close Bs vehicle approached the speed of light. As an example, suppose В took a round trip to a near star at a speed very near that of light (about 186,000 miles per second). It would appear to A that the trip took, say, 45 years -he would be 65 years old when his friend returned. To B, however, the trip might appear to take about 10 years, including a year or so for acceleration to light speed and deceleration for the return landing - he would be 30 when he returned.

Different values of vehicle speed will lead to widely different time disparities. By approaching ever closer to the speed of light, В could take more extended trips that would last mil ions of years in earth time, but still appear to him to take only a few years. Achievement of near-light velocities would require great amounts of propulsion energy - not less than complete conversion of matter into usable energy.

3. RELIABILITY OF MISSILES AND SPACE VEHICLES

(Для перевода со словарем)

Reliability is above all a design parameter; it must be thought of as a physical property of a device which behaves in accordance with certain physical laws. In other words, reliability starts with engineering and is a basic property which must be designed into the equipment by engineers. It is true that there are other major factors which influence the performance in the final application, such as manufacturing, quality control, and handling and checkout in the field. If manufacturing process is not carried out with the proper precision and skill, if the inspection and testing in the factory are not done with proper care, and if the field crews at the launch site do not checkout, test, and launch the vehicle in accordance with proper procedures, the net result will certainly be mission failures. To be sure, no amount of manufacturing precision, care in the inspection and testing, -and proficiency of the launch crews can make a missile or space mission succeed if the basic design is not right in the first place.

Although reliability is one of the primary parameters in determining the capability of the missile or space system to perform its overall mission, it must nevertheless be kept in balance with other systems parameters. Therefore, as part о the systems design, a trade-off * between reliability and other systems parameters such as weight, accuracy, speed, and orbital precision must be made. Considerable gain in over-all system effectiveness can sometimes be obtained by sacrificing some accuracy or performance of the system for the sake of an improvement in reliability. Conversely, gains may also be realized by sacrificing some reliability in favour of improvements in accuracy and reduction of weight. The



important point here is that a balance must be struck between reliability and other systems parameters.

To illustrate the severity of the reliability problem in satellites and space vehicles Table presents some relative reliability requirements for a typical subsystem, say, a 25-watt UHF (ultra-high frequency) transmitter which might be used in any one of three applications.

Typical Reliability Requirements for Electronic Subsystem, 25-watt UHF Transmitter

Application

Mission Time

Reliability, Probability of No Failure during Mission

Mean Time to Failure (MTTF)

Aircraft

8 hr, without maintenance

0.92

100 hr

Missile

1.75 hr

0.99

175 hr

Satellite A

1 month

0.96

25 months (18.000 hr)

Satellite В .

1 yr

0.96

25 yr (2-16,000 hr)

Although the mean time to failure (MTTF) for the transmitter in a missile application is only slightly higher than the MTTF required in an aircraft application, the MTTF requirements for space are several orders of magnitude greater than those for either missile or aircraft.

Hence, the resulting reliability problem is different in nature and much more severe in the case of space vehicles.

trade-ofi - компромисс

4. NOBLE GAS ION LASERS

(Для перевода со словарем)

Experimental observation of laser action involving the excited states of noble gas ions was first reported in 1964.

Since that time, a voluminous literature reporting on the operational characteristics, spectroscopy, - and probable excitation mechanisms for these gaseous ion lasers has appeared from many different parts of the world. These intensive research efforts have



also been accompanied by rapid commercial development of prac-. tical noble gas ion lasers capable,of operating continuously at ttie output power level of several watts from a single mode over a long period of time.

In comparison with gaseous atom lasers (e.g. the helium-neon laser, which operates in the red and near-infra-red region), and the continuous duty gaseous molecule lasers (e.g. the N2-CO2 laser which operates in the infra-red), the noble gas ion lasers generally offer the advantage of shorter wavelength operation, ranging from the blue-green part of the visible spectrum up to the near ultraviolet (where photodetectors are generally more sensitive, which is an important consideration in many scientific research and communication application).

While not nearly as powerful, nor as thermally efficient as the continuous duty molecular lasers, the noble gas ion lasers are at least as efficient as, and much more powerful than (by factors of the order of 10*), the gaseous atom lasers. Even though the pulsed molecular nitrogen laser does operate in the near ultra-violet at very high peak power, the noble gas ion lasers are more flexible, in the sense that they offer a wide selection of wave lengths in the visible and the near ultra-violet regions, and that they can be operated in both the continuous and the pulsed modes.

КОНТРОЛЬНЫЕ ВОПРОСЫ

1. Какими знаками препинания обычно выделяются слова и словосочетания, идущие от автора?

2. Как переводятся следующие словосочетания, характеризующие отнощение автора к тому, что он сообщает:

to be sure. In effect, needless to say, to say the truth, presumably, say, strange to say, strictly speaking, at any rate, curiously enough, at most, in a sense, not to mention, to put it in another way, to say nothing of, so to speak, in plain words.

3. Переведите следующие обороты:

it is true; there is every indication; it is a safe assumption; it is hardly surprising; it is most unfortunate; it is common knowledge; it has been an accepted fact.

4. Укажите способ перевода конструкции, в которой к одному существительному относятся два различных предлога (§ 105):

to receive power from and to deliver power to circuits.

5. Укажите значения слова just (упр. 10).

6. Какое значение имеют префиксы mal- и mis-? Каким приставкам соответствует префикс inter- (упр. 23)?



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